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18.3: Two-species blending - Biology

18.3: Two-species blending - Biology



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Blending two-species systems is a similar process, but has more options in the parameters. Equation 18.3.1 is an example with limited options that produced the phase spaces in Figures 10.1.3 through 10.1.5.

[frac{1}{N_1}frac{dN_1}{dt},=,r_1(N_1),+,s_{1,1}N_1,+,s_{1,2}(N_1)N_2frac{1}{N_2}frac{dN_2}{dt},=,r_2(N_2),+,s_{2,2}N_2,+,s_{2,1}(N_2)N_1]

Changing the parameters uniformly from (a,b) value when the corresponding (N) value is 0 to an (a,+,b) value when the corresponding (N) value is 1 is analogous to the blending that produced Figure 4.4.1. The parameters would vary as follows, using four distinct (a) values ((a_1,,a_2,,a_{1,2},,a_{2,1})), plus four distinct (b) values with matching subscripts ((b_1,,b_2,,b_{1,2},,b_{2,1})).

(r_1(N_1),=,a_1N_1,+,b_1,qquad,s_{1,2}(N_1),=,a_{1,2}N_1,+,b_{1,2})

(r_2(N_2),=,a_2N_2,+,b_2,qquad,s_{2,1}(N_2),=,a_{2,1}N_2,+,b_{2,1})

Substituting the above into Equation 18.3.1 and collecting terms gives an equation having all the RSN terms present, but now with a cross-product in terms of (N_1N_2) added at the end:

[frac{1}{N_1}frac{dN_1}{dt},=,b_1,+,(a_1,+,s_{1,1})N_1,+,b_{1,2}N_2,+,a_{1,2}N_1N_2frac{1}{N_2}frac{dN_2}{dt},=,b_2,+,(a_2,+,s_{2,2})N_2,+,b_{2,1}N_1,+,a_{2,1}N_1N_2]

In the specific case of Figures 10.1.3 through 10.1.5, we used (s_{1,1},=,s_{2,2},=,−0.98) and

(r_1(N_1),=,0.75N_1,−0.5qquad,s_{1,2}(N_1),=,−1.15N_1,+,2.5)

(r_2(N_2),=,0.75N_2,−0.5qquad,s_{2,1}(N_2),=,−0.45N_2,+,1.3)

which gave

(frac{1}{N_1}frac{dN_1}{dt},=,-0.5,-,0.23N_1,+,2.50N_2,-,1.15N_1N_2)

(frac{1}{N_2}frac{dN_2}{dt},=,-0.5,-,0.98N_2,+,2.50N_1,-,0.45N_1N_2)

for the flow in the figures.


Contents

The concept of fatty acid (acide gras) was introduced in 1813 by Michel Eugène Chevreul, [3] [4] [5] though he initially used some variant terms: graisse acide and acide huileux ("acid fat" and "oily acid"). [6]

Fatty acids are classified in many ways: by length, by saturation vs unsaturation, by even vs odd carbon content, and by linear vs branched.

Length of fatty acids Edit

    (SCFA) are fatty acids with aliphatic tails of five or fewer carbons (e.g. butyric acid). [7] (MCFA) are fatty acids with aliphatic tails of 6 to 12 [8]carbons, which can form medium-chain triglycerides. (LCFA) are fatty acids with aliphatic tails of 13 to 21 carbons. [9] (VLCFA) are fatty acids with aliphatic tails of 22 or more carbons.

Saturated fatty acids Edit

Saturated fatty acids have no C=C double bonds. They have the same formula CH3(CH2)nCOOH, with variations in "n". An important saturated fatty acid is stearic acid (n = 16), which when neutralized with lye is the most common form of soap.

Examples of saturated fatty acids
Common name Chemical structure C:D [10]
Caprylic acid CH3(CH2)6COOH 8:0
Capric acid CH3(CH2)8COOH 10:0
Lauric acid CH3(CH2)10COOH 12:0
Myristic acid CH3(CH2)12COOH 14:0
Palmitic acid CH3(CH2)14COOH 16:0
Stearic acid CH3(CH2)16COOH 18:0
Arachidic acid CH3(CH2)18COOH 20:0
Behenic acid CH3(CH2)20COOH 22:0
Lignoceric acid CH3(CH2)22COOH 24:0
Cerotic acid CH3(CH2)24COOH 26:0

Unsaturated fatty acids Edit

Unsaturated fatty acids have one or more C=C double bonds. The C=C double bonds can give either cis or trans isomers.

cis A cis configuration means that the two hydrogen atoms adjacent to the double bond stick out on the same side of the chain. The rigidity of the double bond freezes its conformation and, in the case of the cis isomer, causes the chain to bend and restricts the conformational freedom of the fatty acid. The more double bonds the chain has in the cis configuration, the less flexibility it has. When a chain has many cis bonds, it becomes quite curved in its most accessible conformations. For example, oleic acid, with one double bond, has a "kink" in it, whereas linoleic acid, with two double bonds, has a more pronounced bend. α-Linolenic acid, with three double bonds, favors a hooked shape. The effect of this is that, in restricted environments, such as when fatty acids are part of a phospholipid in a lipid bilayer or triglycerides in lipid droplets, cis bonds limit the ability of fatty acids to be closely packed, and therefore can affect the melting temperature of the membrane or of the fat. Cis unsaturated fatty acids, however, increase cellular membrane fluidity, whereas trans unsaturated fatty acids do not. trans A trans configuration, by contrast, means that the adjacent two hydrogen atoms lie on opposite sides of the chain. As a result, they do not cause the chain to bend much, and their shape is similar to straight saturated fatty acids.

In most naturally occurring unsaturated fatty acids, each double bond has three (n-3), six (n-6), or nine (n-9) carbon atoms after it, and all double bonds have a cis configuration. Most fatty acids in the trans configuration (trans fats) are not found in nature and are the result of human processing (e.g., hydrogenation). Some trans fatty acids also occur naturally in the milk and meat of ruminants (such as cattle and sheep). They are produced, by fermentation, in the rumen of these animals. They are also found in dairy products from milk of ruminants, and may be also found in breast milk of women who obtained them from their diet.

The geometric differences between the various types of unsaturated fatty acids, as well as between saturated and unsaturated fatty acids, play an important role in biological processes, and in the construction of biological structures (such as cell membranes).

Examples of Unsaturated Fatty Acids
Common name Chemical structure Δ x [11] C:D [10] IUPAC [12] nx [13]
Myristoleic acid CH3(CH2)3CH=CH(CH2)7COOH cis-Δ 9 14:1 14:1(9) n−5
Palmitoleic acid CH3(CH2)5CH=CH(CH2)7COOH cis-Δ 9 16:1 16:1(9) n−7
Sapienic acid CH3(CH2)8CH=CH(CH2)4COOH cis-Δ 6 16:1 16:1(6) n−10
Oleic acid CH3(CH2)7CH=CH(CH2)7COOH cis-Δ 9 18:1 18:1(9) n−9
Elaidic acid CH3(CH2)7CH=CH(CH2)7COOH trans-Δ 9 18:1 n−9
Vaccenic acid CH3(CH2)5CH=CH(CH2)9COOH trans-Δ 11 18:1 n−7
Linoleic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH cis,cis-Δ 9 ,Δ 12 18:2 18:2(9,12) n−6
Linoelaidic acid CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH trans,trans-Δ 9 ,Δ 12 18:2 n−6
α-Linolenic acid CH3CH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH cis,cis,cis-Δ 9 ,Δ 12 ,Δ 15 18:3 18:3(9,12,15) n−3
Arachidonic acid CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH NIST cis,cis,cis,cis-Δ 5 Δ 8 ,Δ 11 ,Δ 14 20:4 20:4(5,8,11,14) n−6
Eicosapentaenoic acid CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)3COOH cis,cis,cis,cis,cis-Δ 5 ,Δ 8 ,Δ 11 ,Δ 14 ,Δ 17 20:5 20:5(5,8,11,14,17) n−3
Erucic acid CH3(CH2)7CH=CH(CH2)11COOH cis-Δ 13 22:1 22:1(13) n−9
Docosahexaenoic acid CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)2COOH cis,cis,cis,cis,cis,cis-Δ 4 ,Δ 7 ,Δ 10 ,Δ 13 ,Δ 16 ,Δ 19 22:6 22:6(4,7,10,13,16,19) n−3

Even- vs odd-chained fatty acids Edit

Most fatty acids are even-chained, e.g. stearic (C18) and oleic (C18), meaning they are composed of an even number of carbon atoms. Some fatty acids have odd numbers of carbon atoms they are referred to as odd-chained fatty acids (OCFA). The most common OCFA are the saturated C15 and C17 derivatives, pentadecanoic acid and heptadecanoic acid respectively, which are found in dairy products. [14] [15] On a molecular level, OCFAs are biosynthesized and metabolized slightly differently from the even-chained relatives.

Carbon atom numbering Edit

Most naturally occurring fatty acids have an unbranched chain of carbon atoms, with a carboxyl group (–COOH) at one end, and a methyl group (–CH3) at the other end.

The position of the carbon atoms in the backbone of a fatty acid are usually indicated by counting from 1 at the −COOH end. Carbon number x is often abbreviated or C-x (or sometimes Cx), with x=1, 2, 3, etc. This is the numbering scheme recommended by the IUPAC.

Another convention uses letters of the Greek alphabet in sequence, starting with the first carbon after the carboxyl. Thus carbon α (alpha) is C-2, carbon β (beta) is C-3, and so forth.

Although fatty acids can be of diverse lengths, in this second convention the last carbon in the chain is always labelled as ω (omega), which is the last letter in the Greek alphabet. A third numbering convention counts the carbons from that end, using the labels "ω", "ω−1", "ω−2". Alternatively, the label "ω−x" is written "n−x", where the "n" is meant to represent the number of carbons in the chain. [16]

In either numbering scheme, the position of a double bond in a fatty acid chain is always specified by giving the label of the carbon closest to the carboxyl end. [16] Thus, in an 18 carbon fatty acid, a double bond between C-12 (or ω−6) and C-13 (or ω−5) is said to be "at" position C-12 or ω−6. The IUPAC naming of the acid, such as "octadec-12-enoic acid" (or the more pronounceable variant "12-octadecanoic acid") is always based on the "C" numbering.

The notation Δ x,y. is traditionally used to specify a fatty acid with double bonds at positions x,y. (The capital Greek letter "Δ" (delta) corresponds to Roman "D", for Double bond). Thus, for example, the 20-carbon arachidonic acid is Δ 5,8,11,14 , meaning that it has double bonds between carbons 5 and 6, 8 and 9, 11 and 12, and 14 and 15.

In the context of human diet and fat metabolism, unsaturated fatty acids are often classified by the position of the double bond closest to the ω carbon (only), even in the case of multiple double bonds such as the essential fatty acids. Thus linoleic acid (18 carbons, Δ 9,12 ), γ-linolenic acid (18-carbon, Δ 6,9,12 ), and arachidonic acid (20-carbon, Δ 5,8,11,14 ) are all classified as "ω−6" fatty acids meaning that their formula ends with –CH=CH– CH
2 – CH
2 – CH
2 – CH
2 – CH
3 .

Fatty acids with an odd number of carbon atoms are called odd-chain fatty acids, whereas the rest are even-chain fatty acids. The difference is relevant to gluconeogenesis.

Naming of fatty acids Edit

The following table describes the most common systems of naming fatty acids.

Nomenclature Examples Explanation
Trivial Palmitoleic acid Trivial names (or common names) are non-systematic historical names, which are the most frequent naming system used in literature. Most common fatty acids have trivial names in addition to their systematic names (see below). These names frequently do not follow any pattern, but they are concise and often unambiguous.
Systematic cis-9-octadec-9-enoic acid
(9Z)-octadec-9-enoic acid
Systematic names (or IUPAC names) derive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry, published in 1979, [17] along with a recommendation published specifically for lipids in 1977. [18] Carbon atom numbering begins from the carboxylic end of the molecule backbone. Double bonds are labelled with cis-/trans- notation or E-/Z- notation, where appropriate. This notation is generally more verbose than common nomenclature, but has the advantage of being more technically clear and descriptive.
Δ x cis-Δ 9 , cis-Δ 12 octadecadienoic acid In Δ x (or delta-x) nomenclature, each double bond is indicated by Δ x , where the double bond begins at the xth carbon–carbon bond, counting from carboxylic end of the molecule backbone. Each double bond is preceded by a cis- or trans- prefix, indicating the configuration of the molecule around the bond. For example, linoleic acid is designated "cis-Δ 9 , cis-Δ 12 octadecadienoic acid". This nomenclature has the advantage of being less verbose than systematic nomenclature, but is no more technically clear or descriptive. [ citation needed ]
nx
(or ω−x)
n−3
(or ω−3)
nx (n minus x also ω−x or omega-x) nomenclature both provides names for individual compounds and classifies them by their likely biosynthetic properties in animals. A double bond is located on the x th carbon–carbon bond, counting from the methyl end of the molecule backbone. For example, α-Linolenic acid is classified as a n−3 or omega-3 fatty acid, and so it is likely to share a biosynthetic pathway with other compounds of this type. The ω−x, omega-x, or "omega" notation is common in popular nutritional literature, but IUPAC has deprecated it in favor of nx notation in technical documents. [17] The most commonly researched fatty acid biosynthetic pathways are n−3 and n−6.
Lipid numbers 18:3
18:3n3
18:3, cis,cis,cis-Δ 9 ,Δ 12 ,Δ 15
18:3(9,12,15)
Lipid numbers take the form C:D, [10] where C is the number of carbon atoms in the fatty acid and D is the number of double bonds in the fatty acid. If D is more than one, the double bonds are assumed to be interrupted by CH
2 units, i.e., at intervals of 3 carbon atoms along the chain. For instance, α-Linolenic acid is an 18:3 fatty acid and its three double bonds are located at positions Δ 9 , Δ 12 , and Δ 15 . This notation can be ambiguous, as some different fatty acids can have the same C:D numbers. Consequently, when ambiguity exists this notation is usually paired with either a Δ x or nx term. [17] For instance, although α-Linolenic acid and γ-Linolenic acid are both 18:3, they may be unambiguously described as 18:3n3 and 18:3n6 fatty acids, respectively. For the same purpose, IUPAC recommends using a list of double bond positions in parentheses, appended to the C:D notation. [12] For instance, IUPAC recommended notations for α-and γ-Linolenic acid are 18:3(9,12,15) and 18:3(6,9,12), respectively.

Free fatty acids Edit

When circulating in the plasma (plasma fatty acids), not in their ester, fatty acids are known as non-esterified fatty acids (NEFAs) or free fatty acids (FFAs). FFAs are always bound to a transport protein, such as albumin. [19]

Industrial Edit

Fatty acids are usually produced industrially by the hydrolysis of triglycerides, with the removal of glycerol (see oleochemicals). Phospholipids represent another source. Some fatty acids are produced synthetically by hydrocarboxylation of alkenes. [20]

Hyper-oxygenated fatty acids Edit

Hyper-oxygenated fatty acids are produced by a specific industrial processes for topical skin creams. The process is based on the introduction or saturation of peroxides into fatty acid esters via the presence of ultraviolet light and gaseous oxygen bubbling under controlled temperatures. Specifically linolenic acids have been shown to play an important role in maintaining the moisture barrier function of the skin (preventing water loss and skin dehydration). [21] A study in Spain reported in the Journal of Wound Care in March 2005 compared a commercial product with a greasy placebo and that specific product was more effective and also cost-effective. [22] A range of such OTC medical products is now widely available. However, topically applied olive oil was not found to be inferior in a "randomised triple-blind controlled non-inferiority" trial conducted in Spain during 2015. [23] [24] Commercial products are likely to be less messy to handle and more washable than either olive oil or petroleum jelly, both of which, if applied topically may stain clothing and bedding.

By animals Edit

In animals, fatty acids are formed from carbohydrates predominantly in the liver, adipose tissue, and the mammary glands during lactation. [25]

Carbohydrates are converted into pyruvate by glycolysis as the first important step in the conversion of carbohydrates into fatty acids. [25] Pyruvate is then decarboxylated to form acetyl-CoA in the mitochondrion. However, this acetyl CoA needs to be transported into cytosol where the synthesis of fatty acids occurs. This cannot occur directly. To obtain cytosolic acetyl-CoA, citrate (produced by the condensation of acetyl-CoA with oxaloacetate) is removed from the citric acid cycle and carried across the inner mitochondrial membrane into the cytosol. [25] There it is cleaved by ATP citrate lyase into acetyl-CoA and oxaloacetate. The oxaloacetate is returned to the mitochondrion as malate. [26] The cytosolic acetyl-CoA is carboxylated by acetyl CoA carboxylase into malonyl-CoA, the first committed step in the synthesis of fatty acids. [26] [27]

Malonyl-CoA is then involved in a repeating series of reactions that lengthens the growing fatty acid chain by two carbons at a time. Almost all natural fatty acids, therefore, have even numbers of carbon atoms. When synthesis is complete the free fatty acids are nearly always combined with glycerol (three fatty acids to one glycerol molecule) to form triglycerides, the main storage form of fatty acids, and thus of energy in animals. However, fatty acids are also important components of the phospholipids that form the phospholipid bilayers out of which all the membranes of the cell are constructed (the cell wall, and the membranes that enclose all the organelles within the cells, such as the nucleus, the mitochondria, endoplasmic reticulum, and the Golgi apparatus). [25]

The "uncombined fatty acids" or "free fatty acids" found in the circulation of animals come from the breakdown (or lipolysis) of stored triglycerides. [25] [28] Because they are insoluble in water, these fatty acids are transported bound to plasma albumin. The levels of "free fatty acids" in the blood are limited by the availability of albumin binding sites. They can be taken up from the blood by all cells that have mitochondria (with the exception of the cells of the central nervous system). Fatty acids can only be broken down in mitochondria, by means of beta-oxidation followed by further combustion in the citric acid cycle to CO2 and water. Cells in the central nervous system, although they possess mitochondria, cannot take free fatty acids up from the blood, as the blood-brain barrier is impervious to most free fatty acids, [ citation needed ] excluding short-chain fatty acids and medium-chain fatty acids. [29] [30] These cells have to manufacture their own fatty acids from carbohydrates, as described above, in order to produce and maintain the phospholipids of their cell membranes, and those of their organelles. [25]

Variation between animal species Edit

Studies on the cell membranes of mammals and reptiles discovered that mammalian cell membranes are composed of a higher proportion of polyunsaturated fatty acids (DHA, omega-3 fatty acid) than reptiles. [31] Studies on bird fatty acid composition have noted similar proportions to mammals but with 1/3rd less omega-3 fatty acids as compared to omega-6 for a given body size. [32] This fatty acid composition results in a more fluid cell membrane but also one that is permeable to various ions ( H +
& Na +
), resulting in cell membranes that are more costly to maintain. This maintenance cost has been argued to be one of the key causes for the high metabolic rates and concomitant warm-bloodedness of mammals and birds. [31] However polyunsaturation of cell membranes may also occur in response to chronic cold temperatures as well. In fish increasingly cold environments lead to increasingly high cell membrane content of both monounsaturated and polyunsaturated fatty acids, to maintain greater membrane fluidity (and functionality) at the lower temperatures. [33] [34]

The following table gives the fatty acid, vitamin E and cholesterol composition of some common dietary fats. [35] [36]

Saturated Monounsaturated Polyunsaturated Cholesterol Vitamin E
g/100g g/100g g/100g mg/100g mg/100g
Animal fats
Duck fat [37] 33.2 49.3 12.9 100 2.70
Lard [37] 40.8 43.8 9.6 93 0.60
Tallow [37] 49.8 41.8 4.0 109 2.70
Butter 54.0 19.8 2.6 230 2.00
Vegetable fats
Coconut oil 85.2 6.6 1.7 0 .66
Cocoa butter 60.0 32.9 3.0 0 1.8
Palm kernel oil 81.5 11.4 1.6 0 3.80
Palm oil 45.3 41.6 8.3 0 33.12
Cottonseed oil 25.5 21.3 48.1 0 42.77
Wheat germ oil 18.8 15.9 60.7 0 136.65
Soybean oil 14.5 23.2 56.5 0 16.29
Olive oil 14.0 69.7 11.2 0 5.10
Corn oil 12.7 24.7 57.8 0 17.24
Sunflower oil 11.9 20.2 63.0 0 49.00
Safflower oil 10.2 12.6 72.1 0 40.68
Hemp oil 10 15 75 0 12.34
Canola/Rapeseed oil 5.3 64.3 24.8 0 22.21

Fatty acids exhibit reactions like other carboxylic acids, i.e. they undergo esterification and acid-base reactions.

Acidity Edit

Fatty acids do not show a great variation in their acidities, as indicated by their respective pKa. Nonanoic acid, for example, has a pKa of 4.96, being only slightly weaker than acetic acid (4.76). As the chain length increases, the solubility of the fatty acids in water decreases, so that the longer-chain fatty acids have minimal effect on the pH of an aqueous solution. Near neutral pH, fatty acids exist at their conjugate bases, i.e. oleate, etc.

Solutions of fatty acids in ethanol can be titrated with sodium hydroxide solution using phenolphthalein as an indicator. This analysis is used to determine the free fatty acid content of fats i.e., the proportion of the triglycerides that have been hydrolyzed.

Neutralization of fatty acids, one form of saponification (soap-making), is a widely practiced route to metallic soaps. [38]

Hydrogenation and hardening Edit

Hydrogenation of unsaturated fatty acids is widely practiced. Typical conditions involve 2.0–3.0 MPa of H2 pressure, 150 °C, and nickel supported on silica as a catalyst. This treatment affords saturated fatty acids. The extent of hydrogenation is indicated by the iodine number. Hydrogenated fatty acids are less prone toward rancidification. Since the saturated fatty acids are higher melting than the unsaturated precursors, the process is called hardening. Related technology is used to convert vegetable oils into margarine. The hydrogenation of triglycerides (vs fatty acids) is advantageous because the carboxylic acids degrade the nickel catalysts, affording nickel soaps. During partial hydrogenation, unsaturated fatty acids can be isomerized from cis to trans configuration. [39]

More forcing hydrogenation, i.e. using higher pressures of H2 and higher temperatures, converts fatty acids into fatty alcohols. Fatty alcohols are, however, more easily produced from fatty acid esters.

In the Varrentrapp reaction certain unsaturated fatty acids are cleaved in molten alkali, a reaction which was, at one point of time, relevant to structure elucidation.

Auto-oxidation and rancidity Edit

Unsaturated fatty acids undergo a chemical change known as auto-oxidation. The process requires oxygen (air) and is accelerated by the presence of trace metals. Vegetable oils resist this process to a small degree because they contain antioxidants, such as tocopherol. Fats and oils often are treated with chelating agents such as citric acid to remove the metal catalysts.

Ozonolysis Edit

Unsaturated fatty acids are susceptible to degradation by ozone. This reaction is practiced in the production of azelaic acid ((CH2)7(CO2H)2) from oleic acid. [39]

Digestion and intake Edit

Short- and medium-chain fatty acids are absorbed directly into the blood via intestine capillaries and travel through the portal vein just as other absorbed nutrients do. However, long-chain fatty acids are not directly released into the intestinal capillaries. Instead they are absorbed into the fatty walls of the intestine villi and reassemble again into triglycerides. The triglycerides are coated with cholesterol and protein (protein coat) into a compound called a chylomicron.

From within the cell, the chylomicron is released into a lymphatic capillary called a lacteal, which merges into larger lymphatic vessels. It is transported via the lymphatic system and the thoracic duct up to a location near the heart (where the arteries and veins are larger). The thoracic duct empties the chylomicrons into the bloodstream via the left subclavian vein. At this point the chylomicrons can transport the triglycerides to tissues where they are stored or metabolized for energy.

Metabolism Edit

When metabolized, fatty acids yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. Fatty acids (provided either by ingestion or by drawing on triglycerides stored in fatty tissues) are distributed to cells to serve as a fuel for muscular contraction and general metabolism. They are broken down to CO2 and water by the intra-cellular mitochondria, releasing large amounts of energy, captured in the form of ATP through beta oxidation and the citric acid cycle.

Essential fatty acids Edit

Fatty acids that are required for good health but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food, are called essential fatty acids. There are two series of essential fatty acids: one has a double bond three carbon atoms away from the methyl end the other has a double bond six carbon atoms away from the methyl end. Humans lack the ability to introduce double bonds in fatty acids beyond carbons 9 and 10, as counted from the carboxylic acid side. [40] Two essential fatty acids are linoleic acid (LA) and alpha-linolenic acid (ALA). These fatty acids are widely distributed in plant oils. The human body has a limited ability to convert ALA into the longer-chain omega-3 fatty acids — eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which can also be obtained from fish. Omega-3 and omega-6 fatty acids are biosynthetic precursors to endocannabinoids with antinociceptive, anxiolytic, and neurogenic properties. [41]

Distribution Edit

Blood fatty acids adopt distinct forms in different stages in the blood circulation. They are taken in through the intestine in chylomicrons, but also exist in very low density lipoproteins (VLDL) and low density lipoproteins (LDL) after processing in the liver. In addition, when released from adipocytes, fatty acids exist in the blood as free fatty acids.

It is proposed that the blend of fatty acids exuded by mammalian skin, together with lactic acid and pyruvic acid, is distinctive and enables animals with a keen sense of smell to differentiate individuals. [42]

The chemical analysis of fatty acids in lipids typically begins with an interesterification step that breaks down their original esters (triglycerides, waxes, phospholipids etc) and converts them to methyl esters, which are then separated by gas chromatography. [43] or analyzed by gas chromatography and mid-infrared spectroscopy.

Separation of unsaturated isomers is possible by silver ion (argentation) thin-layer chromatography. [44] [45] Other separation techniques include high-performance liquid chromatography (with short columns packed with silica gel with bonded phenylsulfonic acid groups whose hydrogen atoms have been exchanged for silver ions). The role of silver lies in its ability to form complexes with unsaturated compounds.

Fatty acids are mainly used in the production of soap, both for cosmetic purposes and, in the case of metallic soaps, as lubricants. Fatty acids are also converted, via their methyl esters, to fatty alcohols and fatty amines, which are precursors to surfactants, detergents, and lubricants. [39] Other applications include their use as emulsifiers, texturizing agents, wetting agents, anti-foam agents, or stabilizing agents. [46]

Esters of fatty acids with simpler alcohols (such as methyl-, ethyl-, n-propyl-, isopropyl- and butyl esters) are used as emollients in cosmetics and other personal care products and as synthetic lubricants. Esters of fatty acids with more complex alcohols, such as sorbitol, ethylene glycol, diethylene glycol, and polyethylene glycol are consumed in food, or used for personal care and water treatment, or used as synthetic lubricants or fluids for metal working.


Convergent evolution

In evolutionary biology, convergent evolution is the process whereby organisms not closely related (not monophyletic), independently evolve similar traits as a result of having to adapt to similar environments or ecological niches.

It is the opposite of divergent evolution, where related species evolve different traits.

On a molecular level, this can happen due to random mutation unrelated to adaptive changes see long branch attraction.

In cultural evolution, convergent evolution is the development of similar cultural adaptations to similar environmental conditions by different peoples with different ancestral cultures.

An example of convergent evolution is the similar nature of the flight/wings of insects, birds, pterosaurs, and bats.

All four serve the same function and are similar in structure, but each evolved independently.

Some aspects of the lens of eyes also evolved independently in various animals.

Convergent evolution is similar to, but distinguishable from, the phenomena of evolutionary relay and parallel evolution.

Evolutionary relay refers to independent species acquiring similar characteristics through their evolution in similar ecosystems, but not at the same time (e.g. dorsal fins of extinct ichthyosaurs and sharks).

Parallel evolution occurs when two independent species evolve together at the same time in the same ecospace and acquire similar characteristics (extinct browsing-horses and extinct paleotheres).

Structures that are the result of convergent evolution are called analogous structures or homoplasies they should be contrasted with homologous structures, which have a common origin.


6.5 Compare three groups

6.5.1 Distribution of bill depths by species

For the next exercise, we will compare the mean bill depth among three groups: the three species of penguins. First, let’s look at the distribution of bill depths for each species:

It certainly appears that Gentoo Penguins have shorter bills than the other two species.

6.5.2 Mean bill depth by species

Next, we will estimate the mean bill depth for each species and put a confidence interval around each estimate:

And here are those means and confidence intervals plotted over the raw data:

The graph, which depicts the mean 95% confidence interval for the bill depth of each species, indicates there is likely a statistically significant difference between the means.

6.5.3 ANOVA

To test this hypothesis, we can use a one-way ANOVA, which tests for differences among the means of multiple groups.

The hypotheses for an ANOVA can be state like this:

  • (H_0) : the mean bill depth is equal among all species
  • (H_A) : At least one bill depth is different from the others

The aov() function fits an analysis of variance model to the data. The first argument is the formula specifying how the variables are related, just like the (t) -test, with the numerical response variable, a tilde, and the categorical explanatory variable. The other argument is the data frame.

Printing the results of the ANOVA, as seen above, gives you some information about the test, but using the summary() function gives you more details:

ANOVA works by comparing the variance within groups to the variance between groups. The test statistic is the (F) -ratio, where (F=MS_/MS_) . Under the null hypothesis, F would be close to 1, while under the alternative hypothesis F would be greater than 1. The (P) -value represents the probability of obtaining an F-ratio as great as or greater than the one you obtained. If the (P) -value is less than your alpha level, you can reject the null hypothesis.

In this case, the (P) -value of 2e-16 is below a any alpha level we might choose, so we can reject the null hypothesis and conclude that the mean bill depth for at least one species is different from the means for the other species.


Contents

Cooperation in animals appears to occur mostly for direct benefit or between relatives. [3] Spending time and resources assisting a related individual may at first seem destructive to an organism's chances of survival but is actually beneficial over the long-term. Since relatives share part of the helper's genetic make-up, enhancing each individual's chance of survival may actually increase the likelihood that the helper's genetic traits will be passed on to future generations. [4]

However, some researchers, such as ecology professor Tim Clutton-Brock, assert that cooperation is a more complex process. They state that helpers may receive more direct, and less indirect, gains from assisting others than is commonly reported. These gains include protection from predation and increased reproductive fitness. Furthermore, they insist that cooperation may not solely be an interaction between two individuals but may be part of the broader goal of unifying populations. [5]

Prominent biologists, such as Charles Darwin, E. O. Wilson, and W. D. Hamilton, have found the evolution of cooperation fascinating because natural selection favors those who achieve the greatest reproductive success while cooperative behavior often decreases the reproductive success of the actor (the individual performing the cooperative behavior). Hence, cooperation seemed to pose a challenging problem to the theory of natural selection, which rests on the assumption that individuals compete to survive and maximize their reproductive successes. [2] Additionally, some species have been found to perform cooperative behaviors that may at first sight seem detrimental to their own evolutionary fitness. For example, when a ground squirrel sounds an alarm call to warn other group members of a nearby coyote, it draws attention to itself and increases its own odds of being eaten. [6] There have been multiple hypotheses for the evolution of cooperation, all of which are rooted in Hamilton's models based on inclusive fitness. These models hypothesize that cooperation is favored by natural selection due to either direct fitness benefits (mutually beneficial cooperation) or indirect fitness benefits (altruistic cooperation). [7] [3] As explained below, direct benefits encompass by-product benefits and enforced reciprocity, while indirect benefits (kin selection) encompass limited dispersal, kin discrimination and the greenbeard effect.

Kin selection Edit

One specific form of cooperation in animals is kin selection, which involves animals promoting the reproductive success of their kin, thereby promoting their own fitness. [3] [5] [nb 1]

Different theories explaining kin selection have been proposed, including the "pay-to-stay" and "territory inheritance" hypotheses. The "pay-to-stay" theory suggests that individuals help others rear offspring in order to return the favor of the breeders allowing them to live on their land. The "territory inheritance" theory contends that individuals help in order to have improved access to breeding areas once the breeders depart. [10]

Studies conducted on red wolves support previous researchers' contention that helpers obtain both immediate and long-term gains from cooperative breeding. [5] Researchers evaluated the consequences of red wolves' decisions to stay with their packs for extended periods of time after birth. While delayed dispersal helped other wolves' offspring, studies also found that it extended male helper wolves' life spans. This suggests that kin selection may not only benefit an individual in the long-term through increased fitness but also in the short-term through increased survival chances. [11]

Some research suggests that individuals provide more help to closer relatives. This phenomenon is known as kin discrimination. [12] In their meta-analysis, researchers compiled data on kin selection as mediated by genetic relatedness in 18 species, including the western bluebird, pied kingfisher, Australian magpie, and dwarf mongoose. They found that different species exhibited varying degrees of kin discrimination, with the largest frequencies occurring among those who have the most to gain from cooperative interactions. [12]

Cooperation exists not only in animals but also in plants. In a greenhouse experiment with Ipomoea hederacea, a climbing plant, results show that kin groups have higher efficiency rates in growth than non-kin groups do. This is expected to rise out of reduced competition within the kin groups. [13]

The inclusive fitness theory provides a good overview of possible solutions to the fundamental problem of cooperation. The theory is based on the hypothesis that cooperation helps in transmitting underlying genes to future generations either through increasing the reproductive successes of the individual (direct fitness) or of other individuals who carry the same genes (indirect fitness). [3] Direct benefits can result from simple by-product of cooperation or enforcement mechanisms, while indirect benefits can result from cooperation with genetically similar individuals. [4]

Direct fitness benefits Edit

This is also called mutually beneficial cooperation as both actor and recipient depend on direct fitness benefits, which are broken down into two different types: by-product benefit and enforcement.

By-product benefit arises as a consequence of social partners having a shared interest in cooperation. For example, in meerkats, larger group size provides a benefit to all the members of that group by increasing survival rates, foraging success and conflict wins. [14] This is because living in groups is better than living alone, and cooperation arises passively as a result of many animals doing the same thing. By-product benefit can also arise as a consequence of subordinate animals staying and helping a nest that is dominated by leaders who often suffer high mortality rates. It has been shown that cooperation would be most advantageous for the sex that is more likely to remain and breed in the natal group. This is because the subordinate will have a higher chance to become dominant in the group as time passes. Cooperation in this scenario is often seen between non-related members of the same species, such as the wasp Polistes dominula. [15]

Prisoner's Delight, another term to describe by-product benefit, is a term coined by Kenneth Binmore in 2007 after he found that benefits can result as an automatic consequence of an otherwise "self-interested" act in cooperative hunting. He illustrated this with a scenario having two hunters, each hunter having the choice of hunting (cooperate) or not hunting (free-riding). Assuming that cooperative hunting results in greater rewards than just a one-player hunt, when hunting is not rare, both hunters and non-hunters benefit because either player is likely to be with other hunters, and thus likely to reap the rewards of a successful hunt. This situation demonstrates "Prisoner's Delight" because the food of a successful hunt is shared between the two players regardless of whether or not they participated. [16]

It has been shown that free riding, or reaping the benefits without any effort, is often a problem in collective action. Examples of free riding would be if an employee in a labor union pays no dues, but still benefits from union representation. In a study published in 1995, scientists found that female lions showed individual differences in the extent to which they participated in group-territorial conflict. Some lions consistently 'cooperated' by approaching intruders, while others 'lagged' behind to avoid the risk of fighting. Although the lead female recognized the laggards, she failed to punish them, suggesting that cooperation is not maintained by reciprocity. [17]

Cooperation is maintained in situations where free-riding is a problem through enforcement, which is the mechanism where the actor is rewarded for cooperating or punished for not cooperating. This happens when cooperation is favored in aiding those who have helped the actors in the past. Punishment for noncooperation has been documented in meerkats, where dominant females will attack and evict subordinate females who become pregnant. The pregnancy is seen as a failure to cooperate because only the dominant females are allowed to bear offspring. Dominant females will attack and kill the offspring of subordinate females if they evade eviction and eviction often leads to increased stress and decreased survival. [18]

Enforcement can also be mutually beneficial, and is often called reciprocal cooperation because the act of cooperation is preferentially directed at individuals who have helped the actor in the past (directly), or helped those who have helped the actor in the past (indirectly). [19]

Indirect fitness benefits Edit

The second class of explanations for cooperation is indirect fitness benefits, or altruistic cooperation. There are three major mechanisms that generate this type of fitness benefit: limited dispersal, kin discrimination and the green-beard effect.

Hamilton originally suggested that high relatedness could arise in two ways: direct kin recognition between individuals or limited dispersal, or population viscosity, which can keep relatives together. [20] The easiest way to generate relatedness between social partners is limited dispersal, a mechanism in which genetic similarity correlates with spatial proximity. If individuals do not move far, then kin usually surrounds them. Hence, any act of altruism would be directed primarily towards kin. This mechanism has been shown in Pseudomonas aeruginosa bacteria, where cooperation is disfavored when populations are well mixed, but favored when there is high local relatedness. [21]

Kin discrimination also influences cooperation because the actor can give aid preferentially towards related partners. Since kin usually share common genes, it is thought that this nepotism can lead to genetic relatedness between the actor and the partner's offspring, which affects the cooperation an actor might give.

This mechanism is similar to what happens with the green-beard effect, but with the green-beard effect, the actor has to instead identify which of its social partners share the gene for cooperation. A green-beard system must always co-occur within individuals and alleles to produce a perceptible trait, recognition of this trait in others, and preferential treatment to those recognized. Examples of green-beard behavior have been found in hydrozoans, slime molds, yeast, and ants. An example is in side-blotch lizards, where blue-throated males preferentially establish territories next to each other. Results show that neighboring blue-throats are more successful at mate guarding. However, blue males next to larger, more aggressive orange males suffer a cost. [22] This strategy blue has evolutionary cycles of altruism alternating with mutualism tied to the RPS game.

Multi-level selection theory suggests that selection operates on more than one level: for example, it may operate at an atomic and molecular level in cells, at the level of cells in the body, and then again at the whole organism level, and the community level, and the species level. Any level which is not competitive with others of the same level will be eliminated, even if the level below is highly competitive. A classic example is that of genes which prevent cancer. Cancer cells divide uncontrollably, and at the cellular level, they are very successful, because they are (in the short term) reproducing very well and out competing other cells in the body. However, at the whole organism level, cancer is often fatal, and so may prevent reproduction. Therefore, changes to the genome which prevent cancer (for example, by causing damaged cells to act co-operatively by destroying themselves) are favoured. Multi-level selection theory contends that similar effects can occur, for example, to cause individuals to co-operate to avoid behaviours which favour themselves short-term, but destroy the community (and their descendants) long term.

One theory suggesting a mechanism that could lead to the evolution of co-operation is the "market effect" as suggested by Noe and Hammerstein. [23] The mechanism relies on the fact that in many situations there exists a trade-off between efficiency obtaining a desired resource and the amount of resources one can actively obtain. In that case, each partner in a system could benefit from specializing in producing one specific resource and obtaining the other resource by trade. When only two partners exist, each can specialize in one resource, and trade for the other. Trading for the resource requires co-operation with the other partner and includes a process of bidding and bargaining.

This mechanism can be relied to both within a species or social group and within species systems. It can also be applied to a multi-partner system, in which the owner of a resource has the power to choose its co-operation partner. This model can be applied in natural systems (examples exist in the world of apes, cleaner fish, and more). Easy for exemplifying, though, are systems from international trading. Arabic countries control vast amounts of oil, but seek technologies from western countries. These in turn are in need of Arab oil. The solution is co-operation by trade.

Symbiosis refers to two or more biological species that interact closely, often over a long period of time. Symbiosis includes three types of interactions—mutualism, commensalism, and parasitism—of which only mutualism can sometimes qualify as cooperation. Mutualism involves a close, mutually beneficial interaction between two different biological species, whereas "cooperation" is a more general term that can involve looser interactions and can be interspecific (between species) or intraspecific (within a species). In commensalism, one of the two participating species benefits, while the other is neither harmed nor benefitted. In parasitism, one of the two participating species benefits at the expense of the other.

Symbiosis may be obligate or facultative. In obligate symbiosis, one or both species depends on the other for survival. In facultative symbiosis, the symbiotic interaction is not necessary for the survival of either species.

Two special types of symbiosis include endosymbiosis, in which one species lives inside of another, and ectosymbiosis, in which one species lives on another.

Mutualism Edit

Mutualism is a form of symbiosis in which both participating species benefit.

A classic example of mutualism is the interaction between rhizobia soil bacteria and legumes (Fabaceae). In this interaction, rhizobia bacteria induce root nodule formation in legume plants via an exchange of molecular signals. [24] Within the root nodules, rhizobia fix atmospheric nitrogen into ammonia using the nitrogenase enzyme. The legume benefits from a new supply of usable nitrogen from the rhizobia, and the rhizobia benefits from organic acid energy sources from the plant as well as the protection provided by the root nodule. Since the rhizobia live within the legume, this is an example of endosymbiosis, and since both the bacteria and the plant can survive independently, it is also an example of facultative symbiosis.

Lichens are another example of mutualism. Lichens consist of a fungus (the mycobiont) and a photosynthetic partner (the photobiont), which is usually a green alga or a cyanobacteria. The mycobiont benefits from the sugar products of photosynthesis generated by the photobiont, and the photobiont benefits from the increased water retention and increased surface area to capture water and mineral nutrients conferred by the mycobiont. Many lichens are examples of obligate symbiosis. In fact, one-fifth of all known extant fungal species form obligate symbiotic associations with green algae, cyanobacteria or both. [25]

Not all examples of mutualism are also examples of cooperation. Specifically, in by-product mutualism, both participants benefit, but cooperation is not involved. For example, when an elephant defecates, this is beneficial to the elephant as a way to empty waste, and it is also beneficial to a dung beetle that uses the elephant's dung. However, neither participant's behavior yields a benefit from the other, and thus cooperation is not taking place. [26]

Hidden benefits are benefits from cooperation that are not obvious because they are obscure or delayed. (For example, a hidden benefit would not involve an increase in the number of offspring or offspring viability.)

One example of a hidden benefit involves Malarus cyaneus, the superb fairy-wren. In M. cyaneus, the presence of helpers at the nest does not lead to an increase in chick mass. However, the presence of helpers does confer a hidden benefit: it increases the chance that a mother will survive to breed in the next year. [16]

Another example of a hidden benefit is indirect reciprocity, in which a donor individual helps a beneficiary to increase the probability that observers will invest in the donor in the future, even when the donor will have no further interaction with the beneficiary.

In a study of 79 students, participants played a game in which they could repeatedly give money to others and receive from others. They were told that they would never interact with the same person in the reciprocal role. A player's history of donating was displayed at each anonymous interaction, and donations were significantly more frequent to receivers who had been generous to others in earlier interactions. [27] Indirect reciprocity has only been shown to occur in humans. [28]

Even if all members of a group benefit from cooperation, individual self-interest may not favor cooperation. The prisoner's dilemma codifies this problem and has been the subject of much research, both theoretical and experimental. In its original form the prisoner's dilemma game (PDG) described two awaiting trial prisoners, A and B, each faced with the choice of betraying the other or remaining silent. The "game" has four possible outcomes: (a) they both betray each other, and are both sentenced to two years in prison (b) A betrays B, which sets A free and B is sentenced to four years in prison (c) B betrays A, with the same result as (b) except that it is B who is set free and the other spends four years in jail (d) both remain silent, resulting in a six-month sentence each. Clearly (d) ("cooperation") is the best mutual strategy, but from the point of view of the individual betrayal is unbeatable (resulting in being set free, or getting only a two-year sentence). Remaining silent results in a four-year or six-month sentence. This is exemplified by a further example of the PDG: two strangers attend a restaurant together and decide to split the bill. The mutually best ploy would be for both parties to order the cheapest items on the menu (mutual cooperation). But if one member of the party exploits the situation by ordering the most expensive items, then it is best for the other member to do likewise. In fact, if the fellow diner's personality is completely unknown, and the two diners are unlikely ever to meet again, it is always in one's own best interests to eat as expensively as possible. Situations in nature that are subject to the same dynamics (rewards and penalties) as the PDG define cooperative behavior: it is never in the individual's fitness interests to cooperate, even though mutual cooperation rewards the two contestants (together) more highly than any other strategy. [29] Cooperation cannot evolve under these circumstances.

However, in 1981 Axelrod and Hamilton [30] noted that if the same contestants in the PDG meet repeatedly (in the so-called iterated prisoner's dilemma game, IPD) then tit-for-tat (foreshadowed by Robert Trivers' 1971 reciprocal altruism theory [31] ) is a robust strategy which promotes altruism. [29] [30] [32] In "tit-for-tat" both players' opening moves are cooperation. Thereafter each contestant repeats the other player's last move, resulting in a seemingly endless sequence of mutually cooperative moves. However, mistakes severely undermine tit-for-tat's effectiveness, giving rise to prolonged sequences of betrayal, which can only be rectified by another mistake. Since these initial discoveries, all the other possible IPD game strategies have been identified (16 possibilities in all, including, for instance, "generous tit-for-tat", which behaves like "tit-for-tat", except that it cooperates with a small probability when the opponent's last move was "betray". [33] ), but all can be outperformed by at least one of the other strategies, should one of the players switch to such a strategy. The result is that none is evolutionarily stable, and any prolonged series of the iterated prisoner's dilemma game, in which alternative strategies arise at random, gives rise to a chaotic sequence of strategy changes that never ends. [29] [34] [35]

Results from experimental economics show, however, that humans often act more cooperatively than strict self-interest would dictate. [36]

In the light of the iterated prisoner's dilemma game and the reciprocal altruism theory failing to provide full answers to the evolutionary stability of cooperation, several alternative explanations have been proposed.

There are striking parallels between cooperative behavior and exaggerated sexual ornaments displayed by some animals, particularly certain birds, such as, amongst others, the peacock. Both are costly in fitness terms, and both are generally conspicuous to other members of the population or species. This led Amotz Zahavi to suggest that both might be fitness signals rendered evolutionarily stable by his handicap principle. [37] [38] [39] If a signal is to remain reliable, and generally resistant to falsification, the signal has to be evolutionarily costly. [40] Thus, if a (low fitness) liar were to use the highly costly signal, which seriously eroded its real fitness, it would find it difficult to maintain a semblance or normality. [41] Zahavi borrowed the term "handicap principle" from sports handicapping systems. These systems are aimed at reducing disparities in performance, thereby making the outcome of contests less predictable. In a horse handicap race, provenly faster horses are given heavier weights to carry under their saddles than inherently slower horses. Similarly, in amateur golf, better golfers have fewer strokes subtracted from their raw scores than the less talented players. The handicap therefore correlates with unhandicapped performance, making it possible, if one knows nothing about the horses, to predict which unhandicapped horse would win an open race. It would be the one handicapped with the greatest weight in the saddle. The handicaps in nature are highly visible, and therefore a peahen, for instance, would be able to deduce the health of a potential mate by comparing its handicap (the size of the peacock's tail) with those of the other males. The loss of the male's fitness caused by the handicap is offset by his increased access to females, which is as much of a fitness concern as is his health. A cooperative act is, by definition, similarly costly (e.g. helping raise the young at the nest of an unrelated pair of birds versus producing and raising one's own offspring). It would therefore also signal fitness, and is probably as attractive to females as a physical handicap. If this is the case, cooperation is evolutionarily stabilized by sexual selection. [38]

There is an alternate strategy for identifying fit mates which does not rely on one gender having exaggerated sexual ornaments or other handicaps, but is probably generally applicable to most, if not all sexual creatures. It derives from the concept that the change in appearance and functionality caused by a non-silent mutation will generally stand out in a population. This is because that altered appearance and functionality will be unusual, peculiar, and different from the norm within that population. The norm against which these unusual features are judged is made up of fit attributes that have attained their plurality through natural selection, while less well adapted attributes will be in the minority or frankly rare. [43] Since the overwhelming majority of mutant features are maladaptive, and it is impossible to predict evolution's future direction, sexual creatures would be expected to prefer mates with the fewest unusual or minority features. [43] [44] [45] [46] [47] This will have the effect of a sexual population rapidly shedding peripheral phenotypic features, thereby canalizing the entire outward appearance and behavior of all of its members. They will all very quickly begin to look remarkably similar to one another in every detail, as illustrated in the accompanying photograph of the African pygmy kingfisher, Ispidina picta. Once a population has become as homogeneous in appearance as is typical of most species, its entire repertoire of behaviors will also be rendered evolutionarily stable, including any cooperative, altruistic and social interactions. Thus, in the example above of the selfish individual who hangs back from the rest of the hunting pack, but who nevertheless joins in the spoils, that individual will be recognized as being different from the norm, and will therefore find it difficult to attract a mate (koinophilia). [46] Its genes will therefore have only a very small probability of being passed on to the next generation, thus evolutionarily stabilizing cooperation and social interactions at whatever level of complexity is the norm in that population. [35] [48]

One of the first references to animal cooperation was made by Charles Darwin, who noted it as a potential problem for his theory of natural selection. [49] In most of the 19th century, intellectuals like Thomas Henry Huxley and Peter Kropotkin debated fervently on whether animals cooperate with one another and whether animals displayed altruistic behaviors. [50]

In the late 1900s, some early research in animal cooperation focused on the benefits of group-living. While living in a group produces costs in the form of increased frequency of predator attacks and greater mating competition, some animals find that the benefits outweigh the costs. Animals that practice group-living often benefit from assistance in parasite removal, access to more mates, and conservation of energy in foraging. [51] Initially, the most obvious form of animal cooperation was kin selection, but more recent studies focus on non-kin cooperation, where benefits may seem less obvious. Non-kin cooperation often involves many strategies that include manipulation and coercion, making these interactions more complicated to study. [2] An example of manipulation is presented by the cuckoo, a brood parasite, which lays its eggs in the nest of a bird of another species. [16] That bird then is tricked into feeding and caring for the cuckoo offspring. Although this phenomenon may look like cooperation at first glance, it only presents benefits to one recipient.

In the past, simple game theory models, such as the classic cooperative hunting and Prisoner's dilemma models, were used to determine decisions made by animals in cooperative relationships. However, complicated interactions between animals have required the use of more complex economic models such as the Nash equilibrium. The Nash equilibrium is a type of non-cooperative game theory that assumes an individual's decision is influenced by its knowledge of the strategies of other individuals. This theory was novel because it took into consideration the higher cognitive capabilities of animals. [52] [53] The evolutionarily stable strategy is a refined version of the Nash equilibrium in that it assumes strategies are heritable and are subject to natural selection. Economic models are useful for analyzing cooperative relationships because they provide predictions on how individuals act when cooperation is an option. Economic models are not perfect, but they provide a general idea of how cooperative relationships work.


Hybrid Speciation: When Two Species Become Three

Salvin’s medium-billed prion, Pachyptila salvini, is apparently a hybrid species between the . [+] Antarctic prion, Pachyptila desolata, and the broad-billed prion, Pachyptila vittata. The Crozet Islands, where this bird was photographed, are a sub-Antarctic archipelago of small islands in the southern Indian Ocean. (Credit: Peter Ryan.)

Ligers! Tigons! And bears! Oh my!

Not long ago, I told you about a fascinating songbird that was discovered to be the hybrid offspring of three different species (more here). This unique bird raised an intriguing question: can hybrids give rise to a perfectly valid species?

Hybrid speciation is quite rare in animals, but it does occur naturally. In this scenario, the resulting hybrid population is an independent new species that is reproductively isolated from both parental species. One such example is the Heliconius butterfly (ref). These brightly colored butterflies are widespread throughout South and Central America and are even found in parts of North America. They are remarkable for their astonishing diversity of wing patterns and for extensive mimicry within the group.

Amongst birds, probably the best-known examples of hybrid species are the Italian sparrow, Passer italiae, golden‐crowned manakin, Lepidothrix vilasboasi, and a recently identified but currently unnamed Galapagos finch that was estimated to have first popped up in the 1980s (ref).

Despite these examples, the idea that a new species could evolve through the hybridization of two other species goes against Darwin’s thinking (ref) because it violates the fundamental definition of a species: reproductive isolation. Additionally, because species are adapted to their own special niches, and because hybrid offspring show a more-or-less intermediate blend of their parents’ characters, hybrids should be less adapted to either parent’s niche, and therefore, less likely to survive. As a result, hybrids tend to disappear over time. For these reasons, hybrid speciation is an almost completely foreign concept in the animal kingdom.

A hybrid species results when two species mate to create a fit hybrid that is unable to mate with . [+] members of its parent species. (Credit: Andrew Z. Colvin / CC BY-SA 4.0)

Andrew Z. Colvin via a Creative Commons license

However, in the very rare situation where a hybrid species is more adapted to a specific niche than are both of its parental species, the hybrid may replace one or both of its parent species, or it may establish its own place in a special niche that was previously unoccupied.

There are, of course, genetic constraints that work against hybrid speciation in animals. The most persistent hybrid species possess the same number of chromosomes as both parental species. This means both parental species must be closely related to avoid genetic and developmental problems associated with unpaired chromosomes in their hybrid offspring. This form of hybridization, known as homoploid hybrid speciation, is most common amongst animals. (The most famous mammalian hybrid, the mule, is the product of a horse and a donkey, which have different numbers of chromosomes, thus rendering their hybrids infertile.)

A most surprising discovery

“Actually, we were looking at the relationships among the the prions, of the monophyletic genus Pachyptila, with a distribution exclusive to the Antarctic and sub-Antarctic waters of the Southern Ocean,” said Juan Masello, a Principal Investigator in the Department of Animal Ecology & Systematics at Justus Liebig University. Dr. Masello specializes in the behavioral ecology, parasitology, and molecular ecology of wild populations of birds, particularly parrots and seabirds. Dr. Masello investigates population genetics under the mentorship of co-author, Yoshan Moodley, a professor of zoology at the University of Venda.

Pachyptila prions are a small group of closely-related seabirds that have the same ancestor (“monophyletic”). They are pigeon-sized, with white underparts, blue-grey upper parts, and a soot-colored “M” that extends across their back from one long slender wingtip to the other. They roam widely across the Antarctic Ocean and they all look remarkably similar to each other, especially when glimpsed as they zoom over rough, wind-tossed sub-Antarctic seas.

Dr. Masello, Professor Moodley and their collaborators were carefully examining these enigmatic seabirds to finally identify precisely how many Pachyptila species there are.

“Based on phylogenetics, between two and seven species were recognised, however this was controversial,” Dr. Masello and Professor Moodley explained in email.

But as Dr. Masello, Professor Moodley and their collaborators worked to identify how many species there are, they ran across something . strange.

“We investigated these relationships in two previous studies [ref and ref] but noticed that something was different than expected in [Salvin’s medium-billed prion] salvini,” Dr. Masello said in email. So Dr. Masello, Professor Moodley and their collaborators investigated further.

Because each species of prion breeds only on one or on a few very specific sub-Antarctic islands and at their own distinct times of the year, Dr. Masello, Professor Moodley and their collaborators could map out exactly where and when each species’ nest burrows could be found.

They showed that the hybrid species, Salvin’s medium-billed prion, Pachyptila salvini (grey circle Figure 1), only breeds on Marion Island (grey circle Figure 1), so this species is maintained as genetically separate from both of its parental species, the broad-billed prion, Pachyptila vittata (orange circles Figure 1) and the Antarctic prion, Pachyptila desolata (green circles Figure 1).

FIG. 1. Pachyptila (Aves: Procellariiformes) breeding colonies sampled in this study. The different . [+] species are color-coded. Slender-billed prions (Pachyptila belcheri): blue triangles. Antarctic prions (Pachyptila desolata): green circles. Broad-billed prions (Pachyptila vittata): orange circles. Salvin’s prions (Pachyptila salvini): grey circle. Fairy prions (Pachyptila turtur): purple circles. Colonies are named after the island where they are located: Rangatira I. (Chatham Is.), Noir I. (Chile), New I. (Falkland/Malvinas Is.), Beauchêne I. (Falkland/Malvinas Is.), Bird I. (South Georgia/ Georgias del Sur), Gough I., Nightingale I. (Tristan da Cunha), Marion I. (Prince Edward Is.), Verte I. (Kerguelen Is.), Mayes I. (Kerguelen Is.), Macquarie I., Stephens I. (New Zealand). (doi:10.1093/molbev/msz090)

Bird bills are specialized cutlery that evolved for particular diets

Not only can prions be identified by where and when they breed, but their bills are different, too. In fact, the length, width and heighth of bird bills are critically important for efficient foraging. Thus, Pachyptila prion species can be distinguished in-hand by carefully examining their bills: three of the six species in the genus have flattened bills with a fringe (lamellae) on the sides that act as strainers to retain small marine crustaceans and fishes, similar to how baleen whales feed. This structure is reflected in these birds’ common name, which comes from the Greek priōn (“saw”), a reference to the serrated edges of the birds’ saw-like bill. They also are commonly known as “whalebirds”.

When Dr. Masello, Professor Moodley and their collaborators measured the dimensions of the bills for all six of the Pachyptila species, they found no overlap between any of the species (Figure 2):

FIG. 2. Bill width versus bill length for all Pachyptila (Aves, Procellariiformes) species sampled. . [+] Species are color-coded [Broad-billed prions (Pachyptila vittata): orange circles. Salvin’s prions (Pachyptila salvini): grey circles. Antarctic prions (Pachyptila desolata): green circles. Slender-billed prions (Pachyptila belcheri): blue circles. Fairy prions (Pachyptila turtur): purple circles.], circles denote means per colony, and error bars correspond to standard deviations. Only data from live individuals or fresh corpses were included. (doi:10.1093/molbev/msz090)

What do the genes tell us?

Dr. Masello, Professor Moodley and their collaborators sequenced and analyzed DNA from 425 individuals for five of the Pachyptila species, and for the closely-related blue petrel, Halobaena caerulea. Genetically, the mitochondrial DNA (mtDNA) groups Salvin’s medium-billed prion in with the Antarctic prion, yet nuclear microsatellite DNA places it with either the Antarctic prion or the broad-billed prion, depending on the method used to estimate genetic distance. A hybrid origin for Salvin’s medium-billed prion could explain these unusual results.

But what surprised Dr. Masello most about this study’s findings? That the combination of parental traits led to both increased fitness and reproductive isolation for Salvin’s medium-billed prion, he said.

This study shows that “hybridization between species is not necessarily the end of the line for evolution, and that sometimes, a new species can be formed this way,” Dr. Masello elaborated in email.

“It also draws our attention to the idea that this method of speciation might be more common than first thought, and especially in recently or rapidly evolving groups of species, where reproduction isolation has not fully developed.”

Juan F. Masello, Petra Quillfeldt, Edson Sandoval-Castellanos, Rachael Alderman, Luciano Calderón, Yves Cherel, Theresa L. Cole, Richard J. Cuthbert, Manuel Marin, Melanie Massaro, Joan Navarro, Richard A. Phillips, Peter G. Ryan, Lara D. Shepherd, Cristián G. Suazo, Henri Weimerskirch, and Yoshan Moodley (2019). Additive Traits Lead to Feeding Advantage and Reproductive Isolation, Promoting Homoploid Hybrid Speciation, Molecular Biology and Evolution, msz090 | doi:10.1093/molbev/msz090

Although I look like a parrot in my profile picture, I'm an evolutionary ecologist and ornithologist as well as a science writer and journalist.

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Although I look like a parrot in my profile picture, I'm an evolutionary ecologist and ornithologist as well as a science writer and journalist.


Conclusions

Here we studied the biogeography of the rat snake E. sauromates from the Balkans, Anatolia, Caucasus, and Ponto-Caspian region using both molecular and morphological data. We found that the taxon is, in fact, comprised of two distinct evolutionary lineages and the cryptic lineage represents a new species that we name E. urartica sp. nov. Both species split from their common ancestor around the Miocene-Pliocene boundary and their recent genetic structure was mainly influenced by Pleistocene climatic oscillations.


Watch the video: Η θεωρία της εξέλιξης των ειδών του ΚΑΡΟΛΟΥ ΔΑΡΒΙΝΟΥ (August 2022).