Term Paper: Kin Selection the Organization

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[. . .] Deleterious genetic mutations would be purged from the population and the inbred species may be prone to evolve sociality as all members of a colony have nearly identical genetic backgrounds. In addition to consanguineous matings (inbreeding), the process of genetic drift can also produce high levels of inbreeding.

Genetic drift is the random loss of alleles from a population owing to small population size. As increasing number of alleles are lost over a period of time, a single allele has the chance to increase in frequency and become predominant in a population. In extreme cases all copies of alleles are identical by descent. In a colony of a small number of individuals who do not intermix with other colonies the conditions are ideal for kin selection. Naked mole rats are a good example of such small colonies, which have a high degree of relatedness and show great differences between colonies. Such inbreeding might promote eusociality. (Inbreeding and genetic relatedness)

The genetic makeup of a given population is subject to changes resulting from interaction with the environment. The basic premise of Darwinian Theory of evolution is that natural selection acts on the individual, specifically on differences in the phenotypes within the population. However, in recent years, researchers tend to view selection as acting at several different levels and that these levels are loosely structured according to hierarchies of biological organization: gene - individuals - kin - groups - species. These five levels of selection are arranged along a continuum describing the degree of genetic relationship. Genes are fundamental unit, which is used to define genetic relationships. In a lineal relationship, a gene is identified its descent from another gene. That is at some time in its history the two genes were derived from a single gene by duplication, specially, meiosis during sexual reproduction.

Dawkins strongly advocates that selection acts on genes rather than on individuals as such and his theory of gene selection is provocatively referred to as the selfish gene theory. Next in the hierarchy is individual selection. Kin selection is a concept closely related to individual selection. Closely related individuals benefit from altruistic acts that promote inclusive fitness of an individual. Related individuals are likely to share many genes with a given individual. Asexual clones share all their genes. A sexual individual inherits genes fro male and female parents. Kin share genes. Siblings share 0.5 of alleles at most loci and cousins share 1/8 of their genes as they are further removed in their genetic relationships. Members of a group may not have to share genes. However, the group survives or dies as a function of how their genes and individuals react. Group selection is a concept that is subject to much debate in evolutionary biology because is difficult concept to grasp.

Selection at the group level occurs when a group of individuals produce more groups and therefore the process of group selection is analogous to individual selection, though acting at the level of groups. The traits underlying group selection must be genetic if the species is to evolve as by group selection. Species selection acts at a higher level, with members of each species sharing more genes than two individuals from a different species. Members of a group of closely related species, clade, that produce more species, have a long evolutionary history and lower extinction probability, will become overly represented at the expense of other species in much the same way as that one allele at a particular locus spreads through a population of individuals and increase in frequency at the expense of alternative alleles. (Levels of selection)

Kin selection does not operate only in on organisms that live as eusocial colonies. It is likely to operate wherever kin live in close proximity. Cannibalism is a widespread trait often found in monotypic stands of a species and when food becomes scarce or limited. Under such conditions cannibalism is resorted to. Pfenning, in his experiments with larvae of tiger salamander found that the incidence of cannibalism was less in tubs that housed siblings than in those that housed half sibs. Tubs, which housed unrelated individuals, scored the highest incidence of cannibalism. These results suggest that the larvae have kin recognition and that kin recognition alters the behavior of cannibalism. Presumably, the larva that does not eat kin will be favored by kin selection by inclusive fitness. Pfennig suggests that recognition of self or, more appropriately kin may form the distinct food eaten by groups of larvae. The larvae aggregate after hatching and a group of related larvae may remain in the group long enough to assimilate the common set of food odors that they share with their kin. (Kin selection and cannibalism)

Dawkins and other supporters of the theory of genic selection base their argument on the fact that selection changes the combination of alleles at a genetic locus. Therefore, they argue gene or genic locus must be the fundamental unit of selection. This however, is a reductionist approach according to Sinervo. If natural selection alters the allele frequency at a gene locus, the reductionist approach will reduce the problem to the lowest common denominator is all evolutionary theories, namely the gene. What is needed is a theory that connects selection and inheritance to at least some aspect of the phenotype. For example, since a gene codes for a protein, the protein could be considered as the smallest unit of the phenotype that comprises a functional unit. Studies on the selection of individual traits tend to reduce the phenotype to small parts, as a simplification necessary for statistical analysis.

However, it must be noted that individual traits are not units of selection. Every trait in an organism must be analyzed and their correlation between other traits studied, in order to completely describe the evolution of a species. In the study of behavioral traits the selection on morphological and physiological traits that might be functionally or mechanistically correlated with behavior must be considered. This approach to studying individual selection focuses on the whole organism. A good example for correlated selection is Brodie's study on garter snake morphology (striped vs. spotty) and behavior (straight slither vs. reversals) (Is the unit of selection the gene? Or the individual organism?)

The case of t-allele illustrates a 'selfish gene'. Some population of mice possesses a mutation that distorts the normal mitotic products of male mice. This mutation is located in at the t-locus. If the wild type allele at the t-locus is denoted as t+ and the mutant allele at the t-locus as t, then +/+ will produce normal wild type sperm; t/+ will produce normal sperm, however, the ratio of sperm of t-allele vs. +- allele will be distorted from the expected 50:50 by meiotic process. These heterozygotes produce 85-95% t allele sperm and only 5-15% +-allele sperm. t/t homozygotes are sterile. Because t/+ produces an over abundance of t-allele, the t-allele is termed as a selfish gene. Such a mutation, when it arises in a population, will spread rapidly and is a classic notion of a selfish gene.

The t-allele cannot spread beyond a certain frequency since that will result in the entire population becoming sterile. The t-allele needs a few +- alleles to propagate it. However, when two t-alleles end up in a single individual selection limits the spread of the allele. In this example, the genic selection that favored the production of t-allele over wild type allele is counterbalanced by individual selection that favored wild type or homozygous t-alleles. The question that now arises is: Is it also possible for genic selection to be counterbalanced by kin selection? Though there is no concrete example of such a process, it is possible to imagine a hypothetical example. (Selfish gene)

Suppose two parental birds are rearing a brood of young and a new "greedy" arises in the nest causing a chick to eat all the food, depriving other chicks of food. While the chick that has the "greedy" allele may grow up successfully, the other chicks might die. The greedy gene thus acquires a great selection advantage. However, the nests with the greedy gene produce fewer fledglings than nests containing wild type individuals. Those kin groups, which do not have the greedy gene, have a fecundity advantage relative to the kin groups where the greedy gene is present. To extend this analogy to groups of individuals not genetically related raises the question: can altruistic gene spread in such groups or will the non-altruistic (greedy) gene spread faster? Action of gene selection can be counterbalanced by the action of individual or kin selection, and the action of kin selection can be counterbalanced by the action of kin selection. The additional possibility of social selection is seen in fire ants in which non-reproductive castes alter the fitness outcome of reproductive castes and pose challenges for the study of levels of selection. (Genic, individual and kin selection)

The term "siblings" is applied to full… [END OF PREVIEW]

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