An Evolutionary Basis for Eusociality

An Evolutionary Basis for Eusociality

Meganeura
Meganeura
Aug 6, 2011, 6:26 PM |
0

Theory of Labor Specialization in Apocrita

This is where the true mechanics of life and the most accurate descriptions of evolution are to be found. Selfish Gene Theory has plenty of interesting discussion regarding the interplay between sex ratios, segregation distorters, parasites, altruism, symbiosis, and game theory, all of which empirically support the thesis. There is also one example that is particularly revealing - why do the social insects, such as ants, bees, and wasps, have sterile castes (workers/soldiers) while only their queen is fertile...would it not be far more advantageous to the species to have every female reproducing? From the perspective of the individual it makes no sense...for posterity, naturally every viable contender should want to make their own unique contribution to the gene pool rather than rely on another's, especially in the event that they are more fit with respect to any changing environmental conditions. In his On the Origin of Species, Charles Darwin mentioned this manifestation specifically as the "one special difficulty, which at first appeared to me insuperable, and actually fatal to the whole theory. I allude to the neuters or sterile females in insect communities". The evolution of sterile traits seems to defy selective fitness; unproductive genomes cannot themselves replicate and so must be ultimately considered to be no more than evolutionary dead ends themselves!

The answer thus lies in individual gene perspectives: In hymenoptera there are several different sex alleles; heterozygous diploid eggs become females while haploid (and the much rarer homozygous diploid) eggs become male. A mother with 100 maternal genes will give her daughter or arrhenotokous (unfertilized) son 50 maternal genes. The daughter will also have 50 paternal genes, which is the full set of genes of the father (who was haploid). So both daughters and sons are only 50% related to the mother because they only share half of her genes with her. Sisters, on the other hand, are at the very least 50% related to each other because their father's sperm, being haploid, were all identical. If there is a 50% chance that they share the same maternal genes as well, then they are 75% related. Because of this, sisters are more closely related to each other than they would be to their own offspring and it is thus far more feasible for a gene to reproduce by promoting the replication of sisters (which will house 75% of the genes, 100% of which would individually 'like' to be passed on) over offspring (which will only house 50% of the genes) in the hopes that it will then replicate along with the other genes. This way (in an asymmetric mating scheme) it is possible for any genes that encourage forced mass-replication in an individual to become statistically favored for doing so.

Thus, it is the individual gene that is hoping for a shot at replication, and it gets a better chance by protecting the queen than protecting itself - the queen genes (which provide little more to the colony than genitalia) are merely considered a sister-harvesting mechanism that is harnessed and controlled by the more powerful caste genes (after all, it is the workers that select the queen as a larva when they feed her a special diet and the soldiers that have the most sophisticated and powerful roles). This segregation of duties has allowed a diversification of specialized labor to occur as selective expressions of the strain's own hereditary information that mimics the variation of function in our own internal organs and rivals the scope of our entire civilization unlike any other animal - ants are able to harvest food, conquer other species of ants in actual warfare, and harness sterile workers as slaves to their own colony, a benefit for their sister genes alone. You may wonder, what is the point of meiotic sex if the ultimate goal is to replicate all of the genes in a genotype, which is better accomplished by simple mitosis? The merit of sex lies in that although agamogenetic species might evolve and become selected, the redistribution of these beneficial acquired genes permits a natural process of experimentation with potentially superior recombinations that is not at all inhibited by the sexual bias of apocrita (in mothers) - the offspring of any set of parents are at most 50% related to each one!

As half of the male genome is missing, sisters can reproduce in large quantities but not in many generations because labor divisions allow an excess of resources to support the colony and free the queen to have many young for a long time without stopping. The fact that this reproduction occurs in one generation rather than many also allows the strain to avoid inbreeding depression, which would be more likely to occur if the nearly-identical sisters were to reproduce by themselves repeatedly and so combinatorially pair identical weak alleles (that are better supported by independently viable father alleles and so promote an even quicker imbalance of allele frequencies in favor of a stereotypical male) with males that only contribute one homolog (which in isolation has half the opportunity to adapt or evolve and might also quickly become defective). Eusocial queens are known to mate with many, many drones immediately before founding a colony, and experiments have shown that kin selection (such as that required to maintain centralized organization within all the enterprises of an individual colony despite very competitive conditions) precedes eusociality: matings of many females with a single male (or viable male chromosome in species with feminisation by fertilization) among monogamous insects leads to eusociality and queen mating with multiple males; I believe that hemizygous (or inbred homozygous) male polygyny resulted from the constant selection of the male sexual dimorphism (due either to harsh environments or a lack of eclectic female tastes) in certain insects, which then accelerated a bottlenecking of whole male genotypes (rather than genes) and a preference for diploid females, making (by surplus of organized labor in the form of unique female groups) a caste-defined totipotency (which compensates for gender inequalities, as by virtue of the spontaneous need for a stable genome the castes can now define colony roles more efficiently than the genders) in whole caste phenotypes and eventually even polyandry statistically preferable to monogamy despite even the most contrary evidence.