Evolution of Altruism and Eusociality: Toward a Cost/Benefit Analysis of Fitness and Genetic Relatedness
Kohn, Michael H
Doctor of Philosophy
Altruism is a behavior that benefits others at a cost to one’s own ability of survival and/or reproduction; that is, individual fitness. Thus, altruism poses great challenges to Darwin’s theory of evolution by natural selection on individual fitness. Altruistic behaviors are commonly performed in eusocial animals, such as nearly all hymenoptera (including bees, wasps, and ants), termites, ambrosia beetles, and so on. Inclusive fitness theory predicts that altruistic behavior can evolve when sufficient fitness benefits are given to relatives even though individual fitness is reduced. A different modeling approach has led to a challenge to this theory. The modelers claim that relatedness is not causal, that eusocial behavior is very hard to evolve requiring more workers before the queen increased fitness, and that there is no conflict involved. Here I showed that, even within the terms of this modeling framework, inclusive fitness thinking leads to insights that completely change these conclusions. I showed that relatedness and inclusive fitness indeed are causal and that eusociality does evolve more readily. With regard to the latter this means eusociality can be favored under a lower benefits threshold. I concluded that multiple modeling approaches are useful and that efforts to synthesize them are better than asserting that one is universally better than the other. Moreover, either greenbeard effects or genetic kin recognition requires genetic polymorphisms as cues on which recognition is based. Previous models showed that selection eliminates rare cue alleles and a common allele gets fixed, i.e. altruism cannot persist. So it is unclear how genetic recognition for altruism persists under a Darwinian selection framework. Here, I designed a novel model with three types of genetic components (production, perception, and action). I analyzed my recognition model theoretically toward a cost/benefit analysis of fitness and genetic relatedness. I predicted the stability of recognition for altruism based on my model. Furthermore I tested my recognition model through various computational and biological simulations. My simulation results consistently showed altruism could maintain multiple recognition cues and be evolutionarily stable; given the assumptions of my model. I concluded that cost/benefit of fitness and genetic relatedness both play critical roles in the evolution of altruism and eusociality, and therefore can maintain the stability of recognition for altruism.