The evolution of extreme altruism and inequality in insect societies

Abstract

In eusocial organisms, some individuals specialize in reproduction and others in altruistic helping. The evolution of eusociality is, therefore, also the evolution of remarkable inequality. For example, a colony of honeybees (Apis mellifera) may contain 50 000 females all of whom can lay eggs. But 100 per cent of the females and 99.9 per cent of the males are offspring of the queen. How did such extremes evolve? Phylogenetic analyses show that high relatedness was almost certainly necessary for the origin of eusociality. However, even the highest family levels of kinship are insufficient to cause the extreme inequality seen in e.g. honeybees via 'voluntary altruism'. 'Enforced altruism' is needed, i.e. social pressures that deter individuals from attempting to reproduce. Coercion acts at two stages in an individual's life cycle. Queens are typically larger so larvae can be coerced into developing into workers by being given less food. Workers are coerced into working by 'policing', in which workers or the queen eat worker-laid eggs or aggress fertile workers. In some cases, individuals rebel, such as when stingless bee larvae develop into dwarf queens. The incentive to rebel is strong as an individual is the most closely related to its own offspring. However, because individuals gain inclusive fitness by rearing relatives, there is also a strong incentive to 'acquiesce' to social coercion. In a queenright honeybee colony, the policing of worker-laid eggs is very effective, which results in most workers working instead of attempting to reproduce. Thus, extreme altruism is due to both kinship and coercion. Altruism is frequently seen as a Darwinian puzzle but was not a puzzle that troubled Darwin. Darwin saw his difficulty in explaining how individuals that did not reproduce could evolve, given that natural selection was based on the accumulation of small heritable changes. The recognition that altruism is an evolutionary puzzle, and the solution was to wait another 100 years for William Hamilton.

Evolutionary history predicts the stability of cooperation in microbial communities

“…The increased sensitivity of defectors to genetically related cooperators points to a suppression of close kin refusing to cooperate. This resembles policing in social Hymenoptera suppressing reproductive workers that reinforces cooperation once established 36 ; however, in social Hymenoptera policing increases with genetic distance 37 whereas in P. fluorescens it is most pronounced against closely related defectors. As a result, mixtures of closely related genotypes will stably cooperate because the emerging defector suffers from toxins of all the clonal and close kin cells of the parental strain.…”

Positive effects of multiple gene control on the spread of altruism by group selection

“…For odd g and t = g/2 , the frequency of the altruists p a equals p (the case for models 4,8). We can say that certain allele is active if its change (from altruistic to selfish or vice versa) changes the phenotype of the individual.…”

“…It can be relatively easily explained in systems where either reciprocity [1] or preferential help to genetically related individual, i.e., kin selection [2,3,4] occurs. The origin and persistence of altruistic behavior in systems without reciprocity and preferential help to genetically related organisms, i.e., the evolution by the form of group selection called interdemic selection, can also be explained, but the explanation is much more difficult [5,6,7].…”

The evolution of altruism

“…This leads to a prediction -eusociality should often be associated with a monogamous mating system. William Hughes and his colleagues tested this idea using already published data that suggested that eusociality has independently evolved five times in bees, three times in wasps, and once in ants (Hughes et al, 2008;Ratnieks, Helantera, 2009). …”