Uncertainty and the evolution of altruism

: theory and fieldwork in the paper wasps of Central and South America

Abstract

The evolution of altruism (costly self-sacrifice in the service of others) has fascinated biologists since the origins of evolutionary biology. Why should selection favour altruism over self-interest? Nowhere is the problem more striking than in the social insects, where large numbers of non-reproductive workers raise the offspring of reproductive queens. For over fifty years, the dominant explanation for altruism has been ‘inclusive fitness’ theory and an associated principle known as ‘Hamilton’s rule’, which emphasises the role of relatedness: altruists help carriers of shared genes. In this thesis, I explore two outstanding problems in the evolution of altruism and inclusive fitness theory. First, does altruism evolve differently in unpredictable environments? Second, what explains the evolution of altruism by Neotropical Polistes wasps to foreign queens, a situation in which ‘drifting’ workers paradoxically divert help to distant relatives? To answer the first question, I show that altruism in unpredictable environments can be favoured without any effects on the expected reproductive success of recipients – and, in principle, can evolve even if both altruist and recipient suffer a reduction in expected reproductive success. Instead, altruists can confer volatility-suppressing benefits on recipients, stabilising their otherwise uncertain reproduction. This extends ‘bet-hedging’ theory to social behaviour, and implies a stochastic version of Hamilton’s rule that differs from the interpretation of Hamilton’s rule commonly used empirically. To answer the second question, I use field experiments in the paper wasp Polistes canadensis in French Guiana and Panama, and Polistes satan in Brazil. Using a combination of radio-tagging, queen removals, recognition tests, and a longitudinal study of brood development, I explore various hypotheses for ‘drifting’. I argue that two recently published hypotheses for cooperative ‘drifting’ in Polistes may be unlikely to provide a general explanation for paradoxical altruism. Using longitudinal data, I show strong diminishing returns to cooperation in free-living colonies, which may represent an adaptive context in which altruism to more distantly-related recipients can evolve. Finally, I discuss the tension between adaptive and neutral explanations of subtle social traits.

Date of Award	23 Jan 2019
Original language	English
Awarding Institution	University of Bristol
Supervisor	Andrew N Radford (Supervisor) & Seirian Sumner (Supervisor)