Evolution of insect sociality- a review of some attempts to test modern theories

Abstract

An important feature of insect societies is the presence of a sterile worker caste that makes it possible for the fertile queens to produce a large number of offsprings. The mechanism of evolution by natural selection of such sterility and similar, though less extreme, forms of altruism has long been considered as a paradox. In recent years a large body of theoretical ideas has accumulated that purports to explain altruistic behaviour within the framework of the theory of natural selection. With special reference to insect sociality three theories namely kin selection, parental manipulation and mutualism have been suggested. Some attempts have now been made to empirically test the mutually exclusive predictions arising out of these alternative theories. A somewhat different approach to empirically distinguishing between kin selection and parental manipulation is to measure sex-investment ratios. This approach was at one time believed to have provided overwhelming support in favour of the theory of kin selection. It has now been realised that several complicating factors such as local mate competition and multiple mating have to be considered before arriving at appropriate theoretical predictions of the two rival theories. I argue in this paper that rigorous quantitative studies on inter-individual variations in behavioural strategies in primitively cusocial insects constitutes yet another approach that is likely to help in understanding the forces that mould the evolution of insect societies.