Social environment and the evolution of male reproductive strategy

Abstract

Reproduction is by its very nature a social interaction, and should therefore be considered in a social context. By altering the interactions between individuals, social conditions can modify the costs and benefits of reproductive strategies, and hence the evolution of mating behaviour generally. The effect of the social environment is particularly pertinent to studies of male reproductive behaviour due to the competitive nature of male sexual effort. Males must balance the costs of courtship, risk of competition, likelihood of mating, and abundance of alternative mates when considering where and how to invest their reproductive effort. All these factors are shaped by the social environment, which ultimately changes the selective landscape in which male reproductive strategies operate. Here I examine the interaction between the social environment and reproductive strategies using both empirical studies of fish and theoretical modelling approaches. I show that courtship of male guppies, Poecilia reticulata, changes as a function of their social environment, ultimately modifying the costs of lifelong sexual effort. I then use mathematical modelling to predict how different male reproductive strategies will perform as social conditions change, demonstrating that the success of reproductive strategies depends on the abundance of mates and the reproductive strategies used by competing males. I go on to test these predictions empirically, showing that exposing male guppies to social environments differing in female abundance and variance of female quality affects male reproductive strategies employed in subsequent mate encounters. I also examine how animals choose among social groups that offer different reproductive opportunities using two species of social fish, Neolamprologus pulcher and Dascyllus aruanus. I show that reproductive opportunities may be outweighed by survival benefits when animals choose among social groups, and that the reaction of existing group residents can strongly affect the realisation of an individualʼs group membership preferences. Combined, the results of this thesis demonstrate the strong influence of social conditions on a broad range of reproductive behaviours, highlighting the need to examine the evolution of reproductive behaviour in the context of the social environment.