Emergence of Alternative Reproductive Tactics in Simulated Robot Colonies

Abstract

Alternative reproductive behaviour, in which individuals of one sex adopt different ways to reproduce, is observed in all major taxa, including mammals, amphibians, insects, and particularly fishes. In order to study ecological conditions for emergence of alternative reproductive tactics (ARTs), we developed an embodied evolution framework incorporating ecological features, such as body size and energy maintenance, where male and female robotic agents naturally face both intersexual and intrasexual interactions for survival and reproduction. We performed simulation experiments in environments with different conditions (food density, reproductive cost, and male-female ratio) and found that ARTs emerged both in males and females. Males evolved three kinds of alternative tactics: fixed, genetically distinct ARTs, in which dominant and sneaker males that differ in body size adopt different tactics to gain access to females, conditionally flexible ARTs, in which individuals change tactics according to body size, and mixed ARTs, in which combinations of genetically fixed and conditionally flexible ARTs are employed. Females evolved two genetically distinct ARTs: quality-oriented female, QoF, and number-oriented female, NoF, in which females increase fitness either by offspring quality or quantity, respectively. Analysis of results confirms the experimental notions that genetically fixed male ARTs are strongly affected by intensity of sexual selection. Conditionally flexible male ARTs are significantly affected by competition level, and female ARTs are mainly affected by food availability. To our knowledge, this study is the first to demonstrate emergence of ARTs in both males and females from an initially monomorphic population in a simulated, embodied evolution framework.