Cooperative Breeding in Insects and Vertebrates

by

Anne-Katrin Eggert

• LAST REVIEWED: 13 January 2014
• LAST MODIFIED: 13 January 2014
• DOI: 10.1093/obo/9780199941728-0024

Introduction

Cooperative breeding in the broadest sense occurs in animals with parental care when individuals provide parental care to young that are not their own offspring (“alloparental care”). When defined in this manner, cooperative breeding occurs in about 9 percent of known species of birds, 2 percent of mammals, and less than 1 percent of fishes, less than 0.1 percent of insects (thousands of species, most of them aculeate Hymenoptera), and a few species of arachnids and crustaceans. What has kept evolutionary biologists interested in this phenomenon is the fact that individuals provide potentially costly care to young that are not their direct descendants and thus, do not immediately increase the number of their own offspring (their “direct fitness”). In insects, the existence of sterile worker castes was well recognized by Darwin as a special challenge to his theory of natural selection, but in vertebrates, cooperative breeding was largely written off as an occasional unusual phenomenon, except when it involved group breeding parents rearing young together for a mutual benefit. This perspective was profoundly altered in 1964 by Hamilton’s idea that unselfish acts could be selected for even if the beneficiaries are relatives other than the actor’s direct descendants. His new theory of inclusive fitness or kin selection that elaborated on this idea offered a possible evolutionary explanation for many aspects of social behavior and led to the rapid expansion of the new field of behavioral ecology or sociobiology. George C. Williams and Jerram Brown were the first to recognize the importance of this new theory for cooperative breeding.

Even before the advent of Hamilton’s theory, evolutionary ecologists had begun to explore the influence of ecological factors on social structure and dispersal patterns, including cooperative breeding. Since then, interest in cooperative breeding has steadily expanded, further accelerated by the development of molecular techniques to assess relatedness in natural populations and the application of game theory (a branch of mathematics much utilized in evolutionary biology and mathematical economics) to social behavior. Empirical studies have provided insight into some astonishing adaptations in cooperative breeders. The ecological conditions favorable for helping, direct (own offspring) and indirect (relative’s offspring) fitness benefits of cooperative behavior, and possible conflicts of interest arising in cooperative social groups have all inspired much research, as have possible theoretical explanations of cooperative breeding. Reproductive skew theory, which considers factors that may affect the division of reproductive benefits between cooperative breeders, has produced many new models and predictions for social systems, and had been thought of as a possible avenue toward providing an overarching universal explanation for cooperative breeding in general.

However, many authors have concluded that cooperative breeding will never have a generally applicable and readily testable evolutionary explanation, largely because of the enormous variety of phenomena subsumed under this label, with hugely different ecological situations and genetic social structures between and within different taxonomic groups such as birds, mammals, and insects. Although cooperative breeding remains an active area of research, there is still no generally accepted definition of cooperative breeding and important related terms such as cooperation, communal breeding, and altruism.

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