Occasional cooperative breeding in birds and the robustness of comparative analyses concerning the evolution of cooperative breeding

Michael Griesser,Toshitaka N Suzuki

doi:10.1186/s40851-016-0041-8

Abstract

Cooperative breeding is a widespread and intense form of cooperation, in which individuals help raise offspring that are not their own. This behaviour is particularly well studied in birds, using both long-term and comparative studies that have provided insights into the evolution of reproductive altruism. In most cooperatively breeding species, helpers are offspring that remain with their parents beyond independency and help in the raising of younger siblings. However, many cooperatively breeding species are poorly studied, and in 152 species, this behaviour only has been observed infrequently (i.e., occasional cooperative breeding). Here we argue that the parental care mode of these 152 species needs to be treated with caution, as factors associated with occasional cooperative breeding may differ from those associated with “regular” cooperative breeding. In most cooperatively breeding species, helpers provide alloparental care at the nests of their parents or close relatives; however, only in one occasionally cooperatively breeding species do offspring remain into the next breeding season with their parents. Accordingly, different factors are likely to be associated with regular and occasional cooperative breeding. The latter behaviour resembles interspecific feeding (i.e., individuals feed offspring of another species), which occurs when birds lose their brood and begin feeding at a nearby nest, or when birds mistakenly feed at another nest. Thus, we advise researchers to exclude occasional cooperative breeders in comparative analyses until their status is clarified, or to categorize them separately or according to the typically observed parental care mode. This approach will increase the robustness of comparative analyses and thereby improve our understanding of factors that drive the evolution of cooperative breeding.Electronic supplementary materialThe online version of this article (doi:10.1186/s40851-016-0041-8) contains supplementary material, which is available to authorized users.

Highlights

Cooperation among individuals occurs at all levels of biological organisation [1] and understanding the factors that select for cooperation is a fundamental goal of evolutionary biology
We propose that occasional cooperative breeding shows parallels with interspecific feeding, and should not be categorized together with
In some cooperatively breeding species, helpers are not related to breeders, but these individuals often have a share in reproduction, the species breeds polygynously or polyandrously, or helpers queue for a breeding position [5, 22]

Summary

Introduction

Cooperation among individuals occurs at all levels of biological organisation [1] and understanding the factors that select for cooperation is a fundamental goal of evolutionary biology. We propose that occasional cooperative breeding shows parallels with interspecific feeding (i.e., individuals feed offspring of another species), and should not be categorized together with “regular” cooperatively breeding species in comparative studies. In some cooperatively breeding species, helpers are not related to breeders, but these individuals often have a share in reproduction, the species breeds polygynously or polyandrously (such as ani Crotphasgus sp.), or helpers queue for a breeding position [5, 22] This route to cooperative breeding is most likely facilitated by direct fitness benefits [23]. Three individuals have been observed feeding at the same nest in few instances in 152 species (labelled occasional cooperative breeding [18]), but the factors selecting for this behaviour remain unclear. Comparative data have shown that helping behaviour is higher in species in which helping at the nest provides a greater fitness benefit, and helpers in species that exhibit extra-pair mating have a higher degree of kin discrimination [4]

Conclusions

Findings

Ethical statements