Evolution of non-kin cooperation: Social assortment by cooperative phenotype in guppies

Josefine Bohr Brask, University of Exeter
Darren P. Croft
Mathew Edenbrow, University of Exeter
Richard James, University of Bath
Bronwyn H. Bleakley, Stonehill College
Indar W. Ramnarine, The University of the West Indies, St. Augustine Campus
Robert J.P. Heathcote, University of Exeter
Charles R. Tyler, University of Exeter
Patrick B. Hamilton, University of Exeter
Torben Dabelsteen, Københavns Universitet
Safi K. Darden, University of Exeter

Abstract

© 2019 The Authors. Cooperation among non-kin constitutes a conundrum for evolutionary biology. Theory suggests that non-kin cooperation can evolve if individuals differ consistently in their cooperative phenotypes and assort socially by these, such that cooperative individuals interact predominantly with one another. However, our knowledge of the role of cooperative phenotypes in the social structuring of real-world animal populations is minimal. In this study, we investigated cooperative phenotypes and their link to social structure in wild Trinidadian guppies (Poecilia reticulata). We first investigated whether wild guppies are repeatable in their individual levels of cooperativeness (i.e. have cooperative phenotypes) and found evidence for this in seven out of eight populations, a result which was mostly driven by females. We then examined the social network structure of one of these populations where the expected fitness impact of cooperative contexts is relatively high, and found assortment by cooperativeness, but not by genetic relatedness. By contrast, and in accordance with our expectations, we did not find assortment by cooperativeness in a population where the expected fitness impact of cooperative contexts is lower. Our results provide empirical support for current theory and suggest that assortment by cooperativeness is important for the evolution and persistence of non-kin cooperation in real-world populations.