Adoption and cuckoldry lead to alloparental care in the tessellated darter (Etheostoma olmstedi), a non-group-living species with no evidence of nest site limitation
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While extensive empirical and theoretical work has focused on the evolution of costly cooperation (particularly in group-living species), less attention has been paid to more low-risk or immediately beneficial forms of cooperation. In some non-group-living darters, alloparental care (or allocare) by subordinates has been noted to result from by-product benefits as small territorial (subordinate) males adopt and provide care to the abandoned eggs of large territorial (dominant) males. In the tessellated darter (Etheostoma olmstedi), allocare also results from sneak fertilization. However, information on the rate of allocare by tessellated darters is contradictory: prior behavioral work suggested that it is very common, while a genetic examination showed males to primarily care for their own young. We found behavioral and genetic evidence of very high levels of allocare at our study location. The relative size of the assigned fathers of young to the alloparental male is consistent with the idea that initial allocare primarily results from sneak fertilization (“cuckoldry-based allocare”), but later allocare results from subordinate males caring at previously abandoned nests (“adoption-based allocare”). Larger males appeared to breed more frequently at different nests, but did not father more individual offspring than smaller males. Finally, low relatedness between abandoning and alloparenting males suggests that kin selection does not contribute to alloparental care. We discuss how variation in nest availability may explain the inconsistent findings of the rate of alloparental care in the tessellated darter, and how increased research in this and similar systems can expand our understanding of the evolution of cooperation.
KeywordsCooperation Social evolution By-product benefits Parentage Ecological constraints Kin selection
The research was conducted with the permission and cooperation of Stephen Gephard and the Connecticut Department of Environmental Protection (Inland Fisheries Division). We are grateful to Dr. T.J. Near for his assistance and support and Drs. DE Fletcher and JA DeWoody for information on individual and nest density at their tessellated darter study site. Funding was provided by Yale University, by a grant from the National Science Foundation (IOB-0450807) to S.H.A., and by a Natural Sciences and Engineering Research Council of Canada (NSERC) Postdoctoral Fellowship to K.A.S.
This study conforms to all laws of the United States of America. It was conducted under the ethics guidelines of Yale University (Institutional Animal Care and Use Committee Protocol #2008-10908), and with the permission of the Connecticut Department of Environmental Protection, Inland Fisheries Division (scientific collecting permit number SC-08002).
Conflict of interest
The authors declare that they have no conflict of interest.
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