Sex biases in kin shoaling and dispersal in a cichlid fish
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Animal dispersal is associated with diverse costs and benefits that vary among individuals based on phenotype and ecological conditions. For example, females may disperse when males benefit more from defending territories in familiar environments. Similarly, size differences in dispersal propensity may occur when dispersal costs are size-dependent. When individuals do disperse, they may adopt behavioral strategies that minimize dispersal costs. Dispersing fish, for example, may travel within shoals to reduce predation risks. Further, kin shoaling may augment inclusive fitness by reducing predation of relatives. However, studies are lacking on the role of kin shoaling in dispersal. We explored how sex and size influence dispersal and kin shoaling in the cichlid Neolamprologus caudopunctatus. We microsatellite genotyped over 900 individuals from two populations separated by a potential dispersal barrier, and documented patterns of population structure, migration and within-shoal relatedness. Genetic differentiation across the barrier was greater for smaller than larger fish, suggesting larger fish had dispersed longer distances. Females exhibited weaker genetic differentiation and 11 times higher migration rates than males, indicating longer-distance female-biased dispersal. Small females frequently shoaled with siblings, possibly offsetting dispersal costs associated with higher predation risks. In contrast, small males appeared to avoid kin shoaling, possibly to avoid local resource competition. In summary, long-distance dispersal in N. caudopunctatus appears to be female-biased, and kin-based shoaling by small females may represent a behavioral adaptation that reduces dispersal costs. Our study appears to be the first to provide evidence that sex differences in dispersal influence sex differences in kin shoaling.
KeywordsAnimal movements Fish shoals Grouping behavior Kin selection Population genetics
We thank Florian Sammer for conducting the laboratory work for this study, Valeria Montana for assistance with the IM analyses and Marlene Mann for helping with many aspects of the project. We are grateful to Stefan Fischer, Stefanie Schwamberger, Peter Turai and Hartmut Lemmel for their great field assistance, John, Enoch, and Maxwell Juma for their support in the field, and Bornfirst and family for managing the Tanganyika Lodge. We thank Michael and Barbara Taborsky for the provision of diving bottles and Drs Harris Phiri, Patrick Nagalda, and Justina Kasabila of the Zambian Ministry of Agriculture, Food and Fisheries, as well as Rueben Shappola and the Department of Fisheries in Mpulungu for their logistical support of our research. Thank you to Andrea Manica and three anonymous referees for their comments on earlier versions of this manuscript. This project was funded by the Austrian Academy of Sciences, the Veterinary University of Vienna and by the Austrian Science Fund (FWF; projects P17468 and P20401).
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