Behaviour 2019
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Male social niche conformance? Effects of sperm competition risk on behaviour and hormones in zebra finches
Navina Lilie1, Sepand Riyahi2, Sylvia Kaiser3, Tim Schmoll2, Peter Korsten1. 1Department of Animal Behaviour, Bielefeld University, Bielefeld, NRW, Germany; 2Department of Evolutionary Biology, Bielefeld University, Bielefeld, NRW, Germany; 3Department of Behavioural Biology, University of Muenster, Muenster, NRW, Germany

Sperm competition risk (SCR) is a key dimension of the male social niche to which individuals are expected to adaptively adjust. In this preregistered study we investigated how male zebra finches adjust behaviour to SCR. We manipulated their environment to create two levels of SCR, in which we let the birds breed (Single-pair: no SCR; Double-pair: SCR). We recorded the social behaviour of males and ran intruder tests in which we recorded male aggression. To identify the hormonal correlates of behavioural adjustment, we measured testosterone and corticosterone levels. Opposite to our predictions, males from the Double-pair showed decreased courtship and aggression compared to the Single-pair. Furthermore, males showed a decrease in testosterone levels over the breeding cycle. Although testosterone levels were slightly higher in Double-pairs, we found no significant effect on hormone levels. Our findings suggest that males adjust their behaviour in response to the social environment, but not as predicted. Although zebra finches are a commonly used model in research on sexual selection, we found that the presence of another pair does not induce males to upregulate competitive traits.