Nonmating behavioural differences between male tactics in the invasive round goby

Alternative reproductive tactics (ARTs) exist when individuals of one sex (usually males) adopt different strategies to achieve reproductive success. Although it is well known that the males adopting the different tactics often vary in their morphological, physiological and mating-based behavioural traits, what is not well understood is whether variation also exists in their behaviour outside the mating context. Here, we used the round goby, Neogobius melanostomus, a globally prolific invasive species where males exhibit ARTs, to address this knowledge gap. The nonmating behaviour of sneaker and guarder males were compared for differences in boldness, exploration, activity, aggression, sociality and dispersal. We found that sneaker males were more active, explorative and bold, as well as less aggressive compared to guarder males. Additionally, in an exploratory analysis, we found that while many behavioural traits were positively correlated in guarder males, few were correlated in sneaker males, suggesting that sneaker males might be more behaviourally plastic. The results of this study help expand our knowledge of the many ways that alternative reproductive tactics may differ from each other, particularly in nonmating contexts.