Effects of elevated carbon dioxide on male and female behavioural lateralization in a temperate goby

Behavioural abnormality in fishes has been proposed as a significant consequence of the increasing levels of carbon dioxide occurring in the oceans. Negative effects of elevated CO 2 have been reported for behaviours such as predator–prey interactions, foraging, hearing and behavioural lateralization. Importantly, the effects vary greatly both within and between species, and some recent studies have shown minimal effects of CO 2 on behaviour. Whether the effect of CO 2 also varies between males and females is, however, virtually unexplored. According to resource allocation theory, females are expected to be more sensitive to elevated CO 2 , meaning that non-sex-specific studies may overlook ecologically important differences between the sexes. In this study, we investigated the possible differences between males and females in their response to elevated CO 2 by performing behavioural lateralization tests in adult temperate two-spotted gobies, Gobiusculus flavescens . We found that the strength of the side bias (absolute lateralization) was unaffected by the CO 2 treatment, and there was no difference between males and females. The control fish were slightly right-biased in their behavioural asymmetry (mean relative lateralization of 14). Exposure to high CO 2 affected this pattern, such that treated fish were slightly left-biased (mean relative lateralization of −10), regardless of their sex. The same results were obtained yet again when the study was repeated during a second year. We discuss our results in light of the great variation in lateralization that has been reported to depend on variables such as species, ecological settings and environmental factors.