Adaptive phenotypic differentiation of courtship in response to recent anthropogenic disturbance

Background: Anthropogenic activities are causing ecological changes, including eutrophication, which can induce behavioural alterations in animals. Male threespine stickleback, Gasterosteus aculeatus, need to increase their courtship intensity to maintain a high mating success in eutrophied habitats. Question: Has the courtship behaviour of threespine stickleback populations differentiated in response to spatial variation in human-induced eutrophication? Populations: Parallel pairs of threespine stickleback populations in the Baltic Sea that have been exposed to mild and severe human-induced eutrophication during the last decades. Methods: Males from mildly and severely eutrophied habitats were allowed to court dummy and live females under standardized conditions. We measured the frequency of different courtship behaviours. Results: Males from severely eutrophied habitats courted more intensively. Conclusions: Stickleback populations have differentiated phenotypically in courtship behaviour in response to spatial variation in human-induced eutrophication. The differentiation should improve individual fitness.