Genetic analyses of realized reproductive success have fundamentally changed our understanding of mating behaviour in natural systems. While behavioural ecologists have long been interested in what factors influence mating behaviour, early studies were limited to direct observations of matings and thus provided an incomplete picture of reproductive activity. Genetic assessments of parentage have revolutionized the study of reproductive behaviour, revealing that many individuals engage in extra-pair copulations (Griffith et al. 2002) and that social mating partners frequently invest substantial resources into raising offspring that are unrelated to one or both of them (Avise et al. 2002). While these findings have changed the way we think about reproductive behaviour, most investigations of genetic parentage have been restricted to single populations at a single point in time, obscuring spatial and/or temporal variation in mating behaviour and limiting our ability to determine how environmental changes can lead to shifts in mating strategies. In this issue of Molecular Ecology, Mobley & Jones (2009) compare genetic mating behaviour across five populations of Syngnathus floridae (Fig. 1), a widespread species of pipefish distributed along the Gulf- and Atlantic Coasts of North America. The authors document how genetic mating behaviour varies across space in S. floridae and identify correlations between reproductive variation and particular ecological characteristics. Mobley & Jones’ paper is one of an increasing number of studies which address the question of how ecological variables influence mating behaviour, and highlights how our understanding of mating system variation and evolution is likely to expand through the wider application of high-throughput parentage assessment in a comparative context.