Larval developmental histories shape stage-specific fitness of ‘winners’ and ‘losers’ in a temperate reef fishReef-associated Biodiversity

Jeffrey Shima¹, Stephen Swearer²

¹Victoria University of Wellington, New Zealand - ²University of Western Australia, Australia

Developmental histories shape individual fitness and demographic heterogeneity (i.e., identities of ‘winners’ and ‘losers’) in many systems, yet the consequences of this variation across complex life histories remain relatively underexplored. We sampled cohorts of the common triplefin (Forsterygion lapillum) at successive life stages (larva, juvenile, adult) across six populations, evaluated microchemical profiles within their otoliths, and identified three distinct ‘larval developmental histories’ indicative of time spent in different nearshore coastal environments. Developmental histories showed contrasting survival advantages across different life stage transitions. Specifically, selection across the settlement transition favoured a developmental history that was indicative of nearshore larval development, suggesting that larval retention (or early entrainment) in a coastal boundary layer enhances juvenile recruitment. In contrast, selection across the maturation transition favoured a developmental history that was indicative of offshore larval development, suggesting trade-offs in fitness across life stages. Competitor density and habitat structure were significantly associated with per capita mortality rates, further shaping survival outcomes for ‘winning’ developmental histories. Survival of ‘winners’ at maturation increased when they were surrounded by higher densities of winners and losers. This study highlights the importance of stage-specific selection and demographic heterogeneity (e.g., local patterns of phenotypic composition) on the dynamics of ecological systems.