Hatch date and growth rate drives reproductive success in nest-guarding males of a temperate reef fish

Identifying sources of variation in individual reproductive success is crucial to our understanding of population dynamics and evolutionary ecology. We evaluated sources of variation in reproductive success of the common triplefin Forsterygion lapillum, a species with male parental care. We characterised breeding success of adult males during the breeding season (using presence of eggs and/or breeding territories as proxies for success), measured their phenotypic traits (body size and condition) and used their otoliths to reconstruct life history characteristics (hatch dates and average growth rates). Our reconstructions of life history traits suggested at least 2 alternative pathways to success for adult males. More successful males hatched earlier and therefore had a developmental head-start over less successful males (age of males with eggs > age of male territory holders without eggs > age of males without territories, i.e. 'floaters'). Alternatively, our reconstructions suggested that reproductive success of males was predicted by growth rates: for males born in the same month, those with eggs grew faster than those with territories and no eggs, and both groups grew faster than floaters. These results suggest that accelerated growth rate may compensate for the effects of a later hatch date, and that both hatch dates and growth rates influence the success of adult males, likely through proximate effects on individual phenotypes.