Intra-population variation in reproductive timing co-varies with thermal plasticity of offspring performance in perch (Perca fluviatilis)

Life-history theory posits that organisms should time their reproduction to coincide with environmental conditions that maximize their fitness. Population-level comparisons have contributed important insights on the adaptive value of reproductive timing and its association to environmental variation. Yet, despite its central role to ecology and evolution, the causes and consequences of variation in reproductive timing among individuals within populations are poorly understood in vertebrates other than birds. Using a combination of observational field studies and a split-brood experiment, we investigated whether differences in breeding time were associated with changes in hatching success, reproductive allocation, and reaction norms linking offspring performance to temperature within an anadromous Baltic Sea population of perch (Perca fluviatilis). Field observations revealed substantial variation in reproductive timing, with the breeding period lasting almost two months and occurr...