Abstract
AbstractTiming of reproduction may be of crucial importance for fitness, particularly in environments that vary seasonally in food availability or predation risk. However, for animals with spatially separated feeding and breeding habitats, optimal reproductive timing may differ between parents and their offspring, leading to parent-offspring conflict. We assume that offspring have highest survival and fitness if they are spawned around a fixed date, and use state-dependent life-history theory to explore whether variation in conditions affecting only parents (food availability and survival) may influence optimal timing of reproduction. We apply the model to Pacific herring (Clupea palasii) in Puget Sound, USA, where 20 subpopulations spawn at different times of the year. Our model suggests that relatively small differences in adult food availability can lead to altered prioritization in the trade-off between maternal fecundity and what from the offspring’s perspective is the best time to be spawned. Our model also shows that observed among-population variability in reproductive timing may result from adults using different feeding grounds with divergent food dynamics, or from individual variation in condition caused by stochasticity at a single feeding ground. Identifying drivers of reproductive timing may improve predictions of recruitment, population dynamics, and responses to environmental change.
Highlights
Many fish species do not provide care for offspring after birth, but parents can still play a major role for the success of their offspring by deciding where and when to spawn
A common feature of our results is that food dynamics at the feeding grounds of adults influenced optimal timing of spawning, and that lower food availability lead to a wider spread in timing of spawning
Most research on reproductive phenology and recent shifts associated with climate change has focused on offspring
Summary
Many fish species do not provide care for offspring after birth, but parents can still play a major role for the success of their offspring by deciding where and when to spawn. Populations often return to the same areas year after year for reproduction, but there may be substantial variation in when spawning takes place, both between years and among subpopulations To understand this variation and how reproductive timing may respond to climate change and other stressors, there is a need for evolutionary interpretations of local variation in reproductive timing as the outcome of adaptive behaviour. Consider this baffling example from Puget Sound, WA, USA (Figure 1a), where 20 different Pacific herring (Clupea palasii) subpopulations (stocks) spawn consistently but at different times of the year (between late January and June, Stick et al, 2014; Figure 1b) even though all but two stocks show no discernible genetic variation (Small et al, 2005).
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