Maternal Fitness Consequences of Different Causative Agents of Offspring Mortality in Early Life
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Maternal effects can be key determinants of female fitness through their influence on early life survival. In salmonids, three main sources of mortality in early life can be attributed to redd superimposition, predation, and starvation (meditated by territory limitation). The influence of different agents of mortality will depend on maternal phenotype (e.g. body size) and within-season reproductive timing. An individual-based model, incorporating both stochastic and deterministic processes, was developed to assess how the relationships between maternal fitness, maternal phenotype (body size) and spawning timing were affected by these different sources of mortality. I found that maternal size influenced fitness under some, but not all circumstances. Larger size was beneficial when predation mortality was low, territories were limited, and/or spawner density was high. Spawning time also influenced maternal fitness; early spawned juveniles were favoured when territories were limited, whereas later spawned juveniles were favoured when predation mortality was high. Component Allee effects at low spawned densities were also detected in some simulations. These results suggest that the fitness consequences of maternal phenotype depend on the sources of mortality present. The fact that these context-dependent sources of offspring mortality in early life may vary between habitats or between years increases the difficulty in identifying the correlates of maternal fitness in salmonid fishes.