Temperature Effects on Reproductive Allocation in the Sandhopper Talorchestia capensis

In invertebrates, environmental temperature may induce mothers to invest differently in the early development of their offspring. In ectotherms, temperature affects offspring phenotype so that colder mothers produce larger eggs. However, developmental mode and maternal size also contribute to the determination of optimal offspring size. When the maternal experience closely matches the offspring's probable future conditions (e.g., direct developers), it is expected that mothers will produce eggs of similar size within the same brood. While temperature directly affects the size of the eggs (temperature size rule), with potential indirect links to egg number (trade-off between egg size/number), maternal size can be a limiting factor in determining the optimal number of eggs, especially if eggs are brooded. We evaluated the role of temperature in shaping early ontogeny in the sandhopper Talorchestia capensis (Crustacea: Amphipoda), investigating within-brood and among-female variation in the size of the eggs. To test for causal relationships among temperature, maternal size, egg size and number, we used an information theoretic approach combined with path analysis. Sandhoppers invested in smaller eggs at higher temperatures, with no significant within-brood variation in the size of the eggs. Regardless of temperature, we found significantly different investment in egg size among females. Path analyses showed a simultaneous contribution of temperature and maternal size to the optimal size and number of eggs within a single clutch. Strong inter-individual variability in maternal investment could generate phenotypic variation within a population and promote population fitness.