Trade-offs between size and energy reserves reflect alternative strategies for optimizing larval survival potential in rockfish

Reproductive strategies balancing offspring size and offspring number have been well documented in empirical tests of life-history theory. Here we found an additional trade-off between offspring size and offspring condition. Among 5 species of live-bearing rockfishes (Sebastes spp.) from central Californian populations, we observed a negative relationship between larval length at parturition and the size of their oil globule (a triacylglycerol-rich energy reserve). When compared with a variety of performance variables (resistance to starvation, growth, startle-escape performance and routine activity levels), it appears that this trade-off leads to a conflict when trying to optimize survival potential, with differing benefits to each trait. A large oil globule greatly increases resistance to starvation, whereas larger body size is associated with numerous performance benefits likely to synergistically decrease predation-based mortality and increase success at capturing prey (increased startle speeds and distances, as well as more rapid onset of growth and larger size at age). The trade-off between energy reserves and body size is further reflected in the seasonal patterns of parturition of the 5 species, with larvae having large oil globules and small body size being released in winter, when productivity in the California Current is low but transport is generally onshore, and those with small oil globule reserves and large body size released in late spring, when productivity is high but transport is generally offshore. These 2 apparent reproductive strategies also reflect subgeneric phylogenetic relationships, suggesting a potential lineage-specific basis for the contrast in larval traits. The results highlight the importance of measuring both physical and performance traits of larvae, as well as considering multiple attributes of both, when evaluating progeny quality.