THE INFLUENCE OF LIFE-HISTORY TRADE-OFFS AND THE SIZE OF INCUBATION GRAVELS ON EGG SIZE VARIATION IN SOCKEYE-SALMON (ONCORHYNCHUS-NERKA)

Egg size is a critical life history trail, reflecting female investmen t and affecting offspring fitness. We investigated several factors whi ch may influence variation in egg weight for sockeye salmon (Oncorhync hus nerka). Comparisons were based on collections from 18 Alaskan popu lations, among which adult migration distance and juvenile rearing hab itat were similar but the size composition of incubation gravels was d ifferent. Among populations, most of the variation in egg weight could be explained by a positive correlation with different measures of the size composition of incubation gravels (Pearson's r = 0.45-0.91). Ln contrast, egg weight was poorly correlated with female body length and with female snout length, a morphological feature used during intra-s exual competition. Within each of the Alaskan populations, however, eg g weight and snout length were positively correlated with female body length and hence with each other. A positive association between snout length and egg weight was still evident even after the effects of cov ariance with body size were removed using residuals analysis: for all of the fish pooled and within 6 of the 16 populations. A significant r elationship was not detected in the other populations bur the trend wa s nevertheless positive in 8 of the other 10. Examination of reproduct ive traits (gonad weight, egg weight, egg number, snout length and hum p size) within another population identified a trade-off between egg w eight and egg number for females of a given body length. In contrast, positive correlations between reproductive traits were more common, su ggesting that energy-rich individuals produce large eggs and large sec ondary sexual characteristics rather than sacrificing one for the othe r.