Survival consequences of sex-biased growth and the absence of a growth-mortality trade-off

Growth rate is of considerable importance to the life histories of indeterminately growing organisms. Its determination of size at age can generate positive associations with several traits, although the rate at which size increases with time has been negatively linked with survival. Such a trade-off may not, however, be evident at growth rates considerably less than species-specific maxima, nor need links between growth and life history be similar for both sexes. Based on a 5-year, mark-recapture study of an unexploited population of Brook Trout (Salvelinus fontinalis) near the edge of the species' range, I tested the null hypotheses that seasonal growth does not differ between sexes and that survival is independent of growth rate. Both hypotheses were rejected. Faster growth by males during summer, and by females during winter, can be explained by seasonal differences, by sex, in the proportional allocation of energy to gonads and soma. Survival increased with growth rate per se, independently of the latter's effects on size at age; survival among males appears more dependent on growth than that of females. The results indicate that there can be fitness costs associated with slow growth, that these costs can differ between sexes, and that they may be exacerbated during periods of energetic stress. Trade-offs between growth and survival may depend on the behavioural and developmental contexts in which they are examined, need not be ubiquitous and may vary throughout a species' geographical range.