Reproductive success in wild pink salmon, Oncorhynchus gorbuscha
Dickerson, Bobette Ray
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Reproductive success in pink salmon was investigated by examining the complex interactions among life history, morphological, and behavioral traits and their influence on offspring production. Reproductive success was measured directly (using DNA microsatellites in a parentage analysis) in adult pink salmon (O. gorbuscha) in a small Alaskan creek during the 1997--2000 spawning seasons. Females showed strong positive relationships between body size and both fecundity and egg size, with a trade off between these traits. Duration of nest defense was associated with entry date (early arrivals lived longer) and bear predation, which also affected the proportion of females completing egg deposition. Larger males were more dominant but the benefits of large size were overshadowed by arrival timing. Earlier small males were more dominant than larger later males. The reproductive life span of males was reduced by bear predation but not influenced by body size or arrival timing. Both body size and arrival date affected potential reproductive success but predation also appeared important. When these same traits were compared to the number of adult offspring produced we found that males that arrived earlier, lived longer in the stream, and were more often observed in dominant positions courting females had significantly more offspring, although the importance of dominance was overshadowed by the influence of arrival timing. Female reproductive success was not closely linked to any measured trait (e.g., egg size, instream longevity, or fecundity) but stabilizing selection on arrival timing and length was inferred with intermediate values of these most productive. Size-assortative mating, although seen in many salmonids, was not apparent in this population. Heritabilities from parent-offspring regressions for arrival timing in male offspring (dam 0.72 and sire 0.58) and body size in female offspring (sire 0.48) were estimated and were within the range of those found for controlled breeding experiments. Entry timing showed the greatest influence on reproductive success. It is possible that the optimal entry timing shifts due to environmental factors (predation pressure, temperature, food availability, etc.) and thus is under shifting selective pressures and is not as easily driven to an optimum as traits such as egg size may be.
- Fisheries