Life history variation is maintained by fitness trade-offs and negative frequency-dependent selection

Authored by Mark R Christie, Gordon G McNickle, Rod A French, Michael S Blouin

Date Published: 2018

DOI: 10.1073/pnas.1801779115

Sponsors: Bonneville Power Administration Purdue Department of Forestry and Natural Resources

Platforms: No platforms listed

Model Documentation: Other Narrative Mathematical description

Model Code URLs: Model code not found

Abstract

The maintenance of diverse life history strategies within and among species remains a fundamental question in ecology and evolutionary biology. By using a near-complete 16-year pedigree of 12,579 winter-run steelhead (Oncorhynchus mykiss) from the Hood River, Oregon, we examined the continued maintenance of two life history traits: the number of lifetime spawning events (semelparous vs. iteroparous) and age at first spawning (2-5 years). We found that repeat-spawning fish had more than 2.5 times the lifetime reproductive success of single-spawning fish. However, first-time repeat-spawning fish had significantly lower reproductive success than single-spawning fish of the same age, suggesting that repeat-spawning fish forego early reproduction to devote additional energy to continued survival. For single-spawning fish, we also found evidence for a fitness trade-off for age at spawning: older, larger males had higher reproductive success than younger, smaller males. For females, in contrast, we found that 3-year-old fish had the highest mean lifetime reproductive success despite the observation that 4-and 5-year-old fish were both longer and heavier. This phenomenon was explained by negative frequency-dependent selection: as 4-and 5-year-old fish decreased in frequency on the spawning grounds, their lifetime reproductive success became greater than that of the 3-year-old fish. Using a combination of mathematical and individual-based models parameterized with our empirical estimates, we demonstrate that both fitness trade-offs and negative frequency-dependent selection observed in the empirical data can theoretically maintain the diverse life history strategies found in this population.

Tags

sexual selection Evolutionary game theory fitness Oncorhynchus-mykiss Salmon Pacific salmon Sockeye-salmon Missing data Steelhead trout Lotka-volterra competition Iteroparity Alternative reproductive strategies Bayesian parentage analysis Trout salmo-gairdneri Systematic accountability Genotyping error Systematic accountability