Ecological Influences on the Frequency of Alternative Reproductive Tactics in Bluegill Sunfish Across 25 Lakes

Alternative reproductive tactics (ARTs) in bluegill sunfish (Lepomis macrochirus) provide a striking example of polymorphic mating strategies, with males adopting either a parental or parasitic tactic. Despite the recognized presence of these distinct morphs, little is known about how their relative frequencies vary across populations or what ecological and evolutionary forces drive their variation. To address this gap, we examined the variation in the parental-to-parasite ratio across 25 lakes and explored how lake-specific environmental factors shape this variation. We identified a length-based cutoff to distinguish parental from parasitic males by analyzing the size distribution of mature males. We then assessed the effects of bluegill density, predator density, dissolved organic carbon, and chlorophyll a concentration on the parental-to-parasite ratio. Our results revealed significant differences in ART ratios among lakes, and ART frequencies were associated with ecological conditions, with resource availability positively and conspecific density marginally negatively related to parasitic tactics. Together, these patterns support the hypothesis that competition—manifesting as a trade-off between resource abundance and population density—influences the expression of ARTs. However, further research is necessary to determine whether these patterns reflect stable evolutionary strategies over time or context-dependent plasticity.