Year: 2025
Type: article
Abstract: Plastic phenotypes may often be subject to conflicting demands, which should generate nonlinear selection favoring intermediate optima. However, investigating complex patterns of selection on reaction norms has been challenging. We leveraged data on clutch size from 2 long-term studies (25 and 19 years) of individually marked house sparrows (Passer domesticus). We used a novel multivariate technique for examining linear and nonlinear selection acting on clutch size reaction norms via the fitness components of hatchling number, nestling survival, and nestling body mass at the end of the main parental period. Reaction norm slopes were highly canalized and lacked sufficient among-female variation to detect selection. Stabilizing selection and opposing patterns of directional selection occurred on both intercepts and individual residual variation via hatchling counts and nestling body mass. We also observed changes in these gradients as a function of laying date. Our results support Lack's hypothesis that quantity-quality tradeoffs shape selection on both mean clutch size and the variability of clutch sizes across breeding seasons. Our findings are also consistent with models of adaptation on asymmetric fitness landscapes, where tradeoffs near a local fitness ridge or cliff favor distinct patterns of clutch size plasticity in response to unpredictable environmental variability.
Source: Evolution
Language: English
Domain: Life Sciences
Open Access status: green
Funder: National Science Foundation
OpenAlex ID: W4413116722