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This study investigates how water strider males maintain extreme variation in rear leg length, a trait used in dominance contests, despite strong directional selection that typically reduces variation. Through breeding experiments and experimental evolution, researchers found that directional sexual selection actually increases rather than decreases trait variation, while phenotypic plasticity further expands the range of expression. However, selection favoring dominant males imposed significant reproductive costs on females, revealing that sexual conflict between males and females helps constrain the evolution of exaggerated male traits.
Why it matters
This research provides empirical evidence for how multiple evolutionary forces interact to maintain high trait variation in natural populations, resolving a long-standing puzzle in evolutionary biology. The findings have broader implications for understanding the evolution of sexually selected traits and the role of conflicts between sexes in shaping biodiversity.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
How broad phenotypic variation is maintained in natural populations in the face of selection is a central question in evolutionary biology. We address this question in the water strider Microvelia longipes, where males exhibit striking variation in rear leg length used in male-male contests for dominance. Using reaction norm experiments on inbred lines, we demonstrate that phenotypic plasticity contributes to expanding phenotypic variation, but requires high genetic variation to generate the broad range of trait expression observed in natural populations. Experimental evolution favouring trait exaggeration revealed that directional sexual selection not only fails to erode variation of male rear leg length, but rather amplifies it beyond the natural distribution. Additionally, male-limited selection in favour of dominance generated substantial fecundity costs in females, underscoring the role of sexual conflict driven by females in constraining exaggerated secondary sexual traits in males. Our findings show that sexually antagonistic selection and directional sexual selection jointly generate high genetic variation, which phenotypic plasticity inflates into broad phenotypic distribution of male weapon size. This provides an empirical explanation for the high variability of male exaggerated weapons in nature.