"Biased mutation is insufficient to save runaway sexual selection"Dashtbali, MohammadaliFisher argued that courtship ornaments and mating preferences can exaggerate in tandem in a positive feedback loop that was later dubbed ‘runaway sexual selection’. Modelling in the 1980s cast doubt on the plausibility of such runaway, showing that even a small cost of preferences can prevent exaggerated ornaments from persisting long-term. It was subsequently shown that if mutations acting on the ornament are biased - tending to produce smaller rather than larger ornaments - then exaggeration can persist even in the presence of preference costs, seemingly vindicating the runaway process. I unpack a peculiar implicit assumption of these ‘biased mutation’ models: Mutations are assumed to lead, on average, to both smaller and less costly ornaments. I present a quantitative genetic model that lifts this assumption by separating an individual’s investment in an ornament from their efficiency in converting such investment into ornament size. I explore the consequences for the evolution of ornamentation: Can biased mutation really save runaway sexual selection? |
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