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Dryad

Data for: Static allometries do not reflect evolutionary allometry in exaggerated weaponry of male New Zealand sheetweb spiders (Cambridgea spp.)

Data files

Mar 21, 2023 version files 54.03 KB

Abstract

Across the animal kingdom, exaggerated weaponry is frequently used by one sex to contest access for potential mates. Within species, if disproportionate investment in weaponry confers an advantage to larger individuals, this may result in positive static allometry. It is predicted that the same selective pressures may also lead to positive evolutionary allometry, where larger species bear disproportionately large weapons on average, compared with smaller species. However it is unclear whether the slopes of species-specific static allometries are steeper among larger species, or remain consistent. All adult males across the New Zealand sheet-web spider genus Cambridgea bear exaggerated chelicerae which are used to compete for control of females’ webs. Here, we characterise the distribution of chelicera lengths within each sex of 12 Cambridgea species to show that chelicerae almost always exhibit positive static allometry in males while female chelicera lengths are consistently isometric. We use comparative phylogenetic methods to demonstrate that the slopes of static allometries steepen in males of larger species but that the ratio of average chelicera length to cephalothorax width is tightly conserved across taxa, leading to an isometric evolutionary allometry. While sexual selection may drive weapon exaggeration within species, resulting in steeper or shallower static allometries, this conservation of relative trait size suggests that chelicera length is subject to other stabilising selective pressures. Changes to species body plans might be constrained, while allowing for disproportionate investment in weapon traits at the extremes of body sizes within species.