Population-specific allometry and a reversal in the direction of chela dimorphism in the dwarf crayfish Cambarellus cf. montezumae (Decapoda: Cambaridae)

This repository contains the morphometric data and analytical scripts used in the study "Population-specific allometry and a reversal in the direction of chela dimorphism in the dwarf crayfish Cambarellus cf. montezumae". Abstract: Extreme sexual dimorphism is often attributed to sexual selection on male weapons, but whether its magnitude, direction, and allometric basis are consistent across populations remains unclear. Using the dwarf crayfish Cambarellus cf. montezumae, we examined geographic variation in chela dimorphism and its allometric basis. We measured eight morphometric variables in 363 individuals from three populations in central Mexico, comparing breeding (Form I) males with females and fitting standardized major axis regressions within populations. In every population, Form I males had longer chelae than females, whereas body-size dimorphism varied among populations and was clearly female-biased only in Xhimojay. However, the direction of dimorphism in chela width shifted from male- to female-biased among populations. Chela-width slopes were steeper in females in two populations and in males in the third, although sex-specific slope heterogeneity was statistically supported only in one population (Salazar). Given documented cryptic diversity within the Cambarellus complex, this geographic lability may reflect divergence among structured lineages, while phenotypic plasticity remains an alternative explanation. These results show that both the direction and allometric basis of sexual dimorphism can vary geographically.