Claw morphology of a ghost shrimp species across sandy beaches varying in natural features and human disturbances

The ghost shrimp Callichirus corruptus inhabits sandy beaches along the Brazilian coast. Although various traits can differentiate sex in ghost shrimp, claw asymmetry (heterochely) is often used. This study examined whether habitat features and human disturbance influence claw asymmetry. Controlling for sex, we assessed natural and human factors affecting claw morphology and aimed to establish a reliable asymmetry threshold for identifying males. We analyzed pleopod morphology as a primary sexual attribute and compared the sex ratio obtained by this method with that derived from heterochely analysis. Sex was determined by examining the morphology of the first and second pairs of pleopods. Claw length and width were measured to calculate asymmetry. Traditional sex identification via visual inspection of heterochely was compared with pleopod morphology data. Males showed 2.74 times more asymmetry than females, with heterochely present in 92% of males and 71% of females. Claw asymmetry was not significantly influenced by sediment features or urbanization, but distance to major rivers was a significant predictor variable. The difference in claw asymmetry between males and females decreased by 2.24 times near major river mouths. A binomial generalized linear model (GLM) demonstrated that a claw asymmetry of 1.5 mm² ensured a 100% probability of an individual being male. Since only proximity to major rivers affected asymmetry, the 1.5 mm² threshold is a reliable criterion for sex identification in C. corruptus, especially in areas without significant freshwater influence where rapid sex identification is required.