Changes in claw morphology of a bioindicator species across habitats that differ in human disturbance

Variations in morphological characteristics are frequently important determinants of the physiology, ecology and inter- and intra-specific interactions of organisms. Various causative drivers have been investigated for this morphological variation, such as sexual selection, variations in the available resources to exploit, habitat characteristics, and other environmental factors. However, it is not clear whether human disturbance has any selective role in creating morphological variations other than simply reducing the body size of individuals. We used a bioindicator, the Atlantic ghost crab Ocypode quadrata, to measure how human disturbance influences morphological claw variation. We examined the claw height and the volume of major and minor claws of crabs at 12 South Carolina sandy beaches with various degrees of human disturbance. Crabs from disturbed sites had smaller and shallower claws compared to crabs from pristine sites, and these differences varied with sex and with body size. Additionally, major claw volume and claw height also varied with crab body size, gender, and across beaches with different amounts of human disturbance. Other claw characteristics showed no difference between sexes with the degrees of human disturbance, or with variation in body size. Our results suggest that the magnitude of the human disturbance experienced by populations may have a selective role on the morphology of individual organisms that can differ between males and females. These morphological changes likely have ecological and physiological consequences.