Limb loss and its effect on handedness and growth in the velvet swimming crabNecora puber(Brachyura: Portunidae)

Abstract

The chelipeds of male and female Necora puber are heterochelous. The majority of individuals are right-handed (i.e., the major cheliped is on the right side); however, field collections revealed a progressive increase of left-handedness with increase in crab size. Also, whereas small crabs (60 mm carapace width). Differences in site orientation of limb loss with increasing crab size may be explained by observations of crab behaviour. Large crabs were seen to forage in the open, exposing equally each limb to potential damage and loss, whereas small crabs were restricted to protective habitats where the anterior limbs only were prone to damage. Laboratory experiments confirmed that autotomy of the major cheliped of right-handed crabs is the process resulting in cheliped reversal for N. puber. Growth of chelotomized crabs was variable and appreciably reduced (compared with nonchelotomized crabs) at the two moults following autotomy, and similar to, or higher, at subsequent moults (3rd–5th). Such effects of autotomy on growth help explain some of the variability noted in size-frequency distributions of different cohorts of N. puber.