Effects of sexual dimorphism and body size on feeding behaviour of the fiddler crab, Uca bengali Crane, 1975

Abstract

Uca bengali Crane, 1975 females have two small feeding claws but males have one small feeding claw and another big claw used for waving and fights. On the basis of video recordings of feeding motions and duration, and morphometric measurements of body size (measured as carapace width) and feeding claw size (measured as dactyl length and width), differences in feeding rate per crab and per feeding claw, feeding duration, and feeding claw size between sexes were studied with the main aim to test male ability to compensate for the loss of one functional feeding claw. Additionally, feeding rate of males and females of small and large size classes was studied. Furthermore, correlations between feeding rate and body size, as well as feeding claw size and body size were investigated. Results showed that increased feeding rate per feeding claw coupled with a larger feeding claw allowed males to compensate for the loss of one feeding claw. Smaller males and females fed faster than larger ones. There was a negative correlation between feeding rate and carapace width. Feeding duration did not vary between males and females of comparable size. A positive correlation was observed between feeding claw size and carapace width. RÉSUMÉLes femelles de Uca bengali Crane, 1975, possèdent deux petites pinces servant à la nutrition (pinces alimentaires) mais les mâles ont une petite pince alimentaire et une autre, grosse, utilisée pour faire des signaux et pour les combats. À partir d'enregistrements vidéos des mouvements de nutrition et de leur durée, et de mesures morphométriques de la taille du corps (mesurée par la largeur de la carapace) et de la taille de la pince (longueur et largeur du dactyle), des différences du taux d'alimentation par crabe et par pince alimentaire, de la durée de l'alimentation, de la taille de la pince alimentaire dans les deux sexes ont été étudiées dans le but principal de tester la capacité du mâle à compenser la perte d'une pince alimentaire fonctionnelle. De plus, le taux d'alimentation des mâles et des femelles de classes de taille petites et grandes ont été étudiées. De plus, les corrélations entre le taux d'alimentation et la taille du corps ainsi que, entre la taille de la pince alimentaire et la taille

Sex and size affecting time allocations for activities in Uca annulipes (H. Milne Edwards, 1837)

“…These results indicate that males foraged as fast as females with their remaining single feeding claw and compensated fully for the loss of one functional feeding claw. Similar results were observed in U. tetragonon and U. dussumieri, in where males fed as fast as females on a per crab basis, and compensated fully for the loss of one feeding claw (Weis & Weis, 2004), but this behavioural adjustment is not true for all species, such as U. panacea, U. chlorophthalmus, U. vocans, U. sindensis and U. bengali Crane, 1975 females foraged faster than males (Caravello & Cameron, 1987a;Weis & Weis, 2004;Mokhlesi et al, 2011a;Tina et al, 2015). During considering feeding rate per claw, Caravello & Cameron (1987a) and Tina et al (2015) observed that U. panacea and U. bengali males fed significantly faster than females.…”

“…This result indicates that crab body size affects the foraging rate of U. annulipes males and females. This size effect is a general finding in fiddler crabs (Crane, 1975;Murai et al, 1983;Caravello & Cameron, 1987a;Tina et al, 2015). Smaller crabs may feed faster to satisfy their feeding demand more rapidly than larger crabs (Murai et al, 1983), and the food processing rate of the buccal cavity is probably higher in smaller males than in larger males (Caravello & Cameron, 1987a).…”

“…Afterwards, we divided this number by the total time (5 min) to determine the feeding rate/min. Feeding rate was determined on a per crab basis (one male feeding claw and two female feeding claws), and a per claw basis (one male feeding claw and one female feeding claw) (Tina et al, 2015).…”

“…Sexual dimorphic traits in animals, such as the enlarged major claw in male fiddler crabs, affect their reproductive success (Backwell & Passmore, 1996;Backwell et al, 1999Backwell et al, , 2006Reaney & Backwell, 2007), as well as feeding behaviour (Caravello & Cameron, 1987a;Weissburg 1992Weissburg , 1993Tina et al, 2015), as these enlarged major claws cannot be used for feeding but are employed to attract mate-searching females and to fight with other males (Crane, 1975;Christy, 1983;Rosenberg, 2002). The reproductive demands of animals are very important in shaping their feeding behaviours (Schoener, 1971).…”

“…In this study, four predictions were tested: (1) if sex affects the time allocations for activities, then males should spend more time on building burrows and grooming than females; (2) if size affects the time allocations for activities, then small crabs should spend more time on feeding, and large crabs should spend more time on courtship behaviours, and based on previous studies (Caravello & Cameron, 1987a;Tina et al, 2015), we expected that (3) feeding rate/claw per min should be higher in males than in females to compensate for the loss of one feeding claw and (4) crab body size should be negatively associated with feeding rate/crab per min.…”