Trade-off between brood size and brood interval and the evolution of underground incubation in three fiddler crabs (Uca perplexa, U. vocans, and U. dussumieri)

Abstract

This study compared trade-offs between brood size and brood interval, as well as feeding activity and ovarian development during brood incubation, among fiddler crabs of three subgenera: Uca (Celuca) perplexa, U. (Thalassuca) vocans, and U. (Deltuca) dussumieri. Female U. perplexa remained in their burrows throughout incubation, and egg mortality was low despite relatively large brood sizes. These females did not feed during incubation, and their ovaries remained small until the eggs hatched. Female U. vocans fed actively on the surface during incubation, and egg mortality was high, despite relatively small brood sizes. Female U. dussumieri also fed actively during incubation, but their broods were very small and egg mortality was low. In the latter two species, the ovaries grew rapidly during incubation, and many females produced consecutive broods. Incubation in burrows may be adaptive for females that are exposed to severe heat stress and desiccation in the upper tidal flats, and a simple model demonstrates that large broods may be advantageous for females incubating broods in burrows because of shorter interruptions during feeding.