The reproductive strategies of the pill-box crab Halicarcinus innominatus Richardson, 1949
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
This study examines the reproductive strategies of the Pill-box crab, Halicarcinus innominatus, at the Oaro Platform (24 km south of the Kaikoura Peninsula, New Zealand). As necessary components of reproductive strategies, the population dynamics, reproductive biology and mating behaviour of H. innominetus were examined from December 1997 through December 1998. There were obvious sexually dimorphic differences in secondary sexual traits in this species. Both males and females display a wide range of sizes over which individuals can moult to maturity. H. innominatus females displayed continuous breeding throughout the year, resulting in continuous recruitment. Females were found to outnumber males in each month. However, when comparisons were made between mature males and females with different brood stages (i.e. 0-5), males outnumbered each female type in each month. Investigations into the reproductive biology of H. innominatus females revealed that brood development and ovary development were in phase. This resulted in the ability of females to produce several broods in quick succession. Ovary development began before the moult to maturity, allowing for immediate production of a brood after the moult to maturity. Egg incubation periods were dependent on water temperature, being longest in the winter and shortest in the summer. Egg numbers were found to increase with female body size, but mortality of eggs through development was apparent. Sperm storage was found to occur in this species with possible layering of different ejaculates. Copulations were only observed between males and females in hard-shell conditions. Males mated more often with females carrying stage 5 broods, but also mated with all other female types, including pre-pubescent females. Postcopulatory mate guarding only occurred with stage 5 females. Males can detect females of different reproductive condition, which seems to be linked to the developmental stages of the females' ovaries. In conclusion, H. innominatus males seem to have two tactics to their reproductive strategies: mating with any receptive female, but only guarding stage 5 females.