Geographic variations in life-history traits of the intertidal ocypodid crab Macrophthalmus banzai

Reproductive traits of the mud crab Macrophthalmus banzai were compared in populations from Okinawa (26°13′ N) and Amakusa (32°32′ N). Crabs matured earlier and at a smaller size in Okinawa than in Amakusa, but growth rate did not differ between the two localities. Population density was much higher in Okinawa. Breeding occurred in winter in Okinawa and in summer in Amakusa. In Okinawa, females produced one brood at over 1 year of age and then died. In Amakusa, females produced one brood at over 1 year of age, and one or two broods at around 2 years of age, and then died. Egg weight in the Okinawa population was almost twice that of the Amakusa population. Furthermore, brood weight was larger in Okinawa than in Amakusa. Longevity was 16–19 months in Okinawa and 28–30 months in Amakusa. At high latitudes, the winter low temperature blocks reproduction of M. banzai. At low temperature blocks reproduction of M. banzai. At low latitudes, their short lifespan prevents iterative breeding. Thus, the difference in breeding season greatly affects other life-history traits.