Variation of sperm allocation with male size and recovery rate of sperm numbers in spiny king crab Paralithodes brevipes

Abstract

This study examined whether sperm allocation by males can limit sperm passed to females in fished spiny king crab populations in which large males are selectively fished. We investigated the recovery rate of sperm in vasa deferentia of males of different body sizes, sperm allocation passed to females of different body sizes by males of different body sizes, and sperm allocation in different male:female sex ratios (1:1 or 1:6) by males of different body sizes by laboratory experiments. The recovery rates of sperm were very slow regardless of male size, suggesting that a sperm allocation strategy is important to increase male reproductive success in this species. In large males, the ejaculate size increased significantly with increasing female size, but the ejaculate size of small males did not vary with female size, indicating that small males cannot increase ejaculate size by more than a certain number. Females mated with small males showed significantly lower fertilization rates than females mated with large males. Males showed no difference in pattern of sperm allocation between the different sex ratios in both male size classes. These results suggest that a decrease in mean male size due to male-only fishing would increase the number of females mated with small males without an ability to increase ejaculate size with increasing female size, so that females mating with small males would receive an insufficient sperm supply and have a low fertilization rate due to sperm limitation. © Inter-Research 2006.