SPERM PRECEDENCE AND SPERM STORAGE IN MULTIPLY MATED RED FLOUR BEETLES

In insects, the last male to mate with a female often gains access to a disproportionate number of subsequent fertilizations. This study exa mined last-male sperm precedence patterns in doubly and triply mated T ribolium castaneum females. Sperm storage processes were investigated by measuring the quantity of sperm stored within the female spermathec a following single, double, and triple matings. Both doubly mated and triply mated females exhibited high last-male sperm precedence for pro geny produced during the first 48 h following the last mating, with fe males in both groups exhibiting parallel declines in sperm precedence 1 and 2 weeks later. The number of sperm stored by females increased b y 33% between singly mated and doubly mated females, indicating that t he spermatheca is filled to only two-thirds capacity following insemin ation by the first male. Based on the proportion of stored sperm from first and second matings, we tested predictions about sperm precedence values based on models of random sperm mixing. High initial last-male sperm precedence strongly supports stratification of last-male sperm. By 1-2 weeks after double matings, sperm precedence declined to level s indistinguishable from values expected under random mixing. These re sults provide insight into mechanisms of sperm storage and utilization in this species.