Sperm capacitation and transfer in the orb weaver, Nephila clavipes
Description
Spider sperm are transferred to the female in an immature, encysted and coiled state; thus, sperm capacitation is a major physiological factor in spider mating systems and fecundity. Sperm capacitation refers to changes occurring in sperm after transfer to the female which enable them to fertilize eggs; the changes in spider sperm have not previously been described. Female Nephila clavipes were allowed to mate at different times after reaching maturity and were sacrificed at systematic intervals so that stored sperm could be examined microscopically for morphological changes. To assess female fecundity as a function of time of mating, some females from each mating group were allowed to lay eggs; the egg mass was weighed and number of offspring was counted. When females were mated immediately after final moult, the time of most frequent copulation under natural conditions, sperm changed from an encysted to a flagellate state prior to oviposition. Following oviposition, many sperm became nonflagellate. For females mated later in adulthood, sperm became flagellate quicker, the interval between final moult and oviposition was extended, and one egg clutch, containing only encysted sperm, produced no offspring. Capacitation in N. clavipes was reflected not only in morphological changes in the sperm but also in additional factors such as agglutinization and the extension of the time between final moult and oviposition in late mating females. Findings of the present study relate to sperm competition. It appears to take six-eleven days for sperm to become flagellate and perhaps longer for other changes in sperm to occur. If the interval between matings with the first and second male is long enough, the second male's sperm may be incompletely capacitated at fertilization; sperm priority would then be likely. If successive matings are relatively close together, on the other hand, then sperm priority may not occur