LAST-MALE SPERM PRIORITY IN A HAPLOGYNE SPIDER (ARANEAE, PHOLCIDAE) -CORRELATIONS BETWEEN FEMALE MORPHOLOGY AND PATTERNS OF SPERM USAGE

In species where the female mates more than once, sperm priority patte rns have important implications for the mating behavior of both sexes. The shape of female sperm storage organs may play a role in determini ng priority patterns, although the extent of this effect has been cont roversial. Spiders provide an interesting test of this hypothesis beca use 2 phylogenetically distinct groups differ in the structure of sper m storage organs. In entelegyne spiders, the female sperm-storage orga ns have separate ducts for sperm entrance and exit. The male inseminat es the female through the external fertilization duct. Sperm then trav el through a ''conduit'' and are released from an internal fertilizati on duct to fertilize eggs. This arrangement has been hypothesized to l ead to 1st-male priority. Six species in 3 entelegyne families have be en shown to have 1st-male sperm priority with some mixing; 1 entelegyn e species, however shows last-male priority. Haplogyne females, in con trast, have a sperm-storage area with only a single opening, which may be more likely to lead to last-male sperm priority because the last s perm to enter the storage area would be likely to be the 1st to leave. Few data are available for this group. We used a balanced sterile-mal e design to test the sperm priority pattern in Females mated once with each of a pair of males of a haplogyne spider Holocnemus pluchei Scop oli. Egg sacs from 72.5% of females were sired predominantly by 2nd ma les, 7.5% were predominantly sired by 1st males, and 20% showed mixed paternity (n = 40); these frequencies differed significantly from rand om expectations. The average percentage of eggs fathered by the 2nd ma le, or P-2, was 74%. These data clearly differ from the predominantly 1st-male pattern generally found in entelegynes, thereby supporting th e hypothesized relationship between female reproductive morphology and sperm use patterns. Mating behavior of spiders that exhibit end-male priority should differ from that exhibiting 1st-male priority, and evi dence from H. pluchei and other haplogynes supports this inference.