Several species of the genus Pipistrellus (Vespertilionidae) store spermatozoa for prolonged periods prior to ovulation, but the reproductive strategy used by Pipistrellus kuhlii remains unknown. In order to investigate the prevalence of sperm storage in the bats of this genus we documented endometrial sperm storage in the uterus of two female Pipistrellus kuhlii collected during mid-December in western Iran. The uteri were distended with densely packed spermatozoa, those at the periphery exhibiting perpendicular orientation toward the endometrum. This orientation, together with the fact that copulation is unlikely to occur at this time is used to infer that P. kuhlii stores sperm over the winter.
In many species sperm competition selects for large ejaculates while females eliminate or disable a high percentage of the spermatozoa in their storage organs in order to control paternity. Therefore, sperm viability is an excellent measure of the reproductive success of both males and females. Here we assess the viability of spermatozoa in males, freshly mated queens and old queens at the end of a colony cycle of the monandrous bumblebee Bombus terrestris. We found that the accessory testes of males contained a significantly lower percentage of dead sperm (i.e. higher average viability) than the spermathecae of both freshly mated and old queens. In each case, however, the percentage of dead spermatozoa was very small. No differences could be detected between sperm viability in freshly mated and old queens. To test for the possible incompatibility of the sperm and the environment provided by female spermathecae males and females either from different geographic regions (north and south of the Alps) or the same region were mated. We did not find any differences between matings of individuals from within or between regions. The mechanism that causes the lower sperm viability in females remains unknown.