Abstract
In only a few vespertilionine bats, it has been experimentally proved that spermatozoa retain the fertilizing ability over a period of 6 months in the female reproductive tract. However, there have been few studies focussed on implications of such prolonged sperm storage from the viewpoint of capacitation. In the Japanese house bat, reliable evidence for delayed capacitation was provided by experiments which were designed to vary the duration of sperm storage in the female genital tract. As the duration was lengthened from 4-5 to 150-166 days, each ratio of egg activation and normal development increased from 0% to 100%, suggesting that delayed capacitation evolved with prolonged sperm storage in the heterothermic bat. Thus, both sperm storage and heterothermy seem to be closely associated with the delayed capacitation which is regarded as an adaptive character of spermatozoa in bats.
