Sperm transport and storage in the agile antechinus (Antechinus agilis).

Abstract

This study was an examination of the timing of ejaculation and the dynamics of sperm transport in the female reproductive tract of the agile Antechinus (Antechinus agilis) and the relationship of these parameters to single and multiple matings. Mating in this species is characteristically long compared with that of other mammals, lasting for up to 8-12 h during which time the pair remain locked together. After the first hour of mating, only approximately 40% of males had ejaculated, but by the third hour all males had ejaculated. The total number of spermatozoa extracted from the female tract remained at approximately 30 x 10(3) spermatozoa per side over the next 9 h of copulation. After completion of male/female access (12 h), approximately 56% of spermatozoa extracted were located in the lower isthmic region of the oviduct where specialized sperm storage crypts are located. The number of spermatozoa extracted from the female reproductive tract did not decline over the next 3 days, but there was a change in the distribution of spermatozoa with an increase in the proportion of extracted spermatozoa stored in the lower isthmus (approximately 76%). However, 7 to 14 days after mating, only approximately 30% of the stored spermatozoa ( approximately 9.4 x 10(3) spermatozoa per side) were still present in the isthmus. When females were mated with a second male on a consecutive day, the sperm numbers extracted from the tract were about twice that deposited during single mating, with sperm transport to the lower isthmus occurring over a similar time frame. Although the occurrence of extended copulations in the wild has not yet been confirmed, these laboratory results suggest that similar periods of copulation are likely, since completion of the ejaculation process requires at least 3 h. The extended copulation in A. agilis reduces the possibility of an early second mating, which might interfere with the normal transport and crypt colonization of spermatozoa through competition.