Queue up, please! Spermathecal filling in the rove beetle Drusilla canaliculata (Coleoptera, Staphylinidae)

Abstract

Most studies on insect sperm motility have been conducted in vitro using artificial environments outside the animal's body. Only little is known about the function of motile insect sperm at different sites within the male or female genital tracts. We dissected genital tracts of female rove beetles (Drusilla canaliculata) to show that spermatozoa use their own motility to migrate from the spermatophore into the spermatheca. Our dissection method allowed direct observation and filming of the spermathecal filling process inside the female's genital tract. Spermatozoa were found to enter the spermatheca individually, sometimes in groups of two or three. Although exhibiting only weak motility and no progressive motion in buffer solution, the spermatozoa inside the female show vigorous lashing and reach an average velocity of 47.5 microm s(-1). To gain mobility and speed, the spermatozoa likely utilize the relatively small diameter of the spermathecal duct to push themselves off the duct walls, rather than swimming freely in seminal fluid. The spermatozoa (approximately 1,250 microm) are considerably longer than the distance they have to travel along the spermathecal duct (approximately 800 microm). Our study provides the first direct observation of active sperm migration within the female of an insect stressing the importance of the genital tract as a prerequisite for functional sperm motility.

Insertion and withdrawal of extremely elongated genitalia: a simple mechanism with a highly modified morphology in the leaf beetle, Lema coronata

“…The outer diameter of MEG is too small (less than 2 µm; Matsumura & Akimoto, 2009) to go through the MEG for plural spermatozoa at one time. As shown by Werner et al. (2007) for the rove beetle Drusilla canaliculata , such a small diameter of the extremely elongated MEG can make it possible for spermatozoa to push themselves off the tube wall and migrate into the spermathecal capsule.…”

Co‐evolution of male and female reproductive traits across the Bruchidae (Coleoptera)

“…A similar scenario might occur in relation to spermathecal duct length and sperm length. Indeed, Werner et al . (2007) have shown that the spermatozoa of Drusilla canaliculata (Coleoptera: Staphylinidae) interact with the spermathecal duct to gain progressive motility.…”

Insect Sperm Motility

“…The axonemal wave would then act against the duct wall rather than the surrounding fluid, leading to a crawling motion instead of swimming. Although not yet investigated systematically, observations on Drusilla canaliculata sperm movement within the female genital tract add support to this theory (Werner et al , 2007).…”

“…Spermatozoa of the dipteran Megaselia scalaris for example, exhibit the double helical motility pattern when released in buffer, but express a more random motility pattern, including strong bending of the tail, when observed in pockets of the female genital tract (Curtis & Benner, 1991). In the rove beetle Drusilla canaliculata (Fabricius) the differences are even more marked (Werner et al , 2007). When released in buffer, spermatozoa of this species are unable to progress in the medium and show only feeble movement of the flagellum.…”