Reproduction in the bushmaster (Lachesis muta): Uterine muscular coiling and female sperm storage

Abstract

Prolonged sperm storage in the female reproductive tract is a widespread strategy among vertebrates. In reptiles, especially lizards and snakes, females have specialized structures to store sperm in their oviduct, which occur in the posterior infundibulum and the nonglandular uterus. Many viperids exhibit uterine muscular coiling (UMC) in the nonglandular uterus, and this modification has been proposed as an ancestral trait in this taxon to store sperm. However, UMC and oviductal sperm storage have not been reported in Lachesis. Here, we studied the reproductive tract of L. muta females using histological techniques and describe, for the first time, the occurrence of oviductal sperm storage and UMC in nonglandular uterus of this species. We also describe an increase in secretory activity in the oviduct throughout the reproductive cycle. Our results support the hypothesis that UMC is an ancestral character in Viperidae and suggest that female L. muta must store sperm in the oviduct to fertilize the oocytes. We also propose new hypotheses for reproductive strategies of L. muta in nature.

Exceptional long-term sperm storage by a female vertebrate

“…Post mating, spermatozoa ascend the reproductive tract until reaching these, and sperm is believed to be stored until ovulation. Similarly, uterine muscular twisting has been reported in viperids and also could play a role [ 60 – 65 ]. After copulation, uterine contractions may result in a twisting of the oviducts, with untwisting and therefore sperm migration occurring only after ovulation [ 63 ].…”

“…Within these coils, furrows formed through the process of contraction may then retain sperm within this region [ 63 ]. Interestingly, while uterine muscular twisting has been observed in both non-vitellogenic and vitellogenic females, as might be expected if it serves a sperm storage function, it has also been observed in gravid females [ 61 , 65 ], questioning the anatomical function of this structure in LTSS. However, the finding presented here of multiple litters resulting from LTSS suggests that this mechanism is potentially functional in LTSS and retained until all spermatozoa are depleted; a process which may span multiple seasons.…”