Sperm aggregations in female Agkistrodon piscivorus (Reptilia:Squamata): A histological and ultrastructural investigation

Abstract

Upon copulation in female Agkistrodon piscivorus, sperm migrate up the oviduct to sperm storage tubules (SSTs) in the posterior infundibulum. The epithelium of the SSTs is composed of ciliated and secretory cells and differs ultrastructurally from that of the epithelium lining the lumen of the posterior infundibulum. Sperm pass through an area composed primarily of ciliated cells at the opening of each gland before aligning themselves in parallel arrays with their nuclei facing an area composed primarily of secretory cells at the base of the tubules. Sperm are also found embedded inter- and intracellularly in the SSTs. The secretory vacuoles in the SSTs become highly electron dense after the start of the fall mating season along with the synthesis of lipid droplets. Histochemical analysis reveals that the alteration in secretory material density is caused by the production of neutral carbohydrates. Some sperm remain in aggregates in the nonglandular section of the posterior uterus until the time of ovulation. However, ultrastructural evidence indicates these sperm degrade before ovulation. Therefore, sperm in posterior aggregates have no role in fertilization of ovulated ova. The data presented here support the hypothesis that infundibular sperm storage is the mode that snakes utilize to sequester viable sperm until ovulation.

Sperm storage and morphofunctional bases of the female reproductive tract of the snake Philodryas patagoniensis from southeastern Brazil

“…Histological and cytological characterization of the UVJ is similar to previous descriptions for other snake species (Blackburn 1998;Girling 2002;Saint-Girons 1957;Perkins and Palmer 1996;Uribe et al 1998;Siegel and Sever 2008a;Siegel et al 2011). Nevertheless, the terms vagina and uterus (posterior or nonglandular) are not adequate to designate the UVJ because they are not consistent with the etymology of the word.…”

“…This characteristic provides an optimal arrangement of the space in the coelomic cavity during pregnancy (Perkins and Palmer 1996). The different oviductal regions described herein are also similar to other snakes regarding structure and function (Saint-Girons 1957;Bauman and Metter 1977;Mead et al 1981;Sever et al 2000;Siegel and Sever 2008a; . The epithelial cells secrete neutral carbohydrates and carboxylated glycosaminoglycans throughout the reproductive cycle (Gabe and Saint-Girons 1965;Uribe et al 1998;Sanchez-Martinez et al 2007;De Resende and Nascimento 2015).…”

“…During sperm storage in P. patagoniensis, we described a close contact of spermatozoa nuclei with the terminal portion of SR. This pattern has already been described in snakes of several lineages, such as Viperidae, Natricidae, and Colubridae (Fox 1956;Hoffman and Wimsatt 1972;Aldridge 1992;Sever and Ryan 1999;Siegel and Sever 2008a). Also, there are descriptions of groups of spermatozoa penetrating the secretory cells of SR in A. piscivorus (Siegel and Sever 2008a), and a possible reabsorption of sperm in T. sirtalis (Hoffman and Wimsatt 1972).…”

“…Sperm disappears within the SR soon after ovulation (or after 2 months) in D. punctactus, C. cerastes, and V. aspis (Saint-Girons 1975;Perkins and Palmer 1996). Nevertheless, sperm remains stored for several months after ovulation in A. piscivorus and T. coronata (including postpartum females in A. piscivorus), but it disappears before the next mating season begins (Aldridge 1992;Siegel and Sever 2008a).…”

“…The last hypothesis seems to apply to P. patagoniensis because histochemical reactions for PAS in SR were highly positive in the presence of spermatozoa. Some snakes-T. sirtalis (Hoffman and Wimsatt 1972), T. coronata (Aldridge 1992), D. punctactus (Perkins and Palmer 1996), S. pygaeae (Sever and Ryan 1999), and A. piscivorus (Siegel and Sever 2008a)-showed high positivity to PAS in the SR.…”