Structure of the seminal receptacle and sperm storage in the Japanese pygmy squid

Abstract

To examine the mechanism of sperm storage in Idiosepius paradoxus, here we describe aspects of the mating behavior of I. paradoxus and the morphology of the spermatozoa and the seminal receptacle after copulation. The seminal receptacle is located in the ventral portion of the buccal membrane surrounding the buccal mass, and opens inside the buccal membrane. It branches into approximately six sacs, similar in appearance to a bunch of bananas, and its wall consists of cuboidal ciliated epithelial cells (with oval nuclei) surrounded by a connective tissue. Multiple vacuoles are distributed in the bottom region of each sac. These histological and morphological characteristics differ from previous reports for loliginid squids and cuttlefish. In all except one receptacle observed in this study, sperm were stored near the bottom of each sac, and each sperm was facing the sac bottom. We observed spermatozoa in the entrance of the seminal receptacle in only one squid. These results suggest that spermatozoa were actively moving, and that sperm actively swam to the seminal receptacle. The volume of sperm in the seminal receptacles of the squid that had copulated eight times was the same as that in the squid that had copulated 29 times, which suggests that the seminal receptacle was filled after approximately eight copulation events. A squid that had copulated nine times retained a significant number of sperm in the seminal receptacle after spawning, suggesting that all of the sperm in the receptacle was not depleted after one spawning event.

Brooding and sperm storage by the deep-sea squid Bathyteuthis berryi (Cephalopoda: Decapodiformes)

“…The female may pick up the spermatangium by extending the buccal mass and transferring sperm to the receptacle. Sperm may also actively swim from the spermatangium into the seminal receptacle as recent evidence on pygmy squid suggests (Sato et al, 2010). It is unknown how sperm from the seminal receptacle get to the eggs.…”

Dimorphic ejaculates and sperm release strategies associated with alternative mating behaviors in the squid

“…This sperm aggregation may be one of the possible causes influencing the slow sperm release in these males, as it may obstruct the flux of sperm extrusion from the spermatangium tip. Also, although mechanisms of sperm attraction and storage in the seminal receptacle are still not understood (e.g., Hirohashi & Iwata, ; Sato, Kasugai, Ikeda, & Munehara, ; Van Oordt, 1939), this sperm‐swarming behavior may also help to retain sperm near the seminal receptacle, enabling sperm migration to the organ, as well as avoiding dilution in a more external site of the female body (Hirohashi et al, ; Hirohashi & Iwata, ). Moreover, sperm aggregation has also been proposed as a sneaker strategy for competing for the limited space within the female seminal receptacle, and thus promoting last male precedence (Hirohashi & Iwata, ).…”

Respiratory CO2 Mediates Sperm Chemotaxis in Squids

“…fl agellum laying are temporally independent (Iwata et al 2005 ). Especially, sperm should travel, either actively or passively, for the certain distance from the ejaculation site to the storage site by an unknown mechanism (Iwata et al 2011 ;Sato et al 2010 ;Lumkong 1992 ). Therefore, the sperm swarming trait together with the female arm crown architecture (Naud et al 2005 ) would provide an effective diffusion-resistant situation against water movement.…”