Isolation and Identification of a Novel Fish Substance P and Its Effect on Retinal Cell Responses

Abstract

Sperm displacement is a sperm competition avoidance mechanism that reduces the paternity of males that have already mated with the female. Direct anatomical sperm removal or sperm flushing is known to occur in four insect orders: Odonata, Orthoptera, Coleoptera and Hymenoptera. In a fifth order, Dermaptera (earwigs), I found that the virga (the elongated rod of the male genitalia) of Euborellia plebeja seems to be used to remove rival sperm from the spermatheca (a fine-tubed female sperm storage organ). In this species, copulation lasted on average 4.6 minutes, during which time the male inserted the virga deep into the spermatheca, and then extracted it ejaculating semen from the opening of the virgal tip. The extraction of virgae (with its brim-like tip) appeared to cause removal of stored sperm in the spermatheca. The virga was as long as the body length of males, and the spermatheca was twice the female body length. The long length of the spermatheca and the possible removal function of the virga may select for virgal elongation.

Earwigs from Brazilian caves, with notes on the taxonomic and nomenclatural problems of the Dermaptera (Insecta)

“…directly insert the elongated virga into the female spermatheca during copulation (Kamimura 2000; Lieshout and Elgar 2011). Elongation of the virga (and the genitalia as a whole, which functions as the virgal sheath when in repose) is considered an adaptation for removal of rival sperm from the female spermatheca, which is usually longer than the virga (Kamimura 2000, 2005, 2013, 2015; Lieshout and Elgar 2011). Thus, genital elongation in E. janeirensis suggests intensive sperm competition in this species.…”

A new earwig of the genus Echinosoma from Penang Island, Peninsular Malaysia, with notes on the taxonomic and nomenclatural problems of the genus Cranopygia (Insecta, Dermaptera, Pygidicranidae)

“…In addition to these nomenclatural problems, recent studies have shown that the morphology of earwig virgae, particularly the length, evolves rapidly due to sperm competition, resulting in considerable variation even among very closely related congeners (Kamimura 2000, 2014, Lieshout and Elgar 2011). Therefore, although useful for species diagnosis, generic classification systems based primarily on virgal characteristics (e.g., length, convolution) likely do not reflect accurately the phylogenetic relationships.…”

Impact of low sperm competition on male reproductive trait allometries in a bush-cricket

“…By contrast, offensive pre-emption mechanisms to maximise fertilization success focus either on the mechanical displacement of previously deposited sperm from rival males or other means to ensure either the numerical or qualitative precedence of one’s own sperm. Examples of mechanical displacement can be found in male crickets, damselflies and dragonflies [13–15], who use their genitalia to physically remove or compact the sperm of the female’s prior mates before they inseminate her with their own sperm, with similar methods found also in longicorn beetles Psacothea hilaris [16] and the earwig Euborellia plebeja [17]. By contrast, in other insect groups sperm predominance can be achieved by the production of longer sperm [18], more sperm [19] or a higher sperm viability [20].…”