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Why Did a Female Penis Evolve in a Small Group of Cave Insects?

“…In contrast, long and narrow spermathecal ducts can be frequently seen in Trogiomorpha . This is especially true for Sensitibillini: the spermatheca is located far from the spermapore, and the spermathecal duct is narrow, extremely elongated, and spirally coiled (Figure B).…”

“…D) Genital coupling of Trogium pulsatorium . Male structures are highlighted in blue and female structures in red (redrawn from Klier).…”

“…Therefore, it is connected to the spermatheca via a duct (spermathecal duct) opening at the tip of the female penis (spermapore). Among the three psocopteran suborders, the spermatheca of psocomorphans and troctomorphans is generally situated close to the spermapore and connected to it by a relatively short duct . In this situation, a protrudable penis cannot evolve because the spermatheca and its short duct will disturb the movements of a telescopic penis.…”

“…In most bird species, insemination is accomplished by the close contact between male and female cloacae (the terminal opening of the digestive and urinary systems, also used for insemination and egg laying): the structure of cloacae is almost identical in both sexes . In psocopterans, the seminal transfer is generally achieved by tight contact between the flat spermapore plate (the plate surrounding the spermapore) situated in the female genital cavity and a nonbulging and membranous opening of the male seminal duct . Furthermore, the tight contact between the seminal inlet and outlet openings is achieved not by the insertion of the male penis but by hooking and pulling out the spermapore plate from the female genital chamber toward the male seminal outlet opening by using some nonpenile structures of the male terminalia, the epiproct in Lachesilla (Lachesillidae) or the 9th sternum in Trichadenotecnum (Psocidae), both belonging to the suborder Psocomorpha.…”

“…In psocopterans, the seminal transfer is generally achieved by tight contact between the flat spermapore plate (the plate surrounding the spermapore) situated in the female genital cavity and a nonbulging and membranous opening of the male seminal duct . Furthermore, the tight contact between the seminal inlet and outlet openings is achieved not by the insertion of the male penis but by hooking and pulling out the spermapore plate from the female genital chamber toward the male seminal outlet opening by using some nonpenile structures of the male terminalia, the epiproct in Lachesilla (Lachesillidae) or the 9th sternum in Trichadenotecnum (Psocidae), both belonging to the suborder Psocomorpha. Therefore, it is very likely that, in the most ancestral condition, the psocid males did not have an intromittent organ.…”