If a female cockroach mates with more than one male during her reproductive lifetime, the manner in which she subsequently handles the sperm received from each partner plays a key role in determining the paternity of her offspring. After a copulation is terminated and the male leaves, the fate of his gametes is primarily under female control as they move from the spermatophore to the spermatheca(e), while they are being stored, while traveling from the spermatheca to egg, and at the site of fertilization (Eberhard, 1994,1996). Female control of sperm use and the resultant potential to bias paternity is called cryptic mate choice, so named because it occurs within the recesses of the female body and is difficult to observe or investigate directly (Thornhill, 1983).
If female post-copulatory sperm-use decisions are cued on particular types of stimuli, it will favor the male to elaborate structures and behaviors that produce those stimuli (Eberhard, 1985, 1994, 1996, 2001). Complex genital sclerites, then, may function to increase a male's fertilization success indirectly, via internal courtship of the female. Internal thrusting is known to have a stimulatory function in copulating animals (Eberhard, 1996), and has been noted in a few cockroach species; however, the behavior also may be associated with the deep insertion of the genitalia, the transfer of the spermatophore, or the direct removal of rival sperm. Males of B. fumigata often make rhythmic pumping motions during the first few moments of copulation (Barth, 1964). Likewise, abdominal contractions of male N. cinerea occur throughout copulation but are most frequent in the initial stages (Vidlicka and Huckova, 1993). Late in copulation the male of Eub. posticus "raises up on his forelegs and makes rhythmic pushing movements of his abdomen in a pulsating fashion" (Wendelken and Barth, 1987). Diploptera punctata males move their abdomen from side to side just prior to releasing the female (Roth and Stay, 1961). Conversely, females of Parc. fulvescens assume an arched posture during copulation, and rhythmical movements were observed for which the female appeared responsible (Wendelken and Barth, 1971). In addition to internally stimulating the female with genital structures, males may sing, tap, rub, hit, kick, wave, lick, wet with secretions, bite, feed, rock, and shake females in attempting to influence cryptic choice decisions (Eberhard, 1996). The production of oral liquid during mating by male Parc. fulvescens was listed by Eberhard (1991) as a form of copulatory courtship. A repeating sequence of pronotal butting, abdominal wagging, and circling behavior has been observed in C. punctulatus after genital disengagement (Nalepa, 1988a) and has been interpreted by Eberhard (1991) as post-copulatory courtship.
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