Sperm Removal

At the conclusion of a successful copulation in cockroaches the transferred sperm are housed within a sper-matophore in the female genital tract. The male is long gone before his gametes move to the female spermathe-cae, and is likely to have little direct influence on where, how, and if his sperm are stored. If his female consort is not a virgin, however, there is potential for a copulating male to increase his fertilization success by using genital appendages to move or remove the stored sperm of a rival. Male intromittent organs are known to extract stored sperm in one of three basic ways (Eberhard, 1996; Miller, 1990). First, a genital structure may be inserted into or near a spermatheca and the ejaculate issued with enough force to flush out a rival's sperm. This mechanism is unlikely in cockroaches since sperm transfer is indirect, via a spermatophore. Second, male genital appendages may be used to induce the female to discard the sperm of other males. When a female cockroach oviposits, eggs emerging from the oviduct pass over sensory hairs that trigger a contraction in the peripheral muscle layer of the sper-mathecal bulb and sperm are discharged to fertilize the egg (Roth and Willis, 1954b; Lawson and Thompson, 1970). Copulating males may take advantage of this reflex by using genital armature to tickle the mechanoreceptors, causing the female to expel the sperm of rivals before the male deposits his own. Third, the male may directly remove rival sperm using backward-facing hooks, spines, barbs, or brushes at the tip of elongate appendages (e.g., Yokoi, 1990; Kamimura, 2000). These structures enter the spermatheca, then scrape out, scoop out, or snag and drag the sperm present. This is possible in cockroaches, as in several species genital sclerites have the appearance of organs used for sperm removal or displacement in other insect species; these include brushes (Fig. 6.11A) and hooks (Fig. 6.11C) at the tip of intromittent-type organs.

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