Termination of Investment

If a female cockroach has initiated a reproductive episode that is threatened for lack of food or other reasons, she has several options for converting reproductive investment back into somatic tissue, thereby maintaining and redirecting her resources (Elgar and Crespi, 1992). Termination of investment can occur at several points in the reproductive cycle. Prior to ovulation, starvation increases oocyte resorption in cockroaches (reviewed by Bell and Bohm, 1975). In P. americana, most starved females produce one, sometimes two, oothecae in addition to the one being produced when starvation is initiated (Bell, 1971). Large yolk-filled oocytes are retained in the ovaries of those females that do not deposit a second ootheca, and beginning on about the 10th day of starvation these oocytes are resorbed and the vitellogenins stored. When feeding resumes, these stored yolk proteins are rapidly incorporated into developing oocytes. In Xestoblatta hamata, both resorption of proximal oocytes and an extension of the interval between oothecae are common in the field and are the result of unsuccessful foraging (Schal and Bell, 1982; C. Schal, pers. comm. to WJB).

After ovulation, females have other mechanisms for terminating reproductive investment. Abortion can occur in laboratory cultures if gestating females are disturbed in Pyc. surinamensis, Panchlora irrorata, and Blaberus craniifer (Nutting, 1953b; Willis et al., 1958; Willis, 1966). It is unknown if and under what circumstances ovoviviparous and viviparous cockroaches jettison egg cases under natural circumstances; the possibility exists that they may relieve themselves of their oothecal burden if suddenly pursued by a predator in their natural habitat. This tactic may be more likely in those cockroaches that that use speed/agility to escape predators rather than crypsis or defensive sprays.

Post-partition, cannibalism can be a means of recovering and recycling a threatened reproductive investment. If disturbed when nymphs are freshly hatched, adults of C. punctulatus may cannibalize their entire brood (CAN, unpubl. obs.). Other cockroach species are known to eat their young (Roth and Willis, 1954b), and starved females are often more likely to do so (Roth and Willis, 1960; Rollo, 1984b; WJB, unpubl. obs.).


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