Egg Number And Size

Comparisons of reproductive investment within a taxon require the resolution of differences attributable to body size. Although little information on the subject has been compiled for cockroaches, we do know that the body length of adults in the smallest species can be < 3% the length of the largest (Chapter 1), making them good candidates for investigations on the allometry of reproduction. At the species level there appears to be little relationship between the size of the mother and the packaging of the reproductive product. In the oviparous cockroaches, 18 mm long Cartoblatta pulchra females place about 95 eggs into an ootheca, more than any other species of Blattidae (Roth, 2003b). Ovoviviparous cockroaches average about 30 eggs per ootheca, but the relatively small Panchlora produces broods larger than a Blaberus 10 times its size and mass. Panchlora nivea is 2.5 cm long and internally incubates 60 or more eggs per clutch. The egg case is distorted into a semicircular or J-shape so that it may be internally accommodated (Roth and Willis, 1958b). The record, however, probably belongs to African Gyna henrardi, which somehow puts up to 243 eggs into a z-shaped ootheca that she stuffs into her brood sac (Grandcolas and Deleporte, 1998). Hatch must resemble the endless supply of clowns exiting a miniature car at the circus.

We know little regarding relative egg sizes among cockroaches. Two species with large post-ovulation investment are known to lay small eggs. In C. punctulatus eggs are only 44% of expected size for an oviparous cockroach of its dimensions (Nalepa, 1987). Most resources are channeled into an extensive period of post-hatch parental care and into the maintenance of the long-lived adults (Nalepa and Mullins, 1992). At hatch neonates in this species are tiny, blind, dependent, and fragile (Nalepa and Bell, 1997). Viviparous D. punctata also produces small eggs, with yolk insufficient to complete development (Roth, 1967d). As with all viviparous animals, supplying embryos with gestational nutrients places less reliance on producing large yolky oocytes. Neonates emerge at the precocial extreme of the developmental spectrum, with the largest relative size and shortest postembryonic development known among cockroaches.

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