Parental Investment

In the majority of oviparous type A cockroaches females make their principal direct investment prior to fertilization, by supplying eggs with yolk nutrients. They then envelope the eggs in a protective covering and deposit them in a safe place for incubation. With the exception of Cryp-tocercus, there is no additional parental involvement. In species with external retention, like Blattella, embryos are dependent on yolk to fuel development but are also pro gressively supplied with water and some non-yolk nutrients during gestation (Fig. 7.10). This is likewise true of ovoviviparous cockroaches, but in several species neo-nates continue their dependence on maternally supplied nutrients for a period of time after hatch. These take the form of digestive fluids and glandular secretions; at least six types are known (Chapter 8). Cockroaches tend to have a very glandular integument, allowing for the repeated evolution of nutritive secretions from cuticular surfaces. Williford et al. (2004) recently demonstrated that proteins in the milk secreted by the brood sac of Diploptera are coded by genes from the same family (lipocalin) as those that code for a protein in the tergal gland secretion of R. maderae (Korchi et al., 1999).

One consequence of this variation in investment strategies is that it is not always easy to place cockroaches into distinct reproductive categories. There is a continuum between species that externally retain their egg cases and those that internalize them, obvious in Figs. 7.7 and 7.10. The location of the egg case during gestation differs in the Lophoblatta-Sliferia-Pseudobalta series, but the investment strategy is basically the same. Another example is a comparison between the viviparous Diploptera and the ovoviviparous Gromphadorhina. Both species apparently provision offspring on secretions that originate from the brood sac walls. Diploptera does so progressively, during gestation. Gromphadorhina and possibly other Blaberidae (Byrsotria, Blaberus, Rhyparobia) (Perry and Nalepa, 2003) expel it en masse for consumption by nymphs immediately after partition.

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