Altricial Development

After a parental lifestyle evolves, subsequent developmental adaptations often occur that reduce the cost of care and increase the dependency of offspring (Trumbo, 1996; Burley and Johnson, 2002). This is a universal trend, in that the developmental correlates of parental care are similar in both vertebrates and invertebrates. The pampered juveniles in these parental taxa are altricial, which in young cockroaches is evident in their blindness, delicate exoskeleton, and dependence on adults for food (Nalepa and Bell, 1997). Neonates of Cryptocercus are a good example of altricial development in cockroaches. First instars lack compound eyes; eye pigment begins developing in the second instar. The cuticle is pale and thin, with internal organs clearly visible through the surface of the abdomen. Gut symbionts are not established until the third instar, making young nymphs dependent on adults for food. First instars are small, averaging just 0.06% of their final adult dry weight. The small size of neonates is associated with the production of small eggs by the female. The length of the terminal oocyte is 5% of adult length, contrasting with 9-16% exhibited by six other species of oviparous cockroaches (Nalepa, 1996). Young nymphs of Perisphaerus also lack eyes; in one species at least the first two instars are blind (Roth, 1981b). We have little information on developmental trends in those cockroach species where females carry nymphs. It would be intriguing, however, to determine if, like marsupials, internal gestation in these species is truncated, with nymphs completing their early development in the female's external brood chamber.

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