Altricial Development in Subsocial Wood-Feeding Cockroaches

Species in the wood-feeding genus Salganea within the cockroach subfamily Panesthiinae (Blaberidae) typically live in biparental families; their first instars suffer high mortality when removed from adults, and in at least one species, adults are known to feed neonates on oral liquids. In the closely related gregarious wood-feeding genus Panesthia, no parental interaction with offspring is known. We compared the external morphology of first instars of these two genera and found that eye development and cuticular pigmentation at hatching are correlated with social structure. First instars of Panesthia have a dark cuticle and well-developed eyes. First instars of Salganea have a pale, transparent cuticle, and eyes significantly smaller than those of Panesthia relative to adult eye size. The body size of the first-instar of Salganea esakii is significantly smaller than that of Panesthia angustipennis spadica, relative to adult body size (24.0 and 27.4% of adult head-capsule width, respectively), but a more general survey suggests that, overall, neonate size may be similar in the two genera. We compared the first instars of these two taxa of Panesthiinae to those in the biparental, wood-feeding cockroach Cryptocercus (Cryptocercidae) and discuss how decreased investment in both integumentary and ocular development in subsocial cockroaches parallels that seen in altricial vertebrates.