Parental social environment alters development of nutritionally independent nymphs in Cryptocercus punctulatus (Dictyoptera: Cryptocercidae)

Abstract

Split-brood field studies using the biparental, subsocial wood-feeding cockroach Cryptocercus punctulatus indicate that parental absence in families of three different age classes of nutritionally independent juveniles results in significantly slower growth when compared to sib groups allowed to remain with adults, even when nymphs are more than 2 years old when parents are removed. In one family that was divided when nymphs were 15 months old and followed for 4 years after treatment, 69 % of nymphs allowed to remain with parents reached maturity in the third year of the study, while those isolated from parents remained in the subadult stage at the 3-year mark. In the fourth year, measurements of wet weights and head capsule widths of the newly mature adults in the two treatments of this family were not significantly different. A parental vs. non-parental social environment, then, resulted in different rates of growth to reproductive maturity, but nymphs in both treatments ultimately reached similar adult sizes. The results indicate that parental effects can modify offspring ontogeny independently of the direct transfer of resources in the form of trophallactic food and symbionts. Because cockroaches in this genus are sister group to the developmentally plastic and juvenilized termites, further exploration of the role of the social environment on development in Cryptocercus is warranted. Termites are eusocial cockroaches that exhibit weak or delayed post-embryonic development; the majority of colony members are arrested in the small, soft-bodied, altricial morphotype displayed by early juvenile stages of their subsocial sister group, Cryptocercus. Developmental dynamics in this cockroach genus can therefore provide insight into conditions that may have favored the origin of eusociality in the lineage. Here, we demonstrate that the parental social environment in Cryptocercus punctulatus modifies offspring development independently of the direct transfer of hindgut fluids and does so for more than 2 years after hatch. A system in which parent-offspring interactions modify juvenile ontogeny, whatever the mechanism, contributes to the unique set of circumstances that ultimately resulted in the evolution of termite eusociality.