SHIFTS IN THE LIFE-HISTORY OF PARASITIC WASPS CORRELATE WITH PRONOUNCED ALTERATIONS IN EARLY DEVELOPMENT

Developmental processes have been traditionally viewed to be invariant within higher taxa, However, examples are known whereby closely relat ed species exhibit alterations in early embryogenesis yet appear very similar as adults, Such developmental changes are thought to occur in response to shifts in life history, In insects, the regulation of embr yonic development has been intensively studied in model species like D rosophila melanogaster, Previous comparative studies suggest that the developmental processes documented in Drosophila well describe embryog enesis of advanced, holometabolous, insects generally, There have been few attempts, however, to take into account how life history has infl uenced early development of insects or to characterize early developme nt of species with life histories fundamentally different from flies, Here we compared early development of two species from the same family of parasitic wasps that exhibit very different life histories, Bracon hebetor is an ectoparasite that lays large, yolky eggs on the integum ent of its host that develop much like the free-living honeybee and Dr osophila, In contrast, Aphidius ervi is an endoparasite that lays smal l and apparently yolk-free eggs that develop in the hemocoel of the ho st, This wasp exhibits a radically different mode of early development at both the cellular and molecular level from B. hebetor, The develop mental changes in A. ervi reflect functional adaptations for its deriv ed life history and argue that departures from the fly paradigm may oc cur commonly among insects whose eggs develop under conditions differe nt from typical terrestrial species.