Abstract

Comparative analysis of nematode development has revealed considerable variations in how the fates of embryonic cells are specified. Such early variations seem enigmatic as they do not influence the resultant structure or performance of the emerging animal. Three different nematode species are used to consider why alternative ways to reach the same goal may have been established during evolution and why early steps of embryogenesis are particularly variable. A scenario is sketched with a shift from late to early cell specification, along with an increase in maternal contribution and developmental tempo and a decrease in regulative potential expressing different developmental strategies. Future studies of larger numbers of species are needed to assess the extent of such variations and to understand more fully the under lying mechanisms, rules and driving forces. BioEssays 23:841–847, 2001. © 2001 John Wiley & Sons, Inc.