Temporal control of DNA replication and the adaptive value of chromatin diminution in copepods

Chromatin diminution is a precisely controlled, highly repeatable, genome-w ide deletion of noncoding heterochromatic segments from the presomatic line . The somatic line is reduced in size and reorganized; the germ line remain s unaltered. Little is understood about its mechanistic underpinnings and a daptive significance in the nematodes, copepods, and hagfish in which it oc curs. Here, we propose that microcrustacean copepods, whose cytology, devel opment, and evolutionary ecology are well understood from an adaptationist point of view, provide the vehicle to test how chromatin diminution might o rchestrate certain cell cycle dynamics, with the consequence of influencing the evolution of nuclear DNA contents, organismal development rates, and b ody size. (C) 2001 Wiley-Liss, Inc.