WYNGAARD*, GA; DOMANGUE, R; GERKEN, S; RASCH, EM: A Mechanistic Role for Chromatin Diminution in the Evolution of Genome Size and Life History Characteristics in Zooplankton

We propose a mechanistic explanation of how variation in large scale features of the genome are translated into life history variation at the organismal level in freshwater cyclopoids (Crustacea: Copepoda). Interspecific variation in genome size of copepods is determined, in part, by chromatin diminution. During the early embryonic stages and according to species, 35 � 99% of DNA content is eliminated from the presomatic cell lineage; the germline is unaltered. Much of the eliminated DNA is noncoding heterochromatin with no known function. The result is a dramatic reduction in somatic cell size and reorganization of the genome, followed by presumably reduced cell division rates and development rates. Using a directed ordered- heterogeneity test, we found that somatic genome size correlates positively with body size and negatively with development rate over a wide range of temperatures in five species. Additional species are being measured for DNA contents and life history traits and the correlated evolution of these characters is being examined using the method of phylogenetically independent contrasts. Addressing questions of genome size evolution in the context of macroevolution and life history theory serves to add an integrative, holistic approach that may aid in explaining large scale patterns of body size and development rate, traits which are well known to be under intense selection in many copepod populations.