KELLOGG, ELIZABETH A. Department of Biology, University of Missouri-St. Louis, St. Louis, MO 63121. - Genetics of character evolution.
Rapid advances in plant genomics and in developmental genetics are
providing new tools for plant systematists. Understanding the
developmental and genetic basis of morphology will help to understand
homology and character state delimitation, and to suggest the sorts
of selective pressures that might have been responsible for
diversification. A developmental genetic framework has been used
to investigate macroevolution in the grasses, in which major
morphological change has often involved change in the positionof
developmental programs (heterotopy), possibly via ectopic gene
expression. Heterotopy may have been responsible for 1) long-short
cell alternation in the leaf epidermis of the grasses and their sister
genus, Joinvillea; 2) diversification of function of C-class
genes in the grass flower, and possibly suppression of portions of the
perianth; 3) acquisition of perianth-like characteristics in leaf-like
inflorescence organs ; 4) formation of staminate flowers in the
panicoid grasses; and 5) repeated origin of C4 photosynthesis in
multiple lineages. Not all macroevolutionary changes fit this model.
For example, the novel morphology of the grass embryo can be
described as a change in timing of development (heterochrony) rather
than a change in position. As our understanding of morphological
characters improves in coming years, it will be intriguing to see if
other morphological novelty is created by simply moving old genes to
new places.
Key words: development, grasses, heterochrony, heterotopy, macroevolution