Unequal evolutionary rates between annual and perennial lineages of checker mallows (Sidalcea, Malvaceae): Evidence from 18S-26S rDNA internal and external transcribed spacers

Heterogeneous DNA substitution rates were found in the 18S-26S nuclear ribo somal DNA internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions of Sidalcea (Malvaceae), a putatively young genus of annuals and perennials. The majority of comparisons revealed that the annual speci es had significantly higher molecular evolutionary rates than the perennial s, whereas rates were consistently homogenous between obligate annual speci es. These findings led us to conclude that generation time or possibly anot her biological factor distinguishing annuals and perennials has influenced rates of molecular evolution in Sidalcea. The congruence of relative-rate t est results across both spacer regions reinforced the association between l ife history and rate of rDNA evolution across lineages of checker mallows. Evolutionary rate variation within perennials mainly involved three basally divergent lineages. The faster rate in one lineage, Sidalcea stipularis, c ompared with other perennials may be the result of genetic drift in the onl y known, small, population. The other two basally divergent lineages had sl ower evolutionary rates compared with the remaining perennials; possible ex planations for these differences include rate-reducing effects of a suffrut escent (rather than herbaceous) habit and seed dormancy.