Genetic differentiation, diversity, and inbreeding in the mountain monkeyflower (Mimulus caespitosus) of the Washington Cascades

Publisher Website
Google Scholar
Abstract
Mimulus caespitosus is a stoloniferous yellow monkeyflower that grows in small, perennial mountain streams. Plants from 22 populations around the crest of the Cascade Mountains in Washington State were electrophoretically assayed for 15 allozyme loci. Expected heterozygosity within populations (H), a measure of genetic diversity, averaged 0.17 and was negatively correlated with northeastward aspect. No association of H with elevation or position upstream was detected. Wright's gene fixation F averaged 0.19, indicating 20–30% selfing, and was significantly heterogeneous among populations. Nei's genetic distance D averaged 0.072, significantly above average for conspecific populations, especially considering all populations were within 11 km. Populations from the same stream have lowest D, whereas populations from the same mountainside, mountain, and region show increasing values of D. Thus, gene flow is predominant along streams and a hierarchy of genetic relationships exists. It was expected that because this area was heavily glaciated during the Pleistocene, postglacial colonization by refugial populations would result in strong clusters of populations from adjacent streams sharing the same refugia. However, a dendrogram of genetic distances showed few statistically significant clusters of populations from different streams.