A cline within an ecotype of the yellow monkeyflower,Mimulus guttatus

Abstract

ABSTRACTPremiseA key goal of evolutionary biologists is to understand how and why genetic variation is partitioned within species. In the yellow monkeyflower,Mimulus guttatus(syn.Erythranthe guttata), coastal perennial populations collectively constitute a single genetically and morphologically differentiated ecotype compared to inland populations ofM. guttatus. While the distinctiveness of the coastal ecotype has now been well documented, there is also variation in environmental factors across the range of the coastal ecotype that could drive differentiation among its component populations in a more continuous way.MethodsBased on previous observations of a potential cline within this ecotype, we quantified plant height across coastal perennial accessions from 66 total populations in a greenhouse common garden experiment. To evaluate possible environmental factors driving the relationship between trait variation and latitude, we regressed height against multiple climatic factors, including temperature, precipitation, and coastal wind speeds.ResultsThe most significant relationship discovered in our experiment was a negative correlation between plant height and latitude. Plant height correlated negatively with annual precipitation and mean wind speed. Height was positively correlated with mean annual temperature. We hypothesize that one or more of these climatic factors drove the evolution of clinal variation within the coastal ecotype.ConclusionOverall, our study illustrates the complexity of how the distribution of environmental variation can simultaneously drive the evolution of distinct ecotypes as well as continuous clines within those ecotypes. These results are discussed in the context of the classic criticisms of ecotypes being intermediates in the process of speciation.