Effect of locality on morphological variation in Lupinus nanus and Lupinus bicolor

Recent evolutionary radiations within the California flora provides useful examples for studying adaptive evolution and speciation. The Western North American annual lupines traditionally called section Micranthi, for example, is tentatively supported as a clade, but taxa within the group have been variously divided into as many as nineteen species or consolidated into as few as five. Past experiments found no evidence for interfertility between Lupinus bicolor and L. nanus, implying that they are distinct species. Other studies, however, have hypothesized that L. bicolor, which is small-flowered and self pollinates in the bud, is a polyphyletic group with multiple origins from local L. nanus populations, which exhibit mixed mating systems with varying degrees of outcrossing. Under the latter hypothesis, we predict that, within sympatric pairs of L. nanus and L. bicolor, L. bicolor populations should be morphologically and genetically more similar to their local L. nanus congener than to geographically distant L. bicolor populations. Local adaptation could predict a similar pattern, from convergent evolution of the two taxa. To test this prediction from two different evolutionary models, we used a greenhouse experiment to compare morphological traits of three pairs of sympatric populations of L. nanus and L. bicolor sampled from an ecological gradient from the immediate coast to the interior coast range. We found that in both species, ecologically important vegetative characters, such as leaflet shape and leaf area, vary in a predicted manner across this gradient but that the response to the gradient differs between species. This pattern conflicts with the prediction of both evolutionary models. The heritability and geographic patterns of these and other characters, in particular reproduction characters such as flower morphology, will be discussed in the context of additional evolutionary models.