Floral colour variation across life history and geography in Mimulus ringens (Phrymaceae)

Floral and life history traits play important roles in plant speciation. The genus Mimulus is a model system for studying speciation. It includes examples of species in which floral colour facilitates isolation through pollinator shifts, as well as life history changes that result in temporal or ecogeographic isolation. We investigate the possibility that both floral colour and life history have shifted together in a recently described, genetically distinct group within the species Mimulus ringens. Using a large, range-wide citizen science dataset, we test for geographic trends in flower colour and flowering time. We combine this with greenhouse studies in populations of known life history to test for differences in flower colour with life history. We show that darker-flowered plants are more common at higher latitudes, that annual-like populations have darker flowers, and that flowering time varies with latitude only in the subset of populations that have lighter flowers. This suggests that annual-like populations (with the earlier flowering time typical of this life history) are restricted to the northern part of the species range and may have distinct trends in flowering date.