Two species of snapdragon (Antirrhinum) native to California offer a rare opportunity to bring multiple approaches to bear on the topic of pollinator mediated speciation in plants. A wealth of research on pollination has added dramatically to our understanding of role of animal pollinators in the evolution and diversification of plants. However, few of these studies have been able to say much about the role played by the animal pollinator in the initial divergence of the plant species under investigation because they lack a clear understanding of either the historical relationships of those species or their pollination ecology. The two species of snapdragon examined here, Antirrhinum vexillo-calyculatum and A. subcordatum, have overlapping distributions and have been distinguished almost solely by their flower color. The flowers of the widely distributed Antirrhinum vexillo-calyculatum are purple while the flowers of the narrowly distributed A. subcordatum are white. A phylogeny reconstructed using sequence data from the Internal Transcribed Spacer region (ITS) provides a robust hypothesis of their evolutionary history and shows them to be each others’ closest relative. Meanwhile, sequences of the Third Intron of the Nitrate Reductase gene (NIA) from multiple populations in and out of the zone of sympatry provide an understanding of the current state of their genetic relationship and indicates that these plant taxa are genetically indistinct with respect to one another. Into this background, we add data from the observations of flower visitors and array experiments to show that the flower color difference results in assortative visitation via its effect on pollinator behavior. Together the data suggest that ethological isolation between the two Antirrhinum species is involved in their speciation.

Key words: Antirrhineae, Antirrhinum, California, ethological isolation, flower color, pollination