Monday, August 4, 2008: 4:40 PM
101 B, Midwest Airlines Center
Background/Question/Methods Schizanthus hookeri and S. grahamii (Solanaceae) are two annual herbs with pink to red, bilaterally-symmetrical, showy flowers that grow exclusively in the high Andes of central Chile and Argentina. These two species differ in their floral morphology, pollinator syndromes and breeding systems, with S. hookeri bearing pink flowers, pollinated mainly by bees and S. grahammi bearing reddish flowers visited by mainly by hummingbirds. To explore the evolutionary divergence of these two species, I initiated a phylogeographic study in the central Chilean Andes. Three regions of chloroplast DNA were sequenced for 57 individuals from 10 populations of S. hookeri and 9 populations of S. grahammi. To assess whether genetic flow between these two morphologically distinct species is possible, I observed their flower visitors during three days in a field site where both species co-occur and searched carefully for the presence of plants with intermediate phenotypes.
Results/Conclusions Phylogenetic analyses supported the existence of two differentiated clades that did not match currently accepted taxonomic classification. One clade comprises populations of both S. hookeri and S. grahamii largely restricted to the northern part of their distributional range under extreme aridity, and the second clade comprises populations of both species located in the southern part of the range, under less arid conditions. Plants of S. hookeri in the sympatric population were visited principally by bees, and only occasionally by hummingbirds (8%). In contrast, plants of S. grahamii were visited exclusively by hummingbirds, suggesting limited gene flow among floral morphs. No intermediate phenotypes between these two species were found. Reticulate evolution is usually proposed to explain the discordance between taxonomic (based on morphology) and molecular genetic trees. However, the differences in pollination and breeding systems between these species, and the absence of known hybrids in co-occurring populations, suggest that natural hybridization is unlikely despite their molecular closeness. Other hypotheses, offered to explain the mismatch between taxonomy and chloroplast-DNA phylogenies are considered in this presentation.
Results/Conclusions Phylogenetic analyses supported the existence of two differentiated clades that did not match currently accepted taxonomic classification. One clade comprises populations of both S. hookeri and S. grahamii largely restricted to the northern part of their distributional range under extreme aridity, and the second clade comprises populations of both species located in the southern part of the range, under less arid conditions. Plants of S. hookeri in the sympatric population were visited principally by bees, and only occasionally by hummingbirds (8%). In contrast, plants of S. grahamii were visited exclusively by hummingbirds, suggesting limited gene flow among floral morphs. No intermediate phenotypes between these two species were found. Reticulate evolution is usually proposed to explain the discordance between taxonomic (based on morphology) and molecular genetic trees. However, the differences in pollination and breeding systems between these species, and the absence of known hybrids in co-occurring populations, suggest that natural hybridization is unlikely despite their molecular closeness. Other hypotheses, offered to explain the mismatch between taxonomy and chloroplast-DNA phylogenies are considered in this presentation.
Acknowledgment: Fondecyt 3070030
