Orchids represent approximately 10% to the plant species richness of the tropics, a diversity unsurpassed by any other plant group. Scaphosepalum belongs to the most diverse Neotropical orchid group, the Pleurothallidinae (about 4,000 species). This study seeks to reconstruct the evolutionary history of Scaphosepalum orchids by using DNA sequence data and morphological traits. The goal is to determine whether species living in the same area and sharing habitats are each other's closest relatives or sister species. These co-occurring species may have arisen by the rare process of sympatric speciation. Scaphosepalum may be an ideal group in which to test theories of sympatric speciation because many of its species occur together in natural populations.
This study will provide valuable insights on the formation of species in the montane and cloud forests of the Andes, an area of significant biodiversity (an evolutionary hotspot) highly threatened by habitat destruction. It may also shed light on the poorly understood process of sympatric speciation. This research will also strengthen international collaborations, scientific networks, and education, both within the US and internationally.
This project explores in detail the speciation patterns of Scaphosepalum, a genus of 35 epiphytic Neotropical orchid species that occur primarily in the montane and cloud forests of the Andes. Due to its species distribution patterns (many species living in close sympatry and restricted to small areas) this is an ideal system to find scenarios in which sympatric speciation -the emergence of two species without geographic isolation at any stage- may have occurred. Examples of sympatric speciation are rare and highly controversial, and one of the goals of this project is to contribute to our current understanding of plant speciation in Neotropics. In order to address the relationships of Scaphosepalum species, an evolutionary tree was reconstructed using DNA and morphological characters. The majority of the species of Scaphosepalum (75%) were included in our analyses. Specimens and tissues used for DNA extraction and morphological studies were collected in several field expeditions (Fig. 1), and were imported and deposited in collections of the country of origin of the plants, and in collections in the United States. A well-resolved evolutionary tree was obtained and our results indicate that most species living in sympatry are not each other closest relatives (Fig. 2). Contrary to our initial hypothesis, divergence of species may be the result of geographical isolation (allopatric or parapatric speciation) and subsequent dispersion to the habitats that they currently occupy. Nevertheless, the results generated by this project indicate that the presence of the Andes is a strong barrier for diversification and dispersion (Fig. 3). Two clades are entirely confined to microhabitats on the eastern slopes of the Andes, and one clade contains all the sampled species from the northwestern slopes of the Andes and Central America. These findings contribute to our growing knowledge of how plants have speciated in the Andes, a region that harbors 37% of the plant diversity. By the study of this group combining molecular and morphological information, we have now a better understanding of a) the morphological characters that are shared by the members of the same lineage (synapomorphies), which increases our likelihood to identify them, and b) we were able to detect how morphological characters change in the evolutionary history of the genus. For example, Figure 4A shows a case where three morphologically very different species share the presence of minute hairs in the floral bracts. Figure 4B, illustrates how morphological characters change in a lineage that has shifted from fly pollination to hummingbird or butterfly pollination. The reciprocal illumination of these datasets is important because it provides a more comprehensive understanding of the group, and also when translated to a formal classification, it results into a more stable and easy to use classification. In the different phases of this project we tried to integrate different sectors of society. The phase in the field has been ideal to train and share knowledge, resources and experiences (Fig. 1). The results of this project have been presented in domestic and foreign Scientific Conferences, and several talks have been offered in different chapters of Orchid Societies. Different media (webpages and videos) have also been used to disseminate our results and are accessible through the internet, and are also in display in the permanent exhibit of the Florida Museum of Natural History. As a side project, we have documented all our observations of the populations in the wild, and have incorporated our findings into the assessment of their conservation status. The results were published in the Red List of Endemic Plants of Ecuador 2011.
