Title: Molecular phylogenetic insights into the diversification and historical biogeography of the sun orchids (Thelymitra, Orchidaceae)
Applicant: Rowan Schley
Institution: Australian Tropical Herbarium, James Cook University, Queensland
The sun orchids (Thelymitra) are a characteristic element of Australia’s terrestrial orchid flora and display a striking morphological diversity. The genus diversified nearly exclusively in Australia and displays interesting distribution patterns, with a centre of diversity in southeast Australia. So far, little is known about infrageneric relationships in Thelymitra and its evolutionary history.
This study aims to shed light on the phylogenetic relationships in Thelymitra based on DNA sequence data in order to elucidate infrageneric relationships, to assess the taxonomic value of floral morphological characters, and to infer the historical biogeography of the group. Additionally, ecological niche modelling under past climates will be employed to infer to obtain insights into biogeographic factors that contributed to lineage divergences. Species distribution modelling under predicted future climate scenarios will be used to evaluate potential future threats to species diversity in Thelymitra.
The aim of this project was to examine the relationships between Sun orchid species in the context of their spatio-temporal evolution, and to determine the usefulness of key morphological characters used for identification. We found that Thelymitra first evolved around 5 million years ago during the Miocene, after which there was rapid diversification throughout the late Pliocene and throughout the Pleistocene (<2 million years ago). This rapid speciation was probably due to range shifts and long-distance dispersal caused by climatic fluctuation during these periods. This is evident as Thelymitra is found in four disjunct distributional areas within Australia, which resulted in the formation of distinct species groups with distinct morphological characters. These fluctuations, and the resulting ecological and reproductive isolation they caused, are thought to have driven the rapid evolution of large parts of the unique Australasian biota.
Published papers arising from this research:
Nauheimer L, Schley R, Clements M, Micheneau C, Nagar K (2018)
Australasia orchid biogeography at continental scale: Molecular phylogenetic insights from the Sun Orchids (Thelymitra, Orchidaceae) Molecular Phylogenetics and Evolution 127 (2018) 304-319