Valtentin Heimer (Universität Innsbruck)
Valentin Heimer from the Institute of Botany at the University of Innsbruck with the certificate for his master's thesis that has been recognized by the German Society for Plant Sciences (DBG). Photo: Andreas Holzinger
Valtentin Heimer's Master thesis was awarded with the Prize for the Best Plant Science Master Thesis, which was carried out at Universität Innsbruck in the year 2022
Title: Polyploidisation was not involved in the origin of five endemic species from southern Europe but is otherwise frequent in Euphorbia sect. Esula (Euphorbiaceae)
Heimer elucidated the genetic relationships of five endemic Euphorbia species that have almost not been studied so far. He showed that they are belonging to separate evolutionary groups despite their close geographic proximity.
A key factor for the diversification of flowering plants has been polyploidisation, which, however, appears of minor importance in the evolution of Euphorbia subgen. Esula. An exception is Euphorbia sect. Esula that includes roughly 100 species, many of which are widespread, but several have restricted distribution areas. We used ITS sequencing and relative genome size estimation to explore the evolutionary origin of E. gayi, E. graminifolia, E. tommasiniana, E. valliniana and E. variabilis, which are endemic to disjunct areas along the southern and western margins of the Alps as well as Corsica and Sardinia. In addition, we explored the incidence of polyploidy across different lineages of E. sect. Esula. Our phylogenetic results revealed several lineages with unresolved relationships that likely diverged in the late Miocene, but only one of them, the Eurasian Group, underwent considerable diversification, likely due to numerous polyploidisation events. Several polyploid or ploidy-mixed species from this group are distributed across large areas of Eurasia. All other lineages remained mostly diploid and species-poor, but dispersed to various continents, where most of the species have restricted distribution areas. All five endemic species are diploid but do not share a common ancestor. Both E. graminifolia and E. tommasiniana belong to the Eurasian Group whereas E. gayi, E. valliniana and E. variabilis belong to the Cosmopolitan Group and are thus not closely related to other European members of the section. Phylogenetic analyses recovered E. valliniana and E. variabilis as genetically distinct, although closely related. This, along with a clear morphological differentiation as revealed by morphometric analyses, supports their recognition as independent species. Our study highlights the important role polyploidisation had for plant diversification as well as the effects of other factors such as vicariance in disjunct refugia, which likely shaped the origin of the five endemic species from E. sect. Esula.
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Valtentin Heimer conducted this work at the Botany Institute in Innsbruck University in the working group of Prof. Dr. Peter Schönswetter. The work can be retrieved from: https://diglib.uibk.ac.at/ulbtirolhs/content/titleinfo/7738412?query=valentin%20Heimer