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Povzetek: Polyploidy is an important evolutionary mechanism in flowering plants that can strongly affect their morphological and distributional traits. In this study, we investigated the differences in these traits among di-, tri-, and tetraploid populations of sweet spurge (Euphorbia dulcis), a common understory species in deciduous and mixed forests across Europe. We inferred the ploidy of 188 populations of E. dulcis by estimating relative genome size and chromosome counting. The data indicate that tri- and tetraploids are more widespread compared to the ancestral diploid populations, which are restricted to Liguria (north-western Italy) and adjacent regions. We suggest that polyploidisation was crucial for range expansion and the colonisation of higher latitudes, but not for the colonisation of higher elevations, where diploids appear to be more successful. Similarly, morphological differentiation after polyploidisation is only partly consistent with the classical hypothesis that polyploids are larger and have larger organs. Using nuclear ITS and plastid ndhF–trnL sequences, we inferred the spatio-temporal diversification of E. dulcis. It diverged from its diploid sister species E. duvalii, an endemic of southwestern France and adjacent Spain, in the mid-Pliocene. This divergence was likely due to vicariant speciation accompanied by adaptation to forest and grassland environments in E. dulcis and E. duvallii, respectively. Whereas the diploid populations of both taxa have restricted ranges today, polyploidisation within E. dulcis likely triggered by the Pleistocene climatic oscillations contributed to its significant range expansion and diversification. The species exhibits the highest genetic diversity in the south-western Alps, where all three ploidies co-occur. Based on the ploidy differentiation and the less pronounced genetic and morphological differentiation, we propose treating di- and triploids as well as two geographically and genetically divergent groups of tetraploids (eastern and western) as four subspecies. This challenges various taxonomic treatments previously proposed for this species. Our study highlights the importance of polyploidisation for diversification and range expansion, and indicates the necessity of further research to test hypotheses related to the morphological and distributional characteristics of polyploid organisms.
Ključne besede: forest understory species, morphometry, phylogeography, polyploidisation, taxonomy
Objavljeno v DiRROS: 18.04.2025; Ogledov: 209; Prenosov: 80
Celotno besedilo (6,03 MB)
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Povzetek: Natural hybridization of plants can result in many outcomes with several evolutionary consequences, such as hybrid speciation and introgression. Natural hybrid zones can arise as a result of fluctuating climate during the exchange of glacial and interglacial periods, where species retract and expand their territories, resulting in secondary contacts. On mountain ranges, such as the European Alps, hybrid zones of alpine species are frequently formed where different lineages meet. Willows are a large genus of woody plants with an immense capability of interspecific crossing. About 33 species of this genus inhabit the Alps, where intermediate phenotypes were frequently observed and proclaimed as hybrids, but rarely examined in detail. One of the reasons was a lack of informative molecular markers and suitable analytical tools to analyse this highly diverse and convergent genus. With the development of the RAD-seq technology, several questions regarding willow phylogeny and hybridization could be answered. In this study, a putative hybrid zone of two sister species, S. foetida and S. waldsteiniana, was investigated to study the genomic structure of populations within and outside their contact zone, to find evidence for hybrid speciation or introgression, and to analyse if morphological phenotypes are reflected by their genotypes. Individuals of the two species were sampled across their distribution range in the Alps and examined with the use of RADseq data and morphometric analyses. The results showed that a hybrid zone between the two species was established within the range of their contact zone. Patterns of genetic admixture in homoploid hybrids indicated introgression with asymmetric backcrossing to one of the parental species. Morphometric characteristics of hybrids supported the molecular data and showed intermediacy with a bias towards S. waldsteiniana. Only one potentially divergent hybrid lineage was observed, hinting to a possibility of localised hybrid speciation events.
Ključne besede: alpine plants, hybridization, morphometry, RAD sequencing, master thesis
Objavljeno v DiRROS: 17.01.2025; Ogledov: 306; Prenosov: 100
Celotno besedilo (4,66 MB)