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Plasticity and genetic variation along elevational and latitudinal gradients: Insights from the widespread plant Anthyllis vulneraria
The distribution and population characteristics of plants are largely influenced by the environmental conditions they encounter across their ranges. In response to environmental changes, populations can migrate to new locations, exhibit phenotypic plasticity and undergo evolutionary adaptation. Stud...
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| Format: | Dissertation |
| Sprache: | Englisch |
| Veröffentlicht: |
Philipps-Universität Marburg
2023
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| Zusammenfassung: | The distribution and population characteristics of plants are largely influenced by the environmental conditions they encounter across their ranges. In response to environmental changes, populations can migrate to new locations, exhibit phenotypic plasticity and undergo evolutionary adaptation. Studies comparing population traits along gradients of elevation and latitude provide an opportunity to assess the influence of different environmental and historical factors on plant population characteristics. To investigate plant plasticity and evolutionary potential in response to environmental variation, I employed an integrative approach combining field surveys, population genetic studies, and experiments. The widespread plant Anthyllis vulneraria was selected as a model species because of its large elevational and latitudinal distribution in Europe. In particular, I studied across elevational and latitudinal gradients (1) the characteristics of habitats and populations of A. vulneraria, (2) the neutral molecular genetic diversity and differentiation of populations, (3) the quantitative genetic differentiation and the evolutionary potential of populations. The elevational gradient in the Alps ranged from 500 m to the elevational limit at 2500 m and the latitudinal gradient spanned 2400 km from Central Europe to the range limit in the North. The length of the two gradients was chosen to correspond to a change of c. 11.5 °C in annual mean temperature.
I explored the habitat characteristics of 40 populations of A. vulneraria along both the elevational and latitudinal gradients and studied their influence on population characteristics. Plant size and reproduction decreased, but plant density increased with elevation and latitude, indicating higher recruitment and demographic compensation among vital rates. The results support the view that demographic compensation may be common in widespread species. Temperature variation along both gradients was found to have the strongest effects on population characteristics, followed by differences in precipitation, solar radiation, and soil nutrients. The proportion of plants flowering, seed set and seed mass declined with latitude indicating resource limitation and reduced pollination in the North, while the strong variation in these traits along the elevational gradient was not related to elevation or other covarying environmental variables, but to local environmental variation in alpine habitats.
I examined the molecular genetic diversity and differentiation of the populations of A. vulneraria using microsatellites, which are considered to be neutral markers and unaffected by natural selection. Genetic diversity strongly declined and differentiation increased with latitude. These patterns are likely the outcome of serial founder effects during the northward colonization following glacier retreat after the last ice age. The genetic diversity and differentiation among populations of A. vulneraria was not related to elevation. This observation could be attributed to the higher gene flow facilitated by the much shorter elevational gradient. However, I found evidence of isolation by distance along both gradients, indicating restricted gene flow among populations along both gradients. Subarctic populations differed genetically from alpine populations indicating that the northern populations did not originate from high elevational ones in the Alps.
Plants grown from seeds originating from the studied populations were studied in a common garden experiment to assess the quantitative genetic differentiation and phenotypic plasticity of populations along the elevational and latitudinal gradients and to investigate their evolutionary potential. Most traits measured in the common garden exhibited clinal variation with elevation and latitude of origin indicating adaptive differentiation of traits along the gradients. Divergent selection was indicated by higher QST-values (measuring quantitative genetic differentiation) than FST-values (measuring neutral molecular genetic differentiation) in some traits. Furthermore, I observed that the differences in performance between mothers and their progeny were smaller for populations from high elevations and latitudes, suggesting reduced plasticity of the measured traits in these populations. However, the evolvability of most traits did not vary consistently along the two gradients indicating that the evolutionary potential of peripheral populations was not reduced.
To conclude, this thesis has highlighted the importance of combining field surveys, population genetic studies, and ecological experiments to investigate plasticity and genetic variation in response to different environmental conditions. Gaining a deeper understanding of how plant populations adapt to changing environments is crucial for predicting their future responses to climate change. The results suggest that the abundant centre model (ACM) does not fully account for the observed population characteristics and genetic patterns in A. vulneraria. Other factors such as historical migration and local adaptation driven by varying selection pressures along the elevational and latitudinal gradients have also important effects in shaping the distribution of the species and its traits across different environments, and will shape its future responses to climate change. While the rather low phenotypic plasticity of the arctic and alpine populations of A. vulneraria alone may not be sufficient for them to persist, genetic variability in fitness-related traits together with gene flow may allow their adaptation to changing environmental conditions in the future. |
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| DOI: | 10.17192/z2023.0665 |