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Adaptation to elevation in Brassicaceae species of the central Alps
Thesis (Dissertationen, Habilitationen)
 
ID 4635883
Author Maccagni, Alessio
Author at UniBasel Maccagni, Alessio
Year 2021
Title Adaptation to elevation in Brassicaceae species of the central Alps
Pages 226
Type of Thesis Dissertation
Start of thesis 01.01.2017
End of thesis 31.12.2020
Name of University University of Basel
Name of Faculty Philosophisch-Naturwissenschaftliche Fakultät
Supervisor(s) / Fachvertreter/in Willi, Yvonne
Hoch, Günter
Alexander, Jake
Abstract

Species are restricted in their spatial distribution, but the reasons behind this phenomenon are still not
entirely known. Temperature has been considered to play an important role for a long time, for
example because of the commonly observed overlap between isoclines and distribution limits, or for
the direct impact that temperature has on the physiology of organisms. From an evolutionary point of
view however, it is unclear why the climate niche of species does not seem to evolve such that species
ranges can extend unlimitedly. To shed light on the evolutionary constraints limiting species
distribution, I studied patterns of adaptation along an elevational gradient, which is essentially a
thermal gradient. I chose a macro-evolutionary approach and included in my analyses 100
Brassicaceae species covering a high diversity of restricted elevational ranges in the European Alps.
Species were compared in their thermal responses and thermal adaptation based on a climate chamber
experiment and a transplant experiment on a mountain slope, with 5 transplant sites from 600 to 2000
m of elevation. Climate chamber experiments revealed that low- and high-elevation species mainly
differed in the response of growth to temperature, with high-elevation species being better at growing
when daily temperatures reached a high maximum, but worse at growing to large size when night
frosts occurred. Therefore, results indicated a trade-off between fast growth under warm conditions
and frost tolerance. Analyses on an association between elevational range size and phenotypic
plasticity revealed no support for a positive link. However, I found that increased thermal
heterogeneity selected for stronger thermal specialisation, countering the hypothesis that temporal
environmental variability selects for increased plasticity. The transplant experiment demonstrated
that species were indeed adapted to their optimal elevation of occurrence; lifetime performance
declined if the transplant site was at a different elevation than the typical elevation of occurrence of
a species. Patterns established not via temperature-dependent mortality, but because reproduction
declined with increasing difference in elevation relative to the typical elevation. The probability of
fruit set decreased with increasing distance. Furthermore, I found that reproduction negatively affected survival to the next year, suggesting an allocation trade-off between reproduction and
longevity that may be also important in constraining the climate niche and its evolution. Overall, this
body of work supported that elevational range limits generally reflect niche limits, and that species
seem to have been selected for thermal specialisation. Evolutionary constraints in the widening of the
climate niche seem to include genetic trade-offs in growing fast under warm conditions and being
frost tolerant, and an allocation trade-off between reproduction and longevity. It is these two axes of
trade-offs or four axes of life-history aspects that future micro-evolutionary studies should focus on
to confirm their role in constraining the evolution of the climate niche within species.

edoc-URL https://edoc.unibas.ch/84611/
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