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Climate change and evolution: effects on phenotypic plasticity and genetic pattern

Periodic Reporting for period 1 - ADCLICH (Climate change and evolution: effects on phenotypic plasticity and genetic pattern)

Reporting period: 2018-06-04 to 2020-06-03

With the consensus that climate change will threat species, there has been growing needs to evaluate how species may respond to the change. Some species may keep pace with climate change tracking the new climatic conditions. Differently, species with low dispersal capability like several plants have to locally adapt to the new conditions. So, understand how and whether intraspecific variability may enable species' populations to fit with new environment is of the outmost importance to assure species survival. For this purpose, it is necessary to evaluate whether the environmental variability may explain difference in gene diversity, floral traits related to reproduction and in seed germination traits. A better understanding of these processes will enable us to optimize cost and benefit when planning conservation actions of species and habitats and to define the possible features that might allow the species to thwart future environmental changes. For this purpose, we studied Lilium pomponium, a species spanning across Mediterranean to Alpine climate and it is potentially prone to extinction risk because of range loss induced by climate change.
First, we characterized the climatic space occupied by the species to detect populations growing under different climatic conditions. Then we tested the concordance between geographical and environmental gradients using different measures. Eventually, we collected data about floral traits involved in pollinator attraction and in in flower–pollinator interaction and, leaves for genetic analysis and seeds to analyses relationship between germination pattern and environmental variability from twenty populations.
Despite geographical peripheral populations are expected to grow under ecologically harsh conditions, in Lilium pomponium concordance between geographical and environmental gradients is not supported. The weak association between geographical and environmental distances is closely related to the complex mountain topography that causes a discrete and strongly asymmetrical distribution of environmental conditions across the distributional range. Moreover, the occurrence of central environmental conditions at the geographical margins suggests that in L. pomponium range limits may be due to other factors, such as a gradient in habitat availability, rather than a gradient in habitat quality, and supports the importance of very local environmental conditions to explain its patchy distribution. Quantifying variation in floral traits over the geographical range of species is crucial for understanding the factors driving range dynamics. In fact, floral traits are often less variable and less affected by environmental heterogeneity than vegetative traits because variation in the former may have negative effects on fitness. For this reason, to understand possible effect of future climate change is particularly important to examine phenotypic variation and differences in reproduction in relation to environmental variation across the distribution range. In Lilium pomponium, floral trait variation is related to local environmental conditions with an array of interactions among resource availability, potential pollen limitation and population size that are differentially related to floral traits. Each environmental group is limited by different factors acting on different stages of the life-history strategy.
Another key factor in affecting range dynamics and so the resonse of future climate change is the variation of genetic traits over the geographical range of species. Usually, genetic diversity decreases and genetic differentiation increases toward the geographical periphery due to spatial isolation. Nevertheless, how environmental marginality may affect genetic variation has received much less attention. We used AFLP genetic marker to test the concordance between genetic variation and both geographical and environmental gradients in Lilium pomponium. We found little evidence for concordance between geographical and environmental gradients on genetic variation; although the prediction of an increased differentiation is met, genetic diversity does not decrease towards the geographical periphery. Increased differentiation among peripheral populations, that are not ecologically marginal, may be explained by a decrease in habitat availability that reduces population connectivity. In contrast, a decrease of genetic diversity along environmental but not geographical gradients may be due to low quality habitats scattered in different parts of the range that reduce effective population size or increase environmental pressure for populations. As a result, environmental factors may affect population dynamics irrespective of distance from the geographical centre.
To examine variation in germination among populations from different climatic conditions seeds from fourteen populations were sown at seven different constant temperatures. Timson’s index was used to fit seed germination response to the spatial and temporal pattern of temperatures. We then projected the predicted Timson’s index values of each population on the maps of monthly mean temperature. Our results suggest that germination niche of L. pomponium allows it to avoid at low elevation dry summer in Mediterranean climate using the growing season very early and to grow at high altitude in north Mediterranean mountains, shifting its germination phenology and taking advantage of the relatively warm and wet summer. This result is in line with the idea that the reproduction niche may plays an important role in determining plant distribution boundary. Moreover, our results suggest that the germination phenology of the L. pomponium will shift under future climate assuring germination success. Nevertheless, recruitment failure due to climate change might minimise any benefits arising from this shifts in phenology.
Taken together our results support the hypothesis that variation in floral traits, genetic pattern and germination traits can reflect an adaptive strategy for dealing with unpredictable variable environments. Even if adaptive processes are generally thought to be too slow to allow an accurate response by organisms, this high amount of variability may enable populations to cope with climate change.
The major theory used to explain among-population variation in traits is the centre-periphery hypothesis. The centre-periphery hypothesis postulates that species’ abundance and performance decrease from the geographical centre of the range toward the periphery because of harsher environmental conditions affecting the levels of genetic diversity and differentiation. In plants, a decline in habitat quality towards the periphery of the range is expected to cause either a decline in population size and density resulting in reduced pollinator service or inadequate pollination driving the decline of population size and, whatever the case, little potential for further range expansion.
Nevertheless, contrary to this general expectation, our study provides few support for genetic and morphological predictions of the centre-periphery hypothesis, suggesting that the predictions are confirmed only when its assumptions are met. In region with high topographic complexity, the variability in local conditions drives variation in floral and genetic traits and in seed germination, resulting in patterns more complex that expected by the theory.