Local adaptation and phenotypic plasticity in alpine plants

The Alpine environment is characterized by strong variability causing a mosaic of habitat patches. Two fundamental strategies can be contrasted that allow plants to survive in the heterogeneous Alpine landscape. Plants can either adapt by specializing to locally prevailing conditions, a phenomenon referred to as local adaptation, or they can evolve phenotypic plasticity, the ability to respond to a range of conditions they frequently encounter, thereby maintaining high fitness across environments. In my PhD I have investigated the role of local adaptation and phenotypic plasticity for alpine plant survival using the example of Anthyllis vulneraria. Reciprocal transplantation experiments across two spatial scales show that fitness decreases with increasing distance between population origin and transplantation site, demonstrating local adaptation in Anthyllis vulneraria. I also document large population differentiation in the dates of onset and peak of flowering that exceeds neutral population differentiation at microsatellite loci. Moreover I show a functional relationship between the overlap of female and male phases of individual flowers and the degree of inbreeding in populations of Anthylls vulneraria. Phenotypic plasticity in the measured traits was often only small and could not be shown to be of adaptive value. I conclude that populations of Anthyllis vulneraria are locally adapted to the prevailing environmental conditions, and that phenotypic plasticity in response to drought is unlikely to be of adaptive value in the presently studied traits of Anthyllis vulneraria. Genetic variation in key traits such as the timing of flowering rather than phenotypic plasticity therefore appears to be essential for alpine plant survival under climate change

Strategic mating effort in a simultaneous hermaphrodite: The role of the partner's feeding status

Sexual selection theory for simultaneously hermaphroditic animals predicts an overall preference for inseminating partners that have a relatively higher female fecundity. Previous work on the link between male mating decisions and female fecundity has primarily focused on the effect of the partners' body size using existing variation in this trait within a study population. On the assumption that the body size is positively correlated with female fecundity, sperm donors should preferentially inseminate relatively larger individuals to obtain a higher fitness gain through their male sex function. However, empirical evidence for such size-dependent mate choice in simultaneous hermaphrodites is equivocal, possibly because of confounding variables. We studied the mating behavior of the simultaneously hermaphroditic flatworm Macrostomum lignano and tested for a strategic mating effort in response to the feeding status of the partner. We experimentally manipulated the feeding status of potential mating partners in order to generate variation in female fecundity among them and tested whether this affected the copulation number and the number of sperm that the focal worm managed to store in the partner's sperm storage organ. We found that the manipulation of the feeding status had a strong effect on the body size of the potential mating partners and that focal worms copulated more frequently with, and stored more sperm in well-fed partners compared to unfed partners. Our results suggest that M. lignano adjusts its mating effort in response to the feeding status of the mating partne

Lower plasticity exhibited by high- versus mid-elevation species in their phenological responses to manipulated temperature and drought

Background and Aims Recent global changes, particularly warming and drought, have had worldwide repercussions on the timing of flowering events for many plant species. Phenological shifts have also been reported in alpine environments, where short growing seasons and low temperatures make reproduction particularly challenging, requiring fine-tuning to environmental cues. However, it remains unclear if species from such habitats, with their specific adaptations, harbour the same potential for phenological plasticity as species from less demanding habitats. Methods Fourteen congeneric species pairs originating from mid and high elevation were reciprocally transplanted to common gardens at 1050 and 2000 m a.s.l. that mimic prospective climates and natural field conditions. A drought treatment was implemented to assess the combined effects of temperature and precipitation changes on the onset and duration of reproductive phenophases. A phenotypic plasticity index was calculated to evaluate if mid- and high-elevation species harbour the same potential for plasticity in reproductive phenology. Key Results Transplantations resulted in considerable shifts in reproductive phenology, with highly advanced initiation and shortened phenophases at the lower (and warmer) site for both mid- and high-elevation species. Drought stress amplified these responses and induced even further advances and shortening of phenophases, a response consistent with an ‘escape strategy'. The observed phenological shifts were generally smaller in number of days for high-elevation species and resulted in a smaller phenotypic plasticity index, relative to their mid-elevation congeners. Conclusions While mid- and high-elevation species seem to adequately shift their reproductive phenology to track ongoing climate changes, high-elevation species were less capable of doing so and appeared more genetically constrained to their specific adaptations to an extreme environment (i.e. a short, cold growing season

Lower plasticity exhibited by high- versus mid-elevation species in their phenological responses to manipulated temperature and drought

BACKGROUND AND AIMS: Recent global changes, particularly warming and drought, have had worldwide repercussions on the timing of flowering events for many plant species. Phenological shifts have also been reported in alpine environments, where short growing seasons and low temperatures make reproduction particularly challenging, requiring fine-tuning to environmental cues. However, it remains unclear if species from such habitats, with their specific adaptations, harbour the same potential for phenological plasticity as species from less demanding habitats. METHODS: Fourteen congeneric species pairs originating from mid and high elevation were reciprocally transplanted to common gardens at 1050 and 2000 m a.s.l. that mimic prospective climates and natural field conditions. A drought treatment was implemented to assess the combined effects of temperature and precipitation changes on the onset and duration of reproductive phenophases. A phenotypic plasticity index was calculated to evaluate if mid- and high-elevation species harbour the same potential for plasticity in reproductive phenology. KEY RESULTS: Transplantations resulted in considerable shifts in reproductive phenology, with highly advanced initiation and shortened phenophases at the lower (and warmer) site for both mid- and high-elevation species. Drought stress amplified these responses and induced even further advances and shortening of phenophases, a response consistent with an 'escape strategy'. The observed phenological shifts were generally smaller in number of days for high-elevation species and resulted in a smaller phenotypic plasticity index, relative to their mid-elevation congeners. CONCLUSIONS: While mid- and high-elevation species seem to adequately shift their reproductive phenology to track ongoing climate changes, high-elevation species were less capable of doing so and appeared more genetically constrained to their specific adaptations to an extreme environment (i.e. a short, cold growing season)

New microsatellite markers for Anthyllis vulneraria (Fabaceae), analyzed with Spreadex gel electrophoresis

Premise of the study: New microsatellite primers were developed for the diploid herb Anthyllis vulneraria . These primers will be used in upcoming studies focusing on random genetic variation, local adaptation, and phenotypic plasticity in alpine plants. Methods and Results: The new primers were adjusted to separate PCR amplicons (70 to 170 bp) on precast Spreadex gels using horizontal gel electrophoresis. No capillary sequencer was needed. Three to twelve alleles were found per locus depending on the population studied. Conclusions: Our preliminary results showed that the three studied alpine populations are predominantly outcrossing, but include variable levels of self-fertilization

Novel microsatellite markers for the high-alpine Geum reptans (Rosaceae)

Premise of the study: Geum reptans reproduces by outcrossing or by the formation of stolons. Sexual and clonal reproduction are not exclusive and occur mostly simultaneously. We developed novel microsatellite primers for this species, which will be used in a study about local adaptation, phenotypic plasticity, and random molecular divergence of alpine plants. Methods and Results: Twelve microsatellite primer sets were developed for G. reptans, of which nine were polymorphic. Initially, the forward primers had an M13 tail, and the allelic signals of each locus were amplified using a single fluorescent-labeled M13 forward sequence. In the running phase, a multiplex PCR assay was developed using different fluorophore-labeled forward primers. Two to 11 alleles were found per locus, depending on the studied population. Conclusions: Identical multilocus genotypes (i.e., clonal offspring) were not found because individuals in our sampling were at least 4 m distant from each other. FST–QST analysis will be applied to detect selection processes in populations of G. reptans across the Alps

Plant responses to simulated warming and drought: a comparative study in functional pasticity between congeneric mid and high elevation species

Aims: Effects of climate change, especially changes in temperatures and precipitation patterns, are particularly pronounced in alpine regions. In response, plants may exhibit phenotypic plasticity in key functional traits allowing short-term adjustment to novel conditions. However, little is known about the degree of phenotypic plasticity of high elevation species relative to mid elevation congeners. Methods: We transplanted 14 herbaceous perennial species from high elevation into two common gardens (1050 and 2000 m.a.s.l.) in the Swiss Alps, and we examined plastic responses in key functional traits to changes in temperature and soil water availability. This design was replicated with 14 congeneric species from mid elevation to assess if the degree of phenotypic plasticity differs between mid and high elevation species. Survival was assessed across two growing seasons, while aboveground biomass and specific leaf area (SLA) were measured after the first growing season, and biomass allocation to belowground and reproductive structures after the second. Moreover, a phenotypic plasticity index was calculated for the functional traits to compare the degree of plasticity between mid and high elevation species. Important Findings: Aboveground biomass was higher in mid elevation species relative to high elevation congeners in all treatments, yet decreased for both with elevation and drought. Similarly, SLA decreased with elevation and drought. Root mass fraction (RMF) was generally higher in high elevation species, and decreased with drought at the lower site. Drought increased the allocation to reproductive structures, especially when plants were grown at their elevation of origin. Interestingly, no difference was found in the degree of phenotypic plasticity averaged across mid and high elevation species for any of the studied functional traits. These results indicate that phenotypic plasticity in the focal traits did not depend on the elevation of origin of the species. Plasticity was not related to environmental heterogeneity, nor constrained by selective pressures at high elevation. However, both species groups showed a remarkable capacity for short-term acclimation to a prospective climate through rapid adjustments in key functional traits

Initial offspring size mediates trade-off between fecundity and longevity in the field

An understanding of the effects of intraspecific variation in offspring size is important from both an ecological and an evolutionary perspective. While the relationship between offspring size and overall offspring performance is key, most studies are restricted to examination of the effects of offspring size on early life-history stages only, and too few have examined the effects of offspring size throughout the life history. Here, we examine the effects of offspring size on post-metamorphic survival, growth, and fecundity under field conditions for the polychaete Janua sp. Larger offspring became larger adults and had higher levels of fecundity than those from smaller offspring, though the effect on fecundity was weaker and more variable over different experimental runs. Adults derived from larger larvae had shorter lifespans than adults derived from smaller larvae. Our results suggest that the maternal effect of offspring size can influence the frequently observed trade-off between longevity and fecundity. Future studies should seek to measure the effects of offspring size over as much of the life history as possible in order to avoid misestimating the relationship between offspring size and fitness

Past selection explains differentiation in flowering phenology of nearby populations of a common alpine plant

The timing of and relative investment in reproductive events are crucial fitness determinants for alpine plants, which have limited opportunities for reproduction in the cold and short growing seasons at high elevations. We use the alpine Anthyllis vulneraria to study whether flowering phenology and reproductive allocation have been under diversifying selection, and to assess genetic diversity and plastic responses to drought in these traits. Open-pollinated maternal families from three populations in each of two regions from the Swiss Alps with contrasting precipitation were grown in low and high soil moisture in a common garden. We measured onset, peak, and end of flowering, as well as vegetative and reproductive aboveground biomass. Population differentiation for each character (Q ST) was compared to differentiation at neutral microsatellite loci (F ST) to test for past selection. We found population differentiation in onset and peak of flowering which results from natural selection according to Q ST-F ST. End of flowering and biomass were not significantly differentiated among populations. Reduced soil moisture had no consistent effect on mean onset of flowering, and advanced peak and end of flowering by less than 1week. Reproductive biomass was strongly decreased by lowered soil moisture. No genetic variation within or among populations was found for plasticity in any trait measured. The results suggest past heterogeneous selection on onset and peak of flowering in alpine Anthyllis vulneraria and potentially indicate local adaptation to differences in snowmelt date over distances <5km. Limited variation in plastic responses to reduced soil moisture suggests that soil moisture might not vary between populations

High-elevation plants have reduced plastictiy in flowering time in response to warming compared to low-elevation congeners

Global warming has caused shifts in the flowering time of many plant species. In alpine regions the temperature rise has been especially pronounced and together with decreasing winter precipitation has led to earlier snowmelt. The close association between time of snowmelt and plant growth at high elevations makes climate change for alpine plants particularly threatening. Here we transplanted eleven congeneric pairs of high- and low-elevation herbaceous species to common gardens differing c. 800 m in elevation, and c. 4 °C in mean growing season temperature to test whether reproductive phenologies of high- and low-elevation plants differ in their respective responses to temperature. Results indicate that high-elevation plants were less plastic in response to transplantation than their low-elevation congeners as the onsets of phenophases on average shifted 7 days less than in low-elevation plants. Plasticity of phenophase durations was overall weaker than that of phenophase onsets, and slightly stronger in high-elevation species compared to low-elevation congeners. We suggest that weaker plasticity in the onsets of early stages of reproductive phenology of high-elevation plants is related to spring frost, which constitutes a strong selective agent against early loss of winter hardiness. Some of the plastic responses of both low- and high-elevation species might potentially be adaptive under predicted climate change. However, the observed plasticity can be largely explained as a passive response to temperature and not as the result of natural selection in heterogeneous environments. The strong temperature-sensitivity of low-elevation species might promote their upward range expansion, but only to a certain threshold after which it becomes limited by the short growing season