Plant population differentiation and climate change: responses of grassland species along an elevational gradient.

Mountain ecosystems are particularly susceptible to climate change. Characterizing intraspecific variation of alpine plants along elevational gradients is crucial for estimating their vulnerability to predicted changes. Environmental conditions vary with elevation, which might influence plastic responses and affect selection pressures that lead to local adaptation. Thus, local adaptation and phenotypic plasticity among low and high elevation plant populations in response to climate, soil and other factors associated with elevational gradients might underlie different responses of these populations to climate warming. Using a transplant experiment along an elevational gradient, we investigated reproductive phenology, growth and reproduction of the nutrient-poor grassland species Ranunculus bulbosus, Trifolium montanum and Briza media. Seeds were collected from low and high elevation source populations across the Swiss Alps and grown in nine common gardens at three different elevations with two different soil depths. Despite genetic differentiation in some traits, the results revealed no indication of local adaptation to the elevation of population origin. Reproductive phenology was advanced at lower elevation in low and high elevation populations of all three species. Growth and reproduction of T. montanum and B. media were hardly affected by garden elevation and soil depth. In R. bulbosus, however, growth decreased and reproductive investment increased at higher elevation. Furthermore, soil depth influenced growth and reproduction of low elevation R. bulbosus populations. We found no evidence for local adaptation to elevation of origin and hardly any differences in the responses of low and high elevation populations. However, the consistent advanced reproductive phenology observed in all three species shows that they have the potential to plastically respond to environmental variation. We conclude that populations might not be forced to migrate to higher elevations as a consequence of climate warming, as plasticity will buffer the detrimental effects of climate change in the three investigated nutrient-poor grassland species.

Extensive contemporary pollen-mediated gene flow in two herb species, Ranunculus bulbosus and Trifolium montanum, along an altitudinal gradient in a meadow landscape.

BACKGROUND AND AIMS: Genetic connectivity between plant populations allows for exchange and dispersal of adaptive genes, which can facilitate plant population persistence particularly in rapidly changing environments. METHODS: Patterns of historic gene flow, flowering phenology and contemporary pollen flow were investigated in two common herbs, Ranunculus bulbosus and Trifolium montanum, along an altitudinal gradient of 1200-1800 m a.s.l. over a distance of 1 km among five alpine meadows in Switzerland. KEY RESULTS: Historic gene flow was extensive, as revealed by Fst values of 0·01 and 0·007 in R. bulbosus and T. montanum, respectively, by similar levels of allelic richness among meadows and by the grouping of all individuals into one genetic cluster. Our data suggest contemporary pollen flow is not limited across altitudes in either species but is more pronounced in T. montanum, as indicated by the differential decay of among-sibships correlated paternity with increasing spatial distance. Flowering phenology among meadows was not a barrier to pollen flow in T. montanum, as the large overlap between meadow pairs was consistent with the extensive pollen flow. The smaller flowering overlap among R. bulbosus meadows might explain the slightly more limited pollen flow detected. CONCLUSIONS: High levels of pollen flow among altitudes in both R. bulbosus and T. montanum should facilitate exchange of genes which may enhance adaptive responses to rapid climate change.

Eleven microsatellite markers for the mountain clover Trifolium montanum (Fabaceae).

PREMISE OF THE STUDY: Microsatellite markers were developed in Trifolium montanum to investigate pollen dispersal patterns at landscape scale with a pollen-pool analysis (indirect parentage analysis) as well as in an experimental set-up with a direct paternity analysis. METHODS AND RESULTS: Screening 46 microsatellites developed for T. repens yielded four markers usable in T. montanum. Seven additional ones have been developed specifically for the target species using a 454-sequencing approach. All markers were polymorphic, with an allele number ranging from two to 45 based upon 254 individuals sampled from four populations, and an exclusion probability of 0.999. CONCLUSIONS: These markers proved a useful and reliable molecular tool for use in population genetics and parentage studies of this common grassland herb.

Eight microsatellite markers for the bulbous buttercup Ranunculus bulbosus (Ranunculaceae).

PREMISE OF THE STUDY: Pollen dispersal is a key biological process enabling plant populations to maintain genetic connectivity. Direct estimates of pollen dispersal using paternity assignment or correlated paternity estimates require highly variable genetic markers, of which microsatellites are the markers of choice. • METHODS AND RESULTS: Eight species-specific microsatellites have been developed for Ranunculus bulbosus, combining classical enrichment methods with 454 sequencing. These markers have been used in paternity analysis as well as in pollen-pool analyses and proven to be highly polymorphic (seven to 63 alleles in the largest population studied). An excess of homozygotes in six loci indicate the presence of null alleles. • CONCLUSIONS: These markers are the first microsatellites isolated and tested on R. bulbosus and provide a useful tool for population genetic studies in this common grassland herb.

Patterns of genetic variation across altitude in three plant species of semi-dry grasslands.

BACKGROUND: Environmental gradients caused by altitudinal gradients may affect genetic variation within and among plant populations and inbreeding within populations. Populations in the upper range periphery of a species may be important source populations for range shifts to higher altitude in response to climate change. In this study we investigate patterns of population genetic variation at upper peripheral and lower more central altitudes in three common plant species of semi-dry grasslands in montane landscapes. METHODOLOGY/PRINCIPAL FINDINGS: In Briza media, Trifolium montanum and Ranunculus bulbosus genetic diversity, inbreeding and genetic relatedness of individuals within populations and genetic differentiation among populations was characterized using AFLP markers. Populations were sampled in the Swiss Alps at 1800 (upper periphery of the study organisms) and at 1200 m a.s.l. Genetic diversity was not affected by altitude and only in B. media inbreeding was greater at higher altitudes. Genetic differentiation was slightly greater among populations at higher altitudes in B. media and individuals within populations were more related to each other compared to individuals in lower altitude populations. A similar but less strong pattern of differentiation and relatedness was observed in T. montanum, while in R. bulbosus there was no effect of altitude. Estimations of population size and isolation of populations were similar, both at higher and lower altitudes. CONCLUSIONS/SIGNIFICANCE: Our results suggest that altitude does not affect genetic diversity in the grassland species under study. Genetic differentiation of populations increased only slightly at higher elevation, probably due to extensive (historic) gene flow among altitudes. Potentially pre-adapted genes might therefore spread easily across altitudes. Our study indicates that populations at the upper periphery are not genetically depauperate or isolated and thus may be important source populations for migration under climate change.