Local adaptation through genetic differentiation in highly fragmented Tilia cordata populations

Plastic and quantitative genetic divergence mirror environmental gradients among wild, fragmented populations of Impatiens capensis

PREMISE

Habitat fragmentation generates molecular genetic divergence among isolated populations, but few studies have assessed phenotypic divergence and fitness in populations where the genetic consequences of habitat fragmentation are known. Phenotypic divergence could reflect plasticity, local adaptation, and/or genetic drift.

METHODS

We examined patterns and potential drivers of phenotypic divergence among 12 populations of jewelweed (Impatiens capensis) that show strong molecular genetic signals of isolation and drift among fragmented habitats. We measured morphological and reproductive traits in both maternal plants within natural populations and their self-fertilized progeny grown together in a common garden. We also quantified environmental divergence between home sites and the common garden.

RESULTS

Populations with less molecular genetic variation expressed less maternal phenotypic variation. Progeny in the common garden converged in phenotypes relative to their wild mothers but retained among-population differences in morphology, survival, and reproduction. Among-population phenotypic variance was 3-10× greater in home sites than in the common garden for 6 of 7 morphological traits measured. Patterns of phenotypic divergence paralleled environmental gradients in ways suggestive of adaptation. Progeny resembled their mothers less as the environmental distance between their home site and the common garden increased.

CONCLUSIONS

Despite strong molecular signatures of isolation and drift, phenotypic differences among these Impatiens populations appear to reflect both adaptive quantitative genetic divergence and plasticity. Quantifying the extent of local adaptation and plasticity and how these covary with molecular and phenotypic variation help us predict when populations may lose their adaptive capacity.

Natural population re-sequencing detects the genetic basis of local adaptation to low temperature in a woody plant

Total of 14 SNPs associated with overwintering-related traits and 75 selective regions were detected. Important candidate genes were identified and a possible network of cold-stress responses in woody plants was proposed. Local adaptation to low temperature is essential for woody plants to against changeable climate and safely survive the winter. To uncover the specific molecular mechanism of low temperature adaptation in woody plants, we sequenced 134 core individuals selected from 494 paper mulberry (Broussonetia papyrifera), which naturally distributed in different climate zones and latitudes. The population structure analysis, PCA analysis and neighbor-joining tree analysis indicated that the individuals were classified into three clusters, which showed forceful geographic distribution patterns because of the adaptation to local climate. Using two overwintering phenotypic data collected at high latitudes of 40°N and one bioclimatic variable, genome-phenotype and genome-environment associations, and genome-wide scans were performed. We detected 75 selective regions which possibly undergone temperature selection and identified 14 trait-associated SNPs that corresponded to 16 candidate genes (including LRR-RLK, PP2A, BCS1, etc.). Meanwhile, low temperature adaptation was also supported by other three trait-associated SNPs which exhibiting significant differences in overwintering traits between alleles within three geographic groups. To sum up, a possible network of cold signal perception and responses in woody plants were proposed, including important genes that have been confirmed in previous studies while others could be key potential candidates of woody plants. Overall, our results highlighted the specific and complex molecular mechanism of low temperature adaptation and overwintering of woody plants.

Varying Levels of Genetic Control and Phenotypic Plasticity in Timing of Bud Burst, Flower Opening, Leaf Senescence and Leaf Fall in Two Common Gardens of Prunus padus L.

Several phenological phases mark the seasonal growth pattern in temperate woody perennials. To gain further insight into the way these phases react on an altering growth environment, we tested whether vegetative and reproductive phenophases in a shrub species respond differentially among different genetic entities and between two different planting sites. We scored leaf bud burst, flower opening, leaf senescence and leaf fall on 267 ramets of Prunus padus L. belonging to 53 genotypes that were sampled in 9 local populations, and that were planted in 2 common gardens in the northern part of Belgium. The data were processed with cumulative logistic regression. The contribution of genetic and non-genetic components to the total variability varied between the four studied seasonal phenophases. The timing of flower opening displayed the smallest relative amount of intragenotypic variance (between ramets), suggesting a stronger genetic control and a lesser need at the individual plant level for plastic fine tuning to the micro-environment. In addition, whereas leaf bud burst showed the highest relative variance at the interpopulation level among all phenophases, probably at least partly attributable to local adaptation, flower opening displayed the highest intergenotypic variance, which may have been promoted more by assortative mating. Spring phenophases were strongly correlated (r = 0.89) as well as the autumnal phenophases (r = 0.72). Flower opening was not correlated with the autumnal phenophases. Timing of leaf bud burst and leaf senescence were negatively correlated, demonstrating that the length of the growing season enlarged or diminished among the studied genotypes. Although the two planting sites were only 24 km apart, all phenophases were advanced at the less exposed site, indicating a phenotypic plastic response. Together, our results suggest that in P. padus, flowering is less sensitive to environmental variation than leaf bud break and may show a lesser impact of a changing environment on this reproductive phenophase.

Niche models at inter- and intraspecific levels reveal hierarchical niche differentiation in midwife toads

Variation and population structure play key roles in the speciation process, but adaptive intraspecific genetic variation is commonly ignored when forecasting species niches. Amphibians serve as excellent models for testing how climate and local adaptations shape species distributions due to physiological and dispersal constraints and long generational times. In this study, we analysed the climatic factors driving the evolution of the genus Alytes at inter- and intraspecific levels that may limit realized niches. We tested for both differences among the five recognized species and among intraspecific clades for three of the species (Alytes obstetricans, A. cisternasii, and A. dickhilleni). We employed ecological niche models with an ordination approach to perform niche overlap analyses and test hypotheses of niche conservatism or divergence. Our results showed strong differences in the environmental variables affecting species climatic requirements. At the interspecific level, tests of equivalence and similarity revealed that sister species were non-identical in their environmental niches, although they neither were entirely dissimilar. This pattern was also consistent at the intraspecific level, with the exception of A. cisternasii, whose clades appeared to have experienced a lower degree of niche divergence than clades of the other species. In conclusion, our results support that Alytes toads, examined at both the intra- and interspecific levels, tend to occupy similar, if not identical, climatic environments.