Geographic isolation and climatic variability contribute to genetic differentiation in fragmented populations of the long-lived subalpine conifer Pinus cembra L. in the western Alps

Abstract

Background Genetic processes shape the modern-day distribution of genetic variation within and between populations and can provide important insights into the underlying mechanisms of evolution. The resulting genetic variation is often unequally partitioned within species’ distribution range and especially large differences can manifest at the range limit, where population fragmentation and isolation play a crucial role in species survival. Despite several molecular studies investigating the genetic diversity and differentiation of European Alpine mountain forests, the climatic and demographic constrains which influence the genetic processes are often unknown. Here, we apply non-coding microsatellite markers to evaluate the sporadic peripheral and continuous populations of cembra pine (Pinus cembra L.), a long-lived conifer species that inhabits the subalpine treeline ecotone in the western Alps to investigate how the genetic processes contribute to the modern-day spatial distribution. Moreover, we corroborate our findings with paleoecological records, micro and macro-remains, to infer the species’ possible glacial refugia and expansion scenarios. Results Four genetically distinct groups were identified, with Bayesian and FST based approaches, across the range of the species, situated in the northern, inner and south-western Alps. We found that genetic differentiation is substantially higher in marginal populations than at the center of the range, and marginal stands are characterized by geographic and genetic isolation due to spatial segregation and restricted gene flow. Moreover, multiple matrix regression approaches revealed effects of climatic heterogeneity in species’ spatial genetic pattern. Also, population stability tests indicated that all populations had experienced a severe historical bottleneck, no heterozygosity excess was detected, suggesting that more recently population sizes have remained relatively stable. Conclusions Our study demonstrated that cembra pine might have survived in multiple glacial refugia and subsequently recolonized the Alps by different routes. Modern-day marginal populations, at the edge of the species’ range, could maintain stable sizes over long periods without inbreeding depression and preserve high amounts of genetic variation. Moreover, our analyses indicate that climatic variability has played a major role in shaping differentiation, in addition to past historical events such as migration and demographic changes.

New polymorphic nuclear microsatellites from Aristotelia chilensis (Mol.) Stuntz (Elaeocarpaceae)

“…It was interesting to note that the monomorphic profiles in two loci (Ach45 and Ach54) were evidenced in the southernmost population sampled in this study (Los Lagos Region). Based on the last glacial maximum (LGM) Patagonian ice sheet range (Moreno et al, 2018), we hypothesize that colonization event of Los Lagos population took place more recently than those populations northward, leading to a loss of alleles and decreased genetic diversity southward this region, explained by genetic drift (Hewitt, 2004;Gugerli et al, 2009;Tóth et al, 2019). However, this genetic pattern remains to be studied, and new northern-and southernmost populations of A. chilensis should be considered in order to define possible refugia of this species during LGM period.…”

In-Depth Genetic Diversity and Population Structure of Endangered Peruvian Amazon Rosewood Germplasm Using Genotyping by Sequencing (GBS) Technology

“…Very recently, Guizado et al [29] characterized the Peruvian rosewood using ISSR markers and found higher variations within populations (98.1%) than among (1.9%) populations. A previous study concluded that long-term natural selection and geographical isolation allowed the local population to conserve a specific genotype, thereby increasing the genetic variations between populations [51]. STRUCTURE, neighbor-joining analysis, and PCoA were used as clustering algorithms to elucidate the population structure of Peruvian rosewood germplasm.…”

Unsuspected prevalent tree occurrences in high elevation sky-islands of the western Alps

“…Populations in the peripheral mountain massifs are sporadic and sparse. P. cembra is a long-lived species (>500 years) with long generation intervals, which can maintain stable population size over long periods of time without inbreeding depression and preserve high amount of genetic variation (Gugerli et al 2009;Toth et al 2019). The species produces heavy seeds that are exclusively dispersed by a mutualistic bird (Nucifraga caryocatactes L., spotted nutcracker) specialized in extracting seeds of P. cembra from its non-opening cones and in caching seeds in soil far from the treemother (Crocq 1990).…”