Gradients Of Genetic Diversity Research Articles

Global patterns of nuclear and mitochondrial genetic diversity in marine fishes.

Genetic diversity is a fundamental component of biodiversity. Examination of global patterns of genetic diversity can help highlight mechanisms underlying species diversity, though a recurring challenge has been that patterns may vary by molecular marker. Here, we compiled 6862 observations of genetic diversity from 492 species of marine fish and tested among hypotheses for diversity gradients: the founder effect hypothesis, the kinetic energy hypothesis, and the productivity-diversity hypothesis. We fit generalized linear mixed effect models (GLMMs) and explored the extent to which various macroecological drivers (latitude, longitude, temperature (SST), and chlorophyll-a concentration) explained variation in genetic diversity. We found that mitochondrial genetic diversity followed geographic gradients similar to those of species diversity, being highest near the Equator, particularly in the Coral Triangle, while nuclear genetic diversity did not follow clear geographic patterns. Despite these differences, all genetic diversity metrics were correlated with chlorophyll-a concentration, while mitochondrial diversity was also positively associated with SST. Our results provide support for the kinetic energy hypothesis, which predicts that elevated mutation rates at higher temperatures increase mitochondrial but not necessarily nuclear diversity, and the productivity-diversity hypothesis, which posits that resource-rich regions support larger populations with greater genetic diversity. Overall, these findings reveal how environmental variables can influence mutation rates and genetic drift in the ocean, caution against using mitochondrial macrogenetic patterns as proxies for whole-genome diversity, and aid in defining global gradients of genetic diversity.

Historical demography of Trichothraupis melanops (Aves: Thraupidae) and the Pleistocene Atlantic Forest biogeography

The climatic cycles of the Pleistocene affected the distribution of the vegetation of different biomes, determining the distribution and evolution of the associated fauna. Many studies of Atlantic Forest (AF) organisms suggest that the Pleistocene glacial and interglacial cycles have produced demographically stable populations in the forest’s central region and unstable populations in its southern regions (known as the Carnaval-Moritz model). We studied the phylogeographic structure of an AF passerine, the Black-goggled Tanager (Trichothraupis melanops, Thraupidae) and evaluated questions related to the history of the AF. We analyzed three independent genes, two nuclear and one mitochondrial, using population genetic methods based on summary statistics and traditional phylogeographic methods. Our results suggest that T. melanops shares phylogeographic features with other AF taxa. Even though an effective population size gradient was found between the central and southern populations, which is in agreement with the results of other phylogeographic studies and the forest refugia model (the Carnaval-Moritz model), there is no evidence of a gradient of genetic diversity. In addition, we have found that T. melanops populations show the demographic dynamics expected according to the Carnaval-Moritz model: the inland-southern population was found to be the one with the greatest signs of recent demographic expansion, compared to the central and coastal-southern populations. Although this species is ecologically generalist and not very sensitive to forest fragmentation and degradation, it has been impacted by the historical dynamism of the AF.

Neutral genetic diversity follows a latitudinal gradient in the endangered plant Arnica montana L.: a range-wide study

Arnica montana is a clonal, self-incompatible herb of economic and intrinsic ecological value which is declining in large parts of its range. With the employment of microsatellite markers, we characterized the population structure and distribution of genetic diversity of 40 populations of A. montana sampled throughout Europe. We detected a clear geographical pattern of isolation and strong population structure, indicating limited gene flow. We also observed a negative latitudinal gradient in genetic diversity. Such patterns can be explained by paleo-historical colonization routes following the last glacial maximum, with regions characterized by higher genetic diversity corresponding to former glacial refugia. We recommend the implementation of conservation measures such as assisted gene flow in the populations characterized by low genetic diversity under consideration of the observed population structure. For the populations where high levels of genetic diversity are still retained, we recommend the maintenance of suitable habitat conditions. Our study emphasises the importance of conducting large-scale population genetic studies that consider postglacial recolonization history when planning active conservation measures such as assisted gene flow.

Genetic footprints of a rapid and large-scale range expansion: the case of cyclic common vole in Spain.

In the Anthropocene, many species are rapidly shifting their ranges in response to human-driven habitat modifications. Studying patterns and genetic signatures of range shifts helps to understand how species cope with environmental disturbances and predict future shifts in the face of global environmental change. We investigated the genetic signature of a contemporary wide-range expansion observed in the Iberian common vole Microtus arvalis asturianus shortly after a colonization event. We used mtDNA and microsatellite data to investigate patterns of genetic diversity, structure, demography, and gene flow across 57 localities covering the historical range of the species and the newly colonized area. The results showed a genetic footprint more compatible with a true range expansion (i.e. the colonization of previously unoccupied areas), than with a model of "colonization from within" (i.e. local expansions from small, unnoticed populations). Genetic diversity measures indicated that the source population was likely located at the NE of the historical range, with a declining gradient of genetic diversity towards the more recently invaded areas. At the expansion front, we observed the greatest gene flow and smallest pairwise differences between nearby localities. Both natural landscape features (rivers) and recent anthropogenic barriers (roads, railways) explained a large proportion of genetic variance among populations and had a significant impact on the colonization pathways used by voles.

Whole genome demographic models indicate divergent effective population size histories shape contemporary genetic diversity gradients in a montane bumble bee.

Understanding historical range shifts and population size variation provides an important context for interpreting contemporary genetic diversity. Methods to predict changes in species distributions and model changes in effective population size (N e) using whole genomes make it feasible to examine how temporal dynamics influence diversity across populations. We investigate N e variation and climate-associated range shifts to examine the origins of a previously observed latitudinal heterozygosity gradient in the bumble bee Bombus vancouverensis Cresson (Hymenoptera: Apidae: Bombus Latreille) in western North America. We analyze whole genomes from a latitude-elevation cline using sequentially Markovian coalescent models of N e through time to test whether relatively low diversity in southern high-elevation populations is a result of long-term differences in N e. We use Maxent models of the species range over the last 130,000 years to evaluate range shifts and stability. N e fluctuates with climate across populations, but more genetically diverse northern populations have maintained greater N e over the late Pleistocene and experienced larger expansions with climatically favorable time periods. Northern populations also experienced larger bottlenecks during the last glacial period, which matched the loss of range area near these sites; however, bottlenecks were not sufficient to erode diversity maintained during periods of large N e. A genome sampled from an island population indicated a severe postglacial bottleneck, indicating that large recent postglacial declines are detectable if they have occurred. Genetic diversity was not related to niche stability or glacial-period bottleneck size. Instead, spatial expansions and increased connectivity during favorable climates likely maintain diversity in the north while restriction to high elevations maintains relatively low diversity despite greater stability in southern regions. Results suggest genetic diversity gradients reflect long-term differences in N e dynamics and also emphasize the unique effects of isolation on insular habitats for bumble bees. Patterns are discussed in the context of conservation under climate change.

Detecting steps in spatial genetic data: Which diversity measures are best?

Accurately detecting sudden changes, or steps, in genetic diversity across landscapes is important for locating barriers to gene flow, identifying selectively important loci, and defining management units. However, there are many metrics that researchers could use to detect steps and little information on which might be the most robust. Our study aimed to determine the best measure/s for genetic step detection along linear gradients using biallelic single nucleotide polymorphism (SNP) data. We tested the ability to differentiate between linear and step-like gradients in genetic diversity, using a range of diversity measures derived from the q-profile, including allelic richness, Shannon Information, GST, and Jost-D, as well as Bray-Curtis dissimilarity. To determine the properties of each measure, we repeated simulations of different intensities of step and allele proportion ranges, with varying genome sample size, number of loci, and number of localities. We found that alpha diversity (within-locality) based measures were ineffective at detecting steps. Further, allelic richness-based beta (between-locality) measures (e.g., Jaccard and Sørensen dissimilarity) were not reliable for detecting steps, but instead detected departures from fixation. The beta diversity measures best able to detect steps were: Shannon Information based measures, GST based measures, a Jost-D related measure, and Bray-Curtis dissimilarity. No one measure was best overall, with a trade-off between those measures with high step detection sensitivity (GST and Bray-Curtis) and those that minimised false positives (a variant of Shannon Information). Therefore, when detecting steps, we recommend understanding the differences between measures and using a combination of approaches.

Genetic and species-level biodiversity patterns are linked by demography and ecological opportunity.

The processes that give rise to species richness gradients are not well understood, but may be linked to resource-based limits on the number of species a region can support. Ecological limits placed on regional species richness should also affect population demography, suggesting that these processes could also generate genetic diversity gradients. If true, we might better understand how broad-scale biodiversity patterns are formed by identifying the common causes of genetic diversity and species richness. We develop a hypothetical framework based on the consequences of regional variation in ecological limits set by resource availability and heterogeneity to simultaneously explain spatial patterns of species richness and neutral genetic diversity. Repurposing raw genotypic data spanning 38 mammal species sampled across 801 sites in North America, we show that estimates of genome-wide genetic diversity and species richness share spatial structure. Notably, species richness hotspots tend to harbor lower levels of within-species genetic variation. A structural equation model encompassing eco-evolutionary processes related to resource availability, habitat heterogeneity, and contemporary human disturbance supports the spatial patterns we detect. These results suggest broad-scale patterns of species richness and genetic diversity could both partly be caused by intraspecific demographic and evolutionary processes acting simultaneously across species.

Gradients of genetic diversity and differentiation across the distribution range of a Mediterranean coral: Patterns, processes and conservation implications

AbstractAimHow historical and contemporary eco‐evolutionary processes shape the patterns of genetic diversity and differentiation across species’ distribution range remains an open question with strong conservation implications. Focusing on the orange stony coral, Astroides calycularis, we (a) characterized the pattern of neutral genetic diversity across the distribution range; (b) gave insights into the underlying processes; and (c) discussed conservation implications with emphasis on a national park located on a hotspot of genetic diversity.LocationSouth Mediterranean Sea and Zembra National Park.MethodsWe combined new data from 12 microsatellites in 13 populations located in the Centre and in the Western Periphery of the distribution range with a published dataset including 16 populations from the Western and Eastern Peripheries. We analysed the relationship among parameters of genetic diversity (He, Ar(g)) and structure (population‐specific FST) and two measures of geographic peripherality. We compared two estimators of pairwise genetic structure (GST, DEST) across the distribution range. The evolutionary and demographic history of the populations following the Last Glacial Maximum was reconstructed using approximate Bayesian computations and maximum‐likelihood analyses. We inferred the contemporary connectivity among populations from Zembra National Park and with the neighbouring area of Cap Bon.ResultsWe demonstrate a decrease in genetic diversity and an increase in genetic differentiation from the Centre to the Eastern and Western Peripheries of the distribution range. Populations from Zembra show the highest genetic diversity reported in the species. We identified a spillover effect towards Cap Bon.Main conclusionsThe patterns of genetic diversity and differentiation are most likely explained by “the postglacial range expansion hypothesis” rather than the “central–peripheral hypothesis.” Enforcement of conservation measures should be considered to protect this genetic diversity pattern, in particular when considering the low effective population size inferred at many sites.

Elevated temperature increases genome-wide selection on de novo mutations.

Adaptation in new environments depends on the amount of genetic variation available for evolution, and the efficacy by which natural selection discriminates among this variation. However, whether some ecological factors reveal more genetic variation, or impose stronger selection pressures than others, is typically not known. Here, we apply the enzyme kinetic theory to show that rising global temperatures are predicted to intensify natural selection throughout the genome by increasing the effects of DNA sequence variation on protein stability. We test this prediction by (i) estimating temperature-dependent fitness effects of induced mutations in seed beetles adapted to ancestral or elevated temperature, and (ii) calculate 100 paired selection estimates on mutations in benign versus stressful environments from unicellular and multicellular organisms. Environmental stress per se did not increase mean selection on de novo mutation, suggesting that the cost of adaptation does not generally increase in new ecological settings to which the organism is maladapted. However, elevated temperature increased the mean strength of selection on genome-wide polymorphism, signified by increases in both mutation load and mutational variance in fitness. These results have important implications for genetic diversity gradients and the rate and repeatability of evolution under climate change.

Latitudinal gradients in genetic diversity and natural selection at a highly adaptive gene in terrestrial mammals

Identifying where high genetic diversity is located across our planet and what factors affect the geographical patterns of genetic variation not only provides important insights into distributions of biodiversity but is also crucial for human health, animal and plant breeding and biodiversity conservation. Recent studies show that genetic diversity at nearly neutral genes decreases from the tropics to the poles in different taxa, mirroring the oldest recognized latitudinal gradient of species richness, yet functional genetic diversity has received little attention at such broad spatial or taxonomic scales. Here, we investigated latitudinal gradients in genetic diversity at a polymorphic exon 2 (MHC II DRB gene, 1515 sequences) of the major histocompatibility complex that confers resistance to parasites in 93 terrestrial mammal species at the global scale. We also estimated the effects of species traits, positive selection and anthropogenic biomes on genetic diversity. We found clear latitudinal gradients in genetic diversity and the presence of positive selection at exon 2. Absolute latitude, the presence of positive selection and body mass are important predictors of within‐species genetic diversity. A higher occurrence of positive selection, faster evolutionary speed or slower drift at low latitudes may shape the latitudinal gradient in the within‐species genetic diversity of the gene. Our results contribute to a greater understanding of how species traits, selection and drift geographically shape functional genetic diversity, broadening the generality of latitudinal biodiversity gradient. The results highlight the importance of conservation at low latitudes.

High phylogeographic and genetic diversity of Tidestromia lanuginosa supports full-glacial refugia for arid-adapted plants in southern and central Coahuila, Mexico.

Recent phylogeographic work suggests the existence of latitudinal gradients in genetic diversity in northern Mexican plants, but very few studies have examined plants of the Chihuahuan Desert. Tidestromia lanuginosa is a morphologically variable annual species whose distribution includes the Chihuahuan Desert Region. Here we undertook phylogeographic analyses of chloroplast loci in this species to test whether genetic diversity and differentiation of Mexican populations of T. lanuginosa change along a latitudinal gradient and whether diversity is higher in Coahuila, consistent with ideas of lower plant community turnover during the Pleistocene. Haplotype network, maximum likelihood tree, and Bayesian phylogenetic haplotype were reconstructed, and genetic diversity was assessed among 26 populations. Barrier analysis was used to explore barriers to gene flow. Four major population groups were identified, corresponding with physiographic provinces in Mexico. Each population group displayed high levels of genetic structure, haplotype, and nucleotide diversity. Diversity was highest in southern populations across the species as a whole and among the Chihuahuan Desert populations. Tidestromia lanuginosa provides an important example of high phylogeographic and genetic diversity in plants of northern Mexico. Barriers to gene flow among the major population groups have most likely been due to a combination of orographic, climatic, and edaphic variables. The high genetic diversity of T. lanuginosa in southern and central Coahuila is consistent with the hypothesis of full-glacial refugia for arid-adapted plants in this area, and highlights the importance of this region as a center of diversity for the Chihuahuan Desert flora.

Genetic population structure of the toxigenic dinoflagellate <i>Alexandrium catenella</i> in the Patagonian Fjords System, southern Chile

Alexandrium catenella is the main species that form harmful algae blooms (HABs) in southern Chile. Since its first record in 1972 in the Magallanes region this species apparently has increased its range distribution from south to north. In this study, we investigate the influence of the range expansions distribution on the A. catenella populations genetic diversity and structure. This was achieved by isolating 33 clones from different localities along the Magallanes and Aysén region which were genetically characterized with Amplified Fragment Length Polymorphism (AFLPs) molecular markers. Results showed a latitudinal genetic diversity gradient from the south to north populations. Inter-populations genetic divergences were low but significant between both geographically close and distant populations. Results indicated that the genetic diversity differentiation could be generated by a founder effect, which is expected in populations that have expanded their distribution range. On the other hand, low levels of genetic divergences between distant populations seems point out that high gene flow occurs along coast of the Pacific Ocean, but also, seems hints the connectivity route between the Magallanes and Aysén populations i.e., the vegetative cells dispersion among populations, would occur through coastal Pacific coast and Boca del Guafo. Finally, the high values of multilocus linkage disequilibrium found between closer population of Aysén indicates that divergence could be influenced along with the reproductive dynamic of the vegetative cells.

Tracking diversity and evolutionary pathways of Lebanese oak taxa through plastome analyses

ABSTRACT The aim of this study is to better understand the phylogeography and evolution of the Lebanese oaks and to assess the convergence between their morpho-ecological and molecular characteristics. We investigated DNA sequence variation in four plastid markers (TrnH-psbA, ycf1, trnK-matK and PetD) of the seven species (three sections) occurring in Lebanon: Q. calliprinos, Q. infectoria, Q. kotschyana, Q. cedrorum, Q. cerris, Q. look, and Q. ithaburensis, in addition to Q. libani and Q. cerris from Syria, and possible hybrids. Among the four markers, the TrnH-psbA and trnK-matK loci resulted in the best-resolved genealogies. Quercus calliprinos haplotypes clearly belong to the west Asian-eastern Mediterranean ‘WAHEA’ lineage. Sect. Cerris haplotypes are derived variants of the central Mediterranean ‘Cerris-Ilex’ lineage. Sect. Quercus haplotypes were less differentiated and in close connection with the Caucasian primary refugium of white oaks. Despite the low species-level resolution, a gradient in genetic diversity linked to the ecological plasticity of the sampled species was observed. A close relationship of Q. look with Q. cerris is confirmed. Quercus kotschyana seems an ancient stock of closely related and disjunct oak of sect. Quercus. Finally, our results confirm the relevance of the Levant region as an important biogeographical crossroad between continents, and its key role in stimulating diversification and preservation of ancient genepools. Important areas in Lebanon that should be taken into consideration in future conservation strategies are highlighted, to ensure a wider genetic potential of local oak species to face the current climate change.

Geographical Gradients of Genetic Diversity and Differentiation among the Southernmost Marginal Populations of Abies sachalinensis Revealed by EST-SSR Polymorphism

Research Highlights: We detected the longitudinal gradients of genetic diversity parameters, such as the number of alleles, effective number of alleles, heterozygosity, and inbreeding coefficient, and found that these might be attributable to climatic conditions, such as temperature and snow depth. Background and Objectives: Genetic diversity among local populations of a plant species at its distributional margin has long been of interest in ecological genetics. Populations at the distribution center grow well in favorable conditions, but those at the range margins are exposed to unfavorable environments, and the environmental conditions at establishment sites might reflect the genetic diversity of local populations. This is known as the central-marginal hypothesis in which marginal populations show lower genetic variation and higher differentiation than in central populations. In addition, genetic variation in a local population is influenced by phylogenetic constraints and the population history of selection under environmental constraints. In this study, we investigated this hypothesis in relation to Abies sachalinensis, a major conifer species in Hokkaido. Materials and Methods: A total of 1189 trees from 25 natural populations were analyzed using 19 EST-SSR loci. Results: The eastern populations, namely, those in the species distribution center, showed greater genetic diversity than did the western peripheral populations. Another important finding is that the southwestern marginal populations were genetically differentiated from the other populations. Conclusions: These differences might be due to genetic drift in the small and isolated populations at the range margin. Therefore, our results indicated that the central-marginal hypothesis held true for the southernmost A. sachalinensis populations in Hokkaido.

Freshwater conservation assessments in (semi-)arid regions: Testing river intermittence and buffer strategies using freshwater mussels (Bivalvia, Unionida) in Morocco

The IUCN Red List assessments are essentially based on population trends and range, namely Area of Occupancy (AOO) and Extent of Occupancy (EOO). Range estimations are based on fixed grids, but this is likely inappropriate for species living in river networks. Furthermore, AOO and EOO are measured using the whole hydrographic network, therefore disregarding temporary sections, which is particularly problematic in arid and semi-arid regions. Here we mapped the permanent hydrographic network of Morocco using satellite imagery, complemented with field surveys to collect samples for molecular analyses of the five freshwater mussel species present and assess their distribution. The phylogeographic patterns are described for each species and used to identify priority areas and evolutionary significant units for conservation. Permanent hydrographic river sections represent only 18.3% of the whole hydrographic network. A north-to-south gradient of genetic diversity, species richness and distribution range was found, being coherent with water availability and river intermittence. Isolated evolutionary units were detected in southern basins that should also receive particular attention in conservation planning. We propose the mean river width multiplied by the extent of the river network as the best and the most adequate way to estimate both EOO and AOO. Given the worldwide degradation of freshwater systems and biodiversity, an accurate (re)assessment of species conservation status supported with maps of intermittent water bodies will be essential for prioritizing and guiding conservation actions and management plans, especially in arid and semi-arid regions.

A carnivores’ oasis? An isolated fisher (Pekania pennanti) population provides insight on persistence of a metapopulation

Landscape level species assessments are rarely available to inform conservation planning. Recent advances in multi-taxa survey techniques, however, have made them more obtainable by improving efficiency of collecting species occurrence data and genetic samples. Here, we used a multi-taxa survey technique to provide a landscape level portrait of fisher (Pekania pennanti) population status in a portion of the northern Rockies where the species’ history has been heavily influenced by humans. From 2010 to 2014 we deployed 497 winter forest carnivore bait stations across a 23,000 km2 study area centered on northern Idaho, United States. The stations collected remote camera images and hair samples for DNA analysis. We used 12 microsatellite loci to identify 58 individual fisher in the study area. We identified two fisher populations for which we estimated effective population size (Ne) and genetic neighborhood size (NS). We calculated local genetic diversity measures [observed (Ho) and expected (He) heterozygosity, allelic richness (Ar), fixation index (FST), and number of migrants per generation (Nm)] and mapped continuous gradients of genetic diversity [Ar and inbreeding coefficient (FIS)] across the study area. We identified a fisher population in the West Cabinet Mountains [Ne of 26 (15.3–55.5), NS of 50–60] which is effectively isolated from the small population we detected in the Saint Joe/Coeur d’Alene Mountains [Ne of 6.5 (2.7–15), NS of 10–25]. We determined fisher have been effectively extirpated from the Selkirk and Purcell mountains and the lack of genetic connectivity between the two small remaining populations casts doubt on long term viability. Our study suggests northern Rockies fisher populations are vulnerable to landscape barriers and successful recovery will depend on future management and augmentation. We recommend these factors be considered when determining how, and if, species recovery should proceed.

Genetic diversity and metapopulation structure of the brown swimming crab (Callinectes bellicosus) along the coast of Sonora, Mexico: Implications for fisheries management

Management of commercial fisheries resources is commonly done assuming that populations are spatially homogeneous throughout their geographic range. However, uneven gene flow can result in gradients of genetic diversity that can affect population dynamics and management reference points and may contribute to overfishing. We examined whether the brown swimming crab, Callinectes bellicosus, fished along 1200 km on the coast of Sonora (Mexico) is a homogeneous population. Based on previous empirical evidence of differences in phenology, we hypothesized that C. bellicosus has a metapopulation structure which needs to be included in management tools. We conducted a genetic study of C. bellicosus taken at seven sites along the coast of Sonora and obtained their microsatellite genotypes. Recent gene flow, as well as the role of each site as source or sink, were investigated. We found a latitudinal gradient in genetic diversity and identified sites along the coast acting as sources or sinks of migrants. Central sites act as sources, while northern sites are sinks; the main source of migrants was the southern-most site. A predominantly asymmetric metapopulation structure composed of local populations with moderate connectivity may be explained by larval dispersal in the northward oceanic current during the spawning period. Including migration rates between sites in a metapopulation dynamics model of C. bellicosus and considering that fishing and management decisions in source populations will impact neighboring populations located downstream can improve current management of this important commercial fishery.

Jailed in the mountains: Genetic diversity and structure of an endemic newt species across the Pyrenees.

The Pyrenees represent a natural laboratory for biogeographic, evolutionary and ecological research of mountain fauna as a result of the high variety of habitats and the profound effect of the glacial and interglacial periods. There is a paucity of studies providing a detailed insight into genetic processes and better knowledge on the patterns of genetic diversity and how they are maintained under high altitude conditions. This is of particular interest when considering the course of past climate conditions and glaciations in a species which is considered site tenacious, with long generation times. Here we analyzed the genetic patterns of diversity and structure of the endemic Pyrenean brook newt (Calotriton asper) along its distribution range, with special emphasis on the distinct habitat types (caves, streams, and lakes), and the altitudinal and geographical ranges, using a total set of 900 individuals from 44 different localities across the Pyrenean mountain range genotyped for 19 microsatellite loci. We found evidence for a negative longitudinal and positive altitudinal gradient of genetic diversity in C. asper populations. The fact that genetic diversity was markedly higher westwards is in accordance with other Pyrenean species. However, the impact of altitudinal gradient on the genetic diversity seems to differ from other species, and mostly from other amphibians. We found that lower altitudes can act as a barrier probably because the lowlands do not provide a suitable habitat for C. asper. Regarding the distinct habitat types, caves had significantly lower values of genetic diversity compared to streams or lakes. The mean FST value was relatively high (0.304) with maximum values as high as 0.771, suggesting a highly structured total population. Indeed, populations were grouped into five subclusters, the eastern populations (cluster 1) remained grouped into two subclusters and the central-western Pyrenees (cluster 2) into three subclusters. The increase of isolation with geographical distance is consistent with the population structure detected. In conclusion, C. asper seems to be adapted to high altitude mountain habitats, and its genetic diversity is higher in the western Pyrenees. In terms of conservation priority, we consider more relevant the populations that represent a reservoir of genetic diversity.

Guidelines for the restoration of the tropical timber tree Anacardium excelsum: first input from genetic data

Translocation of trees has been used as a common method to mediate genetic conservation and restoration of forests. However, very few programs include strategies developed to recover or maintain the genetic diversity of the translocated species. Anacardium excelsum is a tree native to the tropics of America that is extensively used in forestry. In Colombia, restoration of forests through the translocation of native species has regained importance, and A. excelsum has been recently included in the National Strategy for Plant Conservation. Thus, in order to define the level of genetic structure and the level of genetic diversity within certain regions where remnants of the seasonally dry tropical forests (SDTF) of Colombia have been retained, we genotyped 106 trees using nuclear inter-simple sequence repeats (ISSR) and sequenced two non-coding chloroplast loci for these specimens. Our ISSR dataset revealed the existence of a gradient in genetic diversity within A. excelsum with the most diverse remnants encountered in the south of the country, while the localities sampled in the Caribbean coast and in the Chicamocha canyon were less diverse. Chloroplast loci also pointed out the very low genetic diversity of A. excelsum from the Chicamocha canyon and we propose to prioritize this area within future conservation programs. Both chloroplast and nuclear markers supported the existence of genetic divergence between distinct regions of Colombia, uncovering genetic differences between inter-Andean, Caribbean, and Chicamocha canyon A. excelsum remnants. Hence, we advise to choose the provenance of seeds or plants carefully before translocation and to consider minimal mixing of material from different regions when initializing restoration programs for A. excelsum, in Colombia.

Contrasting Patterns of Population History and Seed-mediated Gene Flow in Two Endemic Costa Rican Oak Species.

Lower Central America is an important area to study recent population history and diversification of Neotropical species due to its complex and dynamic geology and climate. Phylogeographic studies in this region are few in comparison with other regions and even less for tree species. The aim of the present study was to characterize the phylogeographic structure in 2 partially co-distributed endemic oak species (Quercus costaricensis and Q. bumelioides) of the Costa Rican mountains using chloroplast short sequence repeats (cpSSRs), and to test for the effect of geological and palaeoclimatic processes on their population history. Genetic diversity and structure, haplotype networks, patterns of seed-mediated gene flow and historical demography were estimated for both species. Results suggested contrasting patterns. Quercus costaricensis exhibited high values of genetic diversity, a marked phylogeographic structure, a north-to-south genetic diversity gradient and evidence of a demographic expansion during the Quaternary. Quercus bumelioides did not show significant genetic structure and the haplotype network and historical demography estimates suggested a recent population expansion probably during the Pleistocene-Holocene transition. The phylogeographic structure of Q. costaricensis seems to be related to Pleistocene altitudinal migration due to its higher altitudinal distribution. Meanwhile, historical seed-mediated gene flow through the lower altitudinal distribution of Q. bumelioides may have promoted the homogenization of genetic variation. Population expansion and stable availability of suitable climatic areas in both species probably indicate that palaeoclimatic changes promoted downwards altitudinal migration and formation of continuous forests allowing oak species to expand their distribution into the Panamanian mountains during glacial stages.