Tracking climate change in a dispersal-limited species: reduced spatial and genetic connectivity in a montane salamander

Tropical montane taxa are often locally adapted to very specific climatic conditions, contributing to their lower dispersal potential across complex landscapes. Climate and landscape features in montane regions affect population genetic structure in predictable ways, yet few empirical studies quantify the effects of both factors in shaping genetic structure of montane-adapted taxa. Here, we considered temporal and spatial variability in climate to explain contemporary genetic differentiation between populations of the montane salamander, Pseudoeurycea leprosa. Specifically, we used ecological niche modelling (ENM) and measured spatial connectivity and gene flow (using both mtDNA and microsatellite markers) across extant populations of P. leprosa in the Trans-Mexican Volcanic Belt (TVB). Our results indicate significant spatial and genetic isolation among populations, but we cannot distinguish between isolation by distance over time or current landscape barriers as mechanisms shaping population genetic divergences. Combining ecological niche modelling, spatial connectivity analyses, and historical and contemporary genetic signatures from different classes of genetic markers allows for inference of historical evolutionary processes and predictions of the impacts future climate change will have on the genetic diversity of montane taxa with low dispersal rates. Pseudoeurycea leprosa is one montane species among many endemic to this region and thus is a case study for the continued persistence of spatially and genetically isolated populations in the highly biodiverse TVB of central Mexico.     

Phylogeography of Liquidambar styraciflua (Altingiaceae) in Mesoamerica: survivors of a Neogene widespread temperate forest (or cloud forest) in North America?

We investigate the genetic variation between populations of the American sweetgum (Liquidambar styraciflua), a tree species with a disjunct distribution between northeastern Texas and Mexico, by analyzing sequences of two chloroplast DNA plastid regions in Mesoamerica. Our results revealed phylogeographical structure, with private haplotypes distributed in unique environmental space at either side of the Trans‐Mexican Volcanic Belt, and a split in the absence of gene flow dating back ca. 4.2–1.4 million years ago (MYA). Species distribution modeling results fit a model of refugia along the Gulf and Atlantic coasts but the present ranges of US and Mesoamerican populations persisted disjunct during glacial/interglacial cycles. Divergence between the US and Mesoamerican (ca. 8.4–2.8 MYA) populations of L. styraciflua and asymmetrical gene flow patterns support the hypothesis of a long‐distance dispersal during the Pliocene, with fragmentation since the most recent glacial advance (120,000 years BP) according to coalescent simulations and high effective migration rates from Mesoamerica to the USA and close to zero in the opposite direction. Our findings implicate the Trans‐Mexican Volcanic Belt as a porous barrier driving genetic divergence of L. styraciflua, corresponding with environmental niche differences, during the Pliocene to Quaternary volcanic arc episode 3.6 MYA, and a Mesoamerican origin of populations in the USA.     

Phylogeography of the bark beetle Dendroctonus mexicanus Hopkins (Coleoptera: Curculionidae: Scolytinae)

Dendroctonus mexicanus is polyphagous within the Pinus genus and has a wide geographical distribution in Mexico and Guatemala. We examined the pattern of genetic variation across the range of this species to explore its demographic history and its phylogeographic pattern. Analysis of the mtDNA sequences of 173 individuals from 25 Mexican populations allowed to us identify 53 geographically structured haplotypes. High haplotype and low nucleotide diversities and Tajima’s D indicate that D. mexicanus experienced rapid population expansion during its dispersal across mountain systems within its current range. The nested clade phylogeographic analysis indicates that the phylogeographic pattern of D. mexicanus is explained by continuous dispersion among lineages from the Sierra Madre Occidental, the Sierra Madre Oriental and the Trans-Mexican Volcanic Belt. However, we also observed isolation events among haplotypes from the Cofre de Perote/Trans-Mexican Volcanic Belt/Sierra Madre Oriental and the Trans-Mexican Volcanic Belt/Sierra Madre del Sur, which is consistent with the present conformation of mountain systems in Mexico and the emergence of geographical barriers during the Pleistocene.     

The extraordinary journey of Peperomia subgenus Tildenia (Piperaceae): insights into diversification and colonization patterns from its cradle in Peru to the Trans‐Mexican Volcanic Belt

Aim Peperomia subgenus Tildenia consists of c. 60 species growing in seasonal habitats of Neotropical mountain areas from Mexico to Argentina. The subgenus can be split geographically, with almost equal diversity in the Northern Hemisphere (centred in Mexico and Guatemala) and in the Southern Hemisphere (centred in Peru and Bolivia). Only a few species are known from a limited number of localities between these two hotspots. As such, Tildenia is an ideal candidate with which to test time, direction and mode of migration of high mountain taxa against the background of the ‘Great American Biotic Interchange’. Location The Andes with focus on the Central Andes, and the Mexican mountain chains, especially the Trans‐Mexican Volcanic Belt. Methods To elucidate the spatio‐temporal origin, subsequent colonization and radiation of Tildenia, we combine Bayesian phylogenetics based on the chloroplast trnK–matK–psbA region, georeferenced distribution data, and fossil calibrated molecular dating approaches using both penalized likelihood and relaxed phylogenetics. Reconstruction of the ancestral distribution area was performed using dispersal–vicariance analysis and dispersal–extinction–cladogenesis. Results Peperomia subgenus Tildenia is subdivided into six Andean clades and one Mexican and Central American clade originating from a north/central Peruvian ancestor. Molecular dating approaches converge on a stem age of c. 38 Ma for Tildenia and a mostly Miocene diversification and colonization. Main conclusions We detect a strong correlation between diversification of Tildenia and orogenetic events in the respective distribution centres. In the Andes, distribution was influenced by the Altiplano–Eastern Cordillera System as well as the Amotape‐Huancabamba Zone, where the latter serves as both migration barrier and migration bridge for different clades. In contrast to most studies of high‐elevation taxa, we provide support for a south–north colonization towards Central America and Mexico, and provide additional, independent evidence for the latest view on the timing of the Great American Biotic Interchange. In Mexico, the Trans‐Mexican Volcanic Belt has played a major role in more recent radiations together with climatic oscillation and the formation of refugia.     

High genetic diversity and stable Pleistocene distributional ranges in the widespread Mexican red oak Quercus castanea Née (1801) (Fagaceae)

The Mexican highlands are areas of high biological complexity where taxa of Nearctic and Neotropical origin and different population histories are found. To gain a more detailed view of the evolution of the biota in these regions, it is necessary to evaluate the effects of historical tectonic and climate events on species. Here, we analyzed the phylogeographic structure, historical demographic processes, and the contemporary period, Last Glacial Maximum (LGM) and Last Interglacial (LIG) ecological niche models of Quercus castanea, to infer the historical population dynamics of this oak distributed in the Mexican highlands. A total of 36 populations of Q. castanea were genotyped with seven chloroplast microsatellite loci in four recognized biogeographic provinces of Mexico: the Sierra Madre Occidental (western mountain range), the Central Plateau, the Trans‐Mexican Volcanic Belt (TMVB, mountain range crossing central Mexico from west to east) and the Sierra Madre del Sur (SMS, southern mountain range). We obtained standard statistics of genetic diversity and structure and tested for signals of historical demographic expansions. A total of 90 haplotypes were identified, and 29 of these haplotypes were restricted to single populations. The within‐population genetic diversity was high (mean h_S = 0.72), and among‐population genetic differentiation showed a strong phylogeographic structure (N_ST = 0.630 > G_ST = 0.266; p < .001). Signals of demographic expansion were identified in the TMVB and the SMS. The ecological niche models suggested a considerable percentage of stable distribution area for the species during the LGM and connectivity between the TMVB and the SMS. High genetic diversity, strong phylogeographic structure, and ecological niche models suggest in situ permanence of Q. castanea populations with large effective population sizes. The complex geological and climatic histories of the TMVB help to explain the origin and maintenance of a large proportion of the genetic diversity in this oak species.     

Phylogeography of the Trans‐Volcanic bunchgrass lizard (Sceloporus bicanthalis) across the highlands of south‐eastern Mexico

We quantify the population divergence processes that shaped population genetic structure in the Trans‐Volcanic bunchgrass lizard (Sceloporus bicanthalis) across the highlands of south‐eastern Mexico. Multilocus genetic data from nine nuclear loci and mitochondrial (mt)DNA were used to estimate the population divergence history for 47 samples of S. bicanthalis. Bayesian clustering methods partitioned S. bicanthalis into three populations: (1) a southern population in Oaxaca and southern Puebla; (2) a population in western Puebla; and (3) a northern population with a broad distribution across Hidalgo, Puebla, and Veracruz. The multilocus nuclear data and mtDNA both supported a Late Pleistocene increase in effective population size, and the nuclear data revealed low levels of unidirectional gene flow from the widespread northern population into the southern and western populations. Populations of S. bicanthalis experienced different demographic histories during the Pleistocene, and phylogeographical patterns were similar to those observed in many co‐distributed highland taxa. Although we recommend continuing to recognize S. bicanthalis as a single species, future research on the evolution of viviparity could gain novel insights by contrasting physiological and genomic patterns among the different populations located across the highlands of south‐eastern Mexico. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 852–865.     

Comparative phylogeography of livebearing fishes in the genera Poeciliopsis and Poecilia (Poeciliidae: Cyprinodontiformes) in central Mexico

Aim To test the hypothesis that the vicariant event responsible for north–south divergences in two clades of the fish genus Poeciliopsis Regan was also responsible for north–south divergences in the fish Poecilia butleri Jordan. Location Central Mexico. Methods Parsimony, distance, maximum likelihood and Bayesian phylogenetic analyses of a mitochondrial gene. Molecular clock test and Bayesian analyses of divergence time. Results We report concordant phylogeographical patterns between two clades in the genus Poeciliopsis (i.e. the other formed by P. latidens Garman and P. fasciata Meek, and the other formed by P. presidionis Jordan and P. turneri Miller) and the clade of Poecilia butleri, with northern and southern individuals within each clade grouping into separate lineages. There is also evidence for slower substitution rates in Poecilia compared with Poeciliopsis. After taking into account these substitution rate discrepancies with Bayesian relaxed molecular clock analyses, north–south divergences in Poecilia butleri were equivalent to those reported for Poeciliopsis latidens‐fasciata and P. presidionis‐turneri. Main conclusions The same Plio‐Pleistocene vicariant event associated with geological activity of the Trans‐Mexican Volcanic Belt (TMVB) appears to have caused divergence in three different freshwater fish lineages. This study is an example of how comparative phylogeography can strengthen inferences about vicariant events in regions of high biological diversity and complex geological history such as the TMVB.     

Migration timing and routes,and wintering areas of Flammulated Owls

Determining patterns in annual movements of animals is an important component of population ecology, particularly for migratory birds where migration timing and routes, and wintering habitats have key bearing on population dynamics. From 2009 to 2011, we used light‐level geolocators to document the migratory movements of Flammulated Owls (Psiloscops flammeolus). Four males departed from breeding areas in Colorado for fall migration between ≤5 and 21 October, arrived in wintering areas in Mexico between 11 October and 3 November, departed from wintering areas from ≤6 to 21 April, and returned to Colorado between 15 and 21 May. Core wintering areas for three males were located in the Trans‐Mexican Volcanic Belt Mountains in the states of Jalisco, Michoacán, and Puebla in central and east‐central Mexico, and the core area for the other male was in the Sierra Madre Oriental Mountains in Tamaulipas. The mean distance from breeding to wintering centroids was 2057 ± 128 km (SE). During fall migration, two males took a southeastern path to eastern Mexico, and two males took a path due south to central Mexico. In contrast, during spring migration, all four males traveled north from Mexico along the Sierra Madre Oriental Mountains to the Rio Grande Valley and north through New Mexico. The first stopovers in fall and last stopovers in spring were the longest in duration for all males and located 300–400 km from breeding areas. Final spring stopovers may have allowed male Flammulated Owls to fine tune the timing of their return to high‐elevation breeding areas where late snows are not uncommon. One male tracked in both years had similar migration routes, timing, and wintering areas each year. Core wintering and final stopover areas were located primarily in coniferous forests and woodlands, particularly pine‐oak forests, suggesting that these are important habitats for Flammulated Owls throughout their annual cycle.     

Impact of mountain chains, sea straits and peripheral populations on genetic and taxonomic structure of a freshwater turtle, Mauremys leprosa (Reptilia, Testudines, Geoemydidae)

Mauremys leprosa, distributed in Iberia and North‐west Africa, contains two major clades of mtDNA haplotypes. Clade A occurs in Portugal, Spain and Morocco north of the Atlas Mountains. Clade B occurs south of the Atlas Mountains in Morocco and north of the Atlas Mountains in eastern Algeria and Tunisia. However, we recorded a single individual containing a clade B haplotype in Morocco from north of the Atlas Mountains. This could indicate gene flow between both clades. The phylogenetically most distinct clade A haplotypes are confined to Morocco, suggesting both clades originated in North Africa. Extensive diversity within clade A in south‐western Iberia argues for a glacial refuge located there. Other regions of the Iberian Peninsula, displaying distinctly lower haplotype diversities, were recolonized from within south‐western Iberia. Most populations in Portugal, Spain and northern Morocco contain the most common clade A haplotype, indicating dispersal from the south‐western Iberian refuge, gene flow across the Strait of Gibraltar, and reinvasion of Morocco by terrapins originating in south‐western Iberia. This hypothesis is consistent with demographic analyses, suggesting rapid clade A population increase while clade B is represented by stationary, fragmented populations. We recommend the eight, morphologically weakly diagnosable, subspecies of M. leprosa be reduced to two, reflecting major mtDNA clades: Mauremys l. leprosa (Iberian Peninsula and northern Morocco) and M. l. saharica (southern Morocco, eastern Algeria and Tunisia). Peripheral populations could play an important role in evolution of M. leprosa because we found endemic haplotypes in populations along the northern and southern range borders. Previous investigations in another western Palearctic freshwater turtle (Emys orbicularis) discovered similar differentiation of peripheral populations, and phylogeographies of Emys orbicularis and Mauremys rivulata underline the barrier status of mountain chains, in contrast to sea straits, suggesting common patterns for western Palearctic freshwater turtles.     

Relative roles of Neogene vicariance and Quaternary climate change on the historical diversification of bunchgrass lizards (Sceloporus scalaris group) in Mexico

Neogene vicariance during the Miocene and Pliocene and Quaternary climate change have synergistically driven diversification in Mexican highland taxa. We investigated the impacts of these processes on genetic diversification in the widely distributed bunchgrass lizards in the Sceloporus scalaris group. We searched for correlations between timing in diversification and timing of (1) a period of marked volcanism across the Trans-Mexican Volcanic Belt in central Mexico 3-7.5 million years ago (Ma) and (2) a transition to larger glacial-interglacial cycles during the mid-Pleistocene. From our phylogenetic analyses of mitochondrial DNA we identified two major clades that contained 13 strongly supported lineages. One clade contained lineages from the two northern sierras of Mexico, and the other clade included lineages associated with the Trans-Mexican Volcanic Belt and Central Mexican Plateau. Results provided support for Neogene divergences within the S. scalaris group in response to uplift of the Trans-Mexican Volcanic Belt, a pattern observed in several co-distributed taxa, and suggested that Quaternary climate change likely had little effect on diversification between lineages. Uplift of the Trans-Mexican Volcanic Belt during specific time periods appears to have strongly impacted diversification in Mexican highland taxa.     

Tracing the origins of widespread highland species: a case of Neogene diversification across the Mexican sierras in an endemic lizard

The evolutionary history of the Mexican sierras has been shaped by various geological and climatic events over the past several million years. The relative impacts of these historical events on diversification in highland taxa, however, remain largely uncertain owing to a paucity of studies on broadly‐distributed montane species. We investigated the origins of genetic diversification in widely‐distributed endemic alligator lizards in the genus Barisia to help develop a better understanding of the complex processes structuring biological diversity in the Mexican highlands. We estimated lineage divergence dates and the diversification rate from mitochondrial DNA sequences, and combined divergence dates with reconstructions of ancestral geographical ranges to track lineage diversification across geography through time. Based on our results, we inferred ten geographically structured, well supported mitochondrial lineages within Barisia. Diversification of a widely‐distributed ancestor appears tied to the formation of the Trans‐Mexican Volcanic Belt across central Mexico during the Miocene and Pliocene. The formation of filter barriers such as major river drainages may have later subdivided lineages. The results of the present study provide additional support for the increasing number of studies that suggest Neogene events heavily impacted genetic diversification in widespread montane taxa. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 382–394.     

Population genetic structure of a specialist leafhopper on Zea: likely anthropogenic and ecological determinants of gene flow

Corn leafhopper, Dalbulus maidis DeLong & Wolcott (Hemiptera: Cicadellidae), is a specialist herbivore on the genus Zea (Poaceae). The genera Dalbulus and Zea evolved in central Mexico. We sought to determine whether population genetic structuring is prevalent in corn leafhoppers inhabiting three of its host plants: (1) the highland species perennial teosinte (Zea diploperennis Iltis, Doebley & Guzman), (2) the mid‐ to lowland‐species Balsas teosinte (Zea mays ssp. parviglumis Iltis & Doebley), and (3) the ubiquitous domesticated maize (Zea mays ssp. mays L.). We used amplified fragment length polymorphisms to detect population structuring and genetic differentiation among corn leafhoppers on the three host plants in western‐central and ‐northern Mexico. Our results showed that corn leafhopper in Mexico is composed of at least two genetically discrete populations: an ‘Itinerant’ population associated with the annual hosts maize and Balsas teosinte, which appears to be widely distributed in Mexico, and a ‘Las Joyas’ population restricted to perennial teosinte and confined to a small mountain range (Sierra de Manantlán) in western‐central Mexico. Our results further suggested that population structuring is not due to isolation by distance or landscape features: Las Joyas and Itinerant corn leafhopper populations are genetically distinct despite their geographic proximity (ca. 4 km), whereas Itinerant corn leafhoppers separated by hundreds of kilometers (>800 km), mountain ranges, and a maritime corridor (Sea of Cortez) are not genetically distinct. Based on our results and on published ethnohistorical and archaeological data, we propose pre‐Columbian and modern scenarios, including likely ecological and anthropogenic influences, in which the observed genetic population structuring of corn leafhopper could have originated and could be maintained. Also, we hypothesize that after evolving on the lowland Balsas teosinte, corn leafhopper expanded its host range to include maize and then the highland perennial teosinte, following the domestication and spread of maize within the last 9 000 years.     

Does the Trans‐mexican Volcanic Belt represent a natural biogeographical unit? An analysis of the distributional patterns of Coleoptera

Aim We analysed the geographical distribution of beetle species of the families Buprestidae, Cerambycidae, Dryophthoridae, Melolonthidae, Passalidae and Staphylinidae from the Trans‐mexican Volcanic Belt (TVB) through a track analysis and a parsimony analysis of endemicity (PAE), in order to test its naturalness and determine its affinities. Location The area analysed corresponds to the TVB, which is a biogeographical province of the Mexican Transition Zone. Methods The panbiogeographical analysis was based on the comparison of the individual tracks of 299 species of Buprestidae, Cerambycidae, Dryophthoridae, Melolonthidae, Passalidae and Staphylinidae (Coleoptera). The TVB was divided into 1^o × 1^o grid cells and we also included in the analysis the remaining Mexican biogeographical provinces. Parsimony analysis of endemicity with progressive character elimination (PAE‐PCE) was applied to classify areas by their shared taxa according to the most parsimonious cladograms. The nested sets of areas were represented as generalized tracks. Results Three generalized tracks were obtained: (1) grid cells 9C, 9D, 10D, 10E, Sierra Madre Oriental, Chiapas, Mexican Gulf and the Sierra Madre del Sur; (2) grid cells 3B, 3C, 4B, 4C, 5C, 6C, 7C, Sierra Madre Occidental, Sierra Madre del Sur, Balsas Basin and the Mexican Pacific Coast, and (3) grid cells 8D, 9C, 9D, 10D, 10E, Yucatán Peninsula, Chiapas, Sierra Madre Oriental and the Mexican Gulf. Main conclusions We conclude that the TVB does not represent a natural biogeographical unit because it shows different relationships with other biogeographical provinces, being clearly transitional between the Nearctic and Neotropical provinces. Some parts of the TVB are related to Neotropical provinces (Chiapas, Mexican Gulf and Mexican Pacific Coast) and others to the remaining provinces of the Mexican Transition Zone (Sierra Madre Oriental, Sierra Madre del Sur, Sierra Madre Occidental and Balsas Basin).     

Genetic isolation among mountains but not between stream types in a tropical high‐altitude mayfly

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High levels of diversity and population structure in the potato late blight pathogen at the Mexico centre of origin

Globally destructive crop pathogens often emerge by migrating out of their native ranges. These pathogens are often diverse at their centre of origin and may exhibit adaptive variation in the invaded range via multiple introductions from different source populations. However, source populations are generally unidentified or poorly studied compared to invasive populations. Phytophthora infestans, the causal agent of late blight, is one of the most costly pathogens of potato and tomato worldwide. Mexico is the centre of origin and diversity of P. infestans and migration events out of Mexico have enormously impacted disease dynamics in North America and Europe. The debate over the origin of the pathogen, and population studies of P. infestans in Mexico, has focused on the Toluca Valley, whereas neighbouring regions have been little studied. We examined the population structure of P. infestans across central Mexico, including samples from Michoacán, Tlaxcala and Toluca. We found high levels of diversity consistent with sexual reproduction in Michoacán and Tlaxcala and population subdivision that was strongly associated with geographic region. We determined that population structure in central Mexico has contributed to diversity in introduced populations based on relatedness of U.S. clonal lineages to Mexican isolates from different regions. Our results suggest that P. infestans exists as a metapopulation in central Mexico, and this population structure could be contributing to the repeated re‐emergence of P. infestans in the United States and elsewhere.     

Divergence and evolution of reproductive barriers among three allopatric populations of Rhagoletis cingulata across eastern North America and Mexico

Geography is often a key factor facilitating population divergence and speciation. In this regard, the geographic distributions of flies in the genus Rhagoletis (Diptera: Tephritidae) in temperate North America have been affected by cycles of Pleistocene glaciation and interglacial periods. Fluctuations in climatic conditions may have had their most dramatic effects on geographically isolating Rhagoletis flies in the central highland region of Mexico. During past periods of allopatry, a degree of post‐zygotic reproductive isolation appears to have evolved between hawthorn‐infesting populations of Rhagoletis pomonella (Walsh) in the central Eje Volcanico Trans Mexicano (EVTM) and those from the Sierra Madre Oriental Mountains (SMO) of Mexico, as well as hawthorn flies from the eastern USA. Here, we investigate the generality of this finding in the genus Rhagoletis by testing for reproductive isolation among populations of Rhagoletis cingulata (Loew) (Diptera: Tephritidae) collected from infested domesticated sweet cherry (Prunus avium L.) in the USA and black cherry [Prunus serotina Ehrh. (both Rosaceae)] from the SMO and EVTM. We report evidence for marked post‐mating reproductive isolation among certain R. cingulata populations. The high levels of reproductive isolation were observed between R. cingulata flies from populations in the USA and SMO differed from the pattern seen for R. pomonella, primarily involving the EVTM. In addition, egg hatch was significantly reduced for crosses between SMO males and EVTM females, but not greatly in the opposite direction. We discuss potential causes for the different patterns of post‐mating reproductive isolation among Rhagoletis flies.     

Intraspecific Phylogeography of Red Squirrels (Tamiasciurus hudsonicus) in the Central Rocky Mountain Region of North America

We used variation in a portion of the mitochondrial DNA control region to examine phylogeography of Tamiasciurus hudsonicus, a boreal-adapted small mammal in the central Rocky Mountain region. AMOVA revealed that 65.66% of genetic diversity was attributable to variation within populations, 16.93% to variation among populations on different mountain ranges, and 17.41% to variation among populations within mountain ranges. Nested clade analysis revealed two major clades that likely diverged in allopatry during the Pleistocene: a southern clade from southern Colorado and a northern clade comprising northern Colorado, Wyoming, eastern Utah, and eastern Idaho. Historically restricted gene flow as a result of geographic barriers was indicated between populations on opposite sides of the Green River and Wyoming Basin and among populations in eastern Wyoming. In some instances genetic structure indicated isolation by distance.     

Genetic variation in Vanilla planifolia (Orchidaceae)

Vanilla planifolia, a highly prized tropical crop, produces commercial, vanilla. We investigated RAPD genetic diversity and geographical structure within V. planifolia. Multivariate analyses revealed three separate geographical groups of V. planifolia: a) a Costa Rican group; b) a Mexican group consisting only of cultivated plants from north of the Trans-Mexican Volcanic Belt; and c) a Mexican group from Oaxaca, Chiapas, and Quintana Roo, which are wild and wild-sourced cultivated plants. It appears likely that human action has resulted in movement of northern Mexican plants into the region south of the Volcanic Belt. When supposed translocants are included, a significantly higher genetic diversity is observed south of the Volcanic Belt compared to northern Mexico. Furthermore, cultivar names used in V. planifolia do not appear to reflect genetically defined groups.     

Long‐term in situ persistence of biodiversity in tropical sky islands revealed by landscape genomics

Tropical mountains are areas of high species richness and endemism. Two historical phenomena may have contributed to this: (i) fragmentation and isolation of habitats may have promoted the genetic differentiation of populations and increased the possibility of allopatric divergence and speciation and (ii) the mountain areas may have allowed long‐term population persistence during global climate fluctuations. These two phenomena have been studied using either species occurrence data or estimating species divergence times. However, only few studies have used intraspecific genetic data to analyse the mechanisms by which endemism may emerge at the microevolutionary scale. Here, we use landscape analysis of genomic SNP data sampled from two high‐elevation plant species from an archipelago of tropical sky islands (the Trans‐Mexican Volcanic Belt) to test for population genetic differentiation, synchronous demographic changes and habitat persistence. We show that genetic differentiation can be explained by the degree of glacial habitat connectivity among mountains and that mountains have facilitated the persistence of populations throughout glacial/interglacial cycles. Our results support the ongoing role of tropical mountains as cradles for biodiversity by uncovering cryptic differentiation and limits to gene flow.     

Imprints of multiple glacial refugia in the Pyrenees revealed by phylogeography and palaeodistribution modelling of an endemic spider

Mediterranean mountain ranges harbour highly endemic biota in islandlike habitats. Their topographic diversity offered the opportunity for mountain species to persist in refugial areas during episodes of major climatic change. We investigate the role of Quaternary climatic oscillations in shaping the demographic history and distribution ranges in the spider Harpactocrates ravastellus, endemic to the Pyrenees. Gene trees and multispecies coalescent analyses on mitochondrial and nuclear DNA sequences unveiled two distinct lineages with a hybrid zone around the northwestern area of the Catalan Pyrenees. The lineages were further supported by morphological differences. Climatic niche‐based species distribution models (SDMs) identified two lowland refugia at the western and eastern extremes of the mountain range, which would suggest secondary contact following postglacial expansion of populations from both refugia. Neutrality test and approximate Bayesian computation (ABC) analyses indicated that several local populations underwent severe bottlenecks followed by population expansions, which in combination with the deep population differentiation provided evidence for population survival during glacial periods in microrefugia across the mountain range, in addition to the main Atlantic and Mediterranean (western and eastern) refugia. This study sheds light on the complexities of Quaternary climatic oscillations in building up genetic diversity and local endemicity in the southern Europe mountain ranges.