Across the southern Andes on fin: glacial refugia,drainage reversals and a secondary contact zone revealed by the phylogeographical signal of Galaxias platei in Patagonia

We employed DNA sequence variation at two mitochondrial (control region, COI) regions from 212 individuals of Galaxias platei (Pisces, Galaxiidae) collected throughout Patagonia (25 lakes/rivers) to examine how Andean orogeny and the climatic cycles throughout the Quaternary affected the genetic diversity and phylogeography of this species. Phylogenetic analyses revealed four deep genealogical lineages which likely represent the initial division of G. platei into eastern and western lineages by Andean uplift, followed by further subdivision of each lineage into separate glacial refugia by repeated Pleistocene glacial cycles. West of the Andes, refugia were likely restricted to the northern region of Patagonia with small relicts in the south, whereas eastern refugia appear to have been much larger and widespread, consisting of separate northern and southern regions that collectively spanned most of Argentinean Patagonia. The retreat of glacial ice following the last glacial maximum allowed re‐colonization of central Chile from nonlocal refugia from the north and east, representing a region of secondary contact between all four glacial lineages. Northwestern glacial relicts likely followed pro‐glacial lakes into central Chilean Patagonia, whereas catastrophic changes in drainage direction (Atlantic → Pacific) for several eastern palaeolakes were the likely avenues for invasions from the east. These mechanisms, combined with evidence for recent, rapid and widespread population growth could explain the extensive contemporary distribution of G. platei throughout Patagonia.     

Climate control on ancestral population dynamics: insight from Patagonian fish phylogeography

Changes in lake and stream habitats during the growth and retreat of Pleistocene glaciers repeatedly altered the spatial distributions and population sizes of the aquatic fauna of the southern Andes. Here, we use variation in mtDNA control region sequences to infer the temporal dynamics of two species of southern Andean fish during the past few million years. At least five important climate events were associated with major demographic changes: (i) the widespread glaciations of the mid-Pliocene (c. 3.5 Ma); (ii) the largest Patagonian glaciation (1.1 Ma); (iii) the coldest Pleistocene glaciation as indicated by stacked marine delta(18)O (c. 0.7 Ma); (iv) the last southern Patagonian glaciation to reach the Atlantic coast (180 ka); and (v) the last glacial maximum (LGM, 23-25,000 years ago). The colder-water inhabitant, Galaxias platei, underwent a strong bottleneck during the LGM and its haplotype diversity coalesces c. 0.7 Ma. In contrast, the more warm-adapted and widely distributed Percichthys trucha showed continuous growth through the last two glacial cycles but went through an important bottleneck c. 180,000 years ago, at which time populations east of the Andes may have been eliminated. Haplotype diversity of the most divergent P. trucha populations, found west of the Andes, coalesces c. 3.2 Ma. The demographic timelines obtained for the two species thus illustrate the continent-wide response of aquatic life in Patagonia to climate change during the Pleistocene, but also show how differing ecological traits and distributions led to distinctive responses.     

The galaxiid fishes of South America

Four galaxiid species in two genera are recognized and redescribed from the South American region, viz., Galaxias maculatus (Jenyns), G. platei Steindachner, G. globiceps Eigenmann, and Brachygalaxias bullocki (Regan). All of these species occur in Chile, but G. maculatus and G. platei occur also east of the Andean divide in Argentina, in Tierra del Fuego, and the Falkland Islands. The two species east of the Andes are regarded as having crossed the mountains from west to east. The galaxiids, together with Aplochiton (family Aplochitonidae) and Geotria (family Petromyzonidae), are regarded as southern circumpolar elements in the South American freshwater fish fauna, distinct from the group of species of Amazonian derivation (trichomycterids, Nematogenys, Diplomystes, Cheirodon , etc.) and distinct also from oceanic derivatives, either recent (atherinids) or ancient (serranids).     

Surviving historical Patagonian landscapes and climate: molecular insights from <Emphasis Type="Italic">Galaxias maculatus</Emphasis>

Background  

The dynamic geological and climatic histories of temperate South America have played important roles in shaping the contemporary distributions and genetic diversity of endemic freshwater species. We use mitochondria and nuclear sequence variation to investigate the consequences of mountain barriers and Quaternary glacial cycles for patterns of genetic diversity in the diadromous fish Galaxias maculatus in Patagonia (~300 individuals from 36 locations).     

The distribution of South American galaxiid fishes: the role of biological traits and post-glacial history

Aim The aim of this work is to update the distribution data of Galaxiidae in South America, relating extant distribution to physiological and reproductive characteristics of the species, latitude, temperature, and post-glacial opportunities for colonization. Location Lakes and rivers of Patagonia. Methods We compared, and eventually reconsidered, general data about distribution based on the original literature about capture sites, incorporating several published and unpublished data to the analysis of the biological traits and distribution of Galaxiidae. Results The more consistent issue in the comprehension of galaxiid biogeography in South America is the ability to establish landlocked populations. Different founding events in landlocked populations of Galaxias maculatus suggest the possible existence of older and younger landlocked populations. This difference in the time since the establishment of lacustrine populations could have been expressed in their ability for colonization of post-glacial areas. Galaxias maculatus, Aplochiton and Brachygalaxias are more clearly excluded from the post-glacial area than G. platei. For all the species we could note a more abundant record of lake populations at the area of glacial refuges. It could be noted that the most successful species, Galaxias platei, is a specialized deep bottom dweller. Deep bottom dwelling helps to endure winter constraints and it appears to be an alternative to the colonization of the littoral and limnetic zones of post-glacial lakes, the prefered habitat of the other Patagonian fish species. Main conclusions At the end of this process of post-glacial colonization, in the beginning of twentieth century, man introduced several salmonid species in Patagonia. In addition, antropogenic actions had its more recent consequences in global warming. Nowadays we were able to observe new localities for Brazilian fishes into the Austral Subregion and expect some changes in the distribution of Galaxiidae. Northern limits for all species and southern limits for landlocked G. maculatus, Brachigalaxias bullocki and Aplochiton zebra, could be displaced southward. Probably, the species less affected by the changes will be G. platei. These predictions could be accurately formulated using the model of B.J. Shuter & J.R. Post (1990) Transactions of the American Fisheries Society 119 , 314–336, when biological database on these species are completed.     

Towards a model of postglacial biogeography in shallow marine species along the Patagonian Province: lessons from the limpet Nacella magellanica (Gmelin, 1791)

ABSTRACT: BACKGROUND: Patagonia extends for more than 84,000 km of irregular coasts is an area especially apt to evaluate how historic and contemporary processes influence the distribution and connectivity of shallow marine benthic organisms. The true limpet Nacella magellanica has a wide distribution in this province and represents a suitable model to infer the Quaternary glacial legacy on marine benthic organisms. This species inhabits ice-free rocky ecosystems, has a narrow bathymetric range and consequently should have been severely affected by recurrent glacial cycles during the Quaternary. We performed phylogeographic and demographic analyses of N. magellanica from 14 localities along its distribution in Pacific Patagonia, Atlantic Patagonia, and the Falkland/Malvinas Islands. RESULTS: Mitochondrial (COI) DNA analyses of 357 individuals of N. magellanica revealed an absence of genetic differentiation in the species with a single genetic unit along Pacific Patagonia. However, we detected significant genetic differences among three main groups named Pacific Patagonia, Atlantic Patagonia and Falkland/Malvinas Islands. Migration rate estimations indicated asymmetrical gene flow, primarily from Pacific Patagonia to Atlantic Patagonia (Nem=2.21) and the Falkland/Malvinas Islands (Nem=16.6). Demographic reconstruction in Pacific Patagonia suggests a recent recolonization process (< 10 ka) supported by neutrality tests, mismatch distribution and the median-joining haplotype genealogy. CONCLUSIONS: Absence of genetic structure, a single dominant haplotype, lack of correlation between geographic and genetic distance, high estimated migration rates and the signal of recent demographic growth represent a large body of evidence supporting the hypothesis of rapid postglacial expansion in this species in Pacific Patagonia. This expansion could have been sustained by larval dispersal following the main current system in this area. Lower levels of genetic diversity in inland sea areas suggest that fjords and channels represent the areas most recently colonized by the species. Hence recolonization seems to follow a west to east direction to areas that were progressively deglaciated. Significant genetic differences among Pacific, Atlantic and Falkland/Malvinas Islands populations may be also explained through disparities in their respective glaciological and geological histories. The Falkland/Malvinas Islands, more than representing a glacial refugium for the species, seems to constitute a sink area considering the strong asymmetric gene flow detected from Pacific to Atlantic sectors. These results suggest that historical and contemporary processes represent the main factors shaping the modern biogeography of most shallow marine benthic invertebrates inhabiting the Patagonian Province.     

The relationship between fish assemblages and the helminth communities of a prey fish, in a group of small shallow lakes

Galaxias maculatus (small puyen) is an abundant native fish distributed in lakes and rivers of the Patagonia, and it is the frequent prey of other fishes, fish-eating birds, and mammals. Previous studies have shown that it is parasitized by 33 metazoan species and that the richness and composition of the parasite communities vary between lakes. The aim of the present work was to analyze the relationship between the composition of fish assemblages and the helminth component community structure of G. maculatus . Ten environmentally similar, small, shallow lakes, belonging to the Nahuel Huapi Lake basin, were chosen because of the differences in the native fish assemblages. Parasite community structure in G. maculatus varied according to the fish assemblage of each lake. The presence of the piscivorous fish Percichthys trucha regularly produced variations in the composition and richness at the component and infracommunity levels, as well as the percentage of autogenic parasite species in G. maculatus .     

Latitudinal and ecological correlates of morphological variation in Galaxias platei (Pisces, Galaxiidae) in Patagonia

We examined the morphological variability (23 morphometric traits) among individual Galaxias platei ( N  = 380) collected from 20 postglacial lakes in the southern Andes. The lakes were chosen to cover the latitudinal range of the species in Patagonia. Diet examined for a subset of these fish ( N  = 261) collected during the summer months (January through March), differed among river basins but there were no clear latitudinal trends in the consumption of any prey type. Diet may, however, have partially shaped morphology, as pelvic measures were negatively correlated with consumption of amphipods. Substantial differentiation among populations was observed, primarily in the shape and dimensions of the head, in caudal morphology and in fin length. Our results indicate that the morphology of G. platei varies with latitude, and may be related to risk of predation and diet.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 87 , 69–82.     

Genetic and phenotypic variation among Galaxias maculatus populations reflects contrasting landscape effects between northern and southern Patagonia

1. Understanding the influence of landscape characteristics on genetic and phenotypic intraspecific variability can yield insights into how evolutionary processes work as well as provide essential information for the conservation of biodiversity. 2. Our aim was to compare the genetic structure and phenotypic variation among Galaxias maculatus populations inhabiting two Atlantic Ocean river basins in Patagonia in relation to historical and contemporary landscape characteristics associated with latitude. 3. Population genetic analysis (based on eight microsatellite loci, 505 individuals) indicates that genetic structure is more pronounced in the Río Negro basin (RN) at 39–41°S (10 localities) than in the southernmost Santa Cruz River basin (SCR) at 49–50°S (seven localities). Spatial autocorrelation analysis showed different effects of geographic distance in shaping population differentiation patterns in the two basins. 4. While in northern Patagonia, fragmented populations could have survived the severity of Quaternary climate cycles, at higher latitudes G. maculatus populations were probably extirpated by extensive ice sheets. Extant populations in the upper reaches of the southernmost basin probably originated from refugia close to the Atlantic Ocean. 5. Based on otolith microchemistry, we have documented facultative diadromy for the first time for the species in the SCR basin, while no evidence of migration to the sea was found in individuals from the RN basin. Vertebral number increased with latitude, and within the SCR basin, the higher counts are possibly associated with a migratory life style.     

Extinction and recolonization of maritime Antarctica in the limpet Nacella concinna (Strebel, 1908) during the last glacial cycle: toward a model of Quaternary biogeography in shallow Antarctic invertebrates

Quaternary glaciations in Antarctica drastically modified geographical ranges and population sizes of marine benthic invertebrates and thus affected the amount and distribution of intraspecific genetic variation. Here, we present new genetic information in the Antarctic limpet Nacella concinna, a dominant Antarctic benthic species along shallow ice‐free rocky ecosystems. We examined the patterns of genetic diversity and structure in this broadcast spawner along maritime Antarctica and from the peri‐Antarctic island of South Georgia. Genetic analyses showed that N. concinna represents a single panmictic unit in maritime Antarctic. Low levels of genetic diversity characterized this population; its median‐joining haplotype network revealed a typical star‐like topology with a short genealogy and a dominant haplotype broadly distributed. As previously reported with nuclear markers, we detected significant genetic differentiation between South Georgia Island and maritime Antarctica populations. Higher levels of genetic diversity, a more expanded genealogy and the presence of more private haplotypes support the hypothesis of glacial persistence in this peri‐Antarctic island. Bayesian Skyline plot and mismatch distribution analyses recognized an older demographic history in South Georgia. Approximate Bayesian computations did not support the persistence of N. concinna along maritime Antarctica during the last glacial period, but indicated the resilience of the species in peri‐Antarctic refugia (South Georgia Island). We proposed a model of Quaternary Biogeography for Antarctic marine benthic invertebrates with shallow and narrow bathymetric ranges including (i) extinction of maritime Antarctic populations during glacial periods; (ii) persistence of populations in peri‐Antarctic refugia; and (iii) recolonization of maritime Antarctica following the deglaciation process.     

Distribution of the infection by Camallanus corderoi (Nemata: Spiruroidea) in different autochthonous hosts and localities of the Valdivia river basin, Chile

Six hundred and thirty nine autochthonous fish were examined in 1986-1987 in search for Camallanus corderoi infection on different biotopes from Valdivia River basin (between 39 degrees 30'-40 degrees 00'S, 73 degrees 30'-71 degrees 45' W). Brachigalaxias bullocki, Galaxias maculatus, Galaxias platei, Aplochiton taeniatus, Cheirodon australe, Basilichthys australis and Cauque mauleanum are new hosts for C. corderoi. Infection by C. corderoi in fish is acquired by ingestion of infected copepods and prevalence and intensity of infection showed differences between host fish and biotopes. In general, infrapopulations of C. corderoi showed overdispersion in different hosts.     

Predator associated morphology in Galaxias platei in Patagonian lakes

Among 158 Galaxias platei individuals, collected from nine deep Andean lakes and from one shallow lake on the Patagonian steppe, morphological characters associated with caudal fin length were negatively correlated with predation intensity as measured by the incidence of piscivory. Fish from lakes with high rates of piscivory had relatively short caudal fins and those from lakes with low piscivory had long caudal fins. It is hypothesized that in this species caudal fin length affects swimming ability and thus, ability to escape from predators. The population of G. platei from Lake Espejo with an intermediate level of piscivory contained individuals with both long and short caudal fins. Morphological variation within this lake was related to the exploitation of food resources and habitat; individuals with shorter tails ate more amphipods and inhabited shallower habitats. The results indicated that while the among-lakes morphological variation in G. platei was influenced largely by differences in predation intensity, within-lake morphological variation, where predation was intermediate, appeared to be affected by both predation and differences in the exploitation of food resources.     

Evolutionary history of the oriental fire‐bellied toad (Bombina orientalis) in Northeast China

The evolutionary history of a species is generally affected by the combination of geological events and climate fluctuations. By analyzing the population features, genetic structure and the effective population historical dynamics of existing species, the population evolutionary history can be reestablished. In recent years, geological evidence shows that the Yilan–Yitong fault zone located in Northeast Asia experienced strong and frequent geological changes in the late Quaternary period. Species population history has been shaped by the combination of the complex climatic conditions of the Quaternary and Pleistocene glacial interglacial cycles and palaeogeological events in Northeast Asia and it has become a research focus for evolutionary biology researchers. In this study, mitochondrial and microsatellite molecular markers were used to reveal the population features, genetic structure, and the effective population historical dynamics of the Oriental fire‐bellied toad (Bombina orientalis). The results showed that the strong seismic activity of the Yilan–Yitong fault zone in the late Quaternary period was the main reason for the population differentiation of Oriental fire‐bellied toad in northeast China. The Quaternary Pleistocene glacial interglacial cycles led to the significant bottleneck effect of the western population located in the Maoer mountain area. As a result, the western population has low genetic diversity. Recent gene flow between eastern and western populations and historical evidence of population expansion proved that the dispersal behavior of the western populations was the main cause of the low genetic diversity and mitochondrial and nuclear discordance. Human economic activity may be the mainly driving factor. These evidences showed that the comprehensive influence of geology, climate, human activities and other factors should be considered in the process of exploring the evolutionary history of species.     

Comparative biogeography of the congener lilies Lilium distichum and Lilium tsingtauense in Korea

The main Korean mountain range (the so-called “Baekdudaegan”), which stretches from north to south across most of the Peninsula, has been thought to harbor glacial refugia for boreal and temperate plant species, where they likely found relatively stable habitats and maintained large population sizes. Under this scenario, high levels of genetic variation for plant populations can be anticipated. To test this hypothesis, we examined levels of allozyme diversity in the boreal herb Lilium distichum, which in Korea occurs largely along the Baekdudaegan and in its closely related congener L. tsingtauense, a temperate species that can occur from the coastal islands to high-altitude mountains in the Baekdudaegan. As expected, L. distichum harbored high levels of genetic variation within populations, and we found significant correlations between percentage of polymorphic loci (and allelic richness) and elevation. For L. tsingtauense we found moderate genetic variation, with its populations showing a significantly positive correlation between intra-population expected heterozygosity and elevation. Our results suggest that populations/species that occur within or near the main ridge of the Baekdudaegan probably endured the glacial periods in macrorefugia, whereas those populations/species located at low elevations (far away from mid- and high-elevation mountains) did it in microrefugia. Palaeodistribution modelling is in agreement with genetic data, indicating that the Baekdudaegan was suitable habitat for both species during the glacial (LGM) and interglacial periods (like the present). This study as well as the data from other studies compiled here provides strong evidence that the Baekdudaegan was a major refugial area for the East Asian flora throughout the Quaternary and, thus, meriting high priority for conservation biogeography.     

Patterns of isozyme variation as indicators of biogeographic history in Pilgerodendron uviferum (D. Don) Florín

The effects of Pleistocene glaciations on the genetic characteristics of the most austral conifer in the world, Pilgerodendron uviferum, were analysed with specific reference to the hypothesis that the species persisted locally in ice‐free areas in temperate South America. It was expected that genetic variation would decrease with latitude, given that ice fields were larger in southern Patagonia and thus refugia were probably located towards the northern distributional limit of the species as suggested by the fossil record. In addition, an increase in among‐population genetic divergence was expected with increasing distance to putative glacial refugia. We examined the relationship between location and within‐population variability indices of 20 Pilgerodendron populations derived from isozyme analyses. We analysed possible refugia hypotheses by the distribution of allele frequencies using multivariate discriminant analysis. The degree of genetic differentiation with geographical distance between all population pairs was investigated by Mantel tests. Results indicated that Pilgerodendron populations are highly monomorphic, probably reflecting past population bottlenecks and reduced gene flow. Southernmost populations tend to be the least genetically variable and were therefore probably more affected by glacial activity than northern ones. Populations located outside ice limits seem to have been isolated during the glacial period. The presence of centres of genetic diversity, together with the lack of a significant correlation between genetic and geographical distances and the absence of geographical patterns of allelic frequencies at most analysed alleles, may indicate that Pilgerodendron did not advance southward after the last glaciation from a unique northern refugium, but spread from several surviving populations in ice‐free areas in Patagonia instead.     

Genetic structuring in Andean landlocked populations of Galaxias maculatus: effects of biogeographic history

Aim To test whether the genetic diversity of diadromous and landlocked populations of the small puyen Galaxias maculatus (known as jollytail in Australia and inanga in New Zealand) follow the same structuring patterns observed for migratory and non‐migratory species of the genus Galaxias. This work also aimed to test whether the genetic structuring of a group of populations could be predicted from differences in the geomorphologic history of the region they inhabit. Location Eight landlocked populations were sampled from cold‐temperate lakes in north‐western Patagonia. The study area could be split latitudinally into two sectors that differed in their geomorphology, each of them hosting four populations. The southern sector shows evidence of a higher degree of glacial coverage, and the lakes are probably remnants of a big proglacial palaeolake. Lakes in the northern sector, on the other hand, suggest no common origin. Results Significant genetic structuring was found among the studied populations (Θ = 0.188), being the highest value reported to date for the species. Significant correlation was found between genetic diversity and lake area and perimeter. Diversity also showed a slight latitudinal variation suggesting the presence of genetically distinct groups of populations. The comparison of populations from the two geographical sectors showed that those from the north had a higher diversity, more private alleles and strong structuring, while those from the south were less diverse and much more homogeneous. Main conclusions Non‐migratory populations of G. maculatus show much higher values of genetic structuring than those reported for diadromous populations. This follows the pattern seen when comparing migratory and non‐migratory species of Galaxias. This agrees with population genetics theory which predicts that restricted gene flow would result in greater among‐population divergence. Also, differences between northern and southern populations agreed with what was predicted by the geomorphologic history of the study area. During the Last Glacial Maximum ice cover in that region may have reduced the habitat of G. maculatus to a refuge with an impoverished gene pool. When the ice receded, leaving a great proglacial lake, that former population expanded and became fragmented after water levels descended. This resulted in present day lakes harbouring homogeneous populations with reduced diversity. The northern sector, in contrast, was less affected by glaciers, resulting in more geomorphologically stable lakes holding genetically diverse populations.     

A new genus of dactylogyrid from the gills of Galaxias maculatus (Osmeriformes: Galaxiidae) in Maullín Basin, Patagonia, Chile

During a parasitological survey of Galaxias maculatus (Jenyns, 1842) in the Maullín Basin (Chilean Patagonia), specimens of a new species of Monogenea were collected from the gills. This species is described as the only member of a proposed new genus, Inserotrema n. gen. (Dactylogyridae, Ancyrocephalinae), characterized by similar hooks with 2 subunits, overlapping gonads, coiled cirrus with counterclockwise rings, articulated accessory piece formed by 2 parts, a needlelike sclerite threading the distal part of the MCO, and a sclerotized midventral vagina. This new genus is proposed for dactylogyrids from gills of galaxiids (Galaxiidae). Inserotrema puyei n. sp. infects gills of G. maculatus from Llanquihue Lake, Maullín River, and Maullín Estuary. This is the first species of Ancyrocephalinae described from gills of a galaxiid.     

Stable persistence of relict populations involved evolutionary shifts of reproductive characters in the genus Tanakaea (Saxifragaceae)

Tertiary relicts often show evolutionary stasis in morphology and ecology and have been hypothesized to retain stable population sizes in refugia. However, recent studies have reported that some relicts evolutionarily shifted their physiology, ecology, and morphology and experienced various patterns of demography. To understand the historical survival of relict plants, a multidimensional study investigating the evolution of ecological and morphological traits as well as population demographic history is needed. The genus Tanakaea (Saxifragaceae) comprises two species in China and Japan. These species share most vegetative characteristics and are sometimes treated as a single species. The distribution pattern is relictual, as the populations are confined to small areas in mesic warm temperate forests less influenced by Quaternary glacial climates. Focusing on the relictual plant group, this study tested the hypotheses of evolutionary stasis and population stability in long-term refugia. Genetic analyses using plastome sequences and genome-wide single-nucleotide polymorphisms revealed divergence of the two species approximately 6.8 million years ago and strong genetic differentiation of the regional populations. Demographic analysis revealed that almost all populations retained stable population sizes during glacial–interglacial climate changes, supporting the traditional view. However, morphological assessments revealed a simultaneous shift in breeding systems (from hermaphrodite to dioecy/non-clonal to clonal reproduction) in Japanese species and intraspecific differentiation of leaf traits. Therefore, the relict species do not show evolutionary stasis in every aspect. Changes in reproductive characteristics may have contributed to their long-term in situ survival.     

Expected coalescence times and segregating sites in a model of glacial cycles

The climatic fluctuations of the Quaternary have influenced the distribution of numerous plant and animal species. Several species suffer population reduction and fragmentation, becoming restricted to refugia during glacial periods and expanding again during interglacials. The reduction in population size may reduce the effective population size, mean coalescence time and genetic variation, whereas an increased subdivision may have the opposite effect. To investigate these two opposing forces, we proposed a model in which a panmictic and a structured phase alternate, corresponding to interglacial and glacial periods. From this model, we derived an expression for the expected coalescence time and number of segregating sites for a pair of genes. We observed that increasing the number of demes or the duration of the structured phases causes an increase in coalescence time and expected levels of genetic variation. We compared numerical results with the ones expected for a panmictic population of constant size, and showed that the mean number of segregating sites can be greater in our model even when population size is much smaller in the structured phases. This points to the importance of population structure in the history of species subject to climatic fluctuations, and helps explain the long gene genealogies observed in several organisms.     

Glacial refugia and modern genetic diversity of 22 western North American tree species

North American tree species, subspecies and genetic varieties have primarily evolved in a landscape of extensive continental ice and restricted temperate climate environments. Here, we reconstruct the refugial history of western North American trees since the last glacial maximum using species distribution models, validated against 3571 palaeoecological records. We investigate how modern subspecies structure and genetic diversity corresponds to modelled glacial refugia, based on a meta-analysis of allelic richness and expected heterozygosity for 473 populations of 22 tree species. We find that species with strong genetic differentiation into subspecies had widespread and large glacial refugia, whereas species with restricted refugia show no differentiation among populations and little genetic diversity, despite being common over a wide range of environments today. In addition, a strong relationship between allelic richness and the size of modelled glacial refugia (r² = 0.55) suggest that population bottlenecks during glacial periods had a pronounced effect on the presence of rare alleles.