Beyond the Mediterranean peninsulas: evidence of central European glacial refugia for a temperate forest mammal species, the bank vole (Clethrionomys glareolus)

This study details the phylogeographic pattern of the bank vole, Clethrionomys glareolus, a European rodent species strongly associated with forest habitat. We used sequences of 1011 base pairs of the mitochondrial DNA cytochrome b gene from 207 bank voles collected in 62 localities spread throughout its distribution area. Our results reveal the presence of three Mediterranean (Spanish, Italian and Balkan) and three continental (western, eastern and 'Ural') phylogroups. The endemic Mediterranean phylogroups did not contribute to the post-glacial recolonization of much of the Palaearctic range of species. Instead, the major part of this region was apparently recolonized by bank voles that survived in glacial refugia in central Europe. Moreover, our phylogeographic analyses also reveal differentiated populations of bank voles in the Ural mountains and elsewhere, which carry the mitochondrial DNA of another related vole species, the ruddy vole (Clethrionomys rutilus). In conclusion, this study demonstrates a complex phylogeographic history for a forest species in Europe which is sufficiently adaptable that, facing climate change, survives in relict southern and northern habitats. The high level of genetic diversity characterizing vole populations from parts of central Europe also highlights the importance of such regions as a source of intraspecific genetic biodiversity.     

Comparative phylogeography and demographic history of the wood lemming (Myopus schisticolor): implications for late Quaternary history of the taiga species in Eurasia

The association between demographic history, genealogy and geographical distribution of mitochondrial DNA cytochrome b haplotypes was studied in the wood lemming (Myopus schisticolor), a species that is closely associated with the boreal forest of the Eurasian taiga zone from Scandinavia to the Pacific coast. Except for a major phylogeographic discontinuity (0.9% nucleotide divergence) in southeastern Siberia, only shallow regional genetic structure was detected across northern Eurasia. Genetic signs of demographic expansions imply that successive range contractions and expansions on different spatial scales represented the primary historical events that shaped geographical patterns of genetic variation. Comparison of phylogeographic structure across a taxonomically diverse array of other species that are ecologically associated with the taiga forest revealed similar patterns and identified two general aspects. First, the major south-north phylogeographic discontinuity observed in five out of six species studied in southeastern Siberia and the Far East implies vicariant separation in two different refugial areas. The limited distribution range of the southeastern lineages provides no evidence of the importance of the putative southeastern refugial area for postglacial colonization of northern Eurasia by boreal forest species. Second, the lack of phylogeographic structure associated with significant reciprocal monophyly and genetic signatures of demographic expansion in all nine boreal forest animal species studied to date across most of northern Eurasia imply contraction of each species to a single refugial area during the late Pleistocene followed by range expansion on a continental scale. Similar phylogeographic patterns observed in this taxonomically diverse set of organisms with different life histories and dispersal potentials reflect the historical dynamics of their shared environment, the taiga forest in northern Eurasia.     

Unravelling the evolutionary history and future prospects of endemic species restricted to former glacial refugia

The contemporary distribution and genetic composition of biodiversity bear a signature of species’ evolutionary histories and the effects of past climatic oscillations. For many European species, the Mediterranean peninsulas of Iberia, Italy and the Balkans acted as glacial refugia and the source of range recolonization, and as a result, they contain disproportionately high levels of diversity. As these areas are particularly threatened by future climate change, it is important to understand how past climatic changes affected their biodiversity. We use an integrated approach, combining markers with different evolutionary rates and combining phylogenetic analysis with approximate Bayesian computation and species distribution modelling across temporal scales. We relate phylogeographic processes to patterns of genetic variation in Myotis escalerai, a bat species endemic to the Iberian Peninsula. We found a distinct population structure at the mitochondrial level with a strong geographic signature, indicating lineage divergence into separate glacial refugia within the Iberian refugium. However, microsatellite markers suggest higher levels of gene flow resulting in more limited structure at recent time frames. The evolutionary history of M. escalerai was shaped by the effects of climatic oscillations and changes in forest cover and composition, while its future is threatened by climatically induced range contractions and the role of ecological barriers due to competition interactions in restricting its distribution. This study warns that Mediterranean peninsulas, which provided refuge for European biodiversity during past glaciation events, may become a trap for limited dispersal and ecologically limited endemic species under future climate change, resulting in loss of entire lineages.     

Insights into the biogeographical history of the Lower Guinea Forest Domain: evidence for the role of refugia in the intraspecific differentiation of Aucoumea klaineana

Determining the biogeographical histories of rainforests is central to our understanding of the present distribution of tropical biodiversity. Ice age fragmentation of central African rainforests strongly influenced species distributions. Elevated areas characterized by higher species richness and endemism have been postulated to be Pleistocene forest refugia. However, it is often difficult to separate the effects of history and of present-day ecological conditions on diversity patterns at the interspecific level. Intraspecific genetic variation could yield new insights into history, because refugia hypotheses predict patterns not expected on the basis of contemporary environmental dynamics. Here, we test geographically explicit hypotheses of vicariance associated with the presence of putative refugia and provide clues about their location. We intensively sampled populations of Aucoumea klaineana, a forest tree sensitive to forest fragmentation, throughout its geographical range. Characterizing variation at 10 nuclear microsatellite loci, we were able to obtain phylogeographic data of unprecedented detail for this region. Using Bayesian clustering approaches, we demonstrated the presence of four differentiated genetic units. Their distribution matched that of forest refugia postulated from patterns of species richness and endemism. Our data also show differences in diversity dynamics at leading and trailing edges of the species' shifting distribution. Our results confirm predictions based on refugia hypotheses and cannot be explained on the basis of present-day ecological conditions.     

At least some meiofaunal species are not everywhere. Indication of geographic,ecological and geological barriers affecting the dispersion of species of Ototyphlonemertes (Nemertea,Hoplonemertea)

Most meiofaunal species are known to have a broad distribution with no apparent barriers to their dispersion. However, different morphological and/or molecular methods supported patterns of diversity and distribution that may be different among taxa while also conflicting within the same group. We accurately assessed the patterns of geographic distribution in actual genetic species of a marine meiofaunal animal model: Ototyphlonemertes. Specimens were collected from several sites around Europe, Northern and Central America, Southern America, Pacific Islands and Asia. We sequenced regions of two mitochondrial and two nuclear genes. Using single‐gene, a concatenated data set, multilocus approaches and different DNA taxonomy methods, we disentangled the actual diversity and the spatial structures of haplotypes and tested the possible correlation between genetic diversity and geographic distance. The results show (i) the importance of using several genes to uncover both diversity and highlight phylogeographic relationships among species and that (ii) independent genetic evolutionary entities have a narrower distribution than morphological species. Moreover, (iii) a Mantel test supported a positive correlation between genetic and geographical distance. By sampling from the two sides of Isthmus of Panama, we were additionally able to identify lineage divergence times that are concordant with vicariance mechanisms caused by the geological closure of the seaway across the Isthmus. We therefore propose that in addition to distance, other geological and ecological conditions are also barriers to the dispersion of and gene flow in marine meiofaunal organisms.     

Chloroplast DNA Polymorphism and Phylogeography of a Central African Tree Species Widespread in Mature Rainforests: Greenwayodendron suaveolens (Annonaceae)

Geographic patterns of genetic variation at chloroplast markers have been successfully used to address the phylogeography and the demographic history of many plant species. Very few studies have however been conducted in important tropical centers of plant biodiversity like the African rainforests. The phylogeography of a tree species widespread in Central African mature forests, Greenwayodendron suaveolens subsp. suaveolens (Annonaceae), was investigated in the Lower Guinea phytogeographic domain (essentially Gabon and Cameroon) by sequencing an intergenic spacer of the chloroplast genome (trnC-petN1R). A total of 11 polymorphic sites, including nine single nucleotide polymorphisms (SNPs), two insertions/deletions and two inversions, defined 12 haplotypes. The taxon is represented by two sympatric varieties (var. suaveolens and var. gabonica) that carried distinct and relatively divergent haplotypes. These varieties, also well distinguishable morphologically, might therefore represent true biological species. The variety suaveolens, more common and more widespread than the variety gabonica, was represented by ten haplotypes. This taxon showed a weak but statistically significant phylogeographic structure, indicating that two sets of related haplotypes essentially occurred respectively in the northern and the southern hemispheres. These results suggest that the distribution of Greenwayodendron suaveolens subsp. suaveolens, which is currently continuous in the Lower Guinea domain, might have been more fragmented in the past, possibly in relation with Pleistocene forest fragmentation.     

Effects of vicariant barriers, habitat stability, population isolation and environmental features on species divergence in the south-western Australian coastal reptile community

Identifying explicit hypotheses regarding the factors determining genetic structuring within species can be difficult, especially in species distributed in historically dynamic regions. To contend with these challenges, we use a framework that combines species distribution models, environmental data and multi-locus genetic data to generate and explore phylogeographic hypotheses for reptile species occupying the coastal sand-dune and sand-plain habitats of the south-western Australian biodiversity hotspot, a community which has both a high diversity of endemics and has varied dramatically in spatial extent over time. We use hierarchical amova, summary statistic and distance-based analyses to explicitly test specific phylogeographic hypotheses. Namely, we test if biogeographic vicariance across barriers, habitat stability, population isolation along a linear habitat or fragmentation across different environments can explain genetic divergence within five co-distributed squamate reptile species. Our results show that patterns of genetic variation reflect complex and species-specific interactions related to the spatial distribution of habitats present currently and during repeated glacial minima, as opposed to being associated with historical factors such as habitat stability between glacial and inter-glacial periods or vicariant barriers. We suggest that the large impact of habitat characteristics over time (i.e. relative levels of habitat connectivity, climatic gradients and spatial heterogeneity of soil types) reflects the ecological restrictions of the sand-dune and sand-plain reptile communities and may explain the lack of concordance across taxa. The study demonstrates the general utility of the approach for assemblage-level, as well as single species, phylogeographic study, including its usefulness for exploring biologically informed hypotheses about what factors have influenced patterns of genetic variation.     

Evolutionary and demographic processes shaping geographic patterns of genetic diversity in a keystone species,the African forest elephant (Loxodonta cyclotis)

The past processes that have shaped geographic patterns of genetic diversity may be difficult to infer from current patterns. However, in species with sex differences in dispersal, differing phylogeographic patterns between mitochondrial (mt) and nuclear (nu) DNA may provide contrasting insights into past events. Forest elephants (Loxodonta cyclotis) were impacted by climate and habitat change during the Pleistocene, which likely shaped phylogeographic patterns in mitochondrial (mt) DNA that have persisted due to limited female dispersal. By contrast, the nuclear (nu) DNA phylogeography of forest elephants in Central Africa has not been determined. We therefore examined the population structure of Central African forest elephants by genotyping 94 individuals from six localities at 21 microsatellite loci. Between forest elephants in western and eastern Congolian forests, there was only modest genetic differentiation, a pattern highly discordant with that of mtDNA. Nuclear genetic patterns are consistent with isolation by distance. Alternatively, male‐mediated gene flow may have reduced the previous regional differentiation in Central Africa suggested by mtDNA patterns, which likely reflect forest fragmentation during the Pleistocene. In species like elephants, male‐mediated gene flow erases the nuclear genetic signatures of past climate and habitat changes, but these continue to persist as patterns in mtDNA because females do not disperse. Conservation implications of these results are discussed.     

Comparison of phylogeographic structure and population history of two Phrynocephalus species in the Tarim Basin and adjacent areas

An aridification of the Tarim Basin and adjacent areas since middle Pleistocene has produced significant genetic structuring of the local fauna. We examined the phylogeographic patterns, population structure and history of Phrynocephalus axillaris and Phrynocephalus forsythii using a mitochondrial fragment ND4-tRNA(LEU). Phylogenetic hypotheses were constructed using maximum parsimony and Bayesian inference, and the divergence times of major lineages were estimated by BEAST. Population structure and history were inferred by nested clade analysis, neutrality tests, mismatch distribution, and isolation by distance analysis. The two species might have experienced different evolutionary history throughout their current distribution. For P. forsythii, a vicariant event, as a consequence of geological isolation and desert expansion, might have produced the significant divergence between the Tarim and the Yanqi populations. For P. axillaris, populations of the Yanqi, Turpan and Hami Basins might have been established through dispersal during demographic expansion. Climatic fluctuations caused alternate expansion and shrinkage of rivers and oases several times, which likely led to habitat fragmentation for both species. Interaction between vicariance, dispersal and habitat fragmentation produced the current distribution and genetic diversity. The observed difference between the two species may be due partially to their different reproductive modes (ovoviviparous vs. oviparous).     

Large-scale phylogeography of the disjunct Neotropical tree species Schizolobium parahyba (Fabaceae-Caesalpinioideae)

Neotropical rainforests exhibit high levels of endemism and diversity. Although the evolutionary genetics of plant diversification has garnered increased interest, phylogeographic studies of widely distributed species remain scarce. Here we describe chloroplast and nuclear variation patterns in Schizolobium parahyba (Fabaceae), a widespread tree in Neotropical rainforests that harbor two varieties with a disjunct distribution. Chloroplast and nuclear sequence analyses yielded 21 and 4 haplotypes, respectively. Two genetic diversity centers that correlate with the two known varieties were identified: the Southeastern Atlantic forest and the Amazonian basin. In contrast, the populations from southern and northeastern Atlantic forests and Andean-Central American forests exhibited low levels of genetic diversity and divergent haplotypes, likely related to historical processes that impact the flora and fauna in these regions, such as a founder's effect after dispersion and demographic expansion. Phylogeographic and demographic patterns suggest that episodes of genetic isolation and dispersal events have shaped the evolutionary history for this species, and different patterns have guided the evolution of S. parahyba. Moreover, the results of this study suggest that the dry corridor formed by Cerrado and Caatinga ecoregions and the Andean uplift acted as barriers to this species' gene flow, a picture that may be generalized to most of the plant biodiversity tropical woodlands and forests. These results also reinforce the importance of evaluating multiple genetic markers for a more comprehensive understanding of population structure and history. Our results provide insight into the conservation efforts and ongoing work on the genetics of population divergence and speciation in these Neotropical rainforests.     

Insights into the origin and distribution of biodiversity in the Brazilian Atlantic forest hot spot: a statistical phylogeographic study using a low-dispersal organism

The relative importance of the processes that generate and maintain biodiversity is a major and controversial topic in evolutionary biology with large implications for conservation management. The Atlantic Forest of Brazil, one of the world''s richest biodiversity hot spots, is severely damaged by human activities. To formulate an efficient conservation policy, a good understanding of spatial and temporal biodiversity patterns and their underlying evolutionary mechanisms is required. With this aim, we performed a comprehensive phylogeographic study using a low-dispersal organism, the land planarian species Cephaloflexa bergi (Platyhelminthes, Tricladida). Analysing multi-locus DNA sequence variation under the Approximate Bayesian Computation framework, we evaluated two scenarios proposed to explain the diversity of Southern Atlantic Forest (SAF) region. We found that most sampled localities harbour high levels of genetic diversity, with lineages sharing common ancestors that predate the Pleistocene. Remarkably, we detected the molecular hallmark of the isolation-by-distance effect and little evidence of a recent colonization of SAF localities; nevertheless, some populations might result from very recent secondary contacts. We conclude that extant SAF biodiversity originated and has been shaped by complex interactions between ancient geological events and more recent evolutionary processes, whereas Pleistocene climate changes had a minor influence in generating present-day diversity. We also demonstrate that land planarians are an advantageous biological model for making phylogeographic and, particularly, fine-scale evolutionary inferences, and propose appropriate conservation policies.     

Testing the divergent adaptation of two congeneric tree species on a rainfall gradient using eco‐physio‐morphological traits

In tropical Africa, evidence of widely distributed genera transcending biomes or habitat boundaries has been reported. The evolutionary processes that allowed these lineages to disperse and adapt into new environments are far from being resolved. To better understand these processes, we propose an integrated approach, based on the eco‐physio‐morphological traits of two sister species with adjacent distributions along a rainfall gradient. We used wood anatomical traits, plant hydraulics (vulnerability to cavitation, wood volumetric water content, and hydraulic capacitance), and growth data from the natural habitat, in a common garden, to compare species with known phylogeny, very similar morphologically, but occupying contrasting habitats: Erythrophleum ivorense (wet forest) and Erythrophleum suaveolens (moist forest and forest gallery). We identified some slight differences in wood anatomical traits between the two species associated with strong differences in hydraulics, growth, and overall species distribution. The moist forest species, E. suaveolens, had narrower vessels and intervessel pits, and higher vessel cell‐wall reinforcement than E. ivorense. These traits allow a high resistance to cavitation and a continuous internal water supply of the xylem during water shortage, allowing a higher fitness during drought periods, but limiting growth. Our results confirm a trade‐off between drought tolerance and growth, controlled by subtle adaptations in wood traits, as a key mechanism leading to the niche partitioning between the two Erythrophleum species. The generality of this trade‐off and its importance in the diversification of the African tree flora remains to be tested. Our integrated eco‐physio‐morpho approach could be the way forward.     

Continental shelf as potential retreat areas for Austral‐Asian estrildid finches (Passeriformes: Estrildidae) during the Pleistocene

Studies dealing with changes of biodiversity in time and space constitute an important part of biogeography, ecology and conservation biology. Areas of long‐term climate stability are particularly interesting as they might have facilitated the survival of species over historical times and thus are crucial for understanding contemporary diversity patterns. In this study, we assessed the potential distribution of 23 estrildid finch species in order to analyse stability in recent and past diversity patterns and diversity centres in the Austral‐Asiatic region. We used Maxent to predict recent distributions of each species and to project them onto the climatic conditions of the Last Glacial Maximum (LGM, 21 000 yr BP) using two different scenarios (CCSM, MIROC). The resulting diversity patterns were tested on presence and possible shifts of distribution centres. Diversity patterns of forest‐ and savannah‐living species were considered combined and separately. During the LGM, potential diversity patterns of forest‐living species corroborated well with postulated rainforest refuges situated on the eastern coast of Cape York Peninsula. Our results indicate a remarkably high stability of existing diversity centres. Although projections into the past show some differences in detail in the extent and exact position of the diversity centres, they reveal largely congruent large scale patterns in both time slices. However, the models suggest a northward shift towards exposed continental shelf areas that where dry during the LGM. Clearly, centres of diversity were situated on this land bridge between Australia and New Guinea, highlighting their importance as areas of retreat for estrildid finches and maybe other savannah species in times of changing climatic conditions and associated sea‐level fluctuations.     

Phylogeographic insights of the lowland species Cheirolophus sempervirens in the southwestern Iberian Peninsula

The southwestern Iberian Peninsula is an important biogeographic region, showing high biodiversity levels and hosting several putative glacial refugia for European flora. Here, we study the genetic diversity and structure of the Mediterranean, thermophilous plant Cheirolophus sempervirens (Asteraceae) across its whole distribution range in SW Iberia, as a tool to disentangle some of the general biogeographic patterns shaping this southern refugia hotspot. Null genetic diversity was observed in the cpDNA sequencing screening. Nonetheless, AFLP data revealed high levels of among-population genetic differentiation correlated to their geographic location. Our results suggest longer species persistence in southern Iberian refugia during glacial periods and subsequent founder effects northwards due to colonizations in warmer stages (i.e., the southern richness to northern purity pattern). Additionally, our phylogeographic analyses indicate the presence of two separate genetic lineages within Ch. sempervirens, supporting the hypothesis of multiple minor refugia for SW Iberia in agreement with the refugia within refugia model.     

Comparative phylogeography of eastern chipmunks and white-footed mice in relation to the individualistic nature of species

Palaeoecological studies have demonstrated that ecological communities as a whole did not remain stable throughout the climatic fluctuations of the Quaternary. The result is that long-term associations of species cannot be inferred by contemporary associations in ecological communities. Therefore, the evolutionary significance of any contemporary ecological interactions among species and of the biotic community within which species have evolved also cannot be assumed from contemporary conditions. Comparative phylogeographic data provide a method to identify species within ecological communities that have shared biogeographic histories. We present an example of a long-term association between populations of two mammalian species, eastern chipmunks (Tamias striatus) and white-footed mice (Peromyscus leucopus), which are commonly associated with deciduous forest habitats. The distribution of mitochondrial DNA variation in T. striatus and P. leucopus from previously glaciated regions of the eastern United States support the hypothesis that, in at least part of their range, genetic lineages of the two species have expanded from similar population sources since the Last Glacial Maximum. In addition, the spatial concordance of genetic lineages of T. striatus and P. leucopus with the oak-savannah forest formations of Wisconsin and Illinois, suggest that populations associated with this community colonized the area in association with a set of arboreal species that comprise their deciduous forest habitat.     

Comparative phylogeography of five widespread tree species: Insights into the history of western Amazonia

Various historical processes have been put forth as drivers of patterns in the spatial distribution of Amazonian trees and their population genetic variation. We tested whether five widespread tree species show congruent phylogeographic breaks and similar patterns of demographic expansion, which could be related to proposed Pleistocene refugia or the presence of geological arches in western Amazonia. We sampled Otoba parvifolia/glycycarpa (Myristicaceae), Clarisia biflora, Poulsenia armata, Ficus insipida (all Moraceae), and Jacaratia digitata (Caricaceae) across the western Amazon Basin. Plastid DNA (trnH–psbA; 674 individuals from 34 populations) and nuclear ribosomal internal transcribed spacers (ITS; 214 individuals from 30 populations) were sequenced to assess genetic diversity, genetic differentiation, population genetic structure, and demographic patterns. Overall genetic diversity for both markers varied among species, with higher values in populations of shade‐tolerant species than in pioneer species. Spatial analysis of molecular variance (SAMOVA) identified three genetically differentiated groups for the plastid marker for each species, but the areas of genetic differentiation were not concordant among species. Fewer SAMOVA groups were found for ITS, with no detectable genetic differentiation among populations in pioneers. The lack of spatially congruent phylogeographic breaks across species suggests no common biogeographic history of these Amazonian tree species. The idiosyncratic phylogeographic patterns of species could be due instead to species‐specific responses to geological and climatic changes. Population genetic patterns were similar among species with similar biological features, indicating that the ecological characteristics of species impact large‐scale phylogeography.     

Phylogeographic incongruence of codistributed amphibian species based on small differences in geographic distribution

Codistributed species may display either congruent phylogeographic patterns, indicating similar responses to a series of shared climatic and geologic events, or discordant patterns, indicating independent responses. This study compares the phylogeographic patterns of two similarly distributed salamander species within the Pacific Northwest of the United States: Cope's giant salamander (Dicamptodon copei) and Van Dyke's salamander (Plethodon vandykei). Previous studies of P. vandykei support two reciprocally monophyletic lineages corresponding to coastal populations, located from the Olympic Mountains to the mouth of the Columbia River, and inland populations within the Cascade Mountains. We hypothesized that D. copei would have a congruent phylogeographic pattern to P. vandykei due to similarity in distribution and dependence upon similar stream and stream-side habitats. We test this hypothesis by estimating the phylogeny of D. copei using approximately 1800bp of mitochondrial DNA and comparing it to that of P. vandykei. Sympatric populations of D. copei and of P. vandykei display an identical phylogeographic pattern, suggesting similar responses within their shared distribution. Populations of D. copei occurring outside the range of P. vandykei displayed high levels of genetic divergence from those sympatric to P. vandykei. Overall, phylogeographic patterns between the two species were ultimately incongruent due to the high divergence of these allopatric populations. These results provide an example of codistributed species displaying overall incongruent phylogeographic patterns while simultaneously displaying congruent patterns within portions of their shared geographic distribution. This pattern demonstrates that a simple dichotomy of congruent and incongruent phylogeographic patterns of codistributed species may be too simplistic and that more complex intermediate patterns can result even from minor differences in species' ranges.     

Deep cox1 divergence and hyperdiversity of Trigonopterus weevils in a New Guinea mountain range (Coleoptera, Curculionidae)

Riedel, A., Daawia, D. & Balke, M. (2009). Deep cox1 divergence and hyperdiversity of Trigonopterus weevils in a New Guinea mountain range (Coleoptera, Curculionidae).— Zoologica Scripta, 39 , 63–74.
Trigonopterus is a little-known genus of flightless tropical weevils. A survey in one locality, the Cyclops Mountains of West New Guinea, yielded 51 species, at least 48 of them undescribed. In this study, we show that mtDNA sequencing, or DNA barcoding, is an effective and useful tool for rapid discovery and identification of these species, most of them morphologically very difficult to distinguish even for expert taxonomists. The genus is hyperdiverse in New Guinea and different species occur on foliage and in the litter layer. Morphological characters for its diagnosis are provided. Despite their external similarity, the genetic divergence between the species is high (smallest interspecific divergence 16%, mean 20%). We show that Trigonopterus are locally hyperdiverse and genetically very strongly structured. Their potential for rapid local biodiversity assessment surveys in Melanesia is outlined (α-diversity); providing a regional perspective on Trigonopterus diversity and biogeography is the next challenge (β-diversity).     

Historical range expansion determines the phylogenetic diversity introduced during contemporary species invasion

For a species rapidly expanding its geographic range, such as during biological invasion, most alleles in the introduced range will have their evolutionary origins in the native range. Yet, the way in which historical processes occurring over evolutionary time in the native range contribute to the diversity sampled during contemporary invasion is largely unknown. We used chloroplast DNA (cpDNA) gene genealogies and coalescent methods to study two congeneric plants, Silene latifolia and S. vulgaris. We examined how phylogenetic diversity was shaped by demographic growth and historical range expansions in the native European range, and how this history affected the diversity sampled during their recent invasion of North America. Genealogies from both species depart from neutrality, likely as a result of demographic expansion in the ancestral range, the timing of which corresponds to shortly after each species originated. However, the species differ in the spatial distribution of cpDNA lineages across the native range. Silene latifolia shows a highly significant phylogeographic structure that most likely reflects different avenues of the post-glacial expansion into northern Europe from Mediterranean refugia. By contrast, cpDNA lineages in S. vulgaris have been widely scattered across Europe during, or since, the most recent post-glacial expansion. These different evolutionary histories resulted in dramatic differences in how phylogenetic diversity was sampled during invasion of North America. In S. latifolia, relatively few, discrete invasion events from a structured native range resulted in a rather severe genetic bottleneck, but also opportunities for admixture among previously isolated lineages. In S. vulgaris, lack of genetic structure was accompanied by more representative sampling of phylogenetic diversity during invasion, and reduced potential for admixture. Our results provide clear insights into how historical processes may feed forward to influence the phylogenetic diversity of species invading new geographic ranges.     

Stream flow alone does not predict population structure of diving beetles across complex tropical landscapes

Recent theoretical advances have hypothesized a central role of habitat persistence on population genetic structure and resulting biodiversity patterns of freshwater organisms. Here, we address the hypothesis that lotic species, or lineages adapted to comparably geologically stable running water habitats (streams and their marginal habitats), have high levels of endemicity and phylogeographic structure due to the persistent nature of their habitat. We use a nextRAD DNA sequencing approach to investigate the population structure and phylogeography of a putatively widespread New Guinean species of diving beetle, Philaccolilus ameliae (Dytiscidae). We find that P. ameliae is a complex of morphologically cryptic, but geographically and genetically well‐differentiated clades. The pattern of population connectivity is consistent with theoretical predictions associated with stable lotic habitats. However, in two clades, we find a more complex pattern of low population differentiation, revealing dispersal across rugged mountains and watersheds of New Guinea up to 430 km apart. These results, while surprising, were also consistent with the original formulation of the habitat template concept by Southwood, involving lineage‐idiosyncratic evolution in response to abiotic factors. In our system, low population differentiation might reflect a young species in a phase of range expansion utilizing vast available habitat. We suggest that predictions of life history variation resulting from the dichotomy between lotic and lentic organisms require more attention to habitat characterization and microhabitat choice. Our results also underpin the necessity to study fine‐scale processes but at a larger geographical scale, as compared to solely documenting macroecological patterns, to understand ecological drivers of regional biodiversity. Comprehensive sampling especially of tropical lineages in complex and threatened environments such as New Guinea remains a critical challenge.