Postglacial colonization of Northern Europe by distinct phylogeographic lineages of the bullhead, Cottus gobio

Three major phylogeographic lineages of the cottid fish Cottus gobio (bullhead) were identified in northern Europe from mitochondrial DNA sequences and allozyme data. The largely separate freshwater distributions of the lineages demonstrate distinct postglacial colonization histories. West of the Baltic Sea, Swedish lakes were invaded from the southwest (Germany). Another, eastern lineage has colonized the inland waters northeast and east of the Baltic, from refugia in northwest Russia; this lineage comprises a distinct subgroup found only from Estonia. The third lineage, found south and southeast of the Baltic, probably descended from rivers draining to the Black Sea from the north (e.g. Dnepr). In coastal waters of the Baltic Sea, and in near-coast inland waters, the lineages are now found intermixed in various combinations. The alternating fresh- and saltwater phases of the Baltic basin have variously enabled and disabled the use of coastal waters as colonization routes. Hypotheses on the chronology of dispersal and lineage mixing can be based on the distribution of the marker genes and the paleohydrographical record. The diversity of the Fennoscandian bullhead thus comprises anciently diverged (probably mid-Pleistocene) refugial lineages that in their freshwater range constitute distinct evolutionarily significant units. The thorough mixing of the various genomic origins in and around the Baltic, however, refutes the controversial view of distinct species status for the western and eastern ('Cottus koshewnikowi') bullheads. The postglacial contact of the lineages has created new diversity that cannot be interpreted in a conventional hierarchical framework of taxonomic or conservation units.     

Refugial races and postglacial colonization history of the freshwater amphipod Gammarus lacustris in Northern Europe

The systematic structure and postglacial population history of the freshwater amphipod Gammarus lacustris were explored in an allozyme survey of 65 populations across Northern Europe. A strong multilocus pattern of differentiation discriminated populations of the north‐east (north‐eastern Norway, northern Finland) from those in the west and the south (southern and central Scandinavia, Denmark, Poland). This principal division is attributed to postglacial colonization of the area by two main refugial races or lineages, one from the east (Russia), the other from the south (north‐western European continent). The strongly diverged Eastern and Western races (Nei's D= 0.3, from 22 loci) now meet in a secondary contact zone across a narrow sector of northernmost Norway. Genetic population compositions in this zone vary in a mosaic pattern, and show no evidence of reproductive incompatibility. Similar contacts of eastern and western lineages, far older than the latest glaciation, are now known from a number of taxa and they constitute a general pattern in Fennoscandian phylogeography. Within the Western Gammarus race, the populations through coastal north‐western Norway are further distinguished from those in southern Scandinavia and Denmark by a set of unique alleles at high frequencies (D = 0.12). This suggests an independent early colonization of the coastal region by another distinct stock, either along an early deglaciated coastal corridor from the south‐west, or directly from the ice‐free continental shelf off the Norwegian coast – a hypothesis that has also previously been presented for G. lacustris, and parallels controversial suggestions of local refugia for other taxa in Scandinavia. The coastal population type only later could come into contact with Gammarus invading over the mountains from the south; these two population types now smoothly intergrade. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79, 523–542.     

Clinal colour variation within a panmictic population of tree squirrels,Tamiasciurus douglasii (Rodentia: Sciuridae), across an ecological gradient

Local adaptation occurs when a population in a heterogeneous environment experiences divergent ecological selection but only if selection is stronger than the homogenizing effects of gene flow. The forest environments of Oregon vary along a physical and biotic gradient from a wet, closed‐canopy forest near the coast to a drier open‐canopy forest eastward across the Cascade Mountains. The present study explores patterns of local adaptation in Douglas squirrels (Tamiasciurus douglasii) in relation to these transitions in forest structure and ecology. We test for the presence of morphological clines in relation to gene flow and, more specifically, whether any such character clines correspond with environmental clines. We sampled animals at six locations (10 specimens each) and evaluated environmental parameters across a 240‐km west‐to‐east transect. Population structure analysis of 18 microsatellite loci indicates a single, panmictic squirrel population across the entire transect. Coalescent‐based estimates show bidirectional gene flow at similar west–east intensities between squirrels in coastal and interior forests. Of the four skull traits examined, none shows a significant clinal transition. By contrast, ventral fur colour shows a strong clinal transition, from deep‐orange in coastal forest to whitish–yellow in the interior forest. This pattern of phenotypic divergence coincides with the gradient in tree‐canopy cover. Ventral fur colour of T. douglasii exemplifies a gradation of continuous phenotypic variation maintained despite ongoing gene flow in a panmictic population. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 536–546.     

Hybrid zone formation and contrasting outcomes of secondary contact over transects in common toads

Much progress in speciation research stems from documenting patterns of morphological and genetic variation in hybrid zones. Contrasting patterns of marker introgression in different sections of the contact can provide valuable insights on the relative importance of various evolutionary mechanisms maintaining species differences in the face of hybridization and gene flow and on hybrid zone temporal and spatial dynamics. We studied species interactions in the common toads Bufo bufo and B. spinosus in France and northwestern Italy using morphological and molecular data from the mitochondrial and nuclear genomes in an extensive survey, including two independent transects west and east of the Alps. At both, we found sharp, coincident and concordant nuclear genetic transitions. However, morphological clines were wider or absent and mtDNA introgression was asymmetric. We discuss alternative, nonexclusive hypotheses about evolutionary processes generating these patterns, including drift, selection, long‐distance dispersal and spatial shifts in hybrid zone location and structure. The distribution of intraspecific mtDNA lineages supports a scenario in which B. bufo held a local refugium during the last glacial maximum. Present‐day genetic profiles are best explained by an advance of B. spinosus from a nearby Iberian refugium, largely superseding the local B. bufo population, followed by an advance of B. bufo from the Balkans, with prongs north and south of the Alps, driving B. spinosus southwards. A pendulum moving hybrid zone, first northwards and then southwards, explains the wide areas of introgression at either side of the current position of the contact zones.     

Distribution and dispersal capacity of the Ponto-Caspian tubificid oligochaete Potamothrix moldaviensis Vejdovský et Mrázek, 1903 in the Baltic Sea Region

Over the last few centuries, several Ponto-Caspian tubificid oligochaetes have gradually dispersed from the Black Sea – Caspian Sea region to the north-west and west over Europe. The present world distribution comprising also the Great Lakes of North America clearly demonstrates that anthropochorous vectors of dispersal are involved. Passive transportation in the ballast water of ships has radically changed the possibilities of dispersal for many invertebrate species and has even made dispersal between continents possible. The construction of navigable canals has furthermore facilitated the crossing of watersheds and continents. Other likely vectors of longway dispersal for oligochaetes, as well as for other small-size aquatic invertebrates, are birds and mammals. The dispersal of the Potamothrixspecies is likely to have taken place in successive waves (three) with front-lines still on the move from the east to the west over the Baltic States and Scandinavia. The rheophilous species Potamothrix moldaviensishas presently reached – apart from the large rivers of Russia and many Central-European water bodies – also the Baltic States and south-eastern Sweden. Trajectories of dispersal demonstrate routes across the Baltic Sea – via the ballast water of ships. In the largest rivers of the Eastern Baltic Region (Neva, Daugava, Nemunas), downstream dispersal is the most likely way of transportation. P. moldaviensis together with P. heuscheri(second wave) and P. vejdovskyi(third wave) are presently forming front-lines running obliquely from the north-east to the south-west over south Sweden. In mesotrophic-eutrophic basins of eastern Lake Mälaren, the abundance as well as the species diversity of oligochaetes is particularly high wherever Ponto-Caspian Potamothrixspecies – often several species together – are involved.     

Speciation and evolution of eco‐climatic ranges in the intertropical African dung beetle genus,Diastellopalpus van Lansberge

We investigate how late Cenozoic orogenics and climatic change might have influenced the history of taxon diversification and current species ranges of an endemic, Afrotropical, insect genus. Diastellopalpus van Lansberge is a near basally‐derived taxon in the dung beetle tribe Onthophagini (Coleoptera: Scarabaeidae: Scarabaeinae) that has diversified into 32 known species primarily centred on intertropical forests. Basal dichotomies in both published and re‐analysed phylogenies divide the species into clades that are geographically centred either to the east or west of the south‐east highlands that underwent uplift from the Miocene. There is broad climatic overlap between many of the species but clear separation along a minimum spanning tree in ordinal space where they are divided into taxa with either lowland or highland centres of distribution. Observed spatial distributions of six defined species groups mostly differ from predicted climatic ranges, presumably as a result of historical constraints on species dispersal. A trend from dominance of montane or wet lowland forest associations in species lineages derived from more basal nodes (Groups A–C) to dominance of drier upland forest and moist woodland associations in species lineages derived from a more terminal node (Groups D–F) is perhaps linked to the stepped trend to cooler, dryer climate in the late Cenozoic. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 407–423.     

Phylogeographic structure in the gilgie (Decapoda: Parastacidae: Cherax quinquecarinatus): a south‐western Australian freshwater crayfish

The gilgie (Cherax quinquecarinatus) is among the more widespread of the six endemic south‐western Australian freshwater crayfish species. In the present study, the phylogeographic structure of the gilgie was investigated across its distribution to determine whether patterns reflected those identified earlier in a co‐distributed congeneric, the koonac (Cherax preissii). Gilgies were sampled from 20 localities, a 412‐bp fragment of the cytochrome c oxidase subunit I mitochondrial DNA gene was amplified from 75 individuals, and allozyme variation was assayed at nine loci. As in the koonac, three geographically‐restricted lineages were identified: from the north‐western, southern coastal, and intermediate/south‐western regions. Phylogeographic breaks appeared to be congruent with those in the koonac. The extent of genetic differentiation among lineages was comparable to that in the koonac, suggesting temporal congruence of the historical events responsible for the observed structure. A relaxed Bayesian molecular clock suggested that the major clades and lineages in each species diverged in the Late Miocene–Early Pliocene (4.0–9.6 Myr ago), possibly resulting from increasing pulses of aridity. The retrieval of almost‐identical phylogeographic structure in two co‐distributed species suggests that biogeographic regions can be more accurately defined in south‐western Australia. With the geographic fidelity of these lineages, the present data also provide evidence of the translocation of a single individual from the north‐west to the south coast. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 385–402.     

Assessing inter‐drainage connections: patterns of genetic diversity in an Iberian cyprinid fish

The phylogeography of Iberian freshwater fish species strongly reflects the geomorphological history of Iberian water drainages and formation of mountain ranges. In particular, the Iberian Central Massif limits two ichthyogeographical districts based on fish distribution assemblages: the Northwest district, which comprises all river basins north of the Central massif, and the Central‐west district, which comprises the Tejo and Sado basins. Despite this scenario, the cyprinid Pseudochondrostoma polylepis occurs in both the Tejo and Mondego rivers (one either side of the Estrela Mountains, in the western end of the Central Massif). By analysing the population structure and demographic history of this straight‐mouth nase, based on both mtDNA and microsatellites, we have found evidence of a relatively recent common origin for both Mondego and Tejo populations. Shared haplotypes and lack of divergent lineages for mitochondrial marker, high levels of admixture and common ancestry at the nuclear level, together with signatures of asymmetrical gene flow from Tejo to Mondego suggest a Mondego colonization through a founder event with an origin in Tejo. We suggest that this colonization might have resulted from the occurrence of river connections/captures between Mondego and Tejo headwater tributaries in the recent past. With this study we reinforce that local‐scale geomorphological events and the adaptation/dispersal ability of a species to new environments can have a major impact on its demographic history, colonization processes, and ultimately its distribution. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 656–669.     

A new cytochrome b phylogroup of the common vole (Microtus arvalis) endemic to the Balkans and its implications for the evolutionary history of the species

The phylogeographic architecture of the common vole, Microtus arvalis, has been well‐studied using mitochondrial DNA and used to test hypotheses relating to glacial refugia. The distribution of the five described cytochrome b (cyt b) lineages in Europe west of Russia has been interpreted as a consequence of postglacial expansion from both southern and central European refugia. A recently proposed competing model suggests that the ‘cradle’ of the M. arvalis lineages is in western central Europe from where they dispersed in different directions after the Last Glacial Maximum. In the present study, we report a new cyt b lineage of the common vole from the Balkans that is not closely related to any other lineage and whose presence might help resolve these issues of glacial refugia. The Balkan phylogroup occurs along the southern distributional border of M. arvalis in central and eastern Bosnia and Herzegovina, Montenegro, and eastern Serbia. Further north and west in Slovenia, Bosnia and Herzegovina, and Serbia, common voles belong to the previously‐described Eastern lineage, whereas both lineages are sympatric in one site in Bosnia and Herzegovina. The Balkan phylogroup most reasonably occupied a glacial refugium already known for various Balkan endemic species, in contrast to the recently proposed model. South‐east Europe is an absolutely crucial area for understanding the postglacial colonization history of small mammals in Europe and the present study adds to the very few previous detailed phylogeographic studies of this region. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 788–796.     

Phylogeography of the parasitic fly Batrachomyia in the Wet Tropics of north-east Australia, and susceptibility of host frog lineages in a mosaic contact zone

Parasites could differentially impact intraspecific host lineages due to genetic, phenotypic, ecological, or behavioural differences between the lineages, or the development of reproductive isolation between them. Batrachomyia (Diptera: Chloropidae) are flies that exclusively parasitize Australian frogs, and in the Wet Tropics rainforest of north‐east Australia larvae are largely restricted to the green‐eyed tree frog Litoria genimaculata (Anura: Hylidae). This frog species consists of two highly divergent genetic lineages that overlap in two nearby, but independent, contact zones. At one contact zone there has been extensive phenotypic divergence and speciation between the lineages whereas, at the other contact relatively lower levels of phenotypic divergence and reproductive isolation suggest that speciation has not occurred. In the present study we tested: (1) whether the deep phylogeographic divergence between northern and southern host populations is mirrored by congruent genetic structuring in the parasite populations and (2) whether the host lineages are differentially impacted by parasitism. We found that the two divergent frog lineages are parasitized by a single lineage of Batrachomyia, which exhibits strikingly little phylogeographic structuring. We found a significant difference in Batrachomyia prevalence between the host lineages at mixed lineage sites in both contact zones, with the magnitude and direction of this effect being consistent in both. The pattern did not differ between the two contacts even though recent phenotypic divergence and speciation has occurred between the lineages at one contact but not the other. Taken together, this suggests a fundamental difference in susceptibility between the genetically divergent host lineages. Using weight relative to body length as a measure of body condition, we found no differential impact of parasitism on the body condition of each host lineage, and no evidence that parasitism impacts the body condition of the host in general. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 593–603.     

The use of geostatistics and GIS for evolutionary history studies: the case of the nose‐horned viper (Vipera ammodytes) in the Balkan Peninsula

Geostatistics and geographical information system (GIS) procedures are novel techniques helpful for the identification of environmental correlates sustaining contact zones among subspecies or closely related species. In this paper, we tried to infer evolutionary scenarios for Vipera ammodytes across the European part of its distribution area using geostatistics and ecological niche‐based models, hence trying to solve several biogeographical questions that remained unclear after the application of classical morphological tools and genetic analyses. Eleven morphological traits from 871 vipers were analysed with geostatistics and ecological niche‐based modelling. Interpolation by kriging was used to generate surfaces of morphological variation, which were combined with spatial principal components analysis (SPCA). SPCA maps were used to test putative morphological differentiated groups with discriminant function analysis (DFA). Maximum entropy modelling and seven environmental variables were used to identify factors limiting the distribution of groups and areas for the potential occurrence of such groups. Three patterns of morphological variation were observed: a north‐west/south‐west cline, transition zones with steep clines of variation in a west–east arc, and particular character traits that disturbed the general cline. SPCA identified between three and nine putative population groups, of which three were supported by DFA. Areas of potential occurrence of these groups were coherent with the range of the three subspecies of V. ammodytes currently recognized. The distribution of all subspecies was mostly related to precipitation in the driest month. Areas of probable sympatry between subspecies are generally small and restricted. The main patterns of geographic variation of morphological characters for V. ammodytes were similar to the patterns obtained for Vipera latastei and Vipera monticola; the same environmental factors limit the distribution of differentiated groups of vipers in the Balkans and the Iberian Peninsula. The influence of humidity on the variation of morphological traits in spatially separated viper taxa from the two European peninsulas coincides with their phylogenetic relatedness. Geostatistics and GIS procedures were successful in the identification of environmental correlates sustaining contact zones among V. ammodytes subspecies in the Balkans. The same techniques should be applied for studying other parapatric forms and refugia regions. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 651–666.     

Phylogeography and population structure of European sea bass in the north‐east Atlantic

The European sea bass Dicentrarchus labrax represents a historically and commercially valuable species in the north‐east Atlantic, although the demographic history and the patterns of geographical structure of the species in the north‐east Atlantic remain poorly understood. The present study investigates the population genetic structure of sea bass in north‐western European waters, employing different genetic markers [a portion of the mitochondrial (mt)DNA control region and 13 nuclear microsatellites] aiming to unravel demographic history and population connectivity. The results obtained show a previously unrecognized pattern of population divergence at mtDNA, with three strikingly different lineages identified. Extant sea bass populations, including the Mediterranean lineage, derive from an Atlantic ancestor. A much increased number of nuclear microsatellite loci (comparatively to previous studies) still fail to detect biologically meaningful patterns of spatial genetic structuring in the North Atlantic. Past Pleistocene glacial and interglacial events and some degree of female philopatry might be at the basis of the current geographical separation of the Atlantic lineages that has been identified. Signatures of sudden demographic expansions are more evident in the most recent mitochondrial lineages, and their slight, yet significant, geographical segregation leads to the hypothesis that present‐day spawning grounds for European sea bass may still to some extent be linked to their most recent glacial refugia. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 364–377.     

Phylogeography of Rhinichthys cataractae (Teleostei: Cyprinidae): pre‐glacial colonization across the Continental Divide and Pleistocene diversification within the Rio Grande drainage

The longnose dace, Rhinichthys cataractae, is a primary freshwater fish inhabiting riffle habitats in small headwater rivers and streams across the North American continent, including drainages east and west of the Continental Divide. The mitochondrially encoded cytochrome b gene (1140 bp) and 2298–2346 bp of the nuclear‐encoded genes S7 and RAG1 were obtained from 87 individuals of R. cataractae (collected from 17 sites throughout its range) and from several close relatives. Phylogenetic analyses recovered a monophyletic R. cataractae species‐group that contained Rhinichthys evermanni, Rhinichthys sp. ‘Millicoma dace’, and a non‐exclusive R. cataractae. Within the R. cataractae species‐group, two well‐supported lineages were identified, including a western lineage (containing R. evermanni, R. sp. ‘Millicoma dace’ and individuals of R. cataractae from Pacific slope drainages) and an eastern lineage (containing individuals of R. cataractae from Arctic, Atlantic, and Gulf slope drainages). Within the eastern lineage of R. cataractae, two well‐supported groups were recovered: a south‐eastern group, containing individuals from the Atlantic slope, southern tributaries to the Mississippi River, and the Rio Grande drainage; and a north‐eastern group, containing individuals from the Arctic slope and northern tributaries to the Mississippi River. Estimates of the timing of divergence within the R. cataractae species‐group, combined with ancestral area‐reconstruction methods, indicate a separation between the eastern and western lineages during the Pliocene to early‐Pleistocene, with a direction of colonization from the west of the Continental Divide eastward. Within the southern portion of its range, R. cataractae likely entered the Rio Grande drainage during the Pleistocene via stream capture events between the Arkansas River (Mississippi River drainage) and headwaters of the Rio Grande. A close relationship between populations of R. cataractae in the Rio Grande drainage and the adjacent Canadian River (Mississippi River drainage) is consistent with hypothesized stream capture events between the Pecos (Rio Grande drainage) and Canadian rivers during the late‐Pleistocene. The population of R. cataractae in the lower Rio Grande may have become separated from other populations in the Rio Grande drainage (upper Rio Grande and Pecos River) and Canadian River during the late‐Pleistocene, well before initiation of recent and significant anthropogenic disturbance within the Rio Grande drainage. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 317–333.     

Gene flow between populations of two invertebrates in springs

1. Using allozymes, we analysed genetic structure of the freshwater gastropod Bythinella dunkeri and the freshwater flatworm Crenobia alpina. The two species are habitat specialists, living almost exclusively in springs. The sampled area in Hesse (Germany) covers a spatial scale of 20 km and includes two river drainages. From the biology of the two species we expected little dispersal along rivers. However, the possibility exists that groundwater provide suitable pathways for dispersal. 2. In B. dunkeri heterozygosity decreased from west to east. For some alleles we found clines in this geographic direction. These clines generated a positive correlation between geographic distance and genetic differentiation. Furthermore patterns of genetic variation within populations suggested that populations may have been faced with bottlenecks and founder effects. If populations are not in population genetic equilibrium, such founder effects would also explain the rather high amount of genetic differentiation between populations (10%). 3. For C. alpina the mean number of alleles decreased with increasing isolation of populations. Genetic differentiation between populations contributed 19% to the total genetic variation. Genetic differentiation was not correlated to geographic distance, but compared with B. dunkeri variability of pairwise differentiation between pairs of populations was higher in C. alpina. 4. Overall B. dunkeri appears to be a fairly good disperser, which may use groundwater as dispersal pathway. Furthermore populations seem to be not in equilibrium. In contrast C. alpina forms rather isolated populations with little dispersal between springs and groundwater seems to play no important role for dispersal.     

A multi-scale biogeographical analysis of Bambusa arnhemica, a bamboo from monsoonal northern Australia

Aims To identify the edaphic, environmental and historical factors influencing the patchy distribution of the semelparous bamboo Bambusa arnhemica F. Muell. at global, catchment and streambank scales. Location The entire range of B. arnhemica, a highly fire‐prone savanna matrix with generally infertile soils in the north‐west of the Northern Territory of Australia above the 1200 mm mean annual rainfall isohyet. Methods Distribution surveys were conducted by air, boat and on the ground. Plot data were collected throughout the range of the species. Results Bambusa arnhemica occurred predominantly in gallery forests on flood‐prone but nevertheless well‐drained and deep alluvial soils on sloping stream banks. It ranged widely along lentic watercourses from ephemeral headwater streams to the banks of major rivers and levees on the coastal floodplain. The species did not occur in savannas; savannas adjacent to B. arnhemica gallery forests were also flood‐prone and on deep alluvial soils, but were upslope on level ground. Bambusa arnhemica's infrequent non‐riparian occurrences were on a wide variety of substrates but generally on soils of moderate fertility and in coastal and/or rocky areas where at least partial topographic protection from fire is likely. Within and between catchments, the distribution of B. arnhemica was idiosyncratic, occurrence being almost always continuous downstream from highly variable ‘starting’ points to the poorly drained coastal floodplain. Main conclusions At local scales, B. arnhemica appears constrained by poor drainage and high fire‐frequencies. Enhanced soil fertility may increase its capacity to cope with fire. At the catchment and global scales, we propose that the distribution of B. arnhemica is the product of infrequent and as yet incomplete dispersal across and away from watercourses by seed that lacks specialized dispersal mechanisms, combined with passive dispersal along streams. From this we infer that B. arnhemica is neither a very recent, nor very ancient colonist from Asia. Bambusa arnhemica's circumscribed global distribution has no parallel amongst co‐occurring rain forest plants and may be the product of poor dispersal capacity and a substantial rock and floodplain barrier to the east. Limited dispersal capacity may be inextricably linked to local domination of space and the subsequent creation of regeneration space by parental death.     

Breach of the northern Rocky Mountain geoclimatic barrier: initiation of range expansion by the mountain pine beetle

Aim Our aim is to examine the historical breach of the geoclimatic barrier of the Rocky Mountains by the mountain pine beetle (Dendroctonus ponderosae Hopkins). This recent range expansion from west of the North American continental divide into the eastern boreal forest threatens to provide a conduit to naïve pine hosts in eastern North America. We examine the initial expansion events and determine potential mechanism(s) of spread by comparing spread patterns in consecutive years to various dispersal hypotheses such as: (1) meso‐scale atmospheric dispersal of insects from source populations south‐west of the Rocky Mountains in British Columbia (i.e. their historical range), (2) anthropogenic transport of infested plant material, and (3) spread of insect populations across adjacent stands via corridors of suitable habitat. Location British Columbia, Canada. Methods We explore potential mechanism(s) of invasion of the mountain pine beetle using spatial point process models for the initial 3 years of landscape‐level data collection, 2004–2006. Specifically, we examine observed patterns of infestation relative to covariates reflecting various dispersal hypotheses. We select the most parsimonious models for each of the initial 3 years of invasion using information criteria statistics. Results The initial range expansion and invasion of the beetle was characterized by aerial deposition along a strong north‐west to south‐east gradient, with additional aerial deposition and localized dispersal from persisting populations in following years. Main conclusions Following deposition of a wave front of mountain pine beetles parallel to the Rocky Mountains via meso‐scale atmospheric dispersal, the areas of highest intensity of infestations advanced up to 25 km north‐east towards jack pine (Pinus banksiana) habitat in a single year. There appeared to be no association between putative anthropogenic movement of infested materials and initial range expansion of the mountain pine beetle across the continental divide.     

Forest monkeys and Pleistocene refugia: a phylogeographic window onto the disjunct distribution of the Chlorocebus lhoesti species group

The reconstruction of evolutionary relationships among a group of closely‐related taxa provides a valuable window onto their biogeographic history. This is the first such molecular phylogenetic study to survey all three taxa of the Chlorocebus lhoesti species group, a group of Old World monkeys that includes C. lhoesti, Chlorocebus preussi, and Chlorocebus solatus. Representatives of each species were surveyed for two Y‐chromosomal genes, TSPY (～2240 bp) and SRY (～780 bp), and one X‐chromosomal intergenic region (～9300 bp) homologous to a portion of human Xq13.3. Maximum likelihood topologies inferred from these sequences confirm that the lhoesti group is monophyletic within the tribe Cercopithecini, as suggested by earlier karyotype studies. Within this group, C. lhoesti (Albertine region) and C. preussi (Cameroon, Nigeria, Bioko) cluster to the exclusion of C. solatus (Gabon). This phylogeographic pattern, evaluated in the context of Pleistocene glacial cycles and lhoesti group ecology, suggests: (1) the common ancestor of the group probably arose in west central Africa, (2) dispersal to the Albertine region is likely to have occurred during a glacial maximum, rather than an interglacial pluvial, and (3) this dispersal probably occurred via a path north of the Congo Basin. Divergence date calculations suggest C. solatus separated from the ancestral stock at ～2.1 Ma, whereas C. preussi and C. lhoesti bifurcated later, at ～0.5 Ma. Taken together, these evolutionary analyses draw attention to one period in the Pleistocene (～0.5 MYA) when a dispersal corridor suitable to montane taxa is likely to have connected the highlands of east central and west central Africa. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154 , 408–418.     

Lineage diversification and historical demography of a sky island salamander,Plethodon ouachitae,from the Interior Highlands

Sky islands provide ideal opportunities for understanding how climatic changes associated with Pleistocene glacial cycles influenced species distributions, genetic diversification, and demography. The salamander Plethodon ouachitae is largely restricted to high‐elevation, mesic forest on six major mountains in the Ouachita Mountains. Because these mountains are separated by more xeric, low‐elevation valleys, the salamanders appear to be isolated on sky islands where gene flow among populations on different mountains may be restricted. We used DNA sequence data along with ecological niche modelling and coalescent simulations to test several hypotheses related to diversifications in sky island habitats. Our results revealed that P. ouachitae is composed of seven well‐supported lineages structured across six major mountains. The species originated during the Late Pliocene, and lineage diversification occurred during the Middle Pleistocene in a stepping stone fashion with a cyclical pattern of dispersal to a new mountain followed by isolation and divergence. Diversification occurred primarily on an east–west axis, which is likely related to the east–west orientation of the Ouachita Mountains and the more favourable cooler and wetter environmental conditions on north slopes compared to south‐facing slopes and valleys. All non‐genealogical coalescent methods failed to detect significant population expansion in any lineages. Bayesian skyline plots showed relatively stable population sizes over time, but indicated a slight to moderate amount of population growth in all lineages starting approximately 10 000–12 000 years ago. Our results provide new insight into sky island diversifications from a previously unstudied region, and further demonstrate that climatic changes during the Pleistocene had profound effects on lineage diversification and demography, especially in species from environmentally sensitive habitats in montane regions.     

Landscape, habitat characteristics and the genetic population structure of two caddisflies

1. In a region of south‐eastern England, we investigated the hierarchical genetic structure of populations of two stream‐dwelling caddisflies (Trichoptera: Polycentropodidae) with contrasting distributions: Plectrocnemia conspersa inhabits numerous small, patchily distributed seeps and streams, while the confamilial Polycentropus flavomaculatus is found in fewer but larger streams and rivers. We also contrasted the genetic structure of P. conspersa in the lowland south‐east with that in an upland region in the north west. 2. Microsatellite genotypes were obtained from samples of both species taken from a ‘core area’ and at sites 15, 40 and 100 km from this core (two regions for P. conspersa, totalling 45 sites and 1405 larvae; one region for P. flavomaculatus, totalling 10 sites and 269 larvae). 3. The genetic structure of P. conspersa differed in the two regions. In the upland north‐west, significant genetic differentiation was observed at a spatial scale of around 40 km from the core, while there was no structure in the lowland south‐east up to around 100 km. Areas of high altitude did not appear directly to reduce gene flow, whereas other potential landscape barriers, including particular geological formations, large urban areas and the sea had a pronounced effect. 4. Weak genetic differentiation in P. conspersa across large distances, particularly in the lowland south‐east, suggests that it disperses strongly, facilitating gene flow within and between catchments. Conversely, for P. flavomaculatus we found strong genetic differentiation between almost all sites, suggesting that dispersal is much more limited. 5. Greater dispersal in the patchily distributed P. conspersa than in P. flavomaculatus, which occupies larger and presumably more persistent habitats, could be a general feature of other similarly distributed aquatic insects. While higher relief is potentially a partial barrier to dispersal, P. conspersamust have effective gene flow through such apparently inhospitable terrain, perhaps attributable to dispersal between neighbouring small and ephemeral populations. Indeed, its exploitation of headwaters and seeps requires the ability to disperse between such sites. Apparently it cannot, however, overcome more continuous barriers, consisting of large tracts of landscape with few habitable larval sites. Such landscapes, including those created by humans, may have a stronger effect on population connectivity and colonization in the longer term.     

Contrasting insights provided by single and multispecies data in a regional comparative phylogeographic study

Many single‐species freshwater phylogeographic studies have been carried out in south‐east Queensland; however comparative phylogeography requires multiple lines of evidence to infer deep, significant relationships between landscape and biota. The present study aimed to test conclusions resulting from single taxon studies in a multispecies comparative framework: (1) how influential are river basins in the genetic structure of freshwater species; (2) are there biogeographic frontiers between groups of basins; and (3) could deep intraspecific lineages be explained by a single event? New and existing data from 33 freshwater species (23 fishes and 10 crustaceans) were combined, and both standard single‐species analyses (haplotype networks, genetic distances, Φ_ST) and multispecies methods (hierarchical ABC) were carried out for 1814 sequences from eight basins. More than half of the species displayed a high phylogeographic structure and contained at least two distinct lineages. Almost all of the lineage divergences displayed an element of north/south geographic breaks, with the most influential boundary being between the Mary and Brisbane rivers. Of the 11 basin‐pair multispecies coalescent analyses, four implied a single divergence as being most likely. A regional analysis of deep lineages within 16 taxon‐pairs resulted in a strongly supported inference of a single divergence, probably dating to the Pleistocene. Basin boundaries are a key determinant of phylogeographic patterns for most of these freshwater species, although the specific biogeographic relationship between basins often varies depending on the species. There are a number of influential biogeographic frontiers, with the Brisbane‐Mary being the most important. The finding that a single event may be responsible for multiple deep lineages across the region implies that a highly influential climate change event may have been detected. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 554–569.