Phylogeography and sympatric differentiation of the Arctic charr Salvelinus alpinus (L.) complex in Siberia as revealed by mtDNA sequence analysis

Sequence variation in the mtDNA control region of Arctic charr Salvelinus alpinus and Dolly Varden Salvelinus malma from 56 Siberian and North American populations was analysed to assess their phylogeographic relationships and the origins of sympatric forms. Phylogenetic trees confirm the integrity of phylogroups reported in previous mtDNA studies except that the Siberian group does not separate as a single cluster. Haplotype network analysis indicates the proximity of Siberian and Atlantic haplotypes. These are considered as one Eurasian group represented by the Atlantic, east Siberian (interior Siberia including Transbaikalia, Taimyr) and Eurosiberian (Finland, Spitsbergen, Taimyr) sub-groups. Salvelinus alpinus with presumably introgressed Bering group (malma) haplotypes were found along eastern Siberian coasts up to the Olenek Bay and the Lena Delta region, where they overlap with the Eurasian group and in the easternmost interior region. It is proposed that Siberia was colonized by S. alpinus in two stages: from the west by the Eurasian group and later from the east by the Bering group. The high diversity of Eurasian group haplotypes in Siberia indicates its earlier colonization by S. alpinus as compared with the European Alps. This colonization was rapid, proceeded from a diverse gene pool, and was followed by differential survival of ancestral mtDNA lineages in different basins and regions, and local mutational events in isolated populations. The results presented here support a northern origin of Transbaikalian S. alpinus , the dispersion of S. alpinus to the Lake Baikal Basin from the Lena Basin, segregation of S. alpinus between Lena tributaries and their restricted migration over the divides between sub-basins. These results also support sympatric origin of intralacustrine forms of S. alpinus .     

Mitochondrial DNA variation of Salvelinus species found in Finland

Mitochondrial DNA (mtDNA) was purified from the Arctic charr, Salvelinus alpinus , the brook charr, Salvelinus fontinalis , and the lake charr, Salvelinus namaycush , and digested with restriction enzymes Ava II, Hinf I, Eco R V, Pst I and Xba I. Two Arctic charr samples were from natural populations and they represented two different morphotypes of Arctic charr. All other studied populations were hatchery maintained. Eight additional restriction enzymes and double digestions were employed to study morphotypes of Arctic charr. We distinguished two morphotypes with restriction enzyme Nci I. Sequence divergence among mtDNA types was 2.9–3.8% between S. alpinus and S. fontinalis , 3.4–4.6% between S. alpinus and S. namaycush , and 4.7–5.3% between S. fontinalis and S. namaycush . lntraspecific variation was lowest in Arctic charr, the average of nucleon diversity for three populations being 0.179, while for brook charr and for lake charr nucleon diversity was 0.334 and 0.550, respectively. According to the number of mtDNA types, it is obvious that introduction to Finland and hatchery propagation have not greatly affected the mtDNA variation of brook charr or lake charr.     

The ghost of hybrids past: fixation of arctic charr (Salvelinus alpinus) mitochondrial DNA in an introgressed population of lake trout (S. namaycush)

Complete fixation of arctic charr ( Salvelinus alpinus ) mitochondrial DNA (mtDNA) was observed in a southern Québec population of lake trout ( S. namaycush ). This introgressed population otherwise appeared to be normal with regard to lake trout morphology and three species-diagnostic microsatellite loci. Arctic charr do not occur in the area, suggesting that the hybridization event was prehistoric. Of several possible hypotheses, the most plausible explanation for this aberrant population is that hybridization occurred in situ soon after deglaciation, with repeated backcrossing of hybrids with lake trout. Fixation of S. alpinus mtDNA in the population may have occurred either by chance (drift) or selection, although indirect evidence and data from similarly introgressed brook trout ( S. fontinalis ) populations in the region suggest that selection favouring the S. alpinus mitochondrial type and/or associated nuclear genes may have been involved.     

Global major histocompatibility Class II β (mh-IIβ)-polymorphism in Arctic charr Salvelinus alpinus

This study explored the use of the gene encoding the β subunit of the major histocompatibility (MH) receptor as a population marker in Arctic charr Salvelinus alpinus. The use of this polymorphic marker allowed differentiation of the S. alpinus lineages previously defined using mitochondrial DNA (mtDNA) but also allowed differentiation between the populations studied within those lineages. The majority of the variation observed here occurred prior to the last glaciation event. Nevertheless, all S. alpinus populations were differentiated using both MH Class II β (mh-IIβ) sequences and allelic frequencies. The fact that all the populations studied presented high rates of non-synonymous: synonymous substitutions and high levels of interpopulation variation, suggested mh-IIβ as an ideal marker to assess differentiation among S. alpinus populations in ways that may represent divergence both by genetic drift and natural adaptation to the local environment.     

Microsatellite and mitochondrial DNA assessment of population structure and stocking effects in Arctic charr Salvelinus alpinus (Teleostei: Salmonidae) from central Alpine lakes

Despite geographical isolation and widespread phenotypic polymorphism, previous population genetic studies of Arctic charr, Salvelinus alpinus , have detected low levels of intra- and interpopulation variation. In this study, two approaches were used to test the generality of low genetic diversity among 15 Arctic charr populations from three major drainages of the central Alpine region of Europe. First, a representative subsample of each drainage was screened by PCR–RFLP analysis of mtDNA using 31 restriction enzymes. All individuals but one shared an identical haplotype. In contrast, microsatellite DNA variation revealed high levels of genetic diversity within and among populations. The number of alleles per locus ranged from six to 49, resulting in an overall expected heterozygosity from 0.72 ± 0.09 to 0.87 ± 0.04 depending on the locus. Despite evidence for fish transfers among Alpine charr populations over centuries, genetic diversity was substantially structured, as revealed by hierarchical Φ statistics. Eighteen per cent of total genetic variance was apportioned to substructuring among Rhône, Rhine, and Danube river systems, whereas 19% was due to partitioning among populations within each drainage. Cluster analyses corroborated these results by drainage-specific grouping of nonstocked populations, but also revealed damaging effects of stocking practices in others. However, these results suggest that long-term stocking practices did not generally alter natural genetic partitioning, and stress the importance of considering genetic diversity of Arctic charr in the Alpine region for sound management. The results also refute the general view of Arctic charr being a genetically depauperate species and show the potential usefulness of microsatellite DNAs in addressing evolutionary and conservation issues in this species.     

Phylogeography and postglacial dispersal of arctic charr Salvelinus alpinus in North America

Restriction fragment length polymorphism analysis of mitochondrial DNA (mtDNA) was used to reconstruct postglacial dispersal routes of arctic charr Salvelinus alpinus in North America. Twelve of 35 restriction enzymes detected polymorphisms among representative populations, revealing two distinct lineages with an estimated nucleotide divergence of 1.32%. Subsequent screening of 869 fish from 54 populations with four diagnostic restriction enzymes showed that these lineages have largely allopatric distributions, suggesting their dispersal from separate northern and eastern glacial refugia. In addition, geographical and genetic structure among eastern populations suggested the existence of a second eastern refuge. Among the three lineages, the most divergent (Arctic) lineage occurred from Alaska east to northern Labrador. Quebec, New Brunswick, and New England were colonized by a second (Laurentian) lineage, and Labrador by a third group. Contact between refugial groups was only detected in two Labrador populations. The Arctic lineage was highly differentiated from eastern North American and European haplotypes, and probably diverged during the early Pleistocene. By contrast, the Laurentian and Labrador groups were similar to Old World charr, suggesting a shared ancestry during the mid-Pleistocene. In addition, the close relationship between Labrador and Laurentian charr indicates their probable divergence during the Wisconsinan glaciation.     

Mitochondrial DNA diversity among four sympatric morphs of Arctic charr, Salvelinus alpinus L., from Thingvallavatn, Iceland

Restriction fragment length polymorphisms in mitochondrial DNA (mtDNA) were examined in progeny of four sympatric morphs of Arctic charr ( Salvelinus alpinus L.) from Thingvallavatn, Iceland. The mtDNA analysis with 46 hexanucleotide restriction enzymes indicates that the Thingvallavatn morphs are very closely related. Sequence divergence was less than 0.2% between any of the five clones detected. Although not significant, the topology of the mtDNA UPGMA dendogram was similar to that from a previous allozyme survey. Icelandic Arctic charr show greater affinity to charr from the British Isles than those from North America supporting their current taxonomic distinction.     

Evolutionary history of the European whitefish Coregonus lavaretus (L.) species complex as inferred from mtDNA phylogeography and gill-raker numbers

We compared mitochondrial DNA and gill-raker number variation in populations of the European whitefish Coregonus lavaretus (L.) species complex to illuminate their evolutionary history, and discuss mechanisms behind diversification. Using single-strand conformation polymorphism (SSCP) and sequencing 528 bp of combined parts of the cytochrome oxidase b (cyt b) and NADH dehydrogenase subunit 3 (ND3) mithochondrial DNA (mtDNA) regions, we documented phylogeographic relationships among populations and phylogeny of mtDNA haplotypes. Demographic events behind geographical distribution of haplotypes were inferred using nested clade analysis (NCA) and mismatch distribution. Concordance between operational taxonomical groups, based on gill-raker numbers, and mtDNA patterns was tested. Three major mtDNA clades were resolved in Europe: a North European clade from northwest Russia to Denmark, a Siberian clade from the Arctic Sea to southwest Norway, and a South European clade from Denmark to the European Alps, reflecting occupation in different glacial refugia. Demographic events inferred from NCA were isolation by distance, range expansion, and fragmentation. Mismatch analysis suggested that clades which colonized Fennoscandia and the Alps expanded in population size 24 500-5800 years before present, with minute female effective population sizes, implying small founder populations during colonization. Gill-raker counts did not commensurate with hierarchical mtDNA clades, and poorly with haplotypes, suggesting recent origin of gill-raker variation. Whitefish designations based on gill-raker numbers were not associated with ancient clades. Lack of congruence in morphology and evolutionary lineages implies that the taxonomy of this species complex should be reconsidered.     

Phylogeography of white-spotted Charr (Salvelinus leucomaenis) inferred from mitochondrial DNA sequences

The white-spotted charr (Salvelinus leucomaenis) is a coldwater-adapted fish distributed in far-eastern Asia. To assess phylogeographic patterns of this species over most of its range in the Japanese archipelago and Sakhalin Island, Russia, we examined nucleotide sequences of the mitochondrial DNA (mtDNA) cytochrome b region (557 bp) in 141 individuals from 50 populations. A total of 33 (5.5%) nucleotide positions were polymorphic and defined 29 haplotypes. Phylogenetic analysis assigned the observed haplotypes to four main clades, which were characterized by the idiosyncrasies and discontinuity of geographic distributions. The nested clade analyses revealed that the geographical distribution patterns of some haplotypes and clades were explained by historical event such as past fragmentation. Although substantial genetic differentiation was found among the four main clades, their geographic distributions overlapped extensively in several regions. Since white-spotted charr can potentially use both freshwater and marine environments, coexistence among different lineages can be attributed to secondary contact through range expansion by migratory individuals during multiple glacial periods after interglacial isolation. Finally, our data demonstrate that the current subspecies designation does not reflect the phylogeography of this species based on mtDNA analysis. Hierarchical analysis (AMOVA) also showed that genetic variation was far more pronounced within subspecies than among subspecies (i.e., among discrete regions). These results suggest that each population, rather than each subspecies, must be treated as an evolutionarily significant unit.     

Evolution of adaptive diversity and genetic connectivity in Arctic charr (Salvelinus alpinus) in Iceland

The ecological theory of adaptive radiation predicts that the evolution of phenotypic diversity within species is generated by divergent natural selection arising from different environments and competition between species. Genetic connectivity among populations is likely also to have an important role in both the origin and maintenance of adaptive genetic diversity. Our goal was to evaluate the potential roles of genetic connectivity and natural selection in the maintenance of adaptive phenotypic differences among morphs of Arctic charr, Salvelinus alpinus, in Iceland. At a large spatial scale, we tested the predictive power of geographic structure and phenotypic variation for patterns of neutral genetic variation among populations throughout Iceland. At a smaller scale, we evaluated the genetic differentiation between two morphs in Lake Thingvallavatn relative to historically explicit, coalescent-based null models of the evolutionary history of these lineages. At the large spatial scale, populations are highly differentiated, but weakly structured, both geographically and with respect to patterns of phenotypic variation. At the intralacustrine scale, we observe modest genetic differentiation between two morphs, but this level of differentiation is nonetheless consistent with strong reproductive isolation throughout the Holocene. Rather than a result of the homogenizing effect of gene flow in a system at migration-drift equilibrium, the modest level of genetic differentiation could equally be a result of slow neutral divergence by drift in large populations. We conclude that contemporary and recent patterns of restricted gene flow have been highly conducive to the evolution and maintenance of adaptive genetic variation in Icelandic Arctic charr.     

Population structure and history of a phenotypically variable teiid lizard (Ameiva chrysolaema) from Hispaniola: the influence of a geologically complex island

Ameiva chrysolaema is distributed across the island of Hispaniola in the West Indies. The species is restricted to dry lowlands between major mountain ranges and along the southern and eastern coasts. Phylogenetic and phylogeographic analyses of mtDNA sequence variation from 14 sampling localities identify at least three independent evolutionary lineages, separated from one another by major mountain ranges. Nested clade phylogeographic analysis (NCPA) suggests a complex history of population fragmentation, consistent with geological evidence of seawater incursions into the Azua and Enriquillo basins during the Pliocene/Pleistocene (approximately 1.6 mya). Significantly negative Fu's F(S) values and parameters of mismatch distributions suggest that formerly fragmented populations have recently expanded their ranges. Significantly large average population clade distances (APCD) for two sampling localities in the Azua basin suggest secondary contact at these localities of previously separated populations. The distribution of haplotypes among polymorphic populations of A. chrysolaema suggests that variation in dorsal pattern represents a polymorphism within evolutionary lineages. Ameiva leberi is ecologically indistinguishable from and syntopic with A. chrysolaema. Genetic data suggest that A. leberi is a junior synonym of A. chrysolaema.     

On the Origin of the Lacustrine Charr <Emphasis Type="Italic">Salvelinus alpinus</Emphasis> Complex from the Kolyma and Sea of Okhotsk Basins

Morphological and genetic characteristics are used for the analysis of the origin of charrs from the lakes of the Kolyma basin (Chuk, Gek, Gulyaevskoe-4, Gulyaevskoe-6, and Lenkovoe) and the Sea of Okhotsk basin (Lake Chistoe). In addition to these samples, the fragments of the control region of mitochondrial DNA (CR mtDNA, 550-bp) and exon 2 of recombination activating gene 1 (RAG1, 899-bp) are sequenced in the charrs from lakes Dzhul’etta and Cherechen’ (Kolyma basin) and lakes Elikchanskie, Bol’shoi Mak-Mak, Ueginskoe (Sea of Okhotsk basin), Ulakhan-Silyan-Kyuel’ (Yana River basin) as well as in northern Dolly Varden from the Kamchatka River. The charr from Lake Chistoe is represented by northern Dolly Varden. In the charrs from lakes Chuk, Gek, Gulyaevskoe-4, Gulyaevskoe-6, Lenkovoe, Cherechen’, Elikchanskie, Bol’shoi Mak-Mak, and Ueginskoe, the haplotypes of mtDNA of the Bering group (a haplogroup of northern Dolly Varden) are revealed. Based on the morphological and RAG1 data, populations of charrs from these lakes belong to the Salvelinus alpinus complex. A transfer of mtDNA of northern Dolly Varden to the charrs from the Kolyma and Sea of Okhotsk basins occurred during the last postglacial expansion and subsequent hybridization. Based on the results of morphological and genetic analysis, the charrs from the Kolyma and Sea of Okhotsk basins cannot be unambiguously referred to the phylogenetic groups of Eurasian Arctic charr or Taranets charr. The presence of mtDNA haplotypes of the Arctic group (a haplogroup of Taranets charr) in the populations of lakes Dzhul’etta, Maksi, and Ueginskoe shows a possibility of their belonging to the group of Taranets charr.     

Speciation and genetic divergence of three species of charr from ancient Lake El'gygytgyn (Chukotka) and their phylogenetic relationships with other representatives of the genus Salvelinus

The diversity of phenotypically different and often reproductively isolated lacustrine forms of charrs of the genus Salvelinus represents a substantial problem for taxonomists and evolutionary biologists. Based on the analysis of variability of ten microsatellite loci and two fragments of mitochondrial DNA (control region and cyt‐b gene), the evolutionary history of three charr species from Lake El'gygytgyn was reconstructed, and phylogenetic relationships between the main representatives of the genus were revealed. Three species from Lake El'gygytgyn were strongly reproductively isolated. Long‐finned charr described previously as Salvethymus svetovidovi, an ancient endemic form in the lake, originated 3.5 Mya (95% Bayesian credible intervals: 1.7, 6.1). Placement of this species in the phylogenetic tree of Salvelinus was not determined strictly, but it should be located in the basal part of the clade Salvelinus alpinus – S. malma species complex. The origin of small‐mouth charr S. elgyticus and Boganida charr S. boganidae in Lake El'gygytgyn was related to allopatric speciation. Their ancestors were represented by two glacial lineages of Taranets charr S. alpinus taranetzi from Asia. In Lake El'gygytgyn, these lineages entered into secondary contact postglacially. A revision of the main phylogenetic groups within the Salvelinus alpinus – S. malma complex is conducted. The Boganida charrs from Lakes El'gygytgyn and Lama (Taimyr) belong to different phylogenetic groups of Arctic charr and should not be regarded as a single species S. boganidae. Using the charrs from Lakes El'gygytgyn and Lama as a case study, we show that a model of sympatric speciation, which seemed more probable based on previous empirical evidence, was rejected by other data.     

Genetic architecture of body weight,condition factor and age of sexual maturation in Icelandic Arctic charr (<Emphasis Type="Italic">Salvelinus alpinus</Emphasis>)

The high commercial value from the aquaculture of salmonid fishes has prompted many studies into the genetic architecture of complex traits and the need to identify genomic regions that have repeatable associations with trait variation both within and among species. We searched for quantitative trait loci (QTL) for body weight (BW), condition factor (CF) and age of sexual maturation (MAT) in families of Arctic charr (Salvelinus alpinus) from an Icelandic breeding program. QTL with genome-wide significance were detected for each trait on multiple Arctic charr (AC) linkage groups (BW: AC-4, AC-20; CF: AC-7, AC-20, AC-23, AC-36; MAT: AC-13/34, AC-39). In addition to the genome-wide significant QTL for both BW and CF on AC-20, linkage groups AC-4, AC-7, AC-8, and AC-16 contain QTL for both BW and CF with chromosome-wide significance. These regions had effects (albeit weaker) on MAT with the exception of the region on AC-8. Comparisons with a North American cultured strain of Arctic charr, as well as North American populations of Atlantic salmon (Salmo salar), and rainbow trout (Oncorhynchus mykiss), reveal some conservation in QTL location and structure, particularly with respect to the joint associations of QTL influencing BW and CF. The detection of some differences in genetic architecture between the two aquaculture strains of Arctic charr may be reflective of the differential evolutionary histories experienced by these fishes, and illustrates the importance of including different strains to investigate genetic variation in a species where the intent is to use that variation in selective breeding programs.     

Phylogeographic signal variation in mitochondrial DNA among geographically isolated grassland butterflies

Aim We surveyed mitochondrial DNA (mtDNA) sequence variation among regionally isolated populations of 10 grassland‐associated butterfly species to determine: (1) the utility of phylogeographic comparisons among multiple species for assessing recent evolutionary patterns, and (2) the respective roles of isolation attributable to range disjunction versus isolation attributable solely to geographic distance in establishing divergence patterns. Location The Peace River grasslands of northern Alberta and British Columbia, Canada, which are isolated by 300+ km from similar communities to the south. Methods We sequenced mtDNA (1420 bp of cytochrome c oxidase subunit I) from five grassland‐restricted butterfly species that have geographically disjunct populations and from five ecologically broader species that have more continuous distributions across the same regions. Using analysis of molecular variance (AMOVA), Mantel and partial Mantel tests, and haplotype networks, we compared population structure within and between species in order to assess the validity of single‐species phylogeographic characterizations. We then contrasted variance components between disjunct and continuously distributed species to assess whether divergences were correlated more with disjunction or with geographic distance. Results Single‐species analyses varied substantially within both the disjunct and the continuous groups. One species in each of these groups had mtDNA with unusually deep intraspecific mitochondrial lineage divergences. On the whole, however, the five species with disjunct ranges exhibited greater divergence between geographically distant populations than did the five species with continuous distributions. Comparison of variance components between disjunct and continuous species indicated that isolation attributable only to geographic distance was responsible for up to half of the total sequence variation between disjunct populations of grassland butterflies. Main conclusions Our findings show that single‐species phylogeographic analyses of post‐Pleistocene butterfly distributions are inadequate for characterizing regional biogeographic divergence histories. However, comparison of mtDNA sequence divergences between groups of disjunct and continuously distributed species can allow isolation attributable to range interruption to be quantitatively distinguished from isolation attributable solely to gene flow attenuation over the same geographic area.     

BIOGEOGRAPHY OF A WIDESPREAD FRESHWATER CRUSTACEAN: PSEUDOCONGRUENCE AND CRYPTIC ENDEMISM IN THE NORTH AMERICAN DAPHNIA LAEVIS COMPLEX

The lack of morphological variation in many freshwater invertebrates over vast distances has been cited as evidence for their frequent, long-distance dispersal. This scenario implies that vicariance will be an insignificant determinant of species distributions or diversity. We carried out a phylogeographic and population genetics study of one widespread crustacean group, the North American Daphnia laevis complex. Allozyme and sequence variation of two mtDNA genes (12S and 16S rRNA) clearly indicates the existence of five morphologically cryptic, largely allopatric groups (Daphnia dubia, D. laevis laevis, D. laevis gessneri, D. magniceps magniceps, and D. magniceps pacifica ssp. n.). Within each of these groups, there is weak or no genetic differentiation over large geographic areas suggesting their recent long-distance dispersal. The present-day distributions and phylogeography of the regional groups suggests the occurrence of both deep and shallow vicariance events. Although divergence times from mtDNA sequences do indicate both deep and shallow divergences, these estimates are incongruent with their proposed vicariance times. The results show that even within closely related freshwater invertebrates, a complex biogeography exists, whose analysis is made difficult by long-distance dispersal, cryptic endemism, and pseudocongruence.     

Genetic differentiation of charrs in the Russian north and far east

Genetic differences and relationships within charrs Salvelinus alpinus , northern and southern S. malma, S. taranetzi, S. levanidovi and S. leucomaenis , were studied by examination of 31–35 allozyme loci and PCR-RFLP analysis of mtDNA segment (about 2600 bp) including the cytochrome b gene and D-loop. Data for mtDNA were also obtained for samples of S. drjagini, S. albus and for European samples of S. alpinus. Generally allozyme and mtDNA segment analyses produced similar pictures of genetic divergence and relationships. The southern S. malma exhibited the greatest genetic variability (allozyme heterozygosity and mtDNA haplotype diversity). S. alpinus, S. malma, S. levanidovi and S. leucomaenis had fixed differences from one another at various allozyme loci, and differed in fixed (but polymorphic in S. malma ) individual mtDNA haplotypes produced with MspI restrictase. Such genetic individuality is typical of distinct taxa. S. taranetzi is closest genetically to allopatric S. alpinus , but exhibited fixed differences from the northern S. malma in sympatry. In all samples of S. alpinus the only mtDNA haplotype was shared with S. drjagini. S. albus shared its single haplotype with the northern S. malma from the same locality. S. leucomaenis is differentiated from the other species to the greatest extent, possibly reflecting an early evolutionary divergence. Some evolutionary and taxonomic implications of the genetic relationships of charrs studied are discussed.     

MATRIARCHAL POPULATION GENETIC STRUCTURE IN AN AVIAN SPECIES WITH FEMALE NATAL PHILOPATRY

We employ mitochondrial (mt) DNA markers to examine the matrilineal component of population genetic structure in the snow goose Chen caerulescens. From banding returns, it is known that females typically nest at their natal or prior nest site, whereas males pair with females on mixed wintering grounds and mediate considerable nuclear gene flow between geographically separate breeding colonies. Despite site philopatry documented for females, mtDNA markers show no clear distinctions between nesting populations across the species' range from Wrangel Island, USSR to Baffin Island in the eastern Canadian Arctic. Two major mtDNA clades (as well as rare haplotypes) are distributed widely and provide one of the few available examples of a phylogeographic pattern in which phylogenetic discontinuity in a gene tree exists without obvious geographic localization within a species' range. The major mtDNA clades may have differentiated in Pleistocene refugia, and colonized current nesting sites through recent range expansion via pulsed or continual low-level dispersal by females. The contrast between results of banding returns and mtDNA distributions in the snow goose raises general issues regarding population structure: direct contemporary observations on dispersal and gene flow can in some cases convey a misleading impression of phylogeographic population structure, because they fail to access the evolutionary component of population connectedness; conversely, geographic distributions of genetic markers can provide a misleading impression of contemporary dispersal and gene flow because they retain a record of evolutionary events and past demographic parameters that may differ from those of the present. An understanding of population structure requires integration of both evolutionary (genetic) and contemporary (direct observational) perspectives.     

Limited Phylogeographic Signal in Sex-Linked and Autosomal Loci Despite Geographically,Ecologically, and Phenotypically Concordant Structure of mtDNA Variation in the Holarctic Avian Genus Eremophila

Phylogeographic studies of Holarctic birds are challenging because they involve vast geographic scale, complex glacial history, extensive phenotypic variation, and heterogeneous taxonomic treatment across countries, all of which require large sample sizes. Knowledge about the quality of phylogeographic information provided by different loci is crucial for study design. We use sequences of one mtDNA gene, one sex-linked intron, and one autosomal intron to elucidate large scale phylogeographic patterns in the Holarctic lark genus Eremophila. The mtDNA ND2 gene identified six geographically, ecologically, and phenotypically concordant clades in the Palearctic that diverged in the Early - Middle Pleistocene and suggested paraphyly of the horned lark (E. alpestris) with respect to the Temminck''s lark (E. bilopha). In the Nearctic, ND2 identified five subclades which diverged in the Late Pleistocene. They overlapped geographically and were not concordant phenotypically or ecologically. Nuclear alleles provided little information on geographic structuring of genetic variation in horned larks beyond supporting the monophyly of Eremophila and paraphyly of the horned lark. Multilocus species trees based on two nuclear or all three loci provided poor support for haplogroups identified by mtDNA. The node ages calculated using mtDNA were consistent with the available paleontological data, whereas individual nuclear loci and multilocus species trees appeared to underestimate node ages. We argue that mtDNA is capable of discovering independent evolutionary units within avian taxa and can provide a reasonable phylogeographic hypothesis when geographic scale, geologic history, and phenotypic variation in the study system are too complex for proposing reasonable a priori hypotheses required for multilocus methods. Finally, we suggest splitting the currently recognized horned lark into five Palearctic and one Nearctic species.     

Mitochondrial DNA phylogeography in northern grasshopper mice (Onychomys leucogaster) — the influence of Quaternary climatic oscillations on population dispersion and divergence

The details of mitochondrial DNA (mtDNA) phylogenetic structure of the northern grasshopper mouse Onychomys leucogaster were examined using populations from a postulated area of endemism that includes three arid regions (Colorado Plateaus, Interior Plains, and Wyoming Basins) in western North America. Fifteen tetra- and heptanucleotide restriction enzymes were used to assay restriction-site variation in a 2150-bp PCR-amplified fragment of mtDNA representing the ND2 and part of the COI gene regions. A total of 18 mtDNA haplotypes were detected. Although overall genetic divergence among these haplotypes was low (average = 1.1%), phylogeographic structuring was apparent. Notably, a clear phylogenetic split separated one group of haplotypes restricted to the Wyoming Basins from all others. This phylogenetic split was further corroborated by examination of nucleotide sequence variation from a 270-bp stretch of the mtDNA cytochrome b gene. Overall geographic and phylogenetic patterns suggest a complex history of geographic structuring and subsequent mixing of populations of grasshopper mice throughout the late Pleistocene. These patterns of variation are evaluated relative to alternative hypotheses about biotic responses to Quaternary climatic oscillations in western North American arid regions.