THE GEOGRAPHY OF MITOCHONDRIAL DNA VARIATION,POPULATION STRUCTURE,HYBRIDIZATION, AND SPECIES LIMITS IN THE FOX SPARROW (PASSERELLA ILIACA)

Geographic variation in mitochondrial DNA (mtDNA) restriction sites was studied in the fox sparrow (Passerella iliaca). Seventy-eight haplotypes were found. Haplotypes fall into four phylogeographic groups that correspond to groups defined by plumage characters. The geographic distribution of these four groups does not appear congruent with mtDNA patterns in other vertebrates. Within each group, there is little geographic variation in mtDNA restriction sites, although there is geographic variation in plumage coloration and body size. The evolution of mtDNA diversity in fox sparrows seems best explained by vicariant events rather than isolation by distance. The mtDNA evidence suggests that Passerella megarhyncha and Passerella schistacea, two nonsister taxa that occur in western North America, have independently undergone bottlenecks. Hybridization is limited between all pairs of taxa except P. megarhyncha and P. schistacea, where mtDNA evidence suggests a narrow contact zone along the interface of the Great Basin and Sierra Nevada/Cascades. Morphometric characters intergrade over a broader area, suggesting that different processes are responsible for the two gradients. The occurrence of limited backcrossing among taxa suggests that cytoplasmic-nuclear incompatibility is lacking. The number of biological species would range from one to four, depending on the degree of hybridization tolerated. The mtDNA and plumage characters suggest four phylogenetic species: P. iliaca, P. megarhyncha, P. unalaschcensis, and P. schistacea.     

Congruence, consensus, and the comparative phylogeography of codistributed species in California

Comparative phylogeography has emerged as a means of understanding the spatial patterns of genetic divergence of codistributed species. However, researchers are often frustrated because of the lack of appropriate statistical tests to assess concordancy of multiple phylogeographic trees. We develop a method for testing congruence across multiple species and synthesizing the data into a regional supertree. Nine phylogeographic data sets of species with different life histories and ecologies were statistically compared using maximum agreement subtrees (MAST) and showed a high degree of concordancy. A supertree combining the different phylogeographic trees was then computed using matrix representation with parsimony, and the groups defined by this supertree were tested against climatic data to investigate a potential mechanism driving divergence. Our data suggest that species and genetic lineages in California are shaped by climatic regimes. The supertree method in combination with MAST represents a new approach to test congruence hypotheses and detect common geographic signals in comparative phylogeography.     

LIFE-HISTORY VARIATION AND COMPARATIVE PHYLOGEOGRAPHY OF DARTERS (PISCES: PERCIDAE) FROM THE NORTH AMERICAN CENTRAL HIGHLANDS

Phylogeography seeks to evaluate the relationship between genetic variation and geographic distribution of a species to examine the influence of historical events on divergence. Congruent phylogeographic patterns in codistributed species indicate historical association of the taxa being compared, and the uniform action of biogeographic events in shaping genetic variation. We sought to evaluate the congruence of patterns of genetic variation of five closely related fish species across a well-defined biogeographic boundary. We gathered allozymic and mitochondrial DNA (mtDNA) sequence data for five species of darters (Percidae: Etheostomatini) from populations distributed among biogeographic regions in the Ozark and Ouachita highlands of the south-central United States. Comparisons among species revealed noncongruence in the magnitude of genetic divergence in both allozymes and mtDNA sequences. We hypothesized that noncongruence resulted, in part, from differences in life histories of the species in our comparison. To address this hypothesis, we evaluated the association between gene flow (measured by N_em) and variation in body size and fecundity variables because they have been shown to influence gene flow in fishes. Correlation analysis revealed an association between gene flow and fecundity (r = 0.88), but not with body size (r = 0.36) or reproductive investment per individual (r = –0.23). The result was similar when independent contrasts of the original variables were used in correlation analyses. Phylogeographic analysis of mtDNA sequence data indicated the importance of history, evident in gene trees of Percina nasuta and Percina phoxocephala. Divergence rates between these two taxa may differ because of historically persistent differences in population sizes, reflected in present-day abundance and fecundity differences. Conversely, Percina caprodes showed little evidence of divergence in mtDNA sequences and yielded the highest mean N_em values from allozyme data. Comparisons among closely related, codistributed taxa may help discriminate among the possibilities for noncongruence in biogeographic studies by allowing evaluation of the influence of life history on patterns of gene flow.     

THE GEOGRAPHY OF MITOCHONDRIAL DNA VARIATION IN TWO SYMPATRIC SPARROWS

Geographic variation in mitochondrial DNA (mtDNA) restriction sites was studied in samples of two sympatric passerine birds, fox (Passerella iliaca) and song (Melospiza melodia) sparrows, collected at the same sites in the western United States. Different levels of variation and differentiation were observed in each species. In 46 fox sparrows taken at nine sites, five clones were observed, partitioned into two distinct east-west groups that meet at the Great Basin-Sierra Nevada interface; percent nucleotide divergence was 0.86 between groups and 0.08 within groups. An additional 43 individuals were examined using at least one of seven diagnostic endonucleases, and all supported the east-west groupings. Considering common mtDNA haplotypes as alleles, an F_ST of 0.50 was computed, which is an order of magnitude greater than that computed from allozyme comparisons (0.019); mtDNA analyses suggest little intergroup gene exchange. Compared to allozymic variation, analysis of mtDNA revealed a greater degree of population structuring and greater consistency with broad patterns of morphological variation. Fifteen clones were observed in 27 song sparrows taken at seven of the same sites at which fox sparrows were sampled; the percent nucleotide divergence averaged 0.27. There was no detectable geographic pattern to the variation, and no evidence of an east-west division as in the fox sparrow. However, the mosaic nature of mtDNA variation in song sparrows suggests limited gene exchange. Considering the 15 clones as alleles yielded an F_st of 0.24, which is reduced to 0.039 when corrected for sampling error. In spite of occupying the same geographic area, mtDNA analyses showed that the two species (or at least their mtDNA gene genealogies) have had different evolutionary histories.     

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.     

One Species, Three Pleistocene Evolutionary Histories: Phylogeography of the Italian Crested Newt, Triturus carnifex

Phylogeographic patterns of temperate species from the Mediterranean peninsulas have been investigated intensively. Nevertheless, as more phylogeographies become available, either unique patterns or new lines of concordance continue to emerge, providing new insights on the evolution of regional biotas. Here, we investigated the phylogeography and evolutionary history of the Italian crested newt, Triturus carnifex, through phylogenetic, molecular dating and population structure analyses of two mitochondrial gene fragments (ND2 and ND4; overall 1273 bp). We found three main mtDNA lineages having parapatric distribution and estimated divergence times between Late Pliocene and Early Pleistocene. One lineage (S) was widespread south of the northern Apennine chain and was further geographically structured into five sublineages, likely of Middle Pleistocene origin. The second lineage (C) was widespread throughout the Padano-Venetian plain and did not show a clear phylogeographic structure. The third lineage (N) was observed in only two populations located on western Croatia/Slovenia. Results of analysis of molecular variance suggested that partitioning populations according to the geographic distribution of these lineages and sublineages explains 76% of the observed genetic variation. The phylogeographic structure observed within T. carnifex and divergence time estimates among its lineages, suggest that responses to Pleistocene environmental changes in this single species have been as diverse as those found previously among several codistributed temperate species combined. Consistent with the landscape heterogeneity, physiographic features, and palaeogeographical evolution of its distribution range, these responses encompass multiple refugia along the Apennine chain, lowland refugia in large peri-coastal plains, and a 'cryptic' northern refugium.     

Phylogeographic Patterns and Evolution of the Mitochondrial DNA Control Region in Two Neotropical Cats (Mammalia, Felidae)

The ocelot (Leopardus pardalis) and margay (L. wiedii) are sister-species of Neotropical cats which evolved from a lineage that migrated into South America during the formation of the Panamanian land bridge 3–5 million years ago. Patterns of population genetic divergence of each species were studied by phylogenetic analyses of mitochondrial DNA (mtDNA) control region sequences in individuals sampled across the distribution of these taxa. Abundant genetic diversity and remarkably concordant phylogeographic partitions for both species were observed, identifying parallel geographic regions which likely reflect historical faunal barriers. Inferred aspects of phylogeography, population genetic structure, and demographic history were used to formulate conservation recommendations for these species. In addition, observed patterns of sequence variation provided insight into the molecular evolution of the mtDNA control region in closely related felids. Received: 26 January 1998 / Accepted: 14 May 1998     

History, ocean channels, and distance determine phylogeographic patterns in three widespread Philippine fruit bats (Pteropodidae)

The comparative phylogeography of widespread, codistributed species provides unique insights into regional biodiversity and diversification patterns. I used partial DNA sequences of the mitochondrial genes ND2 and cyt b to investigate phylogeographic structure in three widespread Philippine fruit bats. Ptenochirus jagori is endemic to the oceanic region of the Philippines and is most abundant in lowland primary forest. Macroglossus minimus and Cynopterus brachyotis are most common in disturbed and open habitats and are not endemic. In all three, genetic differentiation is present at multiple spatial scales and is associated to some degree with Pleistocene landbridge island groups. In P. jagori and C. brachyotis, genetic distance is correlated with geographic distance; in C. brachyotis and M. minimus, it is correlated with the sea-crossing distance between islands. P. jagori has the least overall genetic structure of these three species, whereas C. brachyotis and M. minimus have more geographic association among haplotypes, suggesting that phylogeographic patterns are linked to ecology and habitat preference. However, contrary to expectation, the two widespread, disturbed habitat species have more structure than the endemic species. Mismatch distributions suggest rapid changes in effective population size in C. brachyotis and P. jagori, whereas M. minimus appears to be demographically more stable. Geologic and geographic history are important in structuring variation, and phylogeographic patterns are the result of dynamic long-term processes rather than simply reflecting current conditions.     

Comparative phylogeography of two open forest frogs from eastern Australia

We investigated the phylogeography of two closely related Australian frog species from open forest habitats, Limnodynastes tasmaniensis and L. peronii , using mitochondrial ND4 sequence data. Comparison of our results with previous work on Litoria fallax allowed us to test the generality of phylogeographic patterns among non-rainforest anurans along the east coast of Australia. In general, there was no strong evidence for congruence between overall patterns of genetic structure in the three species. However, phylogenetic breaks congruent with the position of the Burdekin Gap were detected at some level in all species. As previously noted for closed forest taxa, this area of dry habitat appears to have been an important influence on the evolution of several open forest taxa. There were broad geographic similarities in the phylogenetic structuring of southern populations of L. peronii and L. tasmaniensis. Contrarily, although the McPherson Range has previously been noted to coincide geographically with a major mtDNA phylogenetic break in Litoria fallax this pattern is not apparent in L. peronii or L. tasmaniensis. It appears that major phylogeographic splits within L. peronii and L. tasmaniensis may predate the Quaternary. We conclude that phylogeographies of open forest frogs are complex and more difficult to predict than for rainforest taxa, mainly due to an absence of palæomodels for historical distributions of non-rainforest habitats.     

Congeneric phylogeography: hypothesizing species limits and evolutionary processes in Patagonian lizards of the Liolaemus boulengeri group (Squamata: Liolaemini)

In poorly known groups for which data are insufficient to develop biologically plausible model‐based approaches to phylogeographical analyses, a ‘first hypotheses’ protocol is suggested as offering the best way to generate hypotheses for subsequent model‐based tests. Preliminary hypotheses are formulated about species boundaries and population processes in three species complexes of the Liolaemus boulengeri group in the context of mtDNA ‘congeneric phylogeography’. The temperate South American Liolaemus provides a model with ancient and recent allopatric divergence across ecologically and geologically complex landscapes, incipient speciation, secondary contact, and discordance between molecular and morphological patterns of variation. Moderately dense sampling of widely distributed ‘inertial’ species in the Patagonian Steppe has revealed hidden genetic and probably species diversity, and also hinted at demographic and historical processes that may have shaped the histories of these taxa. Five of the seven focal species of the present study were paraphyletic for mtDNA genealogies, suggesting that they represent complexes of species, and nested clade phylogeographical analysis (NCPA) analyses suggest that different historical and demographic processes have shaped the observed patterns. Introgression and incomplete lineage sorting are hypothesized as being the cause of some of the observed paraphyly. Provisional delimitations of species are proposed and NCPA is used to generate hypotheses of population history, all of which are subject to further testing. Multi‐faceted studies, involving phylogenetic assessments of independent molecular markers and morphological variation across codistributed taxa with estimates of niche breadths in a landscape context, will likely yield the most promising returns for cross‐validation of hypotheses of population and speciation histories. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 89 , 241–275.     

Ecology driving genetic variation: a comparative phylogeography of jungle cat (Felis chaus) and leopard cat (Prionailurus bengalensis) in India

Background

Comparative phylogeography links historical population processes to current/ecological processes through congruent/incongruent patterns of genetic variation among species/lineages. Despite high biodiversity, India lacks a phylogeographic paradigm due to limited comparative studies. We compared the phylogenetic patterns of Indian populations of jungle cat (Felis chaus) and leopard cat (Prionailurus bengalensis). Given similarities in their distribution within India, evolutionary histories, body size and habits, congruent patterns of genetic variation were expected.

Methodology/Principal Findings

We collected scats from various biogeographic zones in India and analyzed mtDNA from 55 jungle cats (460 bp NADH5, 141 bp cytochrome b) and 40 leopard cats (362 bp NADH5, 202 bp cytochrome b). Jungle cats revealed high genetic variation, relatively low population structure and demographic expansion around the mid-Pleistocene. In contrast, leopard cats revealed lower genetic variation and high population structure with a F _ST of 0.86 between North and South Indian populations. Niche-model analyses using two approaches (BIOCLIM and MaxEnt) support absence of leopard cats from Central India, indicating a climate associated barrier. We hypothesize that high summer temperatures limit leopard cat distribution and that a rise in temperature in the peninsular region of India during the LGM caused the split in leopard cat population in India.

Conclusions/Significance

Our results indicate that ecological variables describing a species range can predict genetic patterns. Our study has also resolved the confusion over the distribution of the leopard cat in India. The reciprocally monophyletic island population in the South mandates conservation attention.     

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.     

Comparative phylogeography of codistributed aquatic insects in western North America: insights into dispersal and regional patterns of genetic structure

相似文献   

A trans-Amazonian screening of mtDNA reveals deep intraspecific divergence in forest birds and suggests a vast underestimation of species diversity

The Amazonian avifauna remains severely understudied relative to that of the temperate zone, and its species richness is thought to be underestimated by current taxonomy. Recent molecular systematic studies using mtDNA sequence reveal that traditionally accepted species-level taxa often conceal genetically divergent subspecific lineages found to represent new species upon close taxonomic scrutiny, suggesting that intraspecific mtDNA variation could be useful in species discovery. Surveys of mtDNA variation in Holarctic species have revealed patterns of variation that are largely congruent with species boundaries. However, little information exists on intraspecific divergence in most Amazonian species. Here we screen intraspecific mtDNA genetic variation in 41 Amazonian forest understory species belonging to 36 genera and 17 families in 6 orders, using 758 individual samples from Ecuador and French Guiana. For 13 of these species, we also analyzed trans-Andean populations from the Ecuadorian Chocó. A consistent pattern of deep intraspecific divergence among trans-Amazonian haplogroups was found for 33 of the 41 taxa, and genetic differentiation and genetic diversity among them was highly variable, suggesting a complex range of evolutionary histories. Mean sequence divergence within families was the same as that found in North American birds (13%), yet mean intraspecific divergence in Neotropical species was an order of magnitude larger (2.13% vs. 0.23%), with mean distance between intraspecific lineages reaching 3.56%. We found no clear relationship between genetic distances and differentiation in plumage color. Our results identify numerous genetically and phenotypically divergent lineages which may result in new species-level designations upon closer taxonomic scrutiny and thorough sampling, although lineages in the tropical region could be older than those in the temperate zone without necessarily representing separate species. In-depth phylogeographic surveys are urgently needed to avoid underestimating tropical diversity, and the use of mtDNA markers can be instrumental in identifying and prioritizing taxa for species discovery.     

Methods in comparative phylogeography, and their application to studying evolution in the north american aridlands

Historical biogeography and comparative phylogeography havemuch in common. Both seek to discover common historical patternsin the elements of biotas, although typically at different tiersof evolutionary history. Comparative phylogeography is basedon phylogeographic analyses of multiple taxa, usually widespreadspecies. By comparing the phylogeographic structures of numerouswidespread sympatric species, one can infer whether the currentfauna has been historically stable, as evidenced by the relativefrequency of geographically congruent reciprocally monophyleticgroups. Alternatively, if species distributions are ephemeralover evolutionary time, a mixture of phylogeographic structuresis expected. Coalescence analyses contribute information abouthistory irrespective of whether haplotype phylogenies are structuredor not. In the aridlands of North America, several isolatingevents are evident in the phylogeographic patterns of birds,mammals and herps. A mid-peninsular seaway in Baja California,dated at ca. one million years before present, had a pervasiveeffect, with 13 of 16 assayed species showing a concordant split.Hence, this community appears to have been a stable assemblageof species over the past one million years. In contrast, theavifauna of the Sonoran-Chihuahuan deserts consists of two specieswith a concordant split and three other species that are undifferentiatedacross both deserts. Hence, the species in this area have haddifferent histories. The Baja biota appears to resemble itsancestral configuration to a greater degree than the Sonoran-Chihuahuanone. A deeper evolutionary event separated taxa in Baja Californiafrom the eastern deserts, showing that the aridlands fauna wasaffected by events at different times resulting in overlaintiers of history.     

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.     

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.     

Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?

Life traits such as reproductive strategy can be determining factors of species evolutionary history and explain the resulting diversity patterns. This can be investigated using phylogeographic analyses of genetic units. In this work, the genetic structure of five asteroid genera with contrasting reproductive strategies (brooding: Diplasterias, Notasterias and Lysasterias versus broadcasting: Psilaster and Bathybiaster) was investigated in the Southern Ocean. Over 1,400 mtDNA cytochrome C oxidase subunit I (COI) sequences were analysed using five species delineation methods (ABGD, ASAP, mPTP, sGMYC and mGMYC), two phylogenetic reconstructions (ML and BA), and molecular clock calibrations, in order to examine the weight of reproductive strategy in the observed differences among phylogeographic patterns. We hypothesised that brooding species would show higher levels of genetic diversity and species richness along with a clearer geographic structuring than broadcasting species. In contrast, genetic diversity and species richness were not found to be significantly different between brooders and broadcasters, but broadcasters are less spatially structured than brooders supporting our initial hypothesis and suggesting more complex evolutionary histories associated to this reproductive strategy. Broadcasters' phylogeography can be explained by different scenarios including deep‐sea colonisation routes, bipolarity or cosmopolitanism, and sub‐Antarctic emergence for the genus Bathybiaster; Antarctic‐ New Zealand faunal exchanges across the Polar Front for the genus Psilaster. Brooders' phylogeography could support the previously formulated hypothesis of a past trans‐Antarctic seaway established between the Ross and the Weddell seas during the Plio‐Pleistocene. Our results also show, for the first time, that the Weddell Sea is populated by a mixed asteroid fauna originating from both the East and West Antarctic.     

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.     

GENETIC SUBDIVISIONS AMONG SMALL CANIDS: MITOCHONDRIAL DNA DIFFERENTIATION OF SWIFT,KIT, AND ARCTIC FOXES

Gene flow can effectively suppress genetic divergence among widely separated populations in highly mobile species. However, the same may not be true of species that typically disperse over shorter distances. Using mtDNA restriction-site and sequence analyses, we evaluate the extent of divergence among populations of two small relatively sedentary North American canids, the kit and swift foxes (genus Vulpes). We determine the significance of genetic differentiation among populations separated by distance and those separated by discrete topographic barriers. Our results show the among-population component of genetic variation in kit and swift foxes is large and similar to that of small rodents with limited dispersal ability. In addition, we found two distinct groupings of genotypes, separated by the Rocky Mountains, corresponding to the traditional division between kit and swift fox populations. Previous workers have characterized these morphologically similar populations either as separate species or subspecies. Our mtDNA data also suggest that kit and swift fox populations hybridize over a limited geographic area. However, the sequence divergence between kit and swift foxes is similar to that between these taxa and the arctic fox (Alopex lagopus), a morphologically distinct species commonly placed in a separate genus. This result presents a dilemma for species concepts, and we conclude that kit and swift foxes should be recognized as separate species.