Morphological differentiation correlates with ecological but not with genetic divergence in a Gehyra gecko

Body size affects life history, the ecological niche of an organism and its interactions with other organisms. Resultantly, marked differences in body size between related organisms are often an indication of a species boundary. This is particularly evident in the Gehyra variegata species complex of geckos, which displays differential body sizes between genetically divergent species, but high levels of intraspecific morphological conservatism. We report on a Gehyra population that displays extraordinary body size differentiation in comparison with other G. variegata species. We used morphological and environmental data to show this population is phenotypically and ecologically distinct from its parapatric congener Gehyra lazelli and that morphology and ecology are significantly correlated. Contrastingly, mtDNA analysis indicates paraphyly between the two groups, and allele frequencies at six microsatellite loci show no population structure concordant with morpho‐/ecotype. These results suggest either ecological speciation or environmentally induced phenotypic polymorphism, in an otherwise morphologically conservative group.     

The population biology of Gehyra (Gekkonidae). III. Patterns of microgeographic variation

The distribution of allozymic and chromosomal polymorphisms was examined among central Australian populations of the chromosomally variable genus Gehyra to assess whether they typically have the small deme size and low gene flow levels required by some models of chromosomal speciation. Particular attention was given to comparisons between rock-specialists (Gehyra nana) and habitat-generalists (Gehyra variegata) to investigate whether the former have more restricted gene flow. Both allozyme and chromosome data sets showed greater among population differentiation in the rock-specialists than the habitat-generalists, consistent with predictions from a previous ecological study (Moritz, 1987), although this pattern could also be due to historical effects. This was evident from the relationships between genetic and geographic distance, the conditional frequency of alleles, and F-statistics. However, both taxa appear to have substantial levels of gene flow. This indicates that Gehyra populations typically do not meet the stringent conditions for the fixation of strongly underdominant chromosome rearrangements through strong genetic drift. A consistent deficiency of heterozygotes does, however, suggest the possibility of inbreeding which would increase the likelihood of the establishment of underdominant rearrangements.     

Phylogeny and systematics of Melanesia’s most diverse gecko lineage (Cyrtodactylus,Gekkonidae, Squamata)

Oliver, P.M., Richards, S.J. & Sistrom, M. (2012). Phylogeny and systematics of Melanesia’s most diverse gecko lineage (Cyrtodactylus, Gekkonidae, Squamata). —Zoologica Scripta, 41, 437–454. The systematics and biogeographical history of the diverse fauna of New Guinea and surrounding islands (Melanesia) remain poorly known. We present a phylogeny for 16 of the 21 recognised Melanesian bent‐toed geckos in the genus Cyrtodactylus based on mitochondrial sequence data. These analyses reveal two divergent lineages of Cyrtodactylus within Melanesia. One includes a single recognised species with clear affinities to sampled taxa from Asia. The other comprises a relatively diverse radiation (likely 30+ species), not closely related to sampled extralimital taxa and centred on the Melanesian region (including Australia). Many taxa within this second lineage are endemic to islands surrounding New Guinea, and dispersal and speciation on peripheral islands appears to have played an important role in the accumulation of species diversity within this clade. In contrast, little diversity is centred upon montane areas, although we do identify at least one lineage closely associated with hill and lower montane forest that probably dates to at least the late Miocene. Our phylogenetic analyses also reveal numerous divergent lineages that require taxonomic attention, including at least two widespread taxa that are likely to be composite, additional specimens of Cyrtodactylus capreoloides (until recently known only from the holotype) and several divergent and completely novel lineages, two of which we introduce herein: Cyrtodactylus arcanus sp. n. and Cyrtodactylus medioclivus sp. n.     

Phylogeography of the antilopine wallaroo (Macropus antilopinus) across tropical northern Australia

The distribution of antilopine wallaroo, Macropus antilopinus, is marked by a break in the species’ range between Queensland and the Northern Territory, coinciding with the Carpentarian barrier. Previous work on M. antilopinus revealed limited genetic differentiation between the Northern Territory and Queensland M. antilopinus populations across this barrier. The study also identified a number of divergent lineages in the Northern Territory, but was unable to elucidate any geographic structure. Here, we re‐examine these results to (1) determine phylogeographic patterns across the range of M. antilopinus and (2) infer the biogeographic barriers associated with these patterns. The tropical savannahs of northern Australia: from the Cape York Peninsula in the east, to the Kimberley in the west. We examined phylogeographic patterns in M. antilopinus using a larger number of samples and three mtDNA genes: NADH dehydrogenase subunit 2, cytochrome b, and the control region. Two datasets were generated and analyzed: (1) a subset of samples with all three mtDNA regions concatenated together and (2) all samples for just control region sequences that included samples from the previous study. Analysis included generating phylogenetic trees based on Bayesian analysis and intraspecific median‐joining networks. The contemporary spatial structure of M. antilopinus mtDNA lineages revealed five shallow clades and a sixth, divergent lineage. The genetic differences that we found between Queensland and Northern Territory M. antilopinus samples confirmed the split in the geographic distribution of the species. We also found weak genetic differentiation between Northern Territory samples and those from the Kimberley region of Western Australia, possibly due to the Kimberley Plateau–Arnhem Land barrier. Within the Northern Territory, two clades appear to be parapatric in the west, while another two clades are broadly sympatric across the Northern Territory. MtDNA diversity of M. antilopinus revealed an unexpectedly complex evolutionary history involving multiple sympatric and parapatric mtDNA clades across northern Australia. These phylogeographic patterns highlight the importance of investigating genetic variation across distributions of species and integrating this information into biodiversity conservation.     

Closely related species of birds differ more in body size when their ranges overlap—in warm,but not cool,climates

Differences in body size are widely thought to allow closely related species to coexist in sympatry, but body size also varies as an adaptive response to climate. Here, we use a sister lineage approach to test the prediction that body size differences between closely related species of birds worldwide are greater for species whose ranges are sympatric rather than allopatric. We further test if body size differences among sympatric versus allopatric species vary with geography, evolutionary distance, and environmental temperatures. We find greater differences in size among sympatric compared with allopatric lineages, but only in closely related species that live where mean annual temperatures are above 25°C. These size differences in warm environments declined with the evolutionary distance between sister lineages. In species living in cooler regions, closely related allopatric and sympatric species did not differ significantly in size, suggesting either that colder temperatures constrain the evolutionary divergence of size in sympatry, or that the biotic selective pressures favoring size differences in sympatry are weaker in colder environments. Our results are consistent with suggestions by Wallace, Darwin, and Dobzhansky that climatic selective pressures are more important in cooler environments (e.g., high elevations and latitudes) whereas biotic selective pressures dominate in warm environments (e.g., lowland tropics).     

DOES NICHE DIVERGENCE ACCOMPANY ALLOPATRIC DIVERGENCE IN APHELOCOMA JAYS AS PREDICTED UNDER ECOLOGICAL SPECIATION?: INSIGHTS FROM TESTS WITH NICHE MODELS

The role of ecology in the origin of species has been the subject of long‐standing interest to evolutionary biologists. New sources of spatially explicit ecological data allow for large‐scale tests of whether speciation is associated with niche divergence or whether closely related species tend to be similar ecologically (niche conservatism). Because of the confounding effects of spatial autocorrelation of environmental variables, we generate null expectations for niche divergence for both an ecological‐niche modeling and a multivariate approach to address the question: do allopatrically distributed taxa occupy similar niches? In a classic system for the study of niche evolution—the Aphelocoma jays—we show that there is little evidence for niche divergence among Mexican Jay (A. ultramarina) lineages in the process of speciation, contrary to previous results. In contrast, Aphelocoma species that exist in partial sympatry in some regions show evidence for niche divergence. Our approach is widely applicable to the many cases of allopatric lineages in the beginning stages of speciation. These results do not support an ecological speciation model for Mexican Jay lineages because, in most cases, the allopatric environments they occupy are not significantly more divergent than expected under a null model.     

ASYNCHRONOUS EVOLUTION OF PHYSIOLOGY AND MORPHOLOGY IN ANOLIS LIZARDS

Species‐rich adaptive radiations typically diversify along several distinct ecological axes, each characterized by morphological, physiological, and behavioral adaptations. We test here whether different types of adaptive traits share similar patterns of evolution within a radiation by investigating patterns of evolution of morphological traits associated with microhabitat specialization and of physiological traits associated with thermal biology in Anolis lizards. Previous studies of anoles suggest that close relatives share the same “structural niche” (i.e., use the same types of perches) and are similar in body size and shape, but live in different “climatic niches” (i.e., use habitats with different insolation and temperature profiles). Because morphology is closely tied to structural niche and field active body temperatures are tied to climatic niches in Anolis, we expected phylogenetic analyses to show that morphology is more evolutionarily conservative than thermal physiology. In support of this hypothesis, we find (1) that thermal biology exhibits more divergence among recently diverged Anolis taxa than does morphology; and (2) diversification of thermal biology among all species often follows diversification in morphology. These conclusions are remarkably consistent with predictions made by anole biologists in the 1960s and 1970s.     

BODY SIZE DIVERSIFICATION IN ANOLIS: NOVEL ENVIRONMENT AND ISLAND EFFECTS

Extreme morphologies of many insular taxa suggest that islands have unusual properties that influence the tempo and mode of evolution. Yet whether insularity per se promotes rapid phenotypic evolution remains largely untested. We extend a phylogenetic comparative approach to test the influence of novel environments versus insularity on rates of body size and sexual size dimorphism diversification in Anolis . Rates of body size diversification among small-island and mainland species were similar to those of anole species on the Greater Antilles. However, the Greater Antilles taxa that colonized small islands and the mainland are ecologically nonrandom: rates of body size diversification among small-island and mainland species are high compared to their large-island sister taxa. Furthermore, rates of diversification in sexual size dimorphism on small islands are high compared to all large-island and mainland lineages. We suggest that elevated diversifying selection, particularly as a result of ecological release, may drive high rates of body size diversification in both small-island and mainland novel environments. In contrast, high abundance (prevalent among small-island lizard communities) mediating intraspecific resource competition and male–male competition may explain why sexual size dimorphism diversifies faster among small-island lineages than among their mainland and large-island relatives.     

Explosive radiation and spatial expansion across the cold environments of the Old World in an avian family

Our objective was to elucidate the biogeography and speciation patterns in an entire avian family, which shows a complex pattern of overlapping and nonoverlapping geographical distributions, and much variation in plumage, but less in size and structure. We estimated the phylogeny and divergence times for all of the world's species of Prunella based on multiple genetic loci, and analyzed morphometric divergence and biogeographical history. The common ancestor of Prunella was present in the Sino‐Himalayan Mountains or these mountains and Central Asia–Mongolia more than 9 million years ago (mya), but a burst of speciations took place during the mid‐Pliocene to early Pleistocene. The relationships among the six primary lineages resulting from that differentiation are unresolved, probably because of the rapid radiation. A general increase in sympatry with increasing time since divergence is evident. With one exception, species in clades younger than c. 3.7 my are allopatric. Species that are widely sympatric, including the most recently diverged (2.4 mya) sympatric sisters, are generally more divergent in size/structure than allo‐/parapatric close relatives. The distributional pattern and inferred ages suggest divergence in allopatry and substantial waiting time until secondary contact, likely due to competitive exclusion. All sympatrically breeding species are ecologically segregated, as suggested by differences in size/structure and habitat. Colonizations of new areas were facilitated during glacial periods, followed by fragmentation during interglacials—contrary to the usual view that glacial periods resulted mainly in fragmentations.     

Morphometric variation between two morphotypes within the Astyanax Baird and Girard, 1854 (Actinopterygii: Characidae) genus,From a Mexican tropical lake

Phenotypic variation is important for evolutionary processes because it can allow local adaptation, promote genetic segregation, and ultimately give rise to speciation. Lacustrine systems provide a unique opportunity to study the mechanisms by which sister species can co‐occur by means of ecological segregation. The fish genus Astyanax is characterized by high levels of phenotypic variability, providing an excellent model for the study of local specialization. Here, we analyze the morphological specializations through geometric morphometrics of two sympatric species described as different genera: Bramocharax caballeroi endemic to Lake Catemaco, and the widely distributed Astyanax aeneus. Additionally, we assess the correlation between phenotypic and genetic structure, and the phylogenetic signal of morphological variation. We examined body size and shape variation in 196 individuals and analyzed mitochondrial cytochrome b sequences in 298 individuals. Our results confirm the striking morphological divergence among the sympatric characids. Differences between them were mainly found in the body depth and profile and orientation of the head, where B. caballeroi in contrast with the A. aeneus, presented a fusiform body and an upward mouth. Moreover, different growth trajectories were observed among morphotypes, suggesting that a heterochronic process could be involved in the diversification of our study system. Morphological differences did not correspond with the molecular differentiation, suggesting high levels of homoplasy among the lineages of B. caballeroi morphs. J. Morphol. 275:721–731, 2014. © 2014 Wiley Periodicals, Inc.     

Estimating body size of fossil sirenians

Estimates of fossil sirenian body size are important for understanding niche partitioning among possibly sympatric species. Because of the paucity of complete fossil skeletons, we explored the utility of three morphometric predictors of body size: (condylobasal skull length [BSL]; occipital condyle width [OCW]; and foramen magnum width [FMW]) in extant sirenians—Florida manatees (Trichechus manatus latirostris) and dugongs (Dugong dugon)—and then applied these to obtain estimates of body size in extinct sirenian taxa. Condylobasal length of the skull is a more accurate predictor of body size in extant Florida manatees and dugongs than are width of the occipital condyles or width of the foramen magnum. Body length (BL) is predicted more accurately than is body weight (BW) for all three morphometric predictors. For our sample of fossil sirenians, BSL, OCW, and FMW were used to generate predicted BLs and BWs. Preliminary assessments of fossil sirenian faunas from Florida and India suggest that body mass could have been one of several possible important morphological parameters accounting for feeding niche separation.     

Crocodylian Snouts in Space and Time: Phylogenetic Approaches Toward Adaptive Radiation

Recent phylogenetic analyses of fossil and living crocodyliansallow us to compare the taxonomic, geographic, and temporaldistributions of morphological features, such as snout shapes.A few basic snout morphotypes—generalized, blunt, slender,deep, and excessively broad ("duck-faced")—occur multipletimes in distantly-related lineages. Some clades—especiallythose found in the Northern Hemisphere or with minimum originationdates in the Cretaceous or lower Tertiary—are morphologicallyuniform, but geographically widespread; crocodylian faunas ofthe early Tertiary tend to be composite, with sympatric taxabeing distantly related, and similar-looking taxa on differentcontinents being close relatives. In contrast, crocodylian faunasof the later Tertiary tend to be more endemic, with local adaptiveradiations occurring in Africa and Australia containing membersof most basic snout shapes. Endemic radiations in Africa andAustralia have largely been replaced by Crocodylus, which canbe divided into subclades that may individually represent endemicadaptive radiations.     

Constrained body shape among highly genetically divergent allopatric lineages of the supralittoral isopod Ligia occidentalis (Oniscidea)

Multiple highly divergent lineages have been identified within Ligia occidentalis sensu lato, a rocky supralittoral isopod distributed along a ~3000 km latitudinal gradient that encompasses several proposed marine biogeographic provinces and ecoregions in the eastern Pacific. Highly divergent lineages have nonoverlapping geographic distributions, with distributional limits that generally correspond with sharp environmental changes. Crossbreeding experiments suggest postmating reproductive barriers exist among some of them, and surveys of mitochondrial and nuclear gene markers do not show evidence of hybridization. Populations are highly isolated, some of which appear to be very small; thus, the effects of drift are expected to reduce the efficiency of selection. Large genetic divergences among lineages, marked environmental differences in their ranges, reproductive isolation, and/or high isolation of populations may have resulted in morphological differences in L. occidentalis, not detected yet by traditional taxonomy. We used landmark‐based geometric morphometric analyses to test for differences in body shape among highly divergent lineages of L. occidentalis, and among populations within these lineages. We analyzed a total of 492 individuals from 53 coastal localities from the southern California Bight to Central Mexico, including the Gulf of California. We conducted discriminant function analyses (DFAs) on body shape morphometrics to assess morphological variation among genetically differentiated lineages and their populations. We also tested for associations between phylogeny and morphological variation, and whether genetic divergence is correlated to multivariate morphological divergence. We detected significant differences in body shape among highly divergent lineages, and among populations within these lineages. Nonetheless, neither lineages nor populations can be discriminated on the basis of body shape, because correct classification rates of cross‐validated DFAs were low. Genetic distance and phylogeny had weak to no effect on body shape variation. The supralittoral environment appears to exert strong stabilizing selection and/or strong functional constraints on body shape in L. occidentalis, thereby leading to morphological stasis in this isopod.     

Species‐specific ontogenetic diet shifts among Neotropical Crenicichla: using stable isotopes and tissue stoichiometry

Ontogenetic diet shifts were compared among five sympatric pike cichlids Crenicichla in a subtropical South American stream using stable C and N isotopes and tissue stoichiometry (C:N). Within species, stable N isotopes were positively related to body size while C:N showed negative relationships. Stable C isotopes, however, were not related to body size in any species. By modelling the switch to piscivory using gut content‐isotope‐body size relationships, diet shifts were shown to be species‐specific with regard to both rate and degree of piscivory. Compared to other piscivorous lineages, Crenicichla appear to be unusually small‐bodied (based on maximum body size). Because of their diversity, abundance and dynamic size‐structured functional roles, Crenicichla may exert broad and complex predation pressures on the aquatic community.     

Molecules,fossils, and the origin of tetrapods

Summary Since the discovery of the coelacanth, Latimeria chalumnae, more than 50 years ago, paleontologists and comparative morphologists have debated whether coelacanths or lungfishes, two groups of lobe-finned fishes, are the closest living relatives of land vertebrates (Tetrapoda). Previously, Meyer and Wilson (1990) determined partial DNA sequences from two conservative mitochondrial genes and found support for a close relationship of lungfishes to tetrapods. We present additional DNA sequences from the 12S rRNA mitochondria gene for three species of the two lineages of lungfishes that were not represented in the first study: Protopterus annectens and Protopterus aethiopicus from Africa and Neoceratodus forsteri (kindly provided by B. Hedges and L. Maxson) from Australia. This extended data set tends to group the two lepidosirenid lungfish lineages (Lepidosiren and Protopterus) with Neoceratodus as their sister group. All lungfishes seem to be more closely related to tetrapods than the coelacanth is. This result appears to rule out the possibility that the coelacanth lineage gave rise to land vertebrates. The common ancestor of lungfishes and tetrapods might have possessed multiple morphological traits that are shared by lungfishes and tetrapods [Meyer and Wilson (1990) listed 14 such traits]. Those traits that seem to link Latimeria and tetrapods are arguably due to convergent evolution or reversals and not to common descent. In this way, the molecular tree facilitates an evolutionary interpretation of the morphological differences among the living forms. We recommended that the extinct groups of lobe-finned fishes be placed onto the molecular tree that has lungfishes and not the coelacanth more closely related to tetrapods. The placement of fossils would help to further interpret the sequence of morphological events and innovations associated with the origin of tetrapods but appears to be problematic because the quality of fossils is not always high enough, and differences among paleontologists in the interpretation of the fossils have stood in the way of a consensus opinion for the branching order among lobefinned fishes. Marshall and Schultze (1992) criticized the morphological analysis presented by Meyer and Wilson (1990) and suggest that 13 of the 14 morphological traits that support the sister group relationship of lungfishes and tetrapods are not shared derived characters. Here we present further alternative viewpoints to the ones of Marshall and Schultze (1992) from the paleontological literature. We argue that all available information (paleontological, neontological, and molecular data) and rigorous cladistic methodology should be used when relating fossils and extant taxa in a phylogenetic framework. Offprint requests to: Axel Meyer     

Morphological novelty and modest developmental truncation in Barboides,Africa's smallest vertebrates (Teleostei: Cyprinidae)

Miniaturization, the evolution of extremely small adult body size, is widespread amongst animals and commonly associated with novel ecological, physiological, and morphological attributes. The phenotypes of miniaturized taxa are noteworthy because they combine reductions and structural simplifications with novel traits not developed in their larger relatives. Previous research on miniature cyprinid fishes (focused predominantly on South and South East Asian taxa of a single subfamily) has identified two distinct classes of miniature taxa: proportioned dwarves and developmentally truncated miniatures. Miniaturization has also occurred independently in the subfamily Cyprininae, particularly in African lineages. We investigate the skeletal anatomy of Barboides , a genus of miniature African cyprinids that includes Africa's smallest known species of vertebrates, to assess whether miniaturization has resulted in similar organismal outcomes in different lineages of the Cyprinidae. The skeleton of Barboides is characterized by the complete absence of a number of dermal and endochondral ossifications, and marked reduction in size and/or complexity of other skeletal elements, particularly those of the dermatocranium. Absent skeletal elements in Barboides include those which develop relatively late in the ossification sequence of the non‐miniature African relative ‘Barbus ’ holotaenia suggesting that their absence in Barboides can be explained by a simple scenario of developmental truncation. In contrast to this theme of loss and reduction, the os suspensorium of Barboides is enlarged and the outer arm distally trifid and associated with a novel bulbous muscle in males. An evaluation of the skeleton of Barboides provides further evidence for a link between developmental truncation and evolutionary morphological novelty in Cyprinidae. In the spectrum of miniature cyprinids ranging from proportioned dwarves with few bones missing to highly progenetic taxa with dozens of missing bones, the two species of Barboides range roughly in the middle showing that the extremes are connected by intermediate levels of truncatedness.     

Location-specific sympatric morphological divergence as a possible response to species interactions in West Virginia Plethodon salamander communities

1. The competitive interactions of closely related species have long been considered important determinants of community composition and a major cause of phenotypic diversification. However, while patterns such as character displacement are well documented, less is known about how local adaptation influences diversifying selection from interspecific competition. 2. We examined body size and head shape variation among allopatric and sympatric populations of two salamander species, the widespread Plethodon cinereus and the geographically restricted P. nettingi. We quantified morphology from 724 individuals from 20 geographical localities throughout the range of P. nettingi. 3. Plethodon nettingi was more robust in cranial morphology relative to P. cinereus, and sympatric localities were more robust relative to allopatric localities. Additionally, there was significantly greater sympatric head shape divergence between species relative to allopatric communities, and sympatric localities of P. cinereus exhibited greater morphological variation than sympatric P. nettingi. 4. The sympatric morphological divergence and increase in cranial robustness of one species (P. nettingi) were similar to observations in other Plethodon communities, and were consistent with the hypothesis of interspecific competition. These findings suggest that interspecific competition in Plethodon may play an important role in phenotypic diversification in this group. 5. The increase in among-population variance in sympatric P. cinereus suggests a species-specific response to divergent natural selection that is influenced in part by other factors. We hypothesize that enhanced morphological flexibility and ecological tolerance allow P. cinereus to more rapidly adapt to local environmental conditions, and initial differences among populations have allowed the evolutionary response of P. cinereus to vary across replicate sympatric locations, resulting in distinct evolutionary trajectories of morphological change.     

Morphological parallelism of sympatric cave-dwelling microsnails of the genus Georissa at Mount Silabur,Borneo (Gastropoda,Neritimorpha, Hydrocenidae)

Parallel evolution in phenotype may result when closely related taxa are adapting in the face of similar ecological pressures. Here, we discuss possible parallelism in shell morphology in the context of the microgeographic phylogeography of two conchologically distinct sympatric hydrocenid snails inhabiting a limestone outcrop and its cave system, Georissa pyrrhoderma and Georissa silaburensis, respectively, at Mount Silabur in Sarawak, Malaysian Borneo. Our results show a certain degree of morphological parallelism of a third, possibly new, cryptic Georissa species within the same cave that strongly diverged from its above-ground sister species, G. pyrrhoderma. We found that both sympatric cave species have shifted from a more sculptured, conical shell toward a broader, less sculptured form.     

Historical isolation,range expansion,and secondary contact of two highly divergent mitochondrial lineages in spotted salamanders (Ambystoma maculatum)

Abstract.— The high species diversity of aquatic and terrestrial faunas in eastern North America has been attributed to range reductions and allopatric diversification resulting from historical climate change. The role these processes may have played in speciation is still a matter of considerable debate; however, their impacts on intraspecific genetic structure have been well documented. We use mitochondrial DNA sequences to reconstruct an intraspecific phylogeny of the widespread North American spotted salamander, Ambystoma maculatum , and test whether phylogenetic patterns conform to regional biogeographical hypotheses about the origins of diversity in eastern North America. Specifically, we address the number and locations of historical refugia, the extent and patterns of postglacial colonization by divergent lineages, and the origin and affinities of populations in the Interior Highland region. Despite apparent morphological uniformity, genetic discontinuities throughout the range of this species suggest that populations were historically fragmented in at least two refugia in the southern Appalachian Mountains. The ranges of these two highly divergent clades expanded northward, resulting in two widely distributed lineages that are sympatric in regions previously proposed as suture zones for other taxa. The evolutionary history of spotted salamander populations underscores the generality of biogeographical processes in eastern North America: despite differences in population size, glacial refugia, and vagility, similar signatures of differentiation are evident among and within widespread taxa.