Phylogeography and conservation genetics of the hellbender salamander (Cryptobranchus alleganiensis)

We investigated hellbender phylogeography through phylogenetic analyses of individuals sampled from 16 locations throughout their range in the eastern United States. Analyses were conducted on concatenated cytochrome-oxidase I (COI), cytochrome-b (Cytb) and NADH dehydrogenase subunit 4 (ND4) mtDNA sequence, totaling 2160 nucleotides. Hellbender haplotypes differed by 0.1 to 5.8% maximum likelihood (ML) corrected sequence divergence. Phylogenetic analyses reveal that hellbenders are separated into 8 reciprocally monophyletic populations or clades differentiated by a minimum of 0.7 to 5.4% sequence divergence, each of which constitutes a separate Management Unit (MU). High among population divergence and reciprocal monophyly suggest that female-mediated gene flow is severely restricted or non-existent among each MU. Hellbenders are currently divided into two subspecies, Cryptobranchus alleganiensis alleganiensis and C. a. bishopi based on morphological characters. The phylogenetic analyses presented here strongly indicate that these subspecies are paraphyletic. Management priorities for the hellbender should be reconsidered in light of these new molecular data. Results from Bayesian rooting indicate the root of the hellbender mtDNA tree lies on the branch leading to hellbender haplotypes from the Current, Eleven Point and New Rivers. The rooted tree suggests that a common ancestor in the southern Ozarks and/or southern Appalachians gave rise to northern hellbender populations, consistent with a Pleistocene refuge hypothesis.     

Genetic relationships of hellbenders in the Ozark highlands of Missouri and conservation implications for the Ozark subspecies (<Emphasis Type="Italic">Cryptobranchus alleganiensis bishopi</Emphasis>)

The hellbender (Cryptobranchus alleganiensis) is an obligately aquatic salamander that is in decline due to habitat loss and disease. Two subspecies of hellbender have been described based on morphological characteristics: C. a. alleganiensis (eastern subspecies) and C. a. bishopi (Ozark hellbender). Current conservation strategies include captive propagation for restorative releases even though information regarding the current levels of genetic variability and structure within populations is not sufficient to effectively plan for conservation of the genetic diversity of the species. To investigate patterns of population structure in the hellbender, we genotyped 276 hellbenders from eight Missouri River drainages, representing both subspecies. Our results showed low levels of within-drainage diversity but strong population structure among rivers, and three distinct genetic clusters. F _ST values ranged from 0.00 to 0.61 and averaged 0.40. Our results confirmed previous reports that C. a. bishopi and C. a. alleganiensis are genetically distinct, but also revealed an equidistant relationship between two groups within C. a. bishopi and all populations of C. a. alleganiensis. Current subspecies delineations do not accurately incorporate genetic structure, and for conservation purposes, these three groups should be considered evolutionarily significant units.     

PHYLOGENETIC RELATIONSHIPS AND MOLECULAR VARIABILITY WITHIN AND AMONG SIX CHROMOSOME RACES OF SCELOPORUS GRAMMICUS (SAURIA,IGUANIDAE), BASED ON NUCLEAR AND MITOCHONDRIAL MARKERS

Selected populations of Sceloporus grammicus from central Mexico were karyotyped and screened for variability at the protein, ribosomal-DNA, and mitochondrial-DNA levels. Molecular markers were used to construct phylogenies of the chromosome races, which were then qualitatively evaluated for congruence with each other and with the original chromosomal phytogeny proposed by Hall (1973). Between-cytotype protein divergence generally was low, and few allozyme markers were fixed between cytotypes. Hence, these data were combined with the rDNA restriction-site data for phylogeny reconstruction. This combined nuclear data set provided a phylogenetic hypothesis that, with one exception, is reasonably congruent with that based on standard karyotypes. Similar results were obtained from mtDNA restriction-site data, although there are some discrepancies, and trees based on both DNA data sets are complicated by evidence for historical and/or ongoing hybridization. An unexpectedly rapid rate of rDNA divergence is demonstrated relative to the degree of allozyme divergence, suggesting that restriction-site variation in rDNA has systematic utility at lower taxonomic levels.     

HISTORICAL BIOGEOGRAPHY OF THE BANANAQUIT (COEREBA FLAVEOLA) IN THE CARIBBEAN REGION: A MITOCHONDRIAL DNA ASSESSMENT

We analyzed mitochondrial DNA (mtDNA) restriction-site variation in bananaquit (Coereba flaveola; Aves, Coerebinae) populations sampled on 12 Caribbean islands and at 5 continental localities in Central America and northern South America. Multiple fixed restriction-site differences genetically defined several regional bananaquit populations. An mtDNA clade representing all Jamaican bananaquits was the most divergent; the estimated average sequence divergence (d_xy) between Jamaican and all other mtDNA haplotypes surveyed was 0.027. Three groups of populations, representing Central America, northern South America, and the eastern Antilles (Puerto Rico to Grenada) were nearly equally differentiated among themselves (average d_xy = 0.014), and may represent a single, recent range expansion. Within the eastern Antilles, three geographically restricted haplotype groups were identified: Puerto Rico, north-central Lesser Antilles (U.S. Virgin Islands to St. Lucia), and Grenada–St. Vincent. The evolutionary relationships of these groups were not clear. Genetic homogeneity of the island populations from the U.S. Virgin Islands to St. Lucia suggested a recent spread of a specific north-central Lesser Antillean haplotype through most of those islands. Haplotype variation across this region indicated that this spread may have occurred in two waves, first through the southernmost islands of St. Lucia, Martinique, and Dominica, and more recently from Guadeloupe to the north. The geographic distribution of mtDNA haplotypes, and of bananaquit populations, suggests periods of invasiveness followed by relative geographic quiescence. Although most genetic studies of bird populations have revealed homogeneity over large geographic areas, our findings provide a remarkable counterexample of strong geographic structuring of mtDNA variation over relatively small distances. Furthermore, although the mtDNA data were consistent with several subspecific distinctions, it was clear that named subspecies do not define equally differentiated evolutionary entities.     

MITOCHONDRIAL DNA VARIATION WITHIN AND BETWEEN SPECIES OF THE PAPILIO MACHAON GROUP OF SWALLOWTAIL BUTTERFLIES

Species limits and phylogenetic relationships in the Papilio machaon species group are potentially confounded by a complex pattern of Pleistocene range fragmentation, hybridization, and ecological race formation. Mitochondrial DNA (mtDNA) restriction-site analysis has been used to define genetic affinities and genetic population structure within this species group. The distribution of mtDNA haplotypes generally confirms prior phylogenetic hypotheses and species delineations, but there is poor correspondence between ecological races and mtDNA haplotypes. The amount and distribution of mtDNA sequence variation within species vary among species, reflecting differences in current patterns of gene flow and/or historical population structure. In spite of wing pattern characters that ally them with P. polyxenes, both P. joanae and P. brevicauda have mtDNA that is closely related to that of P. machaon. We suggest that P. joanae and P. brevicauda are of hybrid origin.     

Phylogenetic relationships of Amazonetta,Speculanas, Lophonetta,and Tachyeres: four morphologically divergent duck genera endemic to South America

We studied the phylogenetic relationships of four duck genera endemic to South America: Brazilian teal Amazonetta brasiliensis, spectacled duck Speculanas specularis, crested duck Lophonetta specularioides, and four species of steamer ducks Tachyerespatachonicus, T. leucocephalus, T. pteneres, T. brachypterus. Genetic divergence within and among species was compared using population‐level sampling of the mitochondrial DNA (mtDNA) control region, supplemented with three additional mtDNA genes and six independent nuclear loci from one individual of each species and a variety of outgroup taxa. The monophyly of these four morphologically divergent South American genera was strongly supported. Within this clade, Amazonetta and Speculanas were supported as sister species in all analyses, but different gene regions yielded conflicting or ambiguous results for Lophonetta and Tachyeres. This lack of resolution resulted from little informative variation in nuclear loci and high levels of homoplasy in the mtDNA control region. Control region sequences from the four Tachyeres species fell into two distinct clades. In one clade, T. patachonicus and T. leucocephalus share a set of closely related haplotypes (≤0.6% sequence divergence); while no identical haplotypes were shared between species, the control region phylogeny was insufficiently resolved to either support or reject reciprocal monophyly. The second clade, ~1.7% divergent from the first, comprised haplotypes of the Falkland Islands species T. brachypterus and a captive individual of T. pteneres. These distinctive South American ducks likely experienced two bouts of rapid diversification, thus making analysis of their phylogenetic relationships difficult. Incomplete lineage sorting, founder effects, and perhaps introgression likely have contributed to obscuring the relationships among steamer ducks.     

HISTORICAL BIOGEOGRAPHY IN NORTH AMERICAN ARID REGIONS: AN APPROACH USING MITOCHONDRIAL-DNA PHYLOGENY IN GRASSHOPPER MICE (GENUS ONYCHOMYS)

Restriction-endonuclease-site variation of mitochondrial DNA (mtDNA) was used to investigate patterns of geographic and phylogenetic divergence within the rodent genus Onychomys. Onychomys has occupied arid habitats in the western North American deserts, shrub-steppes, and grasslands since the late Tertiary. A phylogenetic analysis of the total mtDNA restriction-site variation throughout the range of Onychomys suggests that the distribution of this genus has been affected by the same Quaternary pluvial-interpluvial climatic fluctuations that have resulted in the periodic fragmentation of arid habitats in western North America. Onychomys mtDNA haplotypes define at least five discrete geographical subsets, suggesting that there are five areas of endemism for biota restricted to arid and semiarid habitats in North America. The mtDNA-haplotype phylogeny can be used to infer an hypothesis of historical relationships among the five areas of endemism as follows: ([{(Wyoming Basin + Interior Plains + Colorado Plateaus) + (Columbia Basin + Great Basin)} + Gulf Coastal Plain] + Chihuahuan) + Western Deserts. The results of this study point to the potential use of mtDNA-haplotype phylogenies to reconstruct historical biogeographic events in Quaternary time. The utility of mtDNA variation depends in part on the ecology and distribution of the species being examined. Therefore, our hypothesized area cladogram can be tested by investigating regional relationships in other western North American taxa with distributions similar to Onychomys.     

DISCORDANCE BETWEEN NUCLEAR AND CHLOROPLAST PHYLOGENIES IN THE HEUCHERA GROUP (SAXIFRAGACEAE)

Various factors, including taxon density, sampling error, convergence, and heterogeneity of evolutionary rates, can potentially lead to incongruence between phylogenetic trees based on different genomes. Particularly at the generic level and below, chloroplast capture resulting from hybridization may distort organismal relationships in phylogenetic analyses based on the chloroplast genome, or genes included therein. However, the extent of such discord between chloroplast DNA (cpDNA) trees and those trees based on nuclear genes has rarely been assessed. We therefore used sequences of the internal transcribed spacer regions (ITS-1 and ITS-2) of nuclear ribosomal DNA (rDNA) to reconstruct phylogenetic relationships among members of the Heuchera group of genera (Saxifragaceae). The Heuchera group presents an important model for the analysis of chloroplast capture and its impact on phylogenetic reconstruction because hybridization is well documented within genera (e.g., Heuchera), and intergeneric hybrids involving six of the nine genera have been reported. An earlier study provided a well-resolved phylogenetic hypothesis for the Heuchera group based on cpDNA restriction-site variation. However, trees based on ITS sequences are discordant with the cpDNA-based tree. Evidence from both morphology and nuclear-encoded allozymes is consistent with the ITS trees, rather than the cpDNA tree, and several points of phylogenetic discord can clearly be attributed to chloroplast capture. Comparison of the organellar and ITS trees also raises the strong likelihood that ancient events of chloroplast capture occurred between lineages during the early diversification of the Heuchera group. Thus, despite the many advantages and widespread use of cpDNA data in phylogeny reconstruction, comparison of relationships based on cpDNA and ITS sequences for the Heuchera group underscores the need for caution in the use of organellar variation for retrieving phylogeny at lower taxonomic levels, particularly in groups noted for hybridization.     

The ontogeny of feeding kinematics in a giant salamander Cryptobranchus alleganiensis: Does current function or phylogenetic relatedness predict the scaling patterns of movement?

Studies of the scaling of feeding movements in vertebrates have included three species that display both near-geometric growth and isometry of kinematic variables. These scaling characteristics allow one to examine the “pure” relationship of growth and movement. Despite similar growth patterns, the feeding movements of toads (Bufo) slow down more with increasing body size than those of bass (Micropterus), and sharks (Ginglymostoma). This variation might be due to major differences in the mechanism of prey capture; the bass and sharks use suction to capture prey in water, while the toad uses tongue prehension to capture prey on land. To investigate whether or not these different scaling patterns are correlated with differences in feeding mechanics, we examined the ontogenetic scaling of prey capture movements in the hellbender salamander (Cryptobranchus alleganiensis), which also has near-geometric growth. The hellbender suction feeds in the same general manner as the teleosts and shark, but is much more closely related to the toad. The feeding movements of the hellbender scale more similarly to the feeding movements of toads than to those of fishes or sharks, indicating that phylogenetic relatedness rather than biomechanical similarity predicts ontogenetic scaling patterns of movement.     

Polytomies,signal and noise: revisiting the mitochondrial phylogeny and phylogeography of the Eurasian blindsnake species complex (Typhlopidae,Squamata)

Polytomies are multifurcating nodes on a phylogenetic tree that represent unresolved relationships. Contrary to ‘hard’ polytomies that hide simultaneous splitting events, ‘soft’ polytomies can theoretically be resolved with the addition of phylogenetic signal. This is not always successful, especially when a radiation is old and rapid, because adding more signal will inevitably increase the noise. The Xerotyphlops vermicularis species complex is an example of a largely unresolved old and rapid radiation. This mtDNA phylogeny is revisited by analysing samples representative of all lineages and generating a 3700‐bp final data set, after preliminary tests found two of the analysed markers responsible for long‐branch attraction. The new enhanced data set increased phylogenetic resolution, resulting in a robust time‐calibrated phylogeny and phylogeographic conclusions. Jordan/south Syria populations separated during the Middle Miocene, and the Messinian salinity crisis (MSC) appears responsible for the second diversification wave. A third radiation occurred during the Early Pliocene, resulting in four mtDNA groups west, east and south of the Amanos mountains in east Turkey/north Syria. Finally, three hypotheses regarding the number of potential ‘species’ within the complex are made, with the most moderate ‘four species’ hypothesis fitting very well with the diversity patterns and established systematics of east Mediterranean reptiles.     

GLOBAL PHYLOGEOGRAPHY OF THE LOGGERHEAD TURTLE (CARETTA CARETTA) AS INDICATED BY MITOCHONDRIAL DNA HAPLOTYPES

Restriction-site analyses of mitochondrial DNA (mtDNA) from the loggerhead sea turtle (Caretta caretta) reveal substantial phylogeographic structure among major nesting populations in the Atlantic, Indian, and Pacific oceans and the Mediterranean sea. Based on 176 samples from eight nesting populations, most breeding colonies were distinguished from other assayed nesting locations by diagnostic and often fixed restriction-site differences, indicating a strong propensity for natal homing by nesting females. Phylogenetic analyses revealed two distinctive matrilines in the loggerhead turtle that differ by a mean estimated sequence divergence p = 0.009, a value similar in magnitude to the deepest intraspecific mtDNA node (p = 0.007) reported in a global survey of the green sea turtle Chelonia mydas. In contrast to the green turtle, where a fundamental phylogenetic split distinguished turtles in the Atlantic Ocean and the Mediterranean Sea from those in the Indian and Pacific oceans, genotypes representing the two primary loggerhead mtDNA lineages were observed in both Atlantic–Mediterranean and Indian-Pacific samples. We attribute this aspect of phylogeographic structure in Caretta caretta to recent interoceanic gene flow, probably mediated by the ability of this temperate-adapted species to utilize habitats around southern Africa. These results demonstrate how differences in the ecology and geographic ranges of marine turtle species can influence their comparative global population structures.     

Morphological and molecular characterization of a new species of leech (Glossiphoniidae,Hirudinida): Implications for the health of its imperiled amphibian host (Cryptobranchus alleganiensis)

The hellbender (Cryptobranchus alleganiensis) is among the most intriguing and imperiled amphibians in North America. Since the 1970s and 80s, western populations of the Ozark and eastern subspecies in Missouri have declined by nearly 80%. As a result of population declines, the Ozark hellbender was recently federally protected as an endangered species, and the eastern subspecies was granted protection under CITES. Although habitat degradation is probably the biggest threat to hellbender populations, recent evidence suggests that pathogens including chytrid fungus and “flesh-eating” bacteria may also contribute to declines in Ozark hellbenders. Leeches, which are very common on Ozark hellbenders, have recently been implicated as possible vectors of disease among Ozark hellbenders but have not been described in eastern hellbenders or outside of Missouri and Arkansas. We discovered a population of leeches on eastern hellbenders in southwest Virginia and confirmed that the species of leech is within the genus Placobdella, but is morphologically and genetically distinct from all previously described leech species. We named the new species Placobdella appalachiensis sp. n. Moser and Hopkins, based on the mountainous region in which it was discovered. Our surveys over a three consecutive year period suggested that this leech species may be patchily distributed and/or have a narrow geographic range. We consistently detected leeches at one site (mean prevalence in 80 hellbenders = 27.5%; median intensity = 3.0 leeches per parasitized hellbender [range 1 – >250 leeches]) during three years of surveys, but we never found leeches in any of our other seven study sites in two streams (mean prevalence in 139 hellbenders = 0%). We found a significant positive relationship between hellbender body size and the intensity of parasitism, and we suggest the possibility that the behavioral ecology of adults leading up to reproduction may increase their encounter rates with parasites. We discuss the potential conservation implications of discovery of leeches in this stream, and make recommendations for future mitigation and monitoring efforts.     

Population structure, mitochondrial polyphyly and the repeated loss of human biting ability in anopheline mosquitoes from the southwest Pacific

Australia and New Guinea contain high levels of endemism and biodiversity, yet there have been few evaluations of population‐level genetic diversity in fauna occurring throughout the Australo‐Papuan region. Using extensive geographical sampling, we examined and compared the phylogenetic relationships, phylogeography and population structure of Anopheles farauti, An. hinesorum and An. irenicus throughout their ranges in the southwest Pacific using mitochondrial (mtDNA COI) and nuclear (ribosomal protein S9 and ribosomal DNA ITS2) loci. Phylogenetic analyses suggest that the ability to utilize humans as hosts has been lost repeatedly, coincident with independent colonizations of the Solomon Islands. As some of the species under investigation transmit malaria in the region, this is a medically important finding. Maximum likelihood and Bayesian phylogenetic analyses of nuclear loci also showed that the three species are monophyletic. However, putative introgression of An. hinesorum mtDNA onto a nuclear background of An. farauti was evident in populations from Queensland, Torres Strait and southern New Guinea. Haplotype networks and pairwise F_ST values show that there is significant genetic structure within New Guinea and Australia in both An. farauti and An. hinesorum, consistent with a long‐term history of low gene flow among populations.     

Within-river gene flow in the hellbender (Cryptobranchus alleganiensis) and implications for restorative release

Understanding how populations are genetically and demographically connected is beneficial for species management, since gene flow and dispersal contribute to genetic diversity and population persistence. For hellbenders (Cryptobranchus alleganiensis), an aquatic salamander species experiencing dramatic declines in population size, fine-scale (i.e. within river) patterns of genetic diversity and gene flow are not well understood. Previous findings indicate that hellbenders are habitat specialists that exhibit extreme site fidelity and low vagility, suggesting that gene flow is restricted among the several, discrete habitat patches within a river. Using 15 polymorphic microsatellite loci and 497 hellbender samples from four Missouri rivers, we assessed fine-scale patterns of genetic diversity in order to infer population connectivity and aid in population management. Results indicate moderate levels of genetic variation (H_O = 0.66–0.78) with little differentiation among habitat patches (avg. F_ST = 0.002) and no evidence of isolation by distance. Our data suggest that hellbender gene flow has been extensive even among habitat patches separated by distances greater than >100 km. These results are useful for hellbender management, especially in terms of making informed decisions regarding restorative releases of captively propagated individuals.     

MOLECULAR PHYLOGENETICS AND EVOLUTION OF SEXUAL DICHROMATISM AMONG POPULATIONS OF THE YARROW'S SPINY LIZARD (SCELOPORUS JARROVII)

Understanding evolution of geographic variation in sexually dimorphic traits is critical for understanding the role that sexual selection may play in speciation. We performed a phylogenetic analysis of geographic variation in sexual dichromatism in the Yarrow's spiny lizard (Sceloporus jarrovii), a taxon that exhibits remarkable diversity in male coloration among populations (e.g., black, red, green, yellow, blue, brown). An mtDNA phylogeny based on approximately 880 bp from the 12S ribosomal RNA gene and 890 bp from the ND4 gene was reconstructed for 30 populations of S. jarrovii and eight other species of the torquatus species group using maximum-likelihood and parsimony methods. The phylogeny suggests that S. jarrovii consists of at least five evolutionary species, none of which are sister taxa. Although intraspecific diversity in male coloration is less than indicated by previous taxonomy, two species formerly referred to as S. jarrovii exhibit impressive geographic variation in sexual dichromatism. In one of these species, the phylogeny shows the independent evolution of a distinctive blue color morph in different parts of the species range. This pattern suggests that sexual selection may lead to striking phenotypic divergence among conspecific populations and striking convergence. Results also demonstrate the importance of a phylogenetic perspective in studies of evolutionary processes within nominal species and the problematic nature of “polytypic” species recognized under the biological species concept.     

Conservation genetics of eastern hellbenders <Emphasis Type="Italic">Cryptobranchus alleganiensis alleganiensis</Emphasis> in the Tennessee Valley

The eastern hellbender has declined across much of its range and is a candidate for listing under the Endangered Species Act. Some of the most viable remaining populations exist in the Southern Appalachian Region in the Tennessee Valley watershed; however these populations are highly isolated and fragmented, and occupy several physiographic provinces, suggesting they may exhibit significant levels of genetic differentiation. We investigated genetic and phylogeographic relationships among eastern hellbender populations across the Tennessee Valley, using nuclear microsatellite markers and mitochondrial sequence data. Our population genetic analyses of microsatellite data revealed a strong pattern of isolation by stream distance, and 4 genetically distinct populations. These four populations were mainly associated with major watersheds, although middle Tennessee samples were difficult to assign to any particular population. Our phylogeographic analysis of mtDNA resulted in a strongly supported monophyletic ingroup containing nine largely allopatric clades, which also largely corresponded to major watersheds. Our findings suggest that hellbenders from different watersheds in the Tennessee Valley should be recognized as genetically distinct populations, and care should be taken to balance the needs of rescuing declining populations with translocation or headstart programs, while also preserving genetic diversity across the region.     

Molecular evidence for hybridization between two Australian desert skinks, Ctenotus leonhardii and Ctenotus quattuordecimlineatus (Scincidae: Squamata)

Australian scincid lizards in the genus Ctenotus constitute the most diverse vertebrate radiation in Australia. However, the evolutionary processes that have generated this diversity remain elusive, in part because both interspecific phylogenetic relationships and phylogeographic structure within Ctenotus species remain poorly known. Here we use nucleotide sequences from a mitochondrial locus and two nuclear introns to investigate broad-scale phylogeographic patterns within Ctenotus leonhardii and C. quattuordecimlineatus, two geographically widespread species of skinks that were found to have a surprisingly close genetic relationship in a previous molecular phylogenetic study. We demonstrate that the apparent close relationship between these ecologically and phenotypically distinct taxa is attributable to mitochondrial introgression from C. quattuordecimlineatus to C. leonhardii. In the western deserts, Ctenotus leonhardii individuals carry mtDNA lineages that are derived from C. quattuordecimlineatus mtDNA lineages from that geographic region. Coalescent simulations indicate that this pattern is unlikely to have resulted from incomplete lineage sorting, implicating introgressive hybridization as the cause of this regional gene-tree discordance.     

Decline of a giant salamander assessed with historical records,environmental DNA and multi‐scale habitat data

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Morphology and mitochondrial DNA variation of the Siberian whitefish <Emphasis Type="Italic">Coregonus lavaretus pidschian</Emphasis> (Gmelin) in the upstream water bodies of the Ob and Yenisei Rivers

Combining morphological, ecological and genetic analyses, we compared patterns of diversification within and among populations of the southern Siberian whitefish species Coregonus lavaretus pidschian (Gmelin) to illuminate their evolutionary history. Using sequencing data from 1,930 bp of NADH dehydrogenase subunit 1 (ND1) mitochondrial DNA regions, we documented phylogeographic relationships among populations and developed a phylogeny of mtDNA haplotypes. We found significant differences in the perforated lateral-line scale numbers within and between some populations. Clear differences in the number of gill rakers on the first branchial arch were only exhibited between populations of C. l. pidschian and Coregonus lavaretus pravdinellus Dulkeit. Concordance between different morphological groups based on two meristic traits and mtDNA patterns was also tested.     

GEOGRAPHIC POPULATION STRUCTURE AND SPECIES DIFFERENCES IN MITOCHONDRIAL DNA OF MOUTHBROODING MARINE CATFISHES (ARIIDAE) AND DEMERSAL SPAWNING TOADFISHES (BATRACHOIDIDAE)

Restriction-fragment length polymorphisms in mitochondrial DNA (mtDNA) were used to evaluate population-genetic structure and matriarchal phylogeny in four species of marine fishes that lack a pelagic larval stage: the catfishes Arius felis and Bagre marinus, and the toadfishes Opsanus tau and O. beta. Thirteen informative restriction enzymes were used to assay mtDNAs from 134 specimens collected from Massachusetts to Louisiana. Considerable genotypic diversity was observed in each species. However, major mtDNA phylogenetic assemblages in catfish and toadfish (as identified in Wagner networks and UPGMA phenograms) exhibited contrasting patterns of geographic distribution: in catfish, distinct mtDNA clades were widespread, while such clades in toadfish tended to be geographically localized. By both the criteria of species' ranges and the geographic pattern of intraspecific mtDNA phylogeny, populations of marine catfish in the western Atlantic have had greater historical interconnectedness than have toadfish. Results are also compared to previously published mtDNA data in freshwater and other marine fishes. Although mtDNA differentiation among conspecific populations of continuously distributed marine fishes is usually lower than that among discontinuously distributed freshwater species inhabiting separate drainages, it is apparent that historical biogeographic factors can importantly influence genetic structure in marine as well as freshwater species.