The historical biogeography of Mammalia

Palaeobiogeographic reconstructions are underpinned by phylogenies, divergence times and ancestral area reconstructions, which together yield ancestral area chronograms that provide a basis for proposing and testing hypotheses of dispersal and vicariance. Methods for area coding include multi-state coding with a single character, binary coding with multiple characters and string coding. Ancestral reconstruction methods are divided into parsimony versus Bayesian/likelihood approaches. We compared nine methods for reconstructing ancestral areas for placental mammals. Ambiguous reconstructions were a problem for all methods. Important differences resulted from coding areas based on the geographical ranges of extant species versus the geographical provenance of the oldest fossil for each lineage. Africa and South America were reconstructed as the ancestral areas for Afrotheria and Xenarthra, respectively. Most methods reconstructed Eurasia as the ancestral area for Boreoeutheria, Euarchontoglires and Laurasiatheria. The coincidence of molecular dates for the separation of Afrotheria and Xenarthra at approximately 100 Ma with the plate tectonic sundering of Africa and South America hints at the importance of vicariance in the early history of Placentalia. Dispersal has also been important including the origins of Madagascar's endemic mammal fauna. Further studies will benefit from increased taxon sampling and the application of new ancestral area reconstruction methods.     

The historical biogeography of Scabiosa (Dipsacaceae): implications for Old World plant disjunctions

Aim To reconstruct the temporal and biogeographical history of Old World disjunctions in Scabiosa (Dipsacaceae) and the timing of diversification in the Mediterranean Basin, in order to evaluate the importance of biogeographical and climatological history (particularly the onset of a mediterranean climate) in shaping Scabiosa distributions. Location Europe and the Mediterranean Basin, southern Africa and eastern Asia. Methods This study uses maximum‐likelihood and Bayesian phylogenetic analyses of chloroplast DNA (atpB–rbcL, trnL–trnF, trnS–trnG, psbA–trnH) and nuclear ribosomal DNA [internal transcribed spacer (ITS) and external transcribed spacer (ETS)] from 24 out of c. 37 ingroup taxa, beast molecular dating, and the dispersal–extinction–cladogenesis method (Lagrange ) to reconstruct ancestral geographical ranges and the timing of diversification of the major clades of Scabiosa. Results Biogeographical and divergence time reconstructions showed that Scabiosa originated during the Miocene and diversified in Europe, followed by independent movements into Asia and Africa. Several of the major clades were inferred to have radiated sometime between the late Miocene and early Pleistocene, a timeframe that encompasses the onset of the mediterranean climate in Europe. More recent middle–late Pleistocene radiations in the Mediterranean Basin and southern Africa have played a large role in Scabiosa diversification. Main conclusions Members of Scabiosa appear to have capitalized on adaptations to montane and/or dry conditions in order to colonize similar habitats in different biogeographical regions. The formation of the East African Rift mountains is potentially of great importance in explaining the southward migration of Scabiosa. The initial diversification of Scabiosa in Europe during the Miocene is not consistent with the initiation of the mediterranean climate, but may instead be associated with increased aridity and the retreat of subtropical lineages during this time. However, the radiation of some of the major subclades within Scabiosa may have been associated with an emerging mediterranean climate. More recent and rapid radiations in both the Mediterranean Basin and southern Africa highlight the probable importance of Pleistocene climate fluctuations in Scabiosa diversification.     

Phylogenetic relationships and historical biogeography of spined loaches (Cobitidae, Cobitis and Sabanejewia) as indicated by variability of mitochondrial DNA

For sequence analysis of the 12S rRNA gene in spined loaches, specimens of the following taxa were used: Sabanejewia balcanica, Cobitis paludica, C. bilineata, C. fahireae, C. elazigensis, C. elongata , two different sub-populations of C. taenia and four different sub-populations of C. turcica . Phylogenetic relationships among taxa were estimated using parsimony, neighbor-joining, and maximum likelihood algorithms. The calculation of the transition-tranversion ratio indicated that the taxa analysed were rather distantly related. Our analyses using the genus Sabanejewia as an outgroup suggest that C. bilineata is separated from the subgenus Cobitis sensu stricto and placed together with C. elongata as basal to all other species of the genus Cobitis . Support for the placement of C. paludica as basal to both the subgenera Bicanestrinia and Cobitis s. s. (without C. bilineata ) is given by outcomes from three independent methods of phylogenetic reconstruction. A sister-taxon relationship for the subgenera Bicanestrinia and Cobitis s. s. without C. bilineata was consistently found. C. elazigensis was closely related to the population of C. turcica from Lake Beysehir in Turkey. Both formed a sister-group to the remaining populations of C. turcica , while C. fahireae was basal to C. taenia . A molecular clock was calculated based on sequence divergence values and palaeogeographical data. This suggests that different historical colonization routes must have been used by different clades of spined loaches.     

Systematics of the Deropristiidae Cable & Hunninen, 1942 (Trematoda) and biogeographical associations with sturgeons (Osteichthyes: Acipenseridae)

The 11 nominal species of the Deropristiidae, belonging to the genera Deropristis (three species), Pristicola (one species), Skrjabinopsolus (five species) and Cestrahelmins (two species) were re-evaluated for a phylogenetic and biogeographical analysis of the group. Skrjabinopsolus elongatus (Madhavi, 1974) (= S. indicus Gupta & Ahmad, 1976, S. kurotchkini Parukhin, 1976), S. sanyaensis Shen, 1990, Deropristis paurosoma Wang, 1989 and Cestrahelmins Fischthal, 1957, do not belong to the Deropristiidae. The genus Opisthodiplomonorchis Madhavi, 1974 is resurrected for its type-species, O. elongatus (= S. elongatus), and D. paurosoma is also transferred to this genus. Species of Opisthodiplomonorchis occur in polynemid fishes of the Indo-Pacific. Five nominal species thus comprise the Deropristiidae, i.e. S. armatus Ivanov in Ivanov and Mrygin, 1937, S. manteri (Cable, 1952), D. hispida (Abildgaard, 1819), D. inflata (Molin, 1859) and P. sturionis (Little, 1930), which corresponds to the original composition of the family. A comparison of Skrjabinopsolus from acipenserids in North America and Europe revealed variability in morphological characters considered diagnostic in the past (body size and position of the ovary and testes). Based on the morphology and biology, the two species of Skrjabinopsolus can be considered incipient species. A phylogenetic analysis of the redefined Deropristiidae indicates that Deropristis and Pristicola may form a monophyletic group with Skrjabinopsolus as the sister taxon. The biogeography of the Deropristiidae suggests an origin and distribution associated with the formation of the North Atlantic basin. Freshwater and marine/estuarine origins for the family are equally parsimonious possibilities. A freshwater origin can be traced at least to Cretaceous Laurasia followed by a drift-vicariance separation and subsequent association with North Atlantic drainages. Support for a marine ancestry of the Deropristiidae is indicated by the biogeography of its sister taxa (outgroups in this study) and of its hosts, and is also consistent with an Atlantic origin. The deropristiids evidently originated and speciated within the Acipenseridae in the Atlantic region, with a host switch into Atlantic Anguilla spp.     

Parasites of lake sturgeon, Acipenser fulvescens (Chondrostei: Acipenseridae), from central Canada

Nineteen species of parasites were recovered from lake sturgeon, Acipenser fulvescens, from four major waterways of Central Canada; the Saskatchewan, Nelson, Winnipeg and Rainy River systems, Twelve of these are new host records. Host specific parasites, Crepidostomum auriculatum , Diclybothrium armatum , Spinitectus acipenseri and Truttaedacnitis clitellarius , forming the core parasite species, were recovered with the highest prevalence (≥70%) and were most widely distributed. Polypodium hydriforme was recovered from only stage IV sturgeon oocytes. With the exception of Pomphorhynchus bulbocolli , prevalence and intensity of endohelminth infections were not correlated with sex or age of host but the distribution of non host-specific parasites among sampling sites was determined by the type and relative abundance of food items consumed. The parasites of lake sturgeon are closely correlated to its diet and the species of parasites recovered are more similar to those of freshwater sturgeon in Eurasia than to other species of Acipenser in North America. The present parasite community of lake sturgeon appears to have been shaped by three major factors; the presence of core parasite species which predates geographic isolation, a benthic freshwater diet which has reshaped the parasite community to one comprising freshwater species and a long association with freshwater habitats which is reflected in the reproductive isolation of the lake sturgeon and lastly, the establishment of a host-specific parasite, Spinitectus acipenseri .     

Mitochondrial DNA diversity and historical biogeography of a wet forest-restricted frog (Litoria pearsoniana) from mid-east Australia

MtDNA sequencing was used to investigate the genetic population structure of Litoria pearsoniana, a wet forest-restricted hylid frog, endemic to southeast Queensland and northeast New South Wales, Australia. L. pearsoniana is regarded as endangered under Queensland legislation. Significant genetic divergence among populations of frogs from different rainforest isolates was identified, but the lack of reciprocal monophyly among adjacent isolates suggests this is the result of a relatively recent disruption to gene flow. A paired catchment study within a single rainforest isolate, the Conondale Range, revealed no substantial genetic structuring, indicating the occurrence of terrestrial dispersal among nearby streams either in the recent past or currently. Two major reciprocally monophyletic clades of mtDNA alleles were identified. These corresponded to two geographical regions separated by the Brisbane River valley; one consisting of the Conondale and D’Aguilar Ranges, and the other of the southern isolates in the Main, Border and Gibraltar Ranges. Sequence divergence between the two regions was more consistent with a late Miocene or Pliocene rather than late Pleistocene separation, and is similar to that found among phylogeographic divisions of rainforest reptiles and amphibians in north Queensland rainforests. The molecular evidence for long-term separation of these two regions is corroborated by the pattern of species turnover in the distributions of species of rainforest-restricted amphibians and reptiles. Bioclimatic modelling suggests that appropriate conditions for L. pearsoniana would have been restricted to isolated refuges in each phylogeographic division under cooler and drier climates, such as predicted for the last glacial maximum. Currently isolated montane areas may have been connected transiently during the past 2000 years. Identification of long-term zoogeographic divisions among southeast Queensland rainforest herpetofauna has important implications for conservation and management. Conservation management of L. pearsoniana should be applied at the scale of major rainforest isolates and the conservation status of the species should be assessed independently north and south of the historical division.     

The other face of Lyell: historical biogeography in his Principles of geology

Although some excellent articles about Lyell's work have been published, they do not explicitly deal with Lyell's biogeographical conceptions. The purpose of this paper is to analyse Lyell's biogeographical model in terms of its own internal structure. Lyell tried to explain the distribution of organisms by appealing to a real cause (climate). However, he was aware that environmental conditions were clearly insufficient to explain the existence of biogeographical regions. Lyell's adherence to ecological determinism generated strong tensions within his biogeographical model. He shifted from granting a secondary weight to dispersal to assigning it a major role. By doing so, Lyell was led into an evident contradiction. A permanent tension in Lyell's ideas was generated by the prevalent explanatory pattern of his time. The explanatory model based on laws did not produce satisfactory results in biology because it did not deal with historical processes. We may conclude that the knowledge of organic distribution interested Lyell as long as it could be explained by the uniformitarian principles of his geological system. The importance of the second volume of the Principles of geology lies in its ample and systematic argumentation about the geographical distribution of organisms. Lyell established, independently from any theory about organic change, the first version of dispersalist biogeography.     

Molecular phylogenetics and historical biogeography of Hawaiian Dryopteris (Dryopteridaceae)

The fern genus Dryopteris (Dryopteridaceae) is represented in the Hawaiian Islands by 18 endemic taxa and one non-endemic, native species. The goals of this study were to determine whether Dryopteris in Hawai'i is monophyletic and to infer the biogeographical origins of Hawaiian Dryopteris by determining the geographical distributions of their closest living relatives. We sequenced two chloroplast DNA fragments, rbcL and the trnL-F intergenic spacer (IGS), for 18 Hawaiian taxa, 45 non-Hawaiian taxa, and two outgroup species. For individual fragments, we estimated phylogenetic relationships using Bayesian inference and maximum parsimony. We performed a combined analysis of both cpDNA fragments employing Bayesian inference, maximum parsimony, and maximum likelihood. These analyses indicate that Hawaiian Dryopteris is not monophyletic, and that there were at least five separate colonizations of the Hawaiian Islands by different species of dryopteroid ferns, with most of the five groups having closest relatives in SE Asia. The results suggest that one colonizing ancestor, perhaps from SE Asia, gave rise to eight endemic taxa (the glabra group). Another colonizing ancestor, also possibly from SE Asia, gave rise to a group of five endemic taxa (the exindusiate group). Dryopteris fusco-atra and its two varieties, which are endemic to Hawai'i, most likely diversified from a SE Asian ancestor. The Hawaiian endemic Nothoperanema rubiginosum has its closest relatives in SE Asia, and while the remaining two species, D. wallichiana and D. subbipinnata, are sister species, their biogeographical origins could not be determined from these analyses due to the widespread distributions of D. wallichiana and its closest non-Hawaiian relative.     

Molecular phylogenetics and the historical biogeography of dippers (Cinclus)

I used combined sequences of mitochondrial cytochrome  b and ND2 genes to determine the molecular phylogenetic relationships of all five extant species of dipper ( Cinclus ), as well as the relationships of Cinclidae to postulated nearest relatives. All methods of analysis resulted in a single best tree of dipper relationships, uniting the two South American taxa (as sisters) with the single North American exemplar, and the two Eurasian taxa forming a sister clade to the New World taxa. Further, each tree identified thrushes (Turdidae) as the closest relative to Cinclidae. Based on relationships within Cinclus , a Eurasian ancestral area is proposed, with subsequent movement into the New World. Dating of species divergences suggest that dippers arose approximately 4 mya, and achieved their present continental distributions soon after.     

The history of a nearctic colonization: molecular phylogenetics and biogeography of the Nearctic toads (Bufo)

Previous hypotheses of phylogenetic relationships among Nearctic toads (Bufonidae) and their congeners suggest contradictory biogeographic histories. These hypotheses argue that the Nearctic Bufo are: (1) a polyphyletic assemblage resulting from multiple colonizations from Africa; (2) a paraphyletic assemblage resulting from a single colonization event from South America with subsequent dispersal into Eurasia; or (3) a monophyletic group derived from the Neotropics. We obtained approximately 2.5 kb of mitochondrial DNA sequence data for the 12S, 16S, and intervening valine tRNA gene from 82 individuals representing 56 species and used parametric bootstrapping to test hypotheses of the biogeographic history of the Nearctic Bufo. We find that the Nearctic species of Bufo are monophyletic and nested within a large clade of New World Bufo to the exclusion of Eurasian and African taxa. This suggests that Nearctic Bufo result from a single colonization from the Neotropics. More generally, we demonstrate the utility of parametric bootstrapping for testing alternative biogeographic hypotheses. Through parametric bootstrapping, we refute several previously published biogeographic hypotheses regarding Bufo. These previous studies may have been influenced by homoplasy in osteological characters. Given the Neotropical origin for Nearctic Bufo, we examine current distributional patterns to assess whether the Nearctic-Neotropical boundary is a broad transition zone or a narrow boundary. We also survey fossil and paleogeographic evidence to examine potential Tertiary and Cretaceous dispersal routes, including the Paleocene Isthmian Link, the Antillean and Aves Ridges, and the current Central American Land Bridge, that may have allowed colonization of the Nearctic.     

Osteology and phylogenetic interrelationships of sturgeons (Acipenseridae)

Sturgeons (Acipenseridae) are an ancient and unique assemblage of fishes historically important to discussions of actinopterygian evolution. Despite their basal position within Actinopterygii, rigorous comparative morphological studies of acipenserids have never been made, and most ideas about acipenserid evolution hinge on an untested impression that shovelnose sturgeons (Scaphirhynchini) are phylogenetically primitive. This impression promoted ideas that: (1) the earliest acipenserids were highly benthic and evolved secondarily into pelagic predators, and (2) paedomorphosis has dominated mechanisms affecting their morphological change. Using cladistic methods, this study examines generic level interrelationships within Acipenseridae. Representatives of the four acipenserid genera Huso, Acipenser, Pseudoscaphirhynchus, and Scaphirhynchus, as well as their acipenseriform outgroups Polyodontidae, Peipiaosteidae, and Chondrosteidae, were surveyed for skeletal characters. Sixty-nine characters are identified and described to support the first generic level cladogram of Acipenseridae. Huso is phylogenetically primitive within Acipenseridae and the sister group to a redefined subfamily Acipenserinae. Acipenser is not supported by any characters identified in this study, but the tribe Scaphirhynchini comprising Scaphirhynchus and Pseudoscaphirhynchus is found to be monophyletic. The cladogram contradicts historical ideas about acipenserid evolution because Huso defines an outgroup morphology and life history founded on pelagic habitats and piscivory. In contrast, acipenserines, and more markedly scaphirhynchines, are benthic predators possessing character complexes for benthic feeding, respiration, locomotion, and protection. Also, the pattern of character acquisition within Acipenseridae suggests that peramorphosis played a central role in acipenserid evolution. Peramorphic addition and enlargement of the skeleton and scalation defines most characters at all nodes within Acipenseridae, and repudiates paedomorphosis as a major trend in evolution within the family Acipenseridae.     

Molecular phylogenetics, historical biogeography, and chromosome number evolution of Portulaca (Portulacaceae)

Portulaca is the only genus in Portulacaceae and has ca. 100 species distributed worldwide, mainly in the tropics and subtropics. Molecular data place the genus as one of the closest relatives of Cactaceae, but phylogenetic relationships within Portulaca are barely known. This study samples 59 species of Portulaca, 10 infraspecific taxa, and three cultivars, including multiple samples of widespread species. The sampled taxa represent all subgenera in the classifications of von Poellnitz (1934), Legrand (1958), and Geesink (1969) and come from around the world. Nuclear ITS and chloroplast ndhF, trnT-psbD intergenic spacer, and ndhA intron DNA sequences were analyzed using maximum likelihood and Bayesian methods to produce a hypothesis of relationships within Portulaca. Divergence times were estimated using Hawaiian endemics for calibration, and biogeographical patterns were examined using a Bayes-DIVA approach. In addition, the evolution of chromosome numbers in the genus was investigated using probabilistic models. The analyses strongly support the monophyly of Portulaca, with an age of the most recent common ancestor (MRCA) of 23 Myr. Within Portulaca are two major lineages: the OL clade (comprising opposite-leaved species) distributed in Africa, Asia, and Australia, and the AL clade (comprising alternate to subopposite-leaved species), which is more widespread and originated in the New World. Sedopsis, a genus sometimes recognized as distinct from Portulaca based on a long corolla tube, is nested within the OL clade and does not merit taxonomic recognition. Samples of Portulaca grandiflora, Portulaca halimoides, and Portulaca oleracea were found to be non-monophyletic. It is hypothesized that the ancestral distribution area of Portulaca included southern hemisphere continents and Asia. The OL clade remained restricted to the Old World (except Portulaca quadrifida, a pantropical weed), while the AL clade, with a South American origin, was able to disperse multiple times to other continents. The base chromosome number for Portulaca is inferred to be x=9, although the analysis was primarily based on the available data for the AL clade. A number of chromosome number change events (polyploidization, demi-polyploidization, gain, and loss) were shown to have occurred in the genus, especially within the Oleracea clade.     

The voice of historical biogeography

Historical biogeography is going through an extraordinary revolution concerning its foundations, basic concepts, methods, and relationships to other disciplines of comparative biology. There are external and internal forces that are shaping the present of historical biogeography. The external forces are: global tectonics as the dominant paradigm in geosciences, cladistics as the basic language of comparative biology and the biologist's perception of biogeography. The internal forces are: the proliferation of competing articulations, recourse to philosophy and the debate over fundamentals. The importance of the geographical dimension of life's diversity to any understanding of the history of life on earth is emphasized. Three different kinds of processes that modify the geographical spatial arrangement of the organisms are identified: extinction, dispersal and vicariance. Reconstructing past biogeographic events can be done from three different perspectives: (1) the distribution of individual groups (taxon biogeography) (2) areas of endemism (area biogeography), and (3) biotas (spatial homology). There are at least nine basic historical biogeographic approaches: centre of origin and dispersal, panbiogeography, phylogenetic biogeography, cladistic biogeography, phylogeography, parsimony analysis of endemicity, event-based methods, ancestral areas, and experimental biogeography. These nine approaches contain at least 30 techniques (23 of them have been proposed in the last 14 years). The whole practice and philosophy of biogeography depend upon the development of a coherent and comprehensive conceptual framework for handling the distribution of organisms and events in space.     

The historical biogeography of Apsilochorema (Trichoptera,Hydrobiosidae) revised,following molecular studies

The genus Apsilochorema Ulmer, 1907 is unique in the family Hydrobiosidae Ulmer, being widely distributed in the Palaearctic, Oriental and Australian Regions. All other 49 genera in the family, except the New World Atopsyche Banks, 1905, are confined to a single biogeographical Region. This unique distribution has independently stimulated researchers to formulate competing hypotheses about the biogeographical history of the genus. Molecular sequence data from mitochondrial cytochrome oxidase I (COI) and nuclear cadherin (CAD) genes of Apsilochorema species from the Oriental and Australian areas were analysed phylogenetically. The results retain a monophyletic Apsilochorema, which forms the sistergroup to the other genera in the subfamily Apsilochorematinae. The results from the biogeographical analyses dispute the earlier assumptions of an Oriental or northern Gondwana origin for the genus, revealing unambiguously an initial Australian radiation of the ancestral Apsilochorema with a subsequent dispersal into the Oriental Region. All but one of the Apsilochorema species occurring on the Pacific islands had an Oriental ancestor. The exception is the sistergroup to the New Caledonian species, which is found in both Australia and Oriental Regions. The molecular dating analysis, using a relaxed clock model, indicates that the genus Apsilochorema is about 36.4 MY old and that it dispersed from Australia into the Oriental Region about 28.3 Ma. It also gives an estimate of the approximate ages of the dispersals into New Caledonia to about 15.3 Ma; to the Solomon Islands at about 16.2 Ma; to the Fiji Islands at about 16.1 Ma; and to the Vanuatu Islands at about 5.4 Ma.     

Molecular phylogeny and historical biogeography of Caltha (Ranunculaceae) based on analyses of multiple nuclear and plastid sequences

Caltha is a widely distributed genus in the buttercup family (Ranunculaceae) showing interesting distribution patterns in both hemispheres. Evolutionary history ofCaltha was examined by means of phylogenetic, molecular dating, and historical biogeographic analyses with a more comprehensive sampling than previous studies. The internal transcribed spacer from the nuclear genome and trnL-F and atpB-rbcL regions from the plastid genome were used and analyzed using parsimony and Bayesian methods. Divergence time was estimated using Bayesian dating analyses with multiple fossil calibrations. Historical biogeography was inferred using the Bayes-DIVA method implemented in RASP. We obtained a well-resolved and well-supported phylogeny within the Caltha lineage. Caltha natansPall. diverged first from the genus and the other species grouped into two clades. Our expanded sampling scheme revealed a complicated evolutionary pattern in theC. palustris complex. Caltha sinogracilis W. T. Wang was resolved to be a member of the C. palustris complex, rather than closely related to C. scaposa Hook. f. & Thomson. Caltha rubriflora B. L. Burtt & Lauener was also revealed to be not just a red-flower form of C. sinogracilis. The diversification of the genus began at 50.5 mya (95% high posterior density: 37.1–63.9 mya), and its ancestral range was very probably in the Northern Hemisphere. The South American species may derive from western North American ancestors that dispersed along the western American Cordillera during the Cenozoic era. The vicariance model of the Southern Hemisphere species proposed by a previous study was rejected in this study.     

New insights into the phylogenetics and biogeography of Arum (Araceae): unravelling its evolutionary history

The heat‐ and odour‐producing genus Arum (Araceae) has interested scientists for centuries. This long‐term interest has allowed a deep knowledge of some complex processes, such as the physiology and dynamics of its characteristic lure‐and‐trap pollination system, to be built up. However, mainly because of its large distributional range and high degree of morphological variation, species' limits and relationships are still under discussion. Today, the genus comprises 28 species subdivided into two subgenera, two sections and six subsections. In this study, the phylogeny of the genus is inferred on the basis of four plastid regions, and the evolution of several morphological characters is investigated. Our phylogenetic hypothesis is not in agreement with the current infrageneric classification of the genus and challenges the monophyly of several species. This demonstrates the need for a new infrageneric classification based on characters reflecting the evolution of this enigmatic genus. To investigate the biogeography of Arum deeply, further spatiotemporal analyses were performed, addressing the importance of the Mediterranean basin in the diversification of Arum. Our results suggest that its centre of origin was the European–Aegean region, and that major diversification happened during the last 10 Myr. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 14–32.     

Molecular phylogenetics and biogeography of galaxiid fishes (Osteichthyes: Galaxiidae): dispersal,vicariance, and the position of Lepidogalaxias salamandroides

The galaxiid fishes exhibit a gondwanan distribution. We use mitochondrial DNA sequences to test conflicting vicariant and dispersal biogeographic hypotheses regarding the Southern Hemisphere range of this freshwater group. Although phylogenetic resolution of cytochrome b and 16S rRNA sequences is largely limited to more recent divergences, our data indicate that the radiation can be interpreted as several relatively recent dispersal events superimposed on an ancient gondwanan radiation. Genetic relationships contradict the findings of recent morphological analyses of galaxioid fishes. In particular, we examine several hypotheses regarding phylogenetic placement of the enigmatic Lepidogalaxias. Although most workers consider Lepidogalaxias to be an unusual scaled member of the Southern Hemisphere galaxioids, it has also been suggested that this species is related to the Northern Hemisphere esocoids. Our data strongly suggest that this species is not a galaxiid, and the alternative hypothesized esocoid relationship cannot be rejected. The species-rich genus Galaxias is shown to be polyphyletic and the generic taxonomy of the Galaxiinae is reassessed in the light of phylogenetic relationships. Juvenile saltwater-tolerance is phylogenetically distributed throughout the Galaxiinae, and the loss of this migratory phase may be a major cause of speciation.