The effect of landscape processes upon gene flow and genetic diversity in an Australian freshwater fish, Neosilurus hyrtlii

1. Flow regime and riverine architecture are two important landscape characteristics that influence genetic diversity and gene flow in riverine species.
2. Using population genetic markers (mtDNA, microsatellites and allozymes), this study aimed to investigate genetic diversity and gene flow in the freshwater fish, Neosilurus hyrtlii , across two major drainage divisions in northern and central Australia (the Gulf of Carpentaria and Lake Eyre basins). These basins lie adjacent to each other and differ in their hydrological inputs and riverine structure, providing an ideal opportunity to identify the impact of landscape processes upon population dynamics of freshwater fish.
3. Populations were strongly structured among basins, among catchments within basins and were weakly structured within catchments in the Lake Eyre Basin, providing support for the Stream Hierarchy Model.
4. Interestingly, mtDNA and microsatellite diversity was much higher in the Gulf of Carpentaria Basin compared to the Lake Eyre Basin. It was concluded that this difference was due to the extreme hydrological variability in this basin and boom-bust population cycles resulting in smaller effective population sizes in the Lake Eyre Basin.     

Phylogeography of the widespread Australian freshwater prawn, Macrobrachium australiense (Decapoda, Palaemonidae)

Aim To investigate the phylogeographic structure of the widespread freshwater prawn, Macrobrachium australiense, within and between major Australian drainage basins using mitochondrial sequence data. This will enable the investigation of historical connections between major drainages and examination of hypotheses of biogeographic associations among Australian freshwater basins. Location Inland, eastern and northern Australia. Methods Sequencing 16S rRNA and ATPase 6 protein coding mitochondrial DNA genes from M. australiense from 19 locations from inland, eastern and northern Australia. Results Within drainage basins, haplotype trees are monophyletic, with the exception of the Finke River from the Lake Eyre Basin. Macrobrachium australiense from the two main inland drainages, the Murray–Darling and Lake Eyre Basin are divergent from each other and do not form a monophyletic group, instead the Murray–Darling Basin haplotypes clade with eastern coastal haplotypes. Haplotypes from neighbouring eastern coastal drainages were found to be quite divergent from each other. Main conclusions The phylogeographic relationships among M. australiense suggest that the two major inland drainages, the Murray–Darling Basin and the Lake Eyre Basin, are not biogeographically closely associated to each other. Instead the Murray–Darling Basin is more closely allied with the eastern coastal drainages across the Great Dividing Range. Despite their proximity the neighbouring southeast Queensland coastal Mary and Brisbane Rivers are also biogeographically divergent from each other. The results also indicate that the Finke River appears to have been isolated from the remainder of the Lake Eyre Basin catchment for a significant period of time.     

Channel country fluvial sands and associated facies of central-eastern Australia: Modern analogues of mesozoic desert sands of south America

The Channel Country, a region of wide fluvial plains criss-crossed by a reticulate pattern of anastomosing channels, and the adjacent sand dunes and clay pans of the Lake Eyre drainage basin occupy an area of 1.3 × 10⁶ km² of internal drainage in the arid east-central part of Australia. Beneath a surface of skin of mud, the sediment of the Channel Country is sand and some mud in the floodplain, as well as in levees and channels. The surface mud represents the overbank deposits of meandering channels that are superimposed on sheet sands of a relict braided system.With the other sediments (aeolian sand and lacustrine mud) of the Lake Eyre drainage basin, the Channel Country sediments represent the latest phase of deposition of the Cainozoic Birdsville Basin, which was initiated as an interior basin behind the dismembered rifted arch of the divergent Pacific margin. In their depositional and tectonic setting, the arid sediments of central-eastern Australia are modern analogues of the Mesozoic desert sands and other non-marine sediments that were deposited behind the pre-breakup arch and post-breakup half-arch of South America. The preceding Mesozoic Great Artesian Basin of central-eastern Australia contains volcanogenic sediment and was covered for a short time by an epeiric sea; its deposition was influenced by an uplift along the convergent Pacific margin, and it is analogous to other Gondwana basins in Antarctica, southern Africa, and South America that were yoked to the convergent Pacific margin.     

The influence of landscape on population structure of four invertebrates in groundwater springs

1. The unique aquatic fauna of the island‐like groundwater springs of arid inland Australia raises important questions as to how aquatic species persist in very isolated and fragmented habitats and the role that dispersal may play in mitigating/mediating the influence of landscape structure and determining population structure. By determining the relationship between genetics and geography (i.e. phylogeography), the historical processes responsible for population structure can be determined. 2. We undertook comparative phylogeographic studies of invertebrates from springs south of Lake Eyre. Clusters of springs lying within and between surface drainage catchments (which provide a potential connection between springs) were sampled, and the phylogeographic structure of four coexisting species, an ostracod Ngarwa dirga, a snail Fonscochlea accepta, an isopod Phreatomerus latipes and an amphipod Wangiannachiltonia guzikae, was examined. 3. Clear differences in the geographic patterns of genetic structure were found amongst the four species. No discernable genetic structure was found in ostracod and snail populations, even amongst springs lying 20 km apart in separate surface catchments; isopod populations were highly genetically structured amongst springs located in separate catchments, but not within catchments, whilst amphipod populations were highly genetically structured amongst springs both within and between catchments. 4. The results suggest that differences in dispersal ability of each species, and not the overall fragmented nature of the springs, may have led to large differences in phylogeographic history. Interestingly, the relative dispersal ability of these species may be related to their vulnerability to and recovery from large‐scale flood events. Therefore, despite the highly isolated and fragmented nature of the springs, the landscape has not strongly influenced the population structure of the aquatic invertebrate community as a whole nor has it led to the evolution of common life histories.     

Mitochondrial DNA phylogenetic structuring suggests similarity between two morphologically plastic genera of Australian freshwater mussels (Unionoida: Hyriidae)

In the Lake Eyre Basin, the Australian hyriid genus Velesunio is represented by three undescribed species, each of which are highly divergent genetically, but morphologically similar to Velesunio wilsonii (Lea 1859). A fourth species, Velesunio ambiguus (Philippi 1847), occurs not only in the Lake Eyre Basin but throughout much of eastern Australia, including the Murray-Darling Basin. In this study, we show that another hyriid, Alathyria jacksoni (Iredale 1934), which is sympatric with V. ambiguus, is genetically deeply nested within the Velesunio species complex, such that the genus Velesunio is paraphyletic with respect to A. jacksoni. Moreover, our mitochondrial phylogenetic reconstructions indicate that A. jacksoni is closely allied to one of the cryptic Velesunio species occurring in the Lake Eyre Basin, but distinct from V. ambiguus and the two other Velesunio species. These data suggest that the genera Alathyria and Velesunio are in need of revision. The shells of A. jacksoni and Velesunio spp. vary with local conditions and sometimes are difficult to distinguish. Our analyses also show that shell characters of these taxa do not closely match the phylogenetic data, and it appears that the traditional taxonomic emphasis on these plastic characters has obscured evolutionary relationships between these, and possibly other, Hyriidae.     

Mitochondrial DNA and allozymes reveal high dispersal abilities and historical movement across drainage boundaries in two species of freshwater fishes from inland rivers in Queensland, Australia

This study used allozymes and mtDNA variation to test that: 1) populations of two fish species, Nematolosa erebi and Retropinna semoni , in lowland rivers in central Australia were highly connected within drainages, 2) populations in different drainages were highly differentiated and 3) there was evidence of historical connections between two major lowland drainages in inland Australia. Levels of genetic differentiation among populations within drainages were low, but still statistically significant, indicating that populations were not as highly connected as had been predicted. Populations from the Murray–Darling and the Lake Eyre drainages were highly differentiated, indicating no contemporary dispersal across drainage boundaries. Both species showed evidence of historical connections between the two drainage basins, although estimates of the time that these last occurred differed between the two species. Nematolosa erebi populations from the two drainages were estimated to have been separated c . 150 000 years ago, whereas populations of R. semoni , were estimated to have been separated c . 1.5 million years ago.     

Flying with the birds? Recent large-area dispersal of four Australian Limnadopsis species (Crustacea: Branchiopoda: Spinicaudata)

Temporary water bodies are important freshwater habitats in the arid zone of Australia. They harbor a distinct fauna and provide important feeding and breeding grounds for water birds. This paper assesses, on the basis of haplotype networks, analyses of molecular variation and relaxed molecular clock divergence time estimates, the phylogeographic history, and population structure of four common temporary water species of the Australian endemic clam shrimp taxon Limnadopsis in eastern and central Australia (an area of >1,350,000 km(2)). Mitochondrial cytochrome c oxidase subunit I sequences of 413 individuals and a subset of 63 nuclear internal transcribed spacer 2 sequences were analyzed. Genetic differentiation was observed between populations inhabiting southeastern and central Australia and those inhabiting the northern Lake Eyre Basin and Western Australia. However, over large parts of the study area and across river drainage systems in southeastern and central Australia (the Murray-Darling Basin, Bulloo River, and southern Lake Eyre Basin), no evidence of population subdivision was observed in any of the four Limnadopsis species. This indicates recent gene flow across an area of ～800,000 km(2). This finding contrasts with patterns observed in other Australian arid zone taxa, particularly freshwater species, whose populations are often structured according to drainage systems. The lack of genetic differentiation within the area in question may be linked to the huge number of highly nomadic water birds that potentially disperse the resting eggs of Limnadopsis among temporary water bodies. Genetically undifferentiated populations on a large geographic scale contrast starkly with findings for many other large branchiopods in other parts of the world, where pronounced genetic structure is often observed even in populations inhabiting pools separated by a few kilometers. Due to its divergent genetic lineages (up to 5.6% uncorrected p-distance) and the relaxed molecular clock divergence time estimates obtained, Limnadopsis parvispinus is assumed to have inhabited the Murray-Darling Basin continuously since the mid-Pliocene (～4 million years ago). This means that suitable temporary water bodies would have existed in this area throughout the wet-dry cycles of the Pleistocene.     

Population structure of Macrobrachium australiense (Decapoda: Palaemonidae) in Western Queensland, Australia: the role of contemporary and historical processes

Rivers of Western Queensland, Australia, represent a discontinuous and variable aquatic habitat for the freshwater fauna of the region. Rivers periodically fluctuate between being highly fragmented, with numerous disconnected waterholes and ephemeral channels, and being highly connected by a dominant system of anastomosing channels. We used mitochondrial sequences to investigate the genetic structure and inferred patterns of dispersal associated with this flow regime for the freshwater prawn, Macrobrachium australiense (Decapoda: Palaemonidae), sampling 28 localities throughout eight catchments. Based on a 505 base pair fragment of mitochondrial cytochrome c oxidase subunit I, we identified 98 haplotypes in a sample of 402 individuals. The haplotypes clustered into two main clades corresponding geographically to the major drainages: the Lake Eyre and Murray-Darling basins. Populations of M. australiense inhabiting the two basins appear to have diverged around 800,000 years ago (estimated sequence divergence of 1.6%). Analysis of population differentiation indicated contemporary high levels of genetic subdivision and restricted gene flow among populations within and among catchments. Phylogenetic analysis detected a series of historical range expansions in the region and we suggest that climate fluctuations during the Pleistocene have resulted in extensive floods that have promoted historical movements of aquatic organisms across catchment boundaries.     

Subdivided population structure and phylogeography of an endangered freshwater snail, Notopala sublineata (Conrad, 1850) (Gastropoda: Viviparidae), in Western Queensland, Australia

Populations of the Australian freshwater snail Notopala sublineata (Conrad, 1850) have declined rapidly over the last decade, but are still abundant in most river systems of Western Queensland. These rivers are characterized by the unpredictable and highly variable nature of their climatic and hydrological regimes, with episodic periods of very large flow and many periods of little or no flow. We used mitochondrial sequences and allozymes to investigate the genetic structure and infer patterns of dispersal of N. sublineata within this unique environment. We sampled 24 waterholes throughout the four major catchments of the Lake Eyre Basin. Based on a 457-bp fragment of the mitochondrial cytochrome oxidase subunit I gene, we identified 55 haplotypes in a sample of 256 individuals. Both nuclear and mitochondrial genetic datasets indicated high levels of genetic subdivision and restricted gene flow among populations within and among catchments. The mitochondrial haplotypes clustered into two main geographical clades, corresponding with two groups of adjacent catchments: Cooper–Bulloo and Diamantina–Georgina, which appear to have diverged 300 000 years ago. Populations of N. sublineata within these adjacent catchments seem to have diverged relatively recently, roughly 130 000 years ago. Contemporary dispersal seems to be absent between catchments but we suggest that climate fluctuations during the Pleistocene resulted in extensive floods that promoted historical movement of aquatic organisms across catchment boundaries.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 1–16.     

Desert springs: deep phylogeographic structure in an ancient endemic crustacean (Phreatomerus latipes)

Desert mound springs of the Great Artesian Basin in central Australia maintain an endemic fauna that have historically been considered ubiquitous throughout all of the springs. Recent studies, however, have shown that several endemic invertebrate species are genetically highly structured and contain previously unrecognised species, suggesting that individuals may be geographically 'stranded in desert islands'. Here we further tested the generality of this hypothesis by conducting genetic analyses of the obligate aquatic phreatoicid isopod Phreatomerus latipes. Phylogenetic and phylogeographic relationships amongst P. latipes individuals were examined using a multilocus approach comprising allozymes and mtDNA sequence data. From the Lake Eyre region in South Australia we collected data for 476 individuals from 69 springs for the mtDNA gene COI; in addition, allozyme electrophoresis was conducted on 331 individuals from 19 sites for 25 putative loci. Phylogenetic and population genetic analyses showed three major clades in both allozyme and mtDNA data, with a further nine mtDNA sub-clades, largely supported by the allozymes. Generally, each of these sub-clades was concordant with a traditional geographic grouping known as spring complexes. We observed a coalescent time between ～2-15 million years ago for haplotypes within each of the nine mtDNA sub-clades, whilst an older total time to coalescence (>15 mya) was observed for the three major clades. Overall we observed that multiple layers of phylogeographic history are exemplified by Phreatomerus, suggesting that major climate events and their impact on the landscape have shaped the observed high levels of diversity and endemism. Our results show that this genus reflects a diverse fauna that existed during the early Miocene and appears to have been regionally restricted. Subsequent aridification events have led to substantial contraction of the original habitat, possibly over repeated Pleistocene ice age cycles, with P. latipes populations becoming restricted in the distribution to desert springs.     

Phylogeography of Bufo fowleri at its northern range limit

Many of the species that recolonized previously glaciated areas in the Great Lakes basin of North America over the past 10-12,000 years exhibit genetic evidence of multiple invasion routes and present-day secondary contact between deeply divergent lineages. With this in mind, we investigated the phylogeographical structure of genetic variability in Fowler's toads (Bufo fowleri) at the northern edge of its distribution where its range encircles the Lake Erie basin. Because B. fowleri is so closely tied to habitats along the Lake Erie shoreline, we would expect to find clear evidence of the number of invasions leading to the species' colonization of the northern shore. A 540 bp sequence from the mitochondrial control region was amplified and analysed for 158 individuals from 21 populations. Interpopulation sequence variation ranged from 0% to 6%. Phylogenetic analysis of p-distance using the neighbor-joining method revealed two deeply divergent (6% sequence divergence) mtDNA lineages (Phylogroup 1 and 2), possibly arising as a result of secondary contact of populations that entered the region from two separate glacial refugia. However, the phylogeographical pattern was not simple. The populations at Long Point, on the north shore of Lake Erie, clustered with the population from Indiana Dunes on Lake Michigan to form Phylogroup 2 whereas all other B. fowleri populations examined from both sides of Lake Erie constituted Phylogroup 1. Furthermore, mtDNA sequences from the related species Bufo americanus, obtained from populations outside the range of B. fowleri, clustered with mtDNA haplotypes of B. fowleri Phylogroup 1, indicating the possibility of partial introgression of mitochondria from one species to the other.     

Continental impacts of water development on waterbirds,contrasting two Australian river basins: Global implications for sustainable water use

The world's freshwater biotas are declining in diversity, range and abundance, more than in other realms, with human appropriation of water. Despite considerable data on the distribution of dams and their hydrological effects on river systems, there are few expansive and long analyses of impacts on freshwater biota. We investigated trends in waterbird communities over 32 years, (1983–2014), at three spatial scales in two similarly sized large river basins, with contrasting levels of water resource development, representing almost a third (29%) of Australia: the Murray–Darling Basin and the Lake Eyre Basin. The Murray–Darling Basin is Australia's most developed river basin (240 dams storing 29,893 GL) while the Lake Eyre Basin is one of the less developed basins (1 dam storing 14 GL). We compared the long‐term responses of waterbird communities in the two river basins at river basin, catchment and major wetland scales. Waterbird abundances were strongly related to river flows and rainfall. For the developed Murray–Darling Basin, we identified significant long‐term declines in total abundances, functional response groups (e.g., piscivores) and individual species of waterbird (n = 50), associated with reductions in cumulative annual flow. These trends indicated ecosystem level changes. Contrastingly, we found no evidence of waterbird declines in the undeveloped Lake Eyre Basin. We also modelled the effects of the Australian Government buying up water rights and returning these to the riverine environment, at a substantial cost (>3.1 AUD billion) which were projected to partly (18% improvement) restore waterbird abundances, but projected climate change effects could reduce these benefits considerably to only a 1% or 4% improvement, with respective annual recovery of environmental flows of 2,800 GL or 3,200 GL. Our unique large temporal and spatial scale analyses demonstrated severe long‐term ecological impact of water resource development on prominent freshwater animals, with implications for global management of water resources.     

Nested clade analysis of the freshwater shrimp, Caridina zebra (Decapoda: Atyidae), from north-eastern Australia

The freshwater shrimp, Caridina zebra, is endemic to montane rainforest streams of the Atherton Tableland, north-eastern Australia. As the confluences of many of the headwater streams are in unsuitable habitat, dispersal is expected to be highly restricted. Results from a previous allozyme survey for this species suggested that historical dispersal between separate river drainages had occurred due to rearrangements of the drainage lines at some stage in the recent past. The aim of this study was to use temporal information from the mitochondrial cytochrome oxidase subunit I (CO-I) gene to determine whether the observed genetic structure was a result of historical processes, or alternatively, due to low levels of terrestrial dispersal. The mitochondrial DNA (mtDNA) data were analysed using nested clade analysis, which can differentiate between historical fragmentation and range expansion vs. contemporary restricted gene flow. The results displayed three divergent clades that were likely to have arisen in allopatry. One widespread clade, with individuals in more than one river drainage, reflected a pattern of restricted gene flow. This suggests that this species is capable of terrestrial dispersal.     

Genetic structure and dispersal of Macrobrachium australiense (Decapoda: Palaemonidae) in western Queensland, Australia

SUMMARY 1. The freshwater prawn, Macrobrachium australiense (Decapoda: Palaemonidae), is an abundant species throughout the rivers of western Queensland, and it is thought to have effective dispersal capabilities. Given the very low topographical relief of the western Queensland landscape and the vast nature of episodic flooding, it was predicted that widespread dispersal in this species would occur within, and possibly between the four major catchments of the region: the Darling, Bulloo, Cooper and Diamantina. We analysed eight polymorphic allozyme systems and a fragment of the cytochrome c oxidase subunit 1 (COI) mitochondrial DNA (mtDNA) gene to determine the extent of recent and historical patterns of dispersal at nested spatial scales, within and between catchments.
2. Large and significant levels of allozyme and mtDNA differentiation were revealed among all catchments, indicating that dispersal of M. australiense does not occur across catchment boundaries, although this species is reportedly capable of overland movement. In contrast, no significant patterns of genetic differentiation were resolved between major subcatchments of the Darling and Cooper, or between sites within these subcatchments, indicating that populations of M. australiense are panmictic within catchments.
3. The MtDNA data resolved two divergent and reciprocally monophyletic clades, with the first representing the Darling catchment, and the second corresponding to the Bulloo, Cooper and Diamantina catchments. We postulate that extreme variation in historical climatic patterns and palaeohydrologic conditions played an important role in shaping the population structure of M. australiense throughout western Queensland during the Quaternary.     

Genetic analysis and uncertain taxonomic status of threatened Foskett Spring speckled dace

Foskett Spring is a small isolated desert spring in the Warner Basin of Oregon containing an undescribed subspecies of speckled dace protected under the US Endangered Species Act. Uncertainty regarding the taxonomic status of Foskett dace has raised questions about their evolutionary relationship to other more abundant populations in the Warner Basin. To address these questions, we sequenced 1,982 base pairs (bp) of the ND2 and cyt-b genes of mitochondrial DNA (mtDNA) for 85 fish from Foskett Spring, the surrounding Warner Basin, and the adjacent Goose Lake Basin. We observed 58 unique mtDNA haplotypes defined by 96 bp substitutions in both genes. MtDNA sequences were highly divergent and reciprocally monophyletic between dace from the Warner and Goose Lake Basins, with sequence divergences (5 and 3% at ND2 and cyt-b, respectively) in the range usually observed between fish species. In contrast, mean sequence divergence between Foskett dace and other Warner Basin populations was less than 1%, with no evidence of reciprocal monophyly among mtDNA lineages. These results indicate that Foskett dace and other populations in the Warner Basin are approximately equally diverged from one another evolutionarily, suggesting similar times of divergence since the late Pleistocene. We believe further studies are needed to determine if rapid evolution of novel traits have occurred in dace inhabiting the unique ecological setting of Foskett Spring during the past 10,000 years.     

PARALLEL EVOLUTION OF LAKE-STREAM PAIRS OF THREESPINE STICKLEBACKS (GASTEROSTEUS) INFERRED FROM MITOCHONDRIAL DNA VARIATION

Three drainage systems in British Columbia, Canada, contain divergent parapatric lake-stream pairs of threespine sticklebacks (Gasterosteus aculeatus): Drizzle and Mayer Lakes on Graham Island, Queen Charlotte Islands, and Misty Lake on northeastern Vancouver Island. Ecological and morphological differences between members of all three lake-stream pairs are strikingly similar; lake fish are melanistic and slim bodied with smaller mouths and more gill rakers than the mottled-brown and robust-bodied stream sticklebacks. We estimated the level of genetic divergence between lake and stream fish in Misty Lake and tested hypotheses of single versus multiple origins of the pairs by assaying mitochondrial DNA (mtDNA) restriction site variation in samples from the three lake systems. MtDNA analysis revealed the existence of two highly divergent lineages differing by 2.7% in sequence. One lineage predominated in Misty stream fish (73%), whereas the other lineage predominated in Misty Lake samples (96%). Comparable forms (lake or stream) in the different lakes did not cluster together in terms of mtDNA nucleotide divergence, suggesting that the pairs have had independent origins. We concluded that: (1) divergent mtDNA lineages in North Pacific sticklebacks stem from historical isolation in the two major glacial refugia proposed for the North Pacific (Beringia and Cascadia); (2) the stream and lake pair in Misty Lake are distinct gene pools; (3) the divergence between parapatric lake and stream Gasterosteus represents parallel evolution having occurred at least twice in the North Pacific; and (4) different scales of evolutionary divergence exist in North Pacific Gasterosteus, that is, a relatively ancient divergence of mtDNA clades as well as recent (i.e., postglacial) divergence of ecotypes within major clades.     

Discordant patterns of morphological and molecular change in broadtail madtoms (genus Noturus)

Two morphologically distinct forms of an undescribed madtom catfish (Noturus sp.) occur in the rivers and lakes of southeastern USA. 'Lake' broadtail madtoms are endemic to Lake Waccamaw and are probably related to nearby 'river' broadtail populations. To investigate phylogenetic relationships, we surveyed mitochondrial DNA (mtDNA) sequence variation in 'lake' and 'river' broadtails and other members of the genus Noturus. Mitochondrial rDNA data suggest a sister group relationship between broadtail madtoms and N. insignis, not N. leptacanthus as posited previously. Population-level analyses using additional mtDNA characters (NADH dehydrogenase subunit 2 (ND2) and cytochrome b (Cytb)) identified two highly divergent genetic lineages within broadtail madtoms that do not correspond to the morphological designations 'river' and 'lake'.     

GEOGRAPHIC DISTRIBUTION OF MITOCHONDRIAL DNA VARIANTS AND THE HISTORICAL BIOGEOGRAPHY OF THE SPOTTED SALAMANDER,AMBYSTOMA MACULATUM

I analyzed geographic partitioning of mitochondrial DNA (mtDNA) restriction-site variants in the spotted salamander, Ambystoma maculatum. Two highly divergent and geographically separate genetic lineages were identified that differed by a minimum of 19 restriction sites (6% sequence divergence). One of the lineages has a disjunct distribution with very closely related haplotypes occurring in Missouri, Arkansas, North Carolina, and Virginia. The other lineage is found in Michigan, Illinois, and Alabama. The geographic separation of highly divergent mtDNA haplotypes, a pattern that was predicted based on the sedentary nature of these salamanders, is evidence for long-term barriers to gene flow. In contrast, the large-scale disjunction of very similar haplotypes suggests recent, long-distance gene flow and does not match the phylogeographic expectation for a small terrestrial vertebrate. I explain this potential contradiction in the level of importance assigned to gene flow by a scenario in which historical barriers to gene flow account for the two divergent mtDNA assemblages, but stochastic sorting of ancestral polymorphism is responsible for the large-scale geographic disjunction. Ten of 16 populations collected in the Ozark Highlands were fixed for the same haplotype. I attribute this lack of detectable variation to recent colonization of this area, a hypothesis that is supported by paleoecological data and demonstrates the potential benefits of combining data from paleobotany, geology, and other disciplines to reconstruct the historical biogeography of a species.     

The diatom flora of Lake Eyre South: a large episodically filled salt lake in South Australia

Thirty-three diatom taxa were collected from the large terminal salt lake, Lake Eyre South, located in south-central Australia. The diatom assemblage included taxa that were widely distributed in marine and saline athalassic habitats in both northern and southern hemispheres, with the diatom flora of Lake Eyre South most similar to that of southern Africa. This study represents the first report on the diatom flora of Lake Eyre South and supports the findings that episodically filled lakes do not appear to be good evolutionary loci.     

Exploring factors shaping population genetic structure of the freshwater fish Sinocyclocheilus grahami (Teleostei, Cyprinidae)

Phylogeographical analyses on Sinocyclocheilus grahami samples from seven localities within the Lake Dianchi Basin in China were conducted to explore the main factors shaping population structure within this species. Phylogenetic and network analyses revealed two major clades in 24 mtDNA haplotypes. One clade included three haplotypes exclusively from samples of the lower basin and another clade encompassed other haplotypes from samples of the upper basin. The estimated divergence time between the two clades predated the river capture event connecting the lower and upper lake basin and thus supported geographical isolation as the main factor shaping genetic divergence between these two clades. Furthermore, analysis of molecular variance and pair-wise Φ_ST distances revealed significant genetic differentiation within the upper basin. Mantel tests clearly supported patterns of differentiation arose purely as a result of isolation by distance. These results further highlight the importance of geographical isolation in shaping differentiation within this species.