Biogeographic history of an Australian freshwater shrimp, Paratya australiensis (Atyidae): the role life history transition in phylogeographic diversification

Mixture Toxicity of Three Unconventional Gas Fracking Chemicals, Barium, O-Cresol, and Sodium Chloride, to the Freshwater Shrimp Paratya australiensis

The 96-h acute toxicity of barium (Ba²⁺ ), o-cresol, and sodium chloride (NaCl) to Paratya australiensis was assessed in single, binary, and ternary combinations in addition to three biochemical assays: glutathione S-transferase, acetylcholinesterase, and sodium-potassium adenosine triphosphatase. The 96-h lethal concentrations that expressed 50% mortality (LC50) in the single-toxicant exposures were Ba²⁺  = 23.4 mg/L, o-cresol = 12.2 mg/L, and NaCl = 4198 mg/L. Mortality from o-cresol exposure occurred between 11 and 22 mg/L, whereas Ba²⁺ was more gradual across 10-105 mg/L, and most of the NaCl mortality occurred between 2050 and 4100 mg/L. Toxic units were used to assess the binary and ternary interactions of the toxicants. A more than additive effect was observed for most combinations in the binary chemical exposures, with the ternary combinations yielding highly synergistic interactions. Greater synergism was observed with the 96-h LC50 of o-cresol in combination with the three concentrations of NaCl (1025, 2050, and 3075 mg/L) compared with Ba²⁺ , with toxic units of 0.38, 0.48, and 0.10 (o-cresol) and 0.71, 0.67, and 0.50 (Ba²⁺ ). No notable enzyme activity trends were observed in the enzyme biomarker responses from both individual and mixture exposures. Although acute single-species toxicity tests tend to underestimate the effects of Ba²⁺ , o-cresol, and NaCl on populations, communities, and ecosystems in seminatural (e.g., mesocosms) and natural systems, there are currently no published acute toxicity data available for P. australiensis and the three toxicants used in the present study. The present study shows that chemicals with different toxicity mechanisms can potentially lead to more synergistic responses. Environ Toxicol Chem 2023;42:481-494. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The roles of aridification and sea level changes in the diversification and persistence of freshwater fish lineages

While the influence of Pleistocene climatic changes on divergence and speciation has been well-documented across the globe, complex spatial interactions between hydrology and eustatics over longer timeframes may also determine species evolutionary trajectories. Within the Australian continent, glacial cycles were not associated with changes in ice cover and instead largely resulted in fluctuations from moist to arid conditions across the landscape. We investigated the role of hydrological and coastal topographic changes brought about by Plio-Pleistocene climatic changes on the biogeographic history of a small Australian freshwater fish, the southern pygmy perch Nannoperca australis. Using 7958 ddRAD-seq (double digest restriction-site associated DNA) loci and 45,104 filtered SNPs, we combined phylogenetic, coalescent and species distribution analyses to assess the various roles of aridification, sea level and tectonics and associated biogeographic changes across southeast Australia. Sea-level changes since the Pliocene and reduction or disappearance of large waterbodies throughout the Pleistocene were determining factors in strong divergence across the clade, including the initial formation and maintenance of a cryptic species, N. 'flindersi'. Isolated climatic refugia and fragmentation due to lack of connected waterways maintained the identity and divergence of inter- and intraspecific lineages. Our historical findings suggest that predicted increases in aridification and sea level due to anthropogenic climate change might result in markedly different demographic impacts, both spatially and across different landscape types.

Contrasting evolutionary responses in two co-distributed species of Galaxias (Pisces, Galaxiidae) in a river from the glaciated range in Southern Chile

Life-history traits are among the most important factors affecting population abundance and genetic diversity of species. Here, we analysed the genetic patterns of two Galaxias species with different life-history traits to investigate how these biological differences impacted their evolution in the Valdivia River basin, Southern Chile. We analysed mitochondrial DNA (mtDNA) sequences from 225 individuals of Galaxias maculatus and 136 of G. platei to compare patterns of genetic diversity, structure and demographic growth across the basin. Galaxias maculatus presented higher genetic diversity and higher genetic structure than G. platei. Demographic analyses showed G. maculatus kept a higher population size over time, with a signal of demographic expansion in the last 250 kyr. Whereas Galaxias platei, exhibited lower, but constant population size over time. Furthermore, haplotype networks revealed higher lineage diversity in G. maculatus with a tendency to occupy different areas of the basin. Coalescent simulations ruled out that genetic differences between species could be explained by stochastic processes (genetic drift), suggesting species-specific biological differences as responsible for the observed genetic differences. We discuss how differences in life-history traits and past glaciations interact to shape the evolutionary history of the two Galaxias species.

Identification of microplastics in surface water and Australian freshwater shrimp Paratya australiensis in Victoria, Australia

Compared to marine microplastics research, few studies have bio-monitored microplastics in inland waters. It is also important to understand the microplastics' uptake and their potential risks to freshwater species. The Australian glass shrimp Paratya australiensis (Family: Atyidae) is commonly found in fresh waterbodies in eastern Australia, and are sensitive to anthropogenic stressors but have a wide tolerance range to the natural environmental conditions. This study aimed to understand the microplastics' occurrence and types in water samples and the shrimp P. australiensis, and identify if the shrimp could be a suitable bioindicator for microplastic pollution. Surface water and P. australiensis across ten urban and rural freshwater sites in Victoria were sampled. In total, 30 water samples and 100 shrimp were analysed for microplastic content, and shrimp body weights and sizes were also recorded. Microplastics were picked, photographed and identified using FT-IR microscopy: in water samples, 57.9% of items including suspect items were selected to identify; all microplastics found in shrimp samples were identified. Microplastics were present in the surface waters of all sites, with an average abundance of 0.40 ± 0.27 items/L. A total of 36% of shrimp contained microplastics with an average of 0.52 ± 0.55 items/ind (24 ± 31 items/g). Fibre was the most common shape, and blue was the most frequent colour in both water and shrimp samples. The dominant plastic types were polyester in water samples, and rayon in shrimp samples. Even though results from this study show a relatively low concentration of microplastics in water samples in comparison with global studies, it is worth noticing that microplastics were regularly detected in fresh waterbodies in Victoria, Australia. Compared with water samples, shrimp contained a wider variety of plastic types, suggesting they may potentially behave as passive samplers of microplastics pollution in freshwater environments.

Genetic structure of Australian glass shrimp, Paratya australiensis, in relation to altitude

Paratya australiensis Kemp (Decapoda: Atyidae) is a widely distributed freshwater shrimp in eastern Australia. The species has been considered as an important stream organism for studying genetics, dispersal, biology, behaviour and evolution in atyids and is a major food source for stream dwelling fishes. Paratya australiensis is a cryptic species complex consisting of nine highly divergent mitochondrial DNA lineages. Previous studies in southeast Queensland showed that “lineage 4” favours upstream sites at higher altitudes, with cooler water temperatures. This study aims to identify putative selection and population structure between high elevation and low elevation populations of this lineage at relatively small spatial scales. Sample localities were selected from three streams: Booloumba Creek, Broken Bridge Creek and Obi Obi Creek in the Conondale Range, southeast Queensland. Six sample localities, consisting of 142 individuals in total were sequenced using double digest Restriction Site Associated DNA-sequencing (ddRAD-seq) technique. Among the 142 individuals, 131 individuals shared 213 loci. Outlier analysis on 213 loci showed that 27 loci were putatively under selection between high elevation and low elevation populations. Outlier analysis on individual streams was also done to test for parallel patterns of adaptation, but there was no evidence of a parallel pattern. Population structure was observed using both the 27 outliers and 186 neutral loci and revealed similar population structure in both cases. Therefore, we cannot differentiate between selection and drift here. The highest genetic differentiation was observed between high elevation and low elevation populations of Booloumba Creek, with small levels of differentiation in the other two streams.

De novo assembly and analysis of changes in the protein-coding transcriptome of the freshwater shrimp Paratya australiensis (Decapoda: Atyidae) in response to acid sulfate drainage water

Background

The atyid shrimp Paratya australiensis occurs in surface freshwater habitats throughout eastern Australia and has been used to study the ecotoxicology of contaminants such as pesticides and metals. The acidification of surface water that can occur after acid sulfate material in soils and sediments is oxidised and subsequently re-wetted is a serious environmental issue in coastal regions and inland riverine floodplains worldwide. Solubilisation of soil-associated minerals can result in high waterborne concentrations of mineral salts and dissolved metals, which together with low pH represent a potential threat to aquatic ecosystems in affected regions. The aims of the present study were to gain insight into stress responses induced by exposure to acid drainage water (ADW) in P. australiensis by determining changes in the abundance of protein-coding transcripts and to generate a comprehensive transcriptomic resource to facilitate further research into gene regulation or protein structure and function in this species. Adult P. australiensis were exposed for 24 h to undiluted ADW, 50 % ADW diluted in river water, or to river water as control, and high-throughput mRNA sequencing (RNA-Seq) conducted on whole-body tissues. A reference transcriptome was generated using de novo assembly and putative protein-coding regions were identified and annotated. Changes in transcript abundance in response to ADW exposure were determined by aligning reads to the reference transcriptome and quantifying coverage.

Results

A high proportion of arthropod benchmarking universal single-copy orthologues were present in the reference transcriptome. Functions associated with cuticle biosynthesis and oxidative stress were significantly enriched in the lists of transcripts exhibiting differential abundance in either direction after exposure to 50 % or 100 % ADW. Transcripts involved in osmoregulation exhibited decreased abundance following exposure to ADW. The transcriptome contained full-length coding sequences for numerous proteins known to be involved in environmental response pathways, including two putative metallothioneins, four glutathione peroxidases and 19 nuclear receptors.

Conclusions

The results of the present study provide insight into stress response pathways induced in crustaceans by short-term exposure to multiple stressors present in ADW such as low pH, high salinity and dissolved metals, and represent a resource for future toxicogenomics and protein functional studies in P. australiensis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3208-y) contains supplementary material, which is available to authorized users.

Genetic and Morphological Characterization of Freshwater Shrimps (Caridina africana Kingsley, 1882) Reveals the Presence of Alien Shrimps in the Cape Floristic Region, South Africa

Morphological identification and molecular data (mtDNA COI) were used to resolve the taxonomic identity of a non-native freshwater shrimp in the Cape Floristic Region (CFR) of South Africa and to evaluate levels of genetic diversity and differentiation in the species' core natural distribution. The species was morphologically and genetically identified as Caridina africana Kingsley, 1882, whose main natural distribution is in the KwaZulu-Natal (KZN) Province, more than 1200 km from the point of new discovery. Subsequently, sequence data from natural populations occurring in seven rivers throughout KZN showed the presence of nuclear copies of the mtDNA COI gene (NUMTs) in 46 out of 140 individuals. Upon removal of sequences containing NUMTs, levels of genetic diversity were low in the alien population (possibly as a consequence of a bottleneck event), while varying levels of genetic diversity and differentiation were found in natural populations, indicating habitat heterogeneity, fragmentation and restricted gene flow between rivers. Following the present study, the alien shrimp has survived the Western Cape's winter and dispersed into a nearby tributary of the Eerste River System, hence posing an additional potential threat to endangered endemics. Understanding the biology of this alien species will aid detection and eradication procedures.

The complete mitogenome of the Australian freshwater shrimp Paratya australiensis Kemp, 1917 (Crustacea: Decapoda: Atyidae)

The mitochondrial genome sequence of the Australian freshwater shrimp, Paratya australiensis, is presented, which is the fourth for genera of the superfamily Atyoidea and the first atyid from the southern hemisphere. The base composition of the P. australiensis, mitogenome is 33.55% for T, 18.24% for C, 35.16% for A, and 13.06% for G, with an AT bias of 71.58%. It has a mitogenome of 15,990 base pairs comprised of 13 protein-coding, 2 ribosomal subunit and 22 transfer RNAs genes and a non-coding AT-rich region. The mitogenome gene order for the species is typical for atyid shrimps, which conform to the primitive pan crustacean model.

The influence of life-history strategy on genetic differentiation and lineage divergence in darters (Percidae: Etheostomatinae)

Recent studies determined that darters with specialized breeding strategies can exhibit deep lineage divergence over fine geographic scales without apparent physical barriers to gene flow. However, the extent to which intrinsic characteristics interact with extrinsic factors to influence population divergence and lineage diversification in darters is not well understood. This study employed comparative phylogeographic and population genetic methods to investigate the influence of life history on gene flow, dispersal ability, and lineage divergence in two sympatric sister darters with differing breeding strategies. Our results revealed highly disparate phylogeographic histories, patterns of genetic structure, and dispersal abilities between the two species suggesting that life history may contribute to lineage diversification in darters, especially by limiting dispersal among large river courses. Both species also showed striking differences in demographic history, indicating that extrinsic factors differentially affected each species during the Pleistocene. Collectively, our results indicate that intrinsic and extrinsic factors have influenced levels of gene flow among populations within both species examined. However, we suggest that life-history strategy may play a more important role in lineage diversification in darters than previously appreciated, a finding that has potentially important implications for understanding diversification of the rich North American freshwater fish fauna.

Local and regional scale genetic variation in the Cape dune mole-rat, Bathyergus suillus

The distribution of genetic variation is determined through the interaction of life history, morphology and habitat specificity of a species in conjunction with landscape structure. While numerous studies have investigated this interplay of factors in species inhabiting aquatic, riverine, terrestrial, arboreal and saxicolous systems, the fossorial system has remained largely unexplored. In this study we attempt to elucidate the impacts of a subterranean lifestyle coupled with a heterogeneous landscape on genetic partitioning by using a subterranean mammal species, the Cape dune mole-rat (Bathyergus suillus), as our model. Bathyergus suillus is one of a few mammal species endemic to the Cape Floristic Region (CFR) of the Western Cape of South Africa. Its distribution is fragmented by rivers and mountains; both geographic phenomena that may act as geographical barriers to gene-flow. Using two mitochondrial fragments (cytochrome b and control region) as well as nine microsatellite loci, we determined the phylogeographic structure and gene-flow patterns at two different spatial scales (local and regional). Furthermore, we investigated genetic differentiation between populations and applied Bayesian clustering and assignment approaches to our data. Nearly every population formed a genetically unique entity with significant genetic structure evident across geographic barriers such as rivers (Berg, Verlorenvlei, Breede and Gourits Rivers), mountains (Piketberg and Hottentots Holland Mountains) and with geographic distance at both spatial scales. Surprisingly, B. suillus was found to be paraphyletic with respect to its sister species, B. janetta-a result largely overlooked by previous studies on these taxa. A systematic revision of the genus Bathyergus is therefore necessary. This study provides a valuable insight into how the biology, life-history and habitat specificity of animals inhabiting a fossorial system may act in concert with the structure of the surrounding landscape to influence genetic distinctiveness and ultimately speciation.

Bicarbonate toxicity to Ceriodaphnia dubia and the freshwater shrimp Paratya australiensis and its influence on zinc toxicity

Bicarbonate is often a major ionic constituent associated with produced waters from methane gas extraction and coal mining, yet few studies have determined its specific toxicity. Currently, the environmental risk of bicarbonate anion in water discharges is assessed based on the toxicity of sodium chloride or artificial seawater and is regulated via electrical conductivity. Increased NaHCO(3) added to Ceriodaphnia dubia in synthetic or natural water gave similar 48-h 10% effective concentration (EC10) values of 1750 ± 125 mg NaHCO(3)/L (mean ± standard error) and 1670 ± 180 mg NaHCO(3)/L, respectively. Bicarbonate was toxic to C. dubia in both waters with conductivities above 1900 µS/cm. In contrast, when conductivity was elevated with NaCl, toxicity to C. dubia was observed only above 2800 µS/cm. Bicarbonate also impaired C. dubia reproduction with an EC10 of 340 mg NaHCO(3)/L. Major ion composition also influenced Zn bioavailability, a common co-occurring metal contaminant in coal mine waters, with sublethal concentrations of NaHCO(3) and elevated pH increasing Zn toxicity. Higher pH was the dominant parameter determining a 10-fold increase in the 48-h 50% effective concentration (EC50) for Zn toxicity to C. dubia at pH 8.6 of 34 µg Zn/L (95% confidence limit = 32-37 µg Zn/L) compared with the Zn toxicity at approximately circumneutral pH. Exposure of the freshwater shrimp Paratya australiensis (Atyidae) in natural water to increasing bicarbonate gave a mean 10-d 10% lethal concentration (LC10) of 850 ± 115 mg NaHCO(3)/L, associated with a mean conductivity EC10 of 1145 µS/cm, which is considerably lower than toxicity of NaCl and artificial seawater to this species reported elsewhere. Because toxicity was influenced by salt composition, specific ions should be regulated rather than conductivity alone in mine wastewater discharges.

Molecular evidence for mid-Pleistocene divergence of populations of three freshwater amphipod species (Talitroidea : Chiltoniidae) on Kangaroo Island, South Australia, with a new spring-associated genus and species

Recent molecular and morphological analyses have shown that chiltoniid amphipods, once thought to be a relictual group, are a diverse and speciose family of Australian freshwater amphipods. As part of a larger examination of the family, chiltoniids from Kangaroo Island in South Australia were collected and analysed using molecular (COI and 28S) and morphological methods in order to understand species distributional patterns and relationships. Kartachiltonia moodyi gen. nov., sp. nov., a spring-associated species endemic to the island, was discovered and populations of three additional mainland species (Austrochiltonia australis, A. dalhousiensis and A. subtenuis) were examined. The island populations of A. australis, A. dalhousiensis and A. subtenuis were found to form natural groups with differing haplotype coalescence times dating from the Early to Mid-Pleistocene. Numerous cycles of regional climate change throughout the Pleistocene are likely to have driven speciation in chiltoniid amphipods in southern Australia and the presence of multiple chiltoniid species at Kangaroo Island indicates that it exists at a likely convergence of species distribution patterns. Three possible hypotheses to explain the evolution and diversity of chiltoniids in southern Australia are discussed as are evidence for potential introduction and long-distance dispersal events.

Multiple colonizations lead to cryptic biodiversity in an island ecosystem: comparative phylogeography of anchialine shrimp species in the Ryukyu Archipelago, Japan

Archipelagos of the Indo-West Pacific are considered to be among the richest in the world in biodiversity, and phylogeographic studies generally support either the center of origin or the center of accumulation hypothesis to explain this pattern. To differentiate between these competing hypotheses for organisms from the Indo-West Pacific anchialine ecosystem, defined as coastal bodies of mixohaline water fluctuating with the tides but having no direct oceanic connections, we investigated the genetic variation, population structure, and evolutionary history of three caridean shrimp species (Antecaridina lauensis, Halocaridinides trigonophthalma, and Metabetaeus minutus) in the Ryukyu Archipelago, Japan. We used two mitochondrial genes--cytochrome c oxidase subunit I (COI) and large ribosomal subunit (16S-rDNA)--complemented with genetic examination of available specimens from the same or closely related species from the Indian and Pacific Oceans. In the Ryukyus, each species encompassed 2-3 divergent (9.52%-19.2% COI p-distance) lineages, each having significant population structure and varying geographic distributions. Phylogenetically, the A. lauensis and M. minutus lineages in the Ryukyus were more closely related to ones from outside the archipelago than to one another. These results, when interpreted in the context of Pacific oceanographic currents and geologic history of the Ryukyus, imply multiple colonizations of the archipelago by the three species, consistent with the center of accumulation hypothesis. While this study contributes toward understanding the biodiversity, ecology, and evolution of organisms in the Ryukyus and the Indo-West Pacific, it also has potential utility in establishing conservation strategies for anchialine fauna of the Pacific Basin in general.

Revision of the freshwater genus Atyaephyra (Crustacea, Decapoda, Atyidae) based on morphological and molecular data

Atyaephyra de Brito Capello, 1867 was described from the Mediterranean region almost 200 years ago. Since then, the genus has been recorded from various freshwater habitats in Europe, North Africa and the Middle East. Despite its long history, the taxonomic status of Atyaephyra species remains confusing and uncertain. Consequently numerous specimens from the known range of Atyaephyra were analysed using morphological characters and mitochondrial COI sequences in an attempt to clarify the taxonomy of this genus. The present study recognises seven Atyaephyra species, more than twice as many as previously recorded (three), four of which are considered as new. The new species are described, additional information to the original descriptions are provided for the remaining three taxa, while neotypes of Atyaephyra desmarestii Millet, 1831 and Atyaephyra stankoi Karaman, 1972 are designated to stabilize their taxonomy. Non-overlapping distinguishing morphological characters are used to discriminate the examined material into five species, e.g., Atyaephyra desmarestii, Atyaephyra stankoi, Atyaephyra orientalis Bouvier, 1913, Atyaephyra thyamisensissp. n., Atyaephyra strymonensissp. n. In addition, the genetic analysis supports the existence of multiple phylogenetic clades in the broader Mediterranean area and distinguishes two new cryptic species, namely Atyaephyra tuerkayisp. n. and Atyaephyra acheronensissp. n. The geographic distribution of these species is confirmed and their phylogenetic relationships are described.

Aquatic Insects in Eastern Australia: A Window on Ecology and Evolution of Dispersal in Streams

Studies of connectivity of natural populations are often conducted at different timescales. Studies that focus on contemporary timescales ask questions about dispersal abilities and dispersal behavior of their study species. In contrast, studies conducted at historical timescales are usually more focused on evolutionary or biogeographic questions. In this paper we present a synthesis of connectivity studies that have addressed both these timescales in Australian Trichoptera and Ephemeroptera. We conclude that: (1) For both groups, the major mechanism of dispersal is by adult flight, with larval drift playing a very minor role and with unusual patterns of genetic structure at fine scales explained by the “patchy recruitment hypothesis”; (2) There is some evidence presented to suggest that at slightly larger spatial scales (∼100 km) caddisflies may be slightly more connected than mayflies; (3) Examinations of three species at historical timescales showed that, in southeast Queensland Australia, despite there being no significant glaciation during the Pleistocene, there are clear impacts of Pleistocene climate changes on their genetic structure; and (4) The use of mitochondrial DNA sequence data has uncovered a number of cryptic species complexes in both trichopterans and ephemeropterans. We conclude with a number of suggestions for further work.

High gene flow due to pelagic larval dispersal among South Pacific archipelagos in two amphidromous gastropods (Neritomorpha: Neritidae)

The freshwater stream fauna of tropical oceanic islands is dominated by amphidromous species, whose larvae are transported to the ocean and develop in the plankton before recruiting back to freshwater habitat as juveniles. Because stream habitat is relatively scarce and unstable on oceanic islands, this life history would seem to favor either the retention of larvae to their natal streams, or the ability to delay metamorphosis until new habitat is encountered. To distinguish between these hypotheses, we used population genetic methods to estimate larval dispersal among five South Pacific archipelagos in two amphidromous species of Neritid gastropod (Neritina canalis and Neripteron dilatatus). Sequence data from mitochondrial cytochrome oxidase I (COI) revealed that neither species is genetically structured throughout the Western Pacific, suggesting that their larvae have a pelagic larval duration (PLD) of at least 8 weeks, longer than many marine species. In addition, the two species have recently colonized isolated Central Pacific archipelagos in three independent events. Since colonization, there has been little or no gene flow between the Western and Central Pacific archipelagos in N. canalis, and high levels of gene flow across the same region in N. dilatatus. Both species show departures from neutrality and recent dates for colonization of the Central Pacific archipelagos, which is consistent with frequent extinction and recolonization of stream populations in this area. Similar results from other amphidromous species suggest that unstable freshwater habitats promote long-distance dispersal capabilities.

An empirical test of freshwater vicariance via river capture

River capture is a geomorphological process through which stream sections are displaced from one catchment to another, and it may represent a dominant facilitator of interdrainage transfer and cladogenesis in freshwater-limited taxa. However, few studies have been conducted in a manner to explicitly test the biological significance of river capture. Here we present a multispecies phylogeographical analysis to test whether the nonmigratory fish fauna of the Von River (South Island, New Zealand) is the product of a well-documented, Late Quaternary capture of a section of the Oreti River (Southland drainage). Specifically, we predict that nonmigratory fishes of the Von River will exhibit closer genetic affinities with those of Southland, rather than those of the Clutha system, into which the Von River presently drains. Mitochondrial DNA phylogeography (control region and cytochrome b sequence data) and analysis of nuclear orthologues of mtDNA sequences indicate that 'flathead'Galaxias of the Von River (n = 31, three sites) have greatest genetic affinities with those of Southland (Galaxias 'southern', n = 216, 38 sites), rather than with those of the Clutha River (Galaxias sp. 'D', n = 73, 32 sites). Likewise, Von River 'roundhead'Galaxias (n = 52, four sites) have greatest genetic affinities with those of Southland drainages (Galaxias gollumoides, n = 223, 58 sites), rather than with those of the Clutha River (Galaxias pullus, Galaxias anomalus, Galaxias gollumoides of the Nevis tributary; n = 68, 32 sites). These findings are consistent with our predictions that genetic affinities of the nonmigratory fish fauna in the Von River would reflect past, rather than present, drainage connections. Consequently, river capture is responsible for the nonmigratory fish fauna of the Von River. In a broader context, river capture has frequently influenced the distribution of genetic lineages among catchments in New Zealand freshwater-limited fish, and its biogeographical significance may have been underestimated in other regions.

Cryptic speciation in two widespread subterranean amphipod genera reflects historical drainage patterns in an ancient landscape

The landscape of the Pilbara region of Western Australia has been relatively unchanged for 100 million years. The ancient river systems of this region might be expected to be sources of isolation and divergence for aquatic species. Hence, the occurrence of widespread groundwater taxa in this landscape offers the opportunity to examine associations between genetic diversity and drainage patterns. Pilbarus and Chydaekata are two widespread genera of subterranean amphipods endemic to the Pilbara, each occupying multiple tributaries. We used molecular data to examine the roles of drainage patterns in structuring genetic diversity. Gene flow within a tributary may be facilitated by the occasional occurrence of these amphipods in springs, which results in their downstream dispersal during episodic flooding. However, tributary boundaries may form hydrological barriers to gene flow, resulting in localised isolation of populations and divergence. Samples of both genera, collected throughout three river basins, were examined for sequence divergence in the cytochrome c oxidase I mitochondrial gene. There was no evidence of contemporary gene flow among populations of either genus, and each tributary contained highly divergent lineages, which were not associated with similar morphological differentiation. This suggests cryptic speciation has occurred, and similar phylogenetic signals in both taxa imply similar evolutionary histories. Surface populations may have been driven into subterranean refugia by the cessation of flow in the rivers, associated with Tertiary climate change, while morphological evolution may have been constrained by stabilising selection. The lack of congruence between molecular diversity and morphology raises important practical issues for conservation.