Terrie Finston

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.

Geographic patterns of genetic diversity in subterranean amphipods of the Pilbara, Western Australia

Twenty-six species of subterranean amphipods have been described from the Pilbara, Western Australia, based on variation in morphological characters. Many are known only from single bores. The Pilbara is rich in iron ore, and thus, an understanding of species’ diversity and their distribution is necessary both to manage resources and to conserve fauna. A previous allozyme study of nine bores in a single catchment in the Pilbara found low levels of genetic differentiation among individuals, but the diversity was not associated with single bores. The area studied appeared to contain a single widespread species common to all nine bores, in sympatry with a second, rare species, represented by a single specimen. The present study analysed allozymic variation in amphipods from 26 bores in four additional catchments in the Pilbara, to test the generality of these findings. At each site, samples with similar allelic arrays were found in multiple bores, in sympatry with rare divergent genotypes. Geological complexity was associated with increased genetic differentiation over short geographical distances. With few exceptions, each catchment contained a unique suite of species, suggesting that catchments may form hydrological barriers to gene flow, resulting in local speciation events.

Biogeography of the stygobitic isopod Pygolabis (Malacostraca: Tainisopidae) in the Pilbara, Western Australia: Evidence for multiple colonisations of the groundwater

COI sequence variation in groundwater amphipods of Western Australia showed multiple highly divergent lineages associated with tributaries. Estimates of the timing of this diversification are consistent with the hypothesis that aridification of the region during the Tertiary forced freshwater fauna into subterranean refugia. The groundwater isopod Pygolabis provides an opportunity to compare phylogenetic signals in co-distributed taxa that might share similar histories. A 549 bp fragment of COI was sequenced for 135 individuals of Pygolabis from 12 sites. Phylogenetic analyses revealed 12 highly divergent lineages associated with tributary boundaries. Lineages were separated by 11.8-27.8% sequence divergence. This level of divergence is consistent with diversification in the Pliocene, supporting the aridification hypothesis. While lineages were associated with distinct tributaries in both amphipods and Pygolabis, the two groups showed different phylogenetic patterns, suggesting that the mode of colonisation of the groundwater differed between the amphipods and Pygolabis.

The recent spread of Artemia parthenogenetica in Western Australia

In Western Australia, populations of Artemia parthenogenetica in coastal salt lakes at Rottnest Island and Lake Hayward, and in salterns at Port Hedland and Shark Bay, are widely accepted to have been introduced by humans. Further, within the past 10 years, populations of A. parthenogenetica have been found in inland playa salt lakes in the wheatbelt of south-west Western Australia, where none had been recorded in previous salt lake studies. Here we hypothesise that birds act as transport vectors for Artemia cysts both within Australia and between the Asian and Australian continents. Allozyme analysis was used to identify clonal types (multi-locus genotypes), clonal frequencies, genotypic diversities and genotypic identity of six populations (three coastal, three inland).Overall, the inland populations displayed almost identical genotypic structure to the coastal population from Lake Hayward, indicating that Lake Hayward could be the major source for dispersal and colonisation of inland populations. Results support the hypothesis of dispersal inland by nomadic bird species. Furthermore, evidence suggests that the inland and Lake Hayward populations may be an example of a metapopulation.The greater variety of genotypes present in the Rottnest population indicates that this population has received a large number of small immigrations, or that it received one large introduction. The former may indicate a long period of suitable salinities, providing a greater time-span over which migration and succession of clonal types could occur in comparison to other populations. While we cannot rule out the possibility of human introduction of A. parthenogenetica to Rottnest, the hypothesis of cyst dispersal along the Austral-Asian flyway remains possible.

Size, shape and development time are plastic traits in salt lake ostracods of the Mytilocypris mytiloides (Ostracoda : Cyprididae) species complex

The taxonomy of the ostracod genus Mytilocypris is based in part on characters of shell morphology. Specifically, M. minuta, M. mytiloides and M. tasmanica chapmani lack distinctive internal characters and are differentiated largely on size and shape of the shell. The three taxa also differ in the salinity of the habitats they occupy. A field study showed a steady decrease in adult size, spanning the size range of all three taxa, over the course of a season within single lakes, in association with changing salinity and other environmental variables. The present study was conducted to investigate whether each phenotype could be produced under laboratory conditions of variable salinity. Offspring of the three parental phenotypes were raised under high and low salinity. Regardless of parental type, offspring grew more quickly, but reached a smaller size at high salinity, and grew more slowly, but reached a larger size at low salinity. The shape of the shell was found to have a significant size component. Plasticity in size and shape suggests these are unreliable characters for taxonomy. Accelerated development may be an adaptation to living in an ephemeral habitat, with salinity being one of the cues Mytilocypris uses to gauge habitat duration.

Groundwater oligochaetes show complex genetic patterns of distribution in the Pilbara region of Western Australia

Abstract. Patterns of genetic diversity in the groundwater fauna of Australia have largely focused on obligate stygobites of relatively large size, namely, crustaceans. Oligochaete worms, with their smaller size and broader ecological niches, provide a contrasting model in which to examine such patterns. Genetic diversity in subterranean oligochaetes in the Pilbara region of Western Australia were examined using one nuclear (18S) and two mitochondrial (COI, 12S) regions. The observed variation was assessed at three levels of hydrology – river basin, creek catchment, and individual bore or site – to document geographic patterns. Most species appeared to be restricted to an individual catchment; however, five species, representing three families, were widespread, with some haplotypes being shared between bores, catchments and even basins. General patterns suggest that while hydrology plays a role in the distribution of oligochaete species, it does not always confine them to catchments, in contrast to patterns observed in groundwater isopods and amphipods in the region. We suggest that intrinsic characteristics of oligochaetes, such as body size, shape, reproductive strategy and ecological requirements, may have allowed them greater dispersal within the subterranean biome of the Pilbara. In particular, oligochaetes may occupy subterranean and surface waters, increasing their opportunities for dispersal.

Geographic patterns of population genetic structure in Mytilocypris (Ostracoda: Cyprididae): interpreting breeding systems, gene flow and history in species with differing distributions

Samples from 83 populations of salt lake Ostracods belonging to the genus Mytilocypris were collected from 74 saline lakes and ponds in the semi‐arid regions of Australia. These populations were examined for variation at six polymorphic enzyme loci to diagnose breeding systems and to measure population structure, to investigate relative levels of gene flow in species with differing distributions and hence different presumed dispersal capabilities. Despite the occurrence of some populations in disjunct, peripheral, and recent ephemeral habitats, all populations of each species were found to reproduce sexually. Gene flow does occur on a local basis and appears to be facilitated by occupation in the same drainage basin for some species. There was considerable gene pool fragmentation among peripheral populations of four of the five species. Only one species, M. mytiloides, was relatively homogeneous across its range. It may be that gene flow is non‐existent into peripheral populations because of poor dispersal abilities, or it may not be frequent enough to overcome local selective pressures. Regardless of these possibilities, the observed gene pool fragmentation has implications for allopatric speciation.

Speciation in fractured rock landforms: Towards understanding the diversity of subterranean cockroaches (Dictyoptera: Nocticolidae: Nocticola) in Western Australia

Three new species of subterranean cockroach of the genus Nocticola from the Pilbara region of Western Australia are described on morphological characters of males. Nocticola quartermainei n. sp., Nocticola cockingi n. sp. and Nocticola currani n. sp. occur in fractured rock landforms and have varying degrees of troglomorphies. Sequence divergence of mitochondrial cytochrome c oxidase subunit I (COXI) clearly demonstrated populations are reproductively isolated over very short distances for the highly troglomorphic Nocticola cockingi n. sp. and Nocticola currani n. sp. and conversely, there is less isolation within the same landforms for the less troglomorphic Nocticola quartermainei n. sp.

Characterisation of microsatellite loci in the groundwater amphipod Chydaekata sp. (Malacostraca: Paramelitidae)

The groundwater fauna (stygofauna) of the Pilbara region of Western Australia is diverse and largely endemic. Extensive mining in the region poses a potential threat to this fragile ecosystem. Knowledge of the dispersal capabilities of groundwater species will aid in managing both fauna and resources. Ten polymorphic microsatellite loci were used to assess variability in 27 specimens of the groundwater amphipod Chydaekata sp. from Marillana Creek in the Pilbara. The number of alleles ranged from 3 to 15, and observed heterozygosity ranged from 0.077 to 0.885. Nine loci were in HWE, and no pairs of loci showed evidence of linkage. The loci will be useful for aiding the management of stygobitic populations in a disturbed landscape, by understanding dispersal patterns and gene flow within and between tributaries.