An early occurrence of Sarcophilus laniarius harrisii (Marsupialia, Dasyuridae) from the early Pleistocene of Nelson Bay, Victoria

The isolated lower molar series of a dasyurid from early Pleistocene sediments at Nelson Bay, near Portland, is referred herein to Sarcophilus laniarius harrisii (Boitard, 1842). Dental measurements and morphological comparisons taken from this tooth series compare closely with those of the extant subspecies. The genus Sarcophilus is known from the early Pleistocene by the species S. moornaensis Crabb 1982. Fossil material assigned to S. laniarius harrisii is now also known from Early Pleistocene sediments. The new specimens from Nelson Bay extend the origin of S. laniarius harrisii to the early Pleistocene.

Effects of Mitochondrial DNA Rate Variation on Reconstruction of Pleistocene Demographic History in a Social Avian Species, Pomatostomus superciliosus

Mitochondrial sequence data is often used to reconstruct the demographic history of Pleistocene populations in an effort to understand how species have responded to past climate change events. However, departures from neutral equilibrium conditions can confound evolutionary inference in species with structured populations or those that have experienced periods of population expansion or decline. Selection can affect patterns of mitochondrial DNA variation and variable mutation rates among mitochondrial genes can compromise inferences drawn from single markers. We investigated the contribution of these factors to patterns of mitochondrial variation and estimates of time to most recent common ancestor (TMRCA) for two clades in a co-operatively breeding avian species, the white-browed babbler Pomatostomus superciliosus. Both the protein-coding ND3 gene and hypervariable domain I control region sequences showed departures from neutral expectations within the superciliosus clade, and a two-fold difference in TMRCA estimates. Bayesian phylogenetic analysis provided evidence of departure from a strict clock model of molecular evolution in domain I, leading to an over-estimation of TMRCA for the superciliosus clade at this marker. Our results suggest mitochondrial studies that attempt to reconstruct Pleistocene demographic histories should rigorously evaluate data for departures from neutral equilibrium expectations, including variation in evolutionary rates across multiple markers. Failure to do so can lead to serious errors in the estimation of evolutionary parameters and subsequent demographic inferences concerning the role of climate as a driver of evolutionary change. These effects may be especially pronounced in species with complex social structures occupying heterogeneous environments. We propose that environmentally driven differences in social structure may explain observed differences in evolutionary rate of domain I sequences, resulting from longer than expected retention times for matriarchal lineages in the superciliosus clade.

Abrupt late Pleistocene ecological and climate change on Tahiti (French Polynesia)

Aim: To reconstruct ecological changes from the fossil record of a unique wetland on the tropical oceanic island of Tahiti, between 44.5 and 38 cal. kyr bp. Location: Vaifanaura'amo'ora, Tamanu Plateau, Punaru'u Valley, Tahiti, Society Islands, French Polynesia (17°38'S, 149°32'50″E). Methods: Fossil pollen, spores, seeds, diatoms and invertebrates were examined from a 3.7 m core consisting of Pleistocene-aged algal sediment overlain by late Holocene peat. Results: Between 44.5 and 41.5 cal. kyr bp, Ficus trees, sub-shrubs including Sigesbeckia orientalis L., the C4 grass species Paspalum vaginatum Sw., and extinct Pritchardia palms dominated the Vaifanaura'amo'ora wetland. This vegetation association is no longer present in the tropical oceanic Pacific islands. After 41.5 cal. kyr bp, the climate rapidly became drier and cooler with grasses, sedges and ferns dominating the vegetation. Algal sediment accumulation ceased after 38 cal. kyr bp due to prolonged dry climate conditions recorded across the Pacific Ocean. Sediment accumulation recommenced in the late Holocene. Main conclusions: The ecological responses identified from Tahiti provide evidence counter to the prevailing view that the tropical oceans buffered the ecological effects of abrupt climate changes during the last glacial period.

Antitropicality of Pacific fishes : molecular insights

Twenty-one molecular genetic studies of thirteen antitropical Pacific fishes are herein reviewed. High dispersal potentials and Plio-Pleistocene transequatorial divergence are suggested for approximately half of the taxa studied, consistent with movement across the tropics during glacial periods. Divergences within two fish groups were mid-Miocene in age, corresponding to a period suggested for vicariant isolation associated with equatorial warming, but high dispersal potentials complicate the interpretation of biogeographic history. Only one study suggested transequatorial divergence older than 20 million years. There is a greater proportion of Pleistocene transequatorial divergences in the East Pacific than the West Pacific, consistent with the suggestion that conditions in the East Pacific are more amenable to the formation of antitropical distributions. Multiple transequatorial divergences have been observed within at least two groups, and instances of cryptic speciation have been identified twice. Areas for future research concern taxa that differ from the majority studied to date with respect to latitudinal distribution, bathymetry, evolutionary age, and dispersal potential. Molecular characters have demonstrated utility for the study of antitropical fishes, but with limitations.

A tangled tale of two teal : population history of the grey Anas gracilis and chestnut teal A. castanea of Australia

Two Australian species of teal (Anseriformes: Anatidae: Anas), the grey teal Anas gracilis and the chestnut teal A. castanea, are remarkable for the zero or near-zero divergence recorded between them in earlier surveys of mitochondrial DNA (mtDNA) diversity. We confirmed this result through wider geographical and population sampling as well as nucleotide sampling in the more rapidly evolving mtDNA control region. Any data set where two species share polymorphism as is the case here can be explained by a model of gene flow through hybridization on one hand or by incomplete lineage sorting on the other hand. Ideally, analysis of such shared polymorphism would simultaneously estimate the likelihood of both phenomena. To do this, we used the underlying principle of the IMa package to explore ramifications to understanding population histories of A. gracilis and A. castanea. We cannot reject that hybridization occurs between the two species but an equally or more plausible finding for their nearly zero divergence is incomplete sorting following very recent divergence between the two, probably in the mid-late Pleistocene. Our data add to studies that explore intermediate stages in the evolution of reciprocal monophyly and paraphyletic or polyphyletic relationships in mtDNA diversity among widespread Australian birds.

Revised stratigraphy of the Blanchetown Clay, Murray Basin: age constraints on the evolution of paleo Lake Bungunnia

Paleo Lake Bungunnia covered more than 40 000 km2 of southern Australia during the Plio-Pleistocene, although the age and origin of the lake remain controversial. The Blanchetown Clay is the main depositional unit and outcrop at Nampoo Station in far-western New South Wales provides the most continuous lacustrine section preserved in the basin. Here the Blanchetown Clay represents the maximum lake fill and comprises: (i) a basal well-sorted sand with interbedded clay (Chowilla Sand), representing initial flooding at the time of lake formation; (ii) a thick sequence of green-grey clay comprised dominantly of kaolinite and illite, with the apparently cyclic occurrence of illite interpreted to represent cool and dry glacial climatic intervals; and (iii) a 2.6 m-thick sequence of finely laminated silt and silty clay, here defined as the Nampoo Member of the Blanchetown Clay. New magnetostratigraphic data constrain the age of the oldest lake sediments to be younger than 2.581 Ma (Matuyama-Gauss boundary) and probably as young as 2.4 Ma. This age is significantly younger than the age of 3.2 Ma previously suggested for lake formation. The youngest Blanchetown Clay is older than 0.781 Ma (Brunhes-Matuyama boundary) and probably as old as 1.2 Ma. The Nampoo Station section provides a framework for the construction of a regional Plio-Pleistocene stratigraphy in the Murray Basin.

Where and when does a ring start and end? Testing the ring-species hypothesis in a species complex of Australian parrots

Speciation, despite ongoing gene flow can be studied directly in nature in ring species that comprise two reproductively isolated populations connected by a chain or ring of intergrading populations. We applied three tiers of spatio-temporal analysis (phylogeny/historical biogeography, phylogeography and landscape/population genetics) to the data from mitochondrial and nuclear genomes of eastern Australian parrots of the Crimson Rosella Platycercus elegans complex to understand the history and present genetic structure of the ring they have long been considered to form. A ring speciation hypothesis does not explain the patterns we have observed in our data (e.g. multiple genetic discontinuities, discordance in genotypic and phenotypic assignments where terminal differentiates meet). However, we cannot reject that a continuous circular distribution has been involved in the group's history or indeed that one was formed through secondary contact at the 'ring's' east and west; however, we reject a simple ring-species hypothesis as traditionally applied, with secondary contact only at its east. We discuss alternative models involving historical allopatry of populations. We suggest that population expansion shown by population genetics parameters in one of these isolates was accompanied by geographical range expansion, secondary contact and hybridization on the eastern and western sides of the ring. Pleistocene landscape and sea-level and habitat changes then established the birds' current distributions and range disjunctions. Populations now show idiosyncratic patterns of selection and drift. We suggest that selection and drift now drive evolution in different populations within what has been considered the ring.

Birth of a biome : insights into the assembly and maintenance of the Australian arid zone biota

The integration of phylogenetics, phylogeography and palaeoenvironmental studies is providing major insights into the historical forces that have shaped the Earth’s biomes. Yet our present view is biased towards arctic and temperate/tropical forest regions, with very little focus on the extensive arid regions of the planet. The Australian arid zone is one of the largest desert landform systems in the world, with a unique, diverse and relatively well-studied biota. With foci on palaeoenvironmental and molecular data, we here review what is known about the assembly and maintenance of this biome in the context of its physical history, and in comparison with other mesic biomes. Aridification of Australia began in the Mid-Miocene, around 15 million years, but fully arid landforms in central Australia appeared much later, around 1–4 million years. Dated molecular phylogenies of diverse taxa show the deepest divergences of arid-adapted taxa from the Mid-Miocene, consistent with the onset of desiccation. There is evidence of arid-adapted taxa evolving from mesicadapted ancestors, and also of speciation within the arid zone. There is no evidence for an increase in speciation rate during the Pleistocene, and most arid-zone species lineages date to the Pliocene or earlier. The last 0.8 million years have seen major fluctuations of the arid zone, with large areas covered by mobile sand dunes during glacial maxima. Some large, vagile taxa show patterns of recent expansion and migration throughout the arid zone, in parallel with the ice sheet-imposed range shifts in Northern Hemisphere taxa. Yet other taxa show high lineage diversity and strong phylogeographical structure, indicating persistence in multiple localised refugia over several glacial maxima. Similar to the Northern Hemisphere, Pleistocene range shifts have produced suture zones, creating the opportunity for diversification and speciation through hybridisation, polyploidy and parthenogenesis. This review highlights the opportunities that development of arid conditions provides for rapid and diverse evolutionary radiations, and re-enforces the emerging view that Pleistocene environmental change can have diverse impacts on genetic structure and diversity in different biomes. There is a clear need for more detailed and targeted phylogeographical studies of Australia’s arid biota and we suggest a framework and a set of a priori hypotheses by which to proceed.

Quaternary beetles : a review and issues for Australian studies

Few Australian entomologists, ecologists, biogeographers or Quaternary researchers are familiar with the details of Quaternary beetle research. Since the 1950s the study of fossil beetles has developed to become an important discipline of the Quaternary sciences. Unfortunately, however, the significance of the discipline for ecological and evolutionary research has been slow to penetrate mainstream entomological, ecological, and evolutionary thought. This paper outlines the history, methods and results of Quaternary beetle studies, based primarily upon research from the well-studied Northern Hemisphere, and then examines issues relevant to Australian research. Analysis of Quaternary beetle assemblages from Australia can contribute to the reconstruction of past environments and climates, in particular quantitative estimation of past temperature regimes, and potentially, effective precipitation. Of more significance to entomology, however, is the potential to reconstruct climatically-induced changes in distribution, essential for understanding the Quaternary biogeographic history of Australia's insect fauna. Furthermore, it will be possible to examine evidence, or the lack thereof, for speciation during the Quaternary, in the context of Quaternary environmental change.

Tasmania : archaeological and palaeo-ecological perspectives

Tasmania, at the south of the land-mass, experienced the Glacial Maximum as a properly cold affair. Recent archaeological work, some in country now difficult of human access, has developed an intricate story of changing adaptations. At the Pleistocene-Holocene boundary, a major reorganization of Aboriginal adaptation strategies is seen in the archaeological record, argued to follow late-Pleistocene environmental amelioration.