Australian Arid Zone Research Articles

Molecular phylogeny and phylogeography of the Australian Diplodactylus stenodactylus (Gekkota; Reptilia) species-group based on mitochondrial and nuclear genes reveals an ancient split between Pilbara and non-Pilbara D. stenodactylus

There is a paucity of research on intra-specific morphological and genetic diversity in Australian arid-zone reptiles, and a number of Australian reptile species have for many years been regarded as "species complexes" that classical morphological analyses could not resolve. We conducted a phylogenetic and phylogeographic study of a widespread species group of Australian geckonid lizards to address two main aims. First, based on a large mitochondrial and nuclear gene data set, we have generated the first molecular phylogeny for the Diplodactylus stenodactylus species group (D. alboguttatus, D. damaeus, D. maini, and D. squarrosus, D. stenodactylus) and multiple outgroups to examine the evolutionary relationships among these arid-zone species and phylogenetic patterns within some species. The edited alignment of 41 individuals comprises 2485 characters (1163 ND2+tRNAs; 490 16s; 832 RAG-1), and of these 717 (29%) were variable and parsimony informative (568 ND2+tRNAs; 89 16s; 60 RAG-1). This broad-scale, multi-gene phylogeny has supported previous conjectures on the higher-level phylogenetic relationships among members of the D. stenodactylus species-group based on morphology, but also has uncovered hidden diversity within the group with two new species identified. Analysis at this broad level has identified patterns associated with the distribution of the D. stenodactylus species group that appear to be influenced by environmental processes operating at large geographic scales. Two major clades within the species group were associated with broad differences in habitat types, with one group largely restricted to the temperate zone of the Southwest Province and another largely restricted to central and northern Western Australia north of Kalgoorlie, in line with the Eremaean Province of the Eremaean Zone and the Northern Province of the Tropical Zone. Second, we have assembled phylogeographic data based on a mitochondrial gene (ND2+tRNAs) for five species (Rhynchoedura ornata, Diplodactylus maini, D. pulcher, D. squarrosus, D. stenodactylus) where larger sampling is available, with particular focus on D. stenodactylus, which is distributed both in the iconic but little-known Pilbara area of endemism in north-western Australia as well as in other parts of the Australian arid zone. The edited alignment of 95 individuals comprises 1142 characters and of these 601 (53%) are variable and parsimony informative. We found significant intra-specific genetic variation in all five species, highlighting the need for large-scale screening of cryptic species, with sampling specifically targeted at determining the geographic limits of such taxa. In particular, within D. stenodactylus, a deep and ancient phylogenetic split distinguishes populations in the Pilbara region from non-Pilbara populations. This split may be the result of broad differences in underlying geological substrate, with the Pilbara clade generally preferring harder soils and the non-Pilbara clade adapted to sand.

Mitochondrial DNA variation in an endemic aquatic snail genus, Caldicochlea (Hydrobiidae; Caenogastropoda) in Dalhousie Springs, an Australian arid-zone spring complex

The gastropod genus Caldicochlea, with two recognized species C. harrisi and C. globosa, is endemic to Dalhousie Springs, an artesian spring system in arid northern South Australia. A previous study using allozymes showed that C. harrisi is found in most of the active outflows but C. globosa is confined to the larger, hotter springs in the northern third of the complex where the species are sympatric and that hybridization may be frequent in only two springs. The evolutionary relationships within Caldicochlea were investigated using 16S ribosomal RNA (16S: 75 sequences) and cytochrome c oxidase I (COI: 27 sequences). Clades corresponding to the two species are seen in both the 16S and COI analyses, the average Kimura 2- parameter distance between the clades being 0.028 ± 0.007 for 16S rRNA and 0.040 ± 0.016 for COI with no evidence that the recognized taxa represent species complexes. Only four of 22 16S haplotypes in C. harrisi were found in more than one spring and only two of 12 in C. globosa. No COI haplotype was found in more than one spring. In one spring where earlier research suggested that interbreeding may occur, all scored DNA sequences belonged to the C. harrisi clade and in the other such spring all scored sequences belonged to the C. globosa clade. The data do not clarify whether the time of primary divergence between the species occurred in situ at Dalhousie Springs. The absence of suitable habitat refugia since the onset of Pleistocene aridity suggests that the species have been sympatric or parapatric over tens of thousands of years, raising questions as to how an incomplete reproductive isolation can be maintained and how both species could persist in such a geographically restricted area.

Phylogeography of sexualHeteronotia binoei(Gekkonidae) in the Australian arid zone: climatic cycling and repetitive hybridization

The biota of much of continental Australia have evolved within the context of gradual aridification of the region over several million years, and more recently of climatic cycling between relatively dry and humid conditions. We performed a phylogeographical study of three sexual chromosome races of the Heteronotia binoei complex of geckos found throughout the Australian arid zone. Two of these three races were involved in two separate hybridization events leading to parthenogenetic lineages (also H. binoei), and the third is widespread and broadly sympatric with the parthenogens. Based on our analyses, the three sexual races diversified approximately 6 million years ago in eastern Australia, during a period of aridification, then each moved west through northern, southern, and central dispersal corridors to occupy their current ranges. In each case, the timing of major phylogeographical inferences corresponds to inferred palaeoclimatic changes in continental Australia. This scenario provides a simple explanation for diversification, secondary contact, and hybridization between the races. However, data presented elsewhere indicate that formation of the parthenogens was considerably more recent than the westward expansion of the hybridizing races, and that multiple hybridization events were geographically and temporally distinct. We suggest that cyclical climate changes may have led to regional range changes that facilitated hybridization between the races, which are not currently known to be in sympatry.

Lower fecundity in parthenogenetic geckos than sexual relatives in the Australian arid zone

Theoretical models of the advantage of sexual reproduction typically assume that reproductive output is equal in sexual and parthenogenetic females. We tested this assumption by comparing fecundity between parthenogenetic and sexual races of gekkonid lizards in the Heteronotia binoei complex, collected across a 1200 km latitudinal gradient through the Australian arid zone. Under laboratory conditions, parthenogenetic geckos had approximately 30% lower fecundity when compared with their sexual progenitors, irrespective of body size. Reflecting clutch-size constraints in gekkonids, this fecundity difference was mainly because of fewer clutches over a shorter period. When parthenogens were compared more broadly with all coexisting sexual races across the latitudinal gradient, parthenogens had lower fecundity than sexuals only when corrected for body size. Differences in fecundity between parthenogens and coexisting sexual races depended on which sexual race was considered. There was no significant relationship between fecundity and parasite (mite) load, despite significantly higher mite loads in parthenogens than in sexual races.

Evidence for simple genetic control of a fruit-colour polymorphism in Acacia ligulata

Fruit-colour polymorphisms are common in nature, but their genetic bases have rarely been examined in wild species. Here, I report on controlled crosses in Acacia ligulata A.Cunn. ex Benth., an Australian arid-zone shrub with a red–yellow–orange aril colour polymorphism. The evidence is consistent with 1-locus, 2-allele control of red v. yellow phenotypes; these phenotypes comprise 98.7% of the adult plants in nature. At this proposed r locus, yellow is dominant to red. Evidence concerning the rare orange morph is limited, but is consistent with models in which orange is produced by either (a) a third allele at the r locus or (b) modification by a second locus. Simple genetic architecture for ecologically relevant traits, such as fruit colour, should aid in linking ecological processes such as frugivory and seed dispersal to the evolutionary trajectories of plant populations.

Modelling stream flow for use in ecological studies in a large, arid zone river, central Australia

AbstractAustralian arid zone ephemeral rivers are typically unregulated and maintain a high level of biodiversity and ecological health. Understanding the ecosystem functions of these rivers requires an understanding of their hydrology. These rivers are typified by highly variable hydrological regimes and a paucity, often a complete absence, of hydrological data to describe these flow regimes. A daily time‐step, grid‐based, conceptual rainfall–runoff model was developed for the previously uninstrumented Neales River in the arid zone of northern South Australia. Hourly, logged stage data provided a record of stream‐flow events in the river system. In conjunction with opportunistic gaugings of stream‐flow events, these data were used in the calibration of the model. The poorly constrained spatial variability of rainfall distribution and catchment characteristics (e.g. storage depths) limited the accuracy of the model in replicating the absolute magnitudes and volumes of stream‐flow events. In particular, small but ecologically important flow events were poorly modelled. Model performance was improved by the application of catchment‐wide processes replicating quick runoff from high intensity rainfall and improving the area inundated versus discharge relationship in the channel sections of the model. Representing areas of high and low soil moisture storage depths in the hillslope areas of the catchment also improved the model performance. The need for some explicit representation of the spatial variability of catchment characteristics (e.g. channel/floodplain, low storage hillslope and high storage hillslope) to effectively model the range of stream‐flow events makes the development of relatively complex rainfall–runoff models necessary for multisite ecological studies in large, ungauged arid zone catchments. Grid‐based conceptual models provide a good balance between providing the capacity to easily define land types with differing rainfall–runoff responses, flexibility in defining data output points and a parsimonious water‐balance–routing model. Copyright © 2004 John Wiley & Sons, Ltd.

Radiation of the Australian flora: what can comparisons of molecular phylogenies across multiple taxa tell us about the evolution of diversity in present–day communities?

The Australian fossil record shows that from ca. 25 Myr ago, the aseasonal-wet biome (rainforest and wet heath) gave way to the unique Australian sclerophyll biomes dominated by eucalypts, acacias and casuarinas. This transition coincided with tectonic isolation of Australia, leading to cooler, drier, more seasonal climates. From 3 Myr ago, aridification caused rapid opening of the central Australian arid zone. Molecular phylogenies with dated nodes have provided new perspectives on how these events could have affected the evolution of the Australian flora. During the Mid-Cenozoic (25-10 Myr ago) period of climatic change, there were rapid radiations in sclerophyll taxa, such as Banksia, eucalypts, pea-flowered legumes and Allocasuarina. At the same time, taxa restricted to the aseasonal-wet biome (Nothofagus, Podocarpaceae and Araucariaceae) did not radiate or were depleted by extinction. During the Pliocene aridification, two Eremean biome taxa (Lepidium and Chenopodiaceae) radiated rapidly after dispersing into Australia from overseas. It is clear that the biomes have different histories. Lineages in the aseasonal-wet biome are species poor, with sister taxa that are species rich, either outside Australia or in the sclerophyll biomes. In conjunction with the fossil record, this indicates depletion of the Australian aseasonal-wet biome from the Mid-Cenozoic. In the sclerophyll biomes, there have been multiple exchanges between the southwest and southeast, rather than single large endemic radiations after a vicariance event. There is need for rigorous molecular phylogenetic studies so that additional questions can be addressed, such as how interactions between biomes may have driven the speciation process during radiations. New studies should include the hitherto neglected monsoonal tropics.

Survival and recruitment of seedlings and suckers of trees and shrubs of the Australian arid zone following habitat management and the outbreak of Rabbit Calicivirus Disease (RCD)

Abstract Recruitment in many shrub and tree species in arid Australia is limited by domestic and feral animal grazing. The outbreak of Rabbit Calicivirus Disease (RCD or RHD) in late 1995 at Kinchega National Park (NP) in arid western NSW, Australia, coincided with intensified warren ripping and other rabbit (Oryctolagus cuniculus) control efforts. We monitored changes in rabbit numbers in response to these factors using spotlight counts and dung‐pellet counts. Rabbit populations declined initially, and were low for the remainder of the study. To assess the impact of rabbit control on vegetation, we examined whether recruitment of seedlings or vegetative suckers was occurring at Kinchega NP, following the arrival of RCD; how long such recruits were likely to survive under current grazing pressures; and whether the magnitude of current seedling and vegetative sucker recruitment and survival is greater than available data prior to RCD and extensive warren control. We followed the survival of individual seedlings and newly emerged suckers of six shrub or tree species, most of which are considered to be at risk of local decline. Three levels of caging were used to exclude all mammalian grazers; all mammalian grazers except rabbits; and no mammalian grazers. Pooled cohorts of seedlings and suckers were analysed using failure‐time analyses. During the course of the study, suckering was observed in four species (Acacia carneorum,Alectryon oleifolius,Casuarina pauperandSantalum acuminatum), with seedlings observed in the other two species (Dodonaea viscosaandAcacia ligulata). Survival of suckers of some species was slightly greater than pre‐RCD estimates, but in general, a pattern of little or nil recruitment is likely in suckers exposed to rabbits or to all grazing mammals. Seedling survival was particularly low regardless of the level of exclusion, largely due to desiccation. Reduction of grazing impacts may only allow recruitment into populations of species reliant on seedlings under more favourable climatic circumstances than experienced in this study, while the probability of successful recruitment into populations of suckering species in western NSW continues to be low even at very low rabbit densities.

Parallel adaptive radiations in arid and temperate Australia: molecular phylogeography and systematics of the Egernia whitii (Lacertilia: Scincidae) species group

It has been an enduring belief that increasing aridity combined with Pliocene-Pleistocene glacial cycles resulted in the formation of distinct arid zone and temperate zone faunas within Australia. We assembled a molecular phylogeny for the Egernia whitii species group, an endemic group of skinks that comprises representatives from arid and temperate Australia, in order to test several biogeographical hypotheses regarding the origin of the Australian arid zone fauna. Sequence data were obtained from ten of the 11 species within the species group, plus three other Egernia species and an outgroup (Eulamprus heatwolei). We targeted portions of the ND4 (696 base pairs) and 16S rRNA (500 bp) mitochondrial genes and the b-Fibrinogen 7th Intron nuclear gene (648 bp). The edited alignment comprised 1844 characters, of which 551 (30%) were variable and 382 (69%) were parsimony informative. We analysed the data using maximum likelihood and Bayesian techniques and produced a single optimal tree. Our phylogeny strongly supports two major clades within the species group, corresponding to temperate-adapted rock-dwelling species and arid-adapted obligate burrowing species. However, the phylogenetic affinities of E. pulchra were not resolved. Our topology indicates that the New South Wales population of E. margaretae is actually E. whitii and reveals that E. margaretae margaretae and E. m. personata are distinct species. There also appears to be a major phylogeographical break within E. whitii occurring in eastern Victoria. Although our data supported several previously proposed phylogenetic relationships, Shimodaira‐Hasegawa tests soundly rejected several suggested affinities between certain species. The arid zone members of the E. whitii species group had been suggested to have originated as a result of multiple periods of colonization during the Pleistocene glaciation cycles. However, our genetic data suggest a single origin (presumably from a semiarid E. multiscutata-like ancestor) for the arid zone members of the group prior to the Plio-Pleistocene, probably during the late Miocene to early Pliocene. Our topology displays substantial sequence divergence between species with short internodes and long terminal branches, indicating rapid adaptive radiations within the arid and temperate zones. The presence of temperate-adapted species within more mesic refugia of the arid zone suggests that the necessary adaptations to aridity for colonizing the dry interior of the continent have not evolved since the initial period of adaptive radiation, despite the long evolutionary history of the species group. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 157‐173. ADDITIONAL KEYWORDS: 16S rRNA ‐ b-fibrinogen ‐ biogeography ‐ mtDNA ‐ ND4 ‐ nuclear gene ‐ phylogeny ‐ skink ‐ taxonomy.

Molecular phylogeography and systematics of the arid-zone members of the Egernia whitii (Lacertilia: Scincidae) species group

We assembled a molecular phylogeny for the arid-zone members of the Egernia whitii species group to test Pianka’s [Zoogeography and speciation of Australian desert lizards: an ecological perspective, Copeia (1972) 127–145] hypothesis that habitat specificity to the three major arid-zone vegetation communities is the primary cause of lizard speciation within the arid interior of Australia. This hypothesis predicts that species should exhibit phylogeographic structuring concordant with the major arid-zone vegetation types. Sequence data were obtained from four of the five arid-zone members of the E. whitii species group, and from across the ranges of the ecologically generalized E. inornata and E. multiscutata and the more specialized E. striata. We targeted a fragment (696 base pair (bp)) of the mitochondrial genome comprising the 3′ half of the ND4 gene. We analysed the data using parsimony, maximum likelihood and Bayesian methods. Our phylogeny confirms the monophyly of the arid-zone members of the species group, although the phylogenetic relationships among species were not fully resolved. Although our topology does not support the recognition of the existing subspecies within E. multiscutata, there is a substantial phylogeographic break between South Australian/Victorian (Clade 1) and Western Australian (Clade 2) populations. We found considerable phylogeographic structure within E. inornata, with six major clades identified. However, these clades were not concordant with the distribution of habitat types in the arid-zone. Phylogeographic structure was also observed in the more specialized E. striata, although our analysis revealed close phylogenetic affinities between the sympatric species E. striata and E. kintorei. Shimodaira–Hasegawa topology tests were equivocal in regard to whether the phylogeographic structure within E. striata was in accordance with Pianka’s predictions. Although our data failed to provide strong support for the suggestion that ecological and habitat factors are responsible for the diversification of arid-zone lizards, most E. inornata and E. striata populations had similar habitats, indicating that adaptation to particular habitats may have some role in the speciation of lizards in the Australian arid-zone.

INSECT SEED PREDATORS AS NOVEL AGENTS OF SELECTIONON FRUIT COLOR

The ecological and evolutionary dynamics of fruit color polymorphisms remain poorly known because patterns and agents of selection have rarely been identified. Here, we examine Acacia ligulata, a shrub of the Australian arid zone characterized by a red/yellow/orange aril color polymorphism. Seed production patterns over four populations and three years suggested that spatially variable selection may be acting to maintain the polymorphism: red and yellow aril color morphs each had the highest seed production in alternate sites. Seed production differences between morphs were a function of both intrinsic plant characters (fruit production) and predispersal seed predation, which affects the number of viable seeds matured per ovule. Fruit production differences are hypothesized to result from a genotype-by-environment interaction, perhaps related to plant vigor. In contrast, morph differences in the numbers of viable seeds per ovule are produced via differential seed predation by heteropteran insects, as demonstrated by exclusion experiments. Because these predators feed when aril color is not visible, differential predation is evidently a response to pleiotropic effects of fruit color alleles. We suggest that such pleiotropic effects may be a common feature of fruit color polymorphisms, and that the most obvious selective agents (that is, seed dispersers) may not always be the most important.

Fruit colour polymorphism in Acacia ligulata: seed and seedling performance, clinal patterns, and chemical variation

Fruit colour polymorphisms are widespread in nature, but their ecological and evolutionary dynamics remain poorly understood. Here we examine Acacia ligulata, a shrub of the Australian arid zone which exhibits a red/orange/yellow aril colour polymorphism. We asked whether the polymorphism had a genetic basis; whether selection acted differentially on morphs during the seed and seedling stages; whether geographic variation in morph frequencies was correlated with environmental factors; and whether morphs differed in physical or chemical characteristics that might influence selection on them. When grown to maturity in a common greenhouse environment, maternal families of seeds showed phenotypic patterns consistent with biparental genetic control of the polymorphism. In contrast to other fruit-colour polymorphic species, progeny of A. ligulata morphs did not vary in rates of seedling emergence or survival in a common garden. Sampling along a 580 km transect revealed clinal variation in morph frequencies. Frequencies of the yellow morph decreased, and frequencies of the red morph increased, across a gradient of decreasing temperature and increasing rainfall. Morphs did not differ in seed mass, aril mass, or in profiles of fatty acids and flavonoids in either arils or seeds. However, morphs showed consistent differences in carotenoid profiles' and elemental content of arils, suggesting that selection by avian and insect seed dispersers, seed predators and herbivores should be investigated. These patterns indicate that both abiotic and biotic factors may contribute to selection on the A. ligulata polymorphism.

The role of torpor in the life of Australian arid zone mammals.

Approximately half of the Australian continent is arid and is characterised by low primary productivity, limited supply of food and pronounced daily fluctuations of ambient temperature (Ta). Despite these adverse conditions the diversity of small mammals in the Australian arid zone is high, although their abundance is generally low. The most successful groups of small arid zone mammals are the dasyurid marsupials, native rodents, and insectivorous bats. A probable reason for the success of the insectivorous dasyurids and bats, which must cope with strong fluctuations in food and water availability, is their extensive use of torpor. Mammalian torpor is characterised by substantial reductions of body temperature (Tb) metabolic rate (MR) and water loss. Small arid zone dasyurids use exclusively daily torpor, some even during the reproductive season, when most mammals maintain strict homeothermy. Dasyurids reduce Tb from ~ 35�C during normothermia to ~ 15�C during torpor, the MR during torpor (TMR) is ~ 30% of basal metabolic rate (BMR). Mass loss, and thus water loss, is related to the duration of torpor bouts. Dasyurids usually enter torpor at night or in the early morning and arouse around midday or in the afternoon. Recent evidence shows that desert dasyurids may bask in the sun during rewarming from torpor. This can minimise energetic cost of arousal to a fraction of that required for endogenous warming. Arid zone bats are also likely to use torpor extensively, but few species, specific to the arid zone, have been studied. Nevertheless, widely distributed bats that occur in the arid zone, such as Nyctophilus geoffroyi, enter brief torpor for part of the day in summer and prolonged torpor (hibernation) for up to two weeks in winter and can reduce Tb to a minimum of 2 - 3�C and TMR to ~ 3% of BMR; mass loss and water loss are minimal during torpor. Patterns of torpor similar to those in bats also have been observed in the insectivorous echidnas and two species of insectivorous / nectarivorous pygmy-possums, which have distribution ranges that include semi-arid and arid areas. In contrast to these species, no detailed information is available on torpor in native Australian rodents, because little work with respect to torpor has been conducted in Australia. However, many arid zone rodents on other continents employ torpor and it is likely that Australian rodents do as well. In addition to reducing energy expenditure and water loss, use of torpor also appears to prolong life span. This is important for bridging adverse conditions and for subsequent re-colonization of areas after droughts and fires in inland Australia. Thus it appears that the success of small insectivorous/nectarivorous mammals and perhaps rodents in the Australian arid zone is partially due to their use of torpor.

Persistence of dead trees and fallen timber in the arid zone: 76 years of data from the T.G.B. Osborn Vegetation Reserve, Koonamore, South Australia

Very little information is available about how long dead trees remain standing, or fallen logs persist, in the Australian arid zone. Data on dead timber longevity were extracted from records of both permanent quadrats and photopoints on the T.G.B. Osborn Vegetation Reserve on Koonamore Station, South Australia. Two species were examined, Acacia aneura (mulga) and Myoporum platycarpum (false sandalwood, sugarwood). Some individuals of mulga are capable of standing dead for over 75 years, while dead M. platycarpum may stand for over 60 years. Dead Myoporum trees remained standing for an average of 31.2 � 5.7 years, fallen trunks persisted for 38.4 � 3.7 years. Standing dead A. aneura persisted on average for 40.0 � 3.7 years, fallen trunks for 22.4� 6.3 years. These figures are almost certainly underestimates. The reasons why are discussed and some comparisons made with temperate forests and tropical mangroves.

Fur versus feathers: the different roles of red kangaroo fur and emu feathers in thermoregulation in the Australian arid zone.

Fur or feathers provide protection against heat loads from solar radiation for birds and mammals. The red kangaroo (Macropus rufus) and the emu (Dromaius novaehollandiae) are conspicuous in arid environments of Australia where there is potential for high solar loads. The diurnal D. novaehollandiae feeds in the open yet it has a dark coat with a high absorptivity (83%), which contrasts with that of M. rufus (61%), but M. rufus generally shelters in shade during the day. We examined the effect of coat characteristics on the heat load from solar radiation at skin level. Coat depth and density (thermal conductance or insulation) and the level of penetration of solar radiation into the coat were important determinants of solar heat load. For M. rufus less than 25% of incident radiation reached the body at low wind speeds and this diminished to below 15% at moderate wind speeds. In the modest shade M. rufus seeks on summer days, their heat load from solar radiation appears minimal. Colour differences among M. rufus did not affect thermal load. D. novaehollandiae on the other hand is exposed to the full incident solar load in the open but its plumage provides almost complete protection from solar radiation. Solar radiation is absorbed at the feather surface and the insulation provided by the deep coat prevents heat transmission to the skin.

Arid zone surface runoff – a significant resource in Australia

The Australian arid zone has quite large resources of surface water. For example in western New South Wales an average of 7 runoff events are observed each year and in these the median depth of runoff is about 0.4mm, or 400m3/km2, providing at least 2.8 ML/km2/yr of surface water. The key to utilisation of this water is to catch it where it is, when it occurs. Simple earthworks, constructed with a blade mounted on a tractor, can be used to direct water from natural small channels to a point of concentration where it can be protected from evaporation and seepage losses, say in an excavated hole or “tank”. Even with 90% loss of the stored water a constant supply of at least 700 litres/km2/day would be available, enough to provide an adequate supply for the average Australian household.

Why is sex so unpopular in the Australian desert?

Sex is by far the most predominant mode of reproduction among eukaryotes. Nevertheless, two new discoveries of asexual reproduction in a lizard and a plant from the Australian arid zone highlight an emerging trend toward the loss of sex in this region. Efforts to understand the processes leading to this pattern should provide important information about the relative advantages and disadvantages of sexual reproduction.

Late Quaternary climates of the Australian arid zone: a review

Aridity in Australia has generally been associated with glacial intervals of the last few glacial cycles. The causes and nature of aridity varied from north to south over the continent. In northern and central Australia, reduced monsoon rain in global cold stages caused lakes and rivers to dry, vegetation to become more sparse, sand dunes to become active, and dust advection to increase. While the monsoon is correlated with warmer global temperatures and high sea levels overall, the exact timing of the greatest development of the monsoon in Stage 5 remains uncertain. In southeastern Australia, the proxy records give a less clear picture. While vegetation seems to have been more sparse in cold stages and sand dune activity and dust flux consequently greater, records of runoff in rivers and lakes have mixed or opposite behaviour to northern or central Australia. The nature of aridity in southeastern Australia is not analogous to conditions anywhere on the continent today. Greatly reduced temperatures over the central and southern interior, greater influence of snow and periglaciation on runoff, high groundwater tables, lower rainfall and reduced atmospheric carbon dioxide levels may all have contributed to and interacted to produce the reconstructed picture of a cold, sparsely vegetated arid landscape with large rivers and perennial lakes. The largest changes in circulation patterns over the glacial cycle probably occurred in the location and/or intensity of summer tropical convergence in northern Australia. Over southern Australia, changes to the temperature and humidity of the westerly circulation have been more significant than the small fluctuations in latitude of the sub-tropical high pressure ridge.

Dispersal for distance? Acacia ligulata seeds and meat ants Iridomyrmex viridiaeneus

Abstract Ant seed dispersal distances are typically small, averaging less than 1 m in published studies. Here, a new record (180 m) for ant seed dispersal distance is reported, and preliminary observations are made on the interaction between meat ants Iridomyrmex viridiaeneus Viehmeyer (Hymenoptera: Formicidae) and diaspores of the sandhill wattle, Acacia ligulata A. Cunn. ex Benth. (Fabaceae) in Kinchega National Park, New South Wales (NSW), Australia. Iridomyrmex viridiaeneus moved diaspores over distances of 7–180 m (mean 93.9 m) from the source trees to their nests, removed the arils underground and discarded the seeds over a 3000‐m2 area surrounding the nest. A germination trial determined that the viability of discarded seeds was 40%, with 80% of the viable seeds in a dormant condition. Although the cumulative effects of I. viridiaeneus on A. ligulata recruitment require further investigation, this study and others raise the possibility that myrmecochorous systems in the Australian arid zone may be characterized by longer dispersal distances than those in other parts of the world. Long‐distance seed movement by ants lends credence to the hypothesis that distance dispersal (in contrast to directed dispersal) could be of benefit to myrmecochorous plants.

Relationship of quantitative X-ray diffraction measurements of geologic materials to cesium sorption

SummaryThe amounts of clay minerals in geologic samples from the Australian arid zone were measured using the SIROQUANT program, which quantifies mineral abundances from X-ray diffraction patterns using the Rietveld method. The sorption of trace cesium on the same samples was investigated in batch experiments. The statistical relationships between the Cs distribution coefficients (Kdvalues) and the smectite, illite and kaolinite contents were assessed. Other characterisation data such as the BET surface area and total clay content were included in the statistical analysis. The correlation of the illite content with the Kdfor trace Cs was stronger than any other correlation that was tested. This can be attributed to the presence of frayed edge sites on illite which are highly selective for the adsorption of trace Cs. Sorption experiments were also carried out with higher Cs concentrations, which were expected to saturate the selective Cs sorption sites on illite. Under these conditions, there was no significant correlation between the illite content and the cesium Kd. However, the Kdwas related to the smectite content of the materials. There was no correlation between the kaolinite content and the Kdfor Cs sorption under any of the experimental conditions. The sorption of Cs on the samples was influenced by the BET surface areas, but normalisation of the Kddata by surface area did not fully explain the sorption results. Only the quantitative XRD data were able to explain the shapes of Cs sorption isotherms. The isotherm was distinctly different for an illite-rich sample and did not conform to the Freundlich isotherm exhibited by other samples. This study demonstrates that quantitative XRD measurements are valuable in predicting Cs sorption properties of complex geologic samples, particularly sorption data obtained with trace Cs levels where bulk measurements such as the BET surface area are less useful.