Bet‐hedging and germination in the Australian arid zone shrub Acacia ligulata

The diaspore of the Australian arid zone shrub Acacia ligulata is dispersed by birds and ants. To investigate the benefits of providing a dispersal structure attractive to both groups, we compared the germination response and viability of seeds eaten by birds, handled by ants or collected from trees to simulated precursors of germination: scarification, fire and rainfall were simulated. Seed germination and viability were related to the degree of preheating disturbance to the seed coat. Heating increased the germinability of seeds not scarified or eaten by birds. In the absence of heating, ingestion by birds increased germinability. Heating increased the mortality of seeds. Our results suggest that ingestion of seeds by birds may break seed dormancy and hence enable some seeds to germinate soon after dispersal. Alternatively, seeds not eaten by birds are likely to remain dormant until sufficiently scarified by soil or stimulated by fire. Consequently, in areas such as the Simpson Desert, A. ligulata may be able to use a range of seedling establishment ‘windows’ provided by monsoon rains, post‐fire environments and unseasonal winter rains, and also spread the risk of unsuccessful seedling establishment by retaining dormant seeds in the seedbank.     

Clonality disguises the vulnerability of a threatened arid zone Acacia

Long‐lived, widespread plant species are expected to be genetically diverse, reflecting the interaction between large population sizes, overlapping generations, and gene flow. Such species are thought to be resilient to disturbance, but may carry an extinction debt due to reproductive failure. Genetic studies of Australian arid zone plant species suggest an unusually high frequency of asexuality, polyploidy, or both. A preliminary AFLP genetic study implied that the naturally fragmented arid zone tree, Acacia carneorum, is almost entirely dependent on asexual reproduction through suckering, and stands may have lacked genetic diversity and interconnection even prior to the onset of European pastoralism. Here we surveyed microsatellite genetic variation in 20 stands to test for variation in life histories and further assessed the conservation status of the species by comparing genetic diversity within protected stands in National Parks and disturbed range lands. Using herbarium records, we estimate that 219 stands are extant, all of which occur in the arid zone, west of the Darling River in southeastern Australia. With two exceptions, all surveyed stands comprised only one multilocus genet and at least eight were putatively polyploid. Although some stands comprise thousands of stems, our findings imply that the species as a whole may represent ~240 distinct genetic individuals, many of which are polyploid, and most are separated by >10 km of unsuitable habitat. With only 34% of stands (and therefore genets) occurring within conservation reserves, A. carneorum may be at much greater risk of extinction than inferred from on‐ground census data. Land managers should prioritize on‐ground preservation of the genotypes within existing reserves, protecting both vegetative suckers and seedlings from herbivory. Importantly, three stands are known to set viable seed and should be used to generate genetically diverse germ‐plasm for ex situ conservation, population augmentation, or translocation.     

Patterns of genotypic diversity suggest a long history of clonality and population isolation in the Australian arid zone shrub Acacia carneorum

For plants capable of both sexual and clonal reproduction, the relative frequency of these reproductive modes is influenced by genetic and ecological factors. Acacia carneorum is a threatened shrub from the Australian arid zone that occurs as a set of small, spatially isolated populations. Sexual reproduction appears to be very rare: despite regular flowering, only two populations set seed. It is not known whether this reflects an ancient pattern, or results from rapid land use changes following arrival of Europeans in the region 150 years ago. We assessed genotypic variation throughout the range of A. carneorum using AFLP markers, to elucidate the relative importance of clonal and sexual reproduction in this species’ history. Clonal diversity (CD) within populations ranged from 0 to 0.820 (mean CD = 0.270, SE = 0.094), but the relative abundances of genets were typically highly skewed. On average, the two fruiting populations had higher CD (mean CD = 0.590, SE = 0.265) than non-fruiting populations (mean CD = 0.179, SE = 0.077) (t = 2.315, p = 0.049), but most populations contained multiple genets. All genets were population-specific, and there was substantial divergence among populations (Φ _ST = 0.690), implying a long history of isolation. We conclude that clonality has predominated in A. carneorum populations, with occasional sexual recruitment, and that current failure of most populations to set seed likely reflects both a long history of asexual reproduction and effects of habitat disturbance. Conservation of this species may benefit from translocations to increase genotypic diversity within populations.     

Acaulon eremicola,a new moss from the Australian arid zone

Abstract

A new species, Acaulon eremicola is described from aridcentral Australia. It differs from A. muticum and A. integrifolium in the leaf with longer cells and longer usually downwardly curved acuminate apex with twisted arista, the strongly incurled leaf margins when dry, and different spore pattern.     

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.     

Palaeoclimate change drove diversification among isolated mountain refugia in the Australian arid zone

Refugia featured prominently in shaping evolutionary trajectories during repeated cycles of glaciation in the Quaternary, particularly in the Northern Hemisphere. The Southern Hemisphere instead experienced cycles of severe aridification but little is known about the temporal presence and role of refugia for arid-adapted biota. Isolated mountain ranges located in the Australian arid zone likely provided refugia for many species following Mio/Pliocene (<15 Ma) aridification; however, the evolutionary consequences of the recent development of widespread sand deserts is largely unknown. To test alternative hypotheses of ancient vs. recent isolation, we generated a 10 gene data set to assess divergence history among saxicolous geckos in the genus Heteronotia that have distributions confined to major rocky ranges in the arid zone. Phylogenetic analyses show that each rocky range harbours a divergent lineage, and substantial intraspecific diversity is likely due to topographic complexity in these areas. Old divergences (~4 Ma) among lineages pre-date the formation of the geologically young sand deserts (<1 Ma), suggesting that Pliocene climate shifts fractured the distributions of biota long before the spread of the deserts.     

Myrmecochory in some plants (F. chenopodiaceae) of the Australian arid zone

Summary Several common plants (Chenopodiaceae) of the Australian arid zone produce diaspores that bear small and inconspicuous food bodies and are adapted for dispersal by ants. For these species, myrmecochory probably represents an adaptation for highly directional dispersal of diaspores to favorable microsites where nutrients are concentrated and possibly more accessible. Dispersal of diaspores by ants can have a pronounced effect on plant dispersion. In habitats characterized by red, crusty alluvial loam soils, myrmecochorous species grow almost exclusively on ant mounds; these same species grow in relatively continuous stands in sandy soil habitats. The flora of the Australia arid zone may contain many plant species that are adapted to use ants as dispersal agents. We consider several factors that may have promoted or facilitated the evolution of myrmecochory in arid zone plants.     

Effects of spines and thorns on Australian arid zone herbivores of different body masses

Summary We investigated the effects of thorns and spines on the feeding of 5 herbivore species in arid Australia. The herbivores were the rabbit (Oryctolagus cuniculus), euro kangaroo (Macropus robustus), red kangaroo (Macropus rufus), sheep (Ovis aries), and cattle (Bos taurus). Five woody plants without spines or thorns and 6 woody plants with thorns were included in the study. The spines and thorns were not found to affect the herbivores' rates of feeding (items ingested/min), but they did reduce the herbivores' rates of biomass ingestion (g-dry/item). The reduction in biomass ingested occurred in two ways: at a given diameter, twigs with spines and thorns had less mass than undefended plants, and the herbivores consumed twigs with smaller diameters on plants with spines and thorns. The relative importance of the two ways that twigs with spines and thorns provided less biomass varied with herbivore body mass. Reduced twig mass was more important for small herbivores, while large herbivores selected smaller diameters. The effectiveness of spines and thorns as anti-herbivore defenses did not vary with the evolutionary history of the herbivores (i.e. native vs. introduced). Spines and thorns mainly affected the herbivores' selection of maximum twig sizes (reducing diameter and mass), but the minimum twig sizes selected were also reduced.     

Some like it cold: summer torpor by freetail bats in the Australian arid zone

Bats are among the most successful groups of Australian arid-zone mammals and, therefore, must cope with pronounced seasonal fluctuations in ambient temperature (T _a), food availability and unpredictable weather patterns. As knowledge about the energy conserving strategies in desert bats is scant, we used temperature-telemetry to quantify the thermal physiology of tree-roosting inland freetail bats (Mormopterus species 3, 8.5 g, n = 8) at Sturt National Park over two summers (2010–2012), when T _a was high and insects were relatively abundant. Torpor use and activity were affected by T _a. Bats remained normothermic on the warmest days; they employed one “morning” torpor bout on most days and typically exhibited two torpor bouts on the coolest days. Overall, animals employed torpor on 67.9 % of bat-days and torpor bout duration ranged from 0.5 to 39.3 h. At any given T _a, torpor bouts were longer in Mormopterus than in bats from temperate and subtropical habitats. Furthermore, unlike bats from other climatic regions that used only partial passive rewarming, Mormopterus aroused from torpor using either almost entirely passive (68.9 % of all arousals) or active rewarming (31.1 %). We provide the first quantitative data on torpor in a free-ranging arid-zone molossid during summer. They demonstrate that this desert bat uses torpor extensively in summer and often rewarms passively from torpor to maximise energy and water conservation.     

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 mesic-adapted 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.     

Hydric balance and locomotor performance of an anuran (Rhinella marina) invading the Australian arid zone

Invasive species often encounter environmental conditions well outside those found in their native geographic ranges, and thus provide ideal model systems with which to explore responses to novel abiotic challenges. Within Australia, the invasive cane toad Rhinella marina has colonized areas that are considerably more arid than those found within its native range. Has the colonization of these novel environments been accompanied by shifts in physiology and/or locomotor performance? We measured rates of evaporative water loss, water gain, and effects of desiccation on locomotor performance of cane toads from two invasion fronts: one mesic (the wet‐dry tropics) and one arid (the semi‐desert). The two populations diverged substantially. Contrary to intuition (but consistent with intra‐specific comparisons between other toad populations from mesic vs arid areas), rates of evaporative water loss were lower (not higher) in toads from the mesic population. However, arid‐zone toads gained water more rapidly through their ventral surfaces, and rates of water loss and gain were highly correlated within individual toads from the arid‐zone population. Rates of water exchange in laboratory‐acclimated toads from the semi‐arid zone did not differ from those of free‐ranging conspecifics from the same population, suggesting that divergences between mesic and semi‐arid toads reflect genetic changes that have occurred during the species’ Australian invasion. Mesic and semi‐arid toads showed similar locomotor performance (endurance, distance per hop) when fully hydrated, but locomotor performance declined much more rapidly with desiccation in the mesic toads. Thus, within the short (decades‐long) timespan of the cane toad's Australian invasion, there has been substantial population divergence in the ability to withstand desiccating conditions. If we are to accurately predict the distributions (and hence impacts) of invading organisms, we will need to include adaptation potential in risk assessment schemes.     

Subterranean archipelago in the Australian arid zone: mitochondrial DNA phylogeography of amphipods from central Western Australia

In 1998, a unique subterranean ecosystem was discovered in numerous isolated calcrete (carbonate) aquifers in the arid Yilgarn region of Western Australia. Previous morphological and genetic analyses of a subterranean water beetle fauna suggest that calcrete aquifers are equivalent to closed island habitats that have been isolated for millions of years. We tested this hypothesis further by phylogeographic analyses of subterranean amphipods (Crangonyctoidea: Paramelitidae and Hyalidae) using mitochondrial DNA sequence data derived from the cytochrome oxidase I gene. Phylogenetic analyses and population genetic analyses (samova) provided strong evidence for the existence of at least 16 crangonyctoid and six hyalid divergent mitochondrial lineages, each restricted in their distribution to a single calcrete aquifer, in support of the 'subterranean island (archipelago) hypothesis' and extending its scope to include entirely water respiring invertebrates. Sequence divergence estimates between proximate calcrete populations suggest that calcretes have been isolated at least since the Pliocene, coinciding with a major aridity phase that led to the intermittent drying of surface water. The distribution of calcretes along palaeodrainage channels and on either side of drainage divides, have had less influence on the overall phylogeographic structure of populations, with evidence that ancestral crangonyctoid and hyalid species moved between catchments multiple times prior to their isolation within calcretes. At least two potential modes of evolution may account for the diversity of subterranean amphipod populations: dispersal/vicariance of stygobitic species or colonization of calcretes by surface species and independent evolution of stygobitic characteristics.     

Phylogeography of sexual Heteronotia 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.     

Experimental trial of Australian arid zone reptiles as early warning indicators of overgrazing by cattle

The value of reptiles as bioindicators of the initial effects of heavy cattle grazing in a South Australian chenopod shrubland was assessed in an experimental trial. Reptiles were sampled in three different subhabitats within two replicate treatment paddocks and a control region. A total of 30 sites was sampled in two sessions before grazing and four sessions after the commencement of intensive pulses of grazing. Capture rates of most common reptile species, fecundity of abundant gecko species and reptile species composition within different subhabitats were largely resilient to the initial effects of overgrazing. However, agamids in general, and particularly Ctenophorus nuchalis, increased at grazed sites relative to controls following grazing. Most changes observed in the reptile assemblages were predictable based upon species response to alteration in vegetation cover. Because vegetation cover can be rapidly and efficiently monitored, the use of reptiles as early warning indicators of unsustainable pastoralism in the study region was not supported.     

Food of the zebra finch (Poephila guttata), and an examination of granivory in birds of the Australian arid zone

Birds are important granivores in the Australian arid zone, and this paper reviews their role by assembling available data on diet and habitat selection of the granivorous species occurring in the region. Paucity of dietary information is alleviated by a study of the food of the zebra finch (Poephila guttata) at two sites in the eastern arid zone. Zebra finches subsisted entirely on grass seeds of a relatively narrow specific range; 17 classes of seeds (at least 19 species) were eaten, but one class dominated the diet at each study site and only five classes (probably six species) were significant overall. Comparative information concerning granivorous species- suggested that the seeds of grasses and shrubs are of most importance in diets, that larger species tended to eat larger seeds from a wider variety of plants because of the addition of shrub species to the diet, and that Acacia shrublands contained most species. Characteristics of the arid zone that are of particular importance to granivorous birds appear to be the abundance of grasses and the patchy and erratic nature of the rainfall.     

Phylogenetics of gall-inducing thrips on Australian Acacia

Analysis of DNA sequence data from four genes ( Elongation Factor-1 α, wingless , 16S rDNA and cytochrome oxidase I ) yielded a well-resolved, well-supported phylogeny for all 21 species of gall-inducing thrips found on Australian Acacia. This phylogeny was then used to investigate the evolution of various behavioural and life history traits, and to examine the level of agreement with the taxonomy of the group. Our results suggest that there may have been a single origin of soldier castes in gall-inducing thrips. Examination of the distribution of the three primary life history strategies employed by these thrips (pupating in the gall, pupating in soil with soldier castes and pupating in soil without soldier castes) indicates that two of the strategies may have evolved as a result of factors associated with host plant affiliations or through parasite pressure. Our phylogeny does not support the existing generic classification of the group in that the genera are not monophyletic, nor does it lend itself to a clear solution to improve the classification in accordance with the phylogeny.     

Parallel diversification of Australian gall-thrips on Acacia

The diversification of gall-inducing Australian Kladothrips (Insecta: Thysanoptera) on Acacia has produced a pair of sister-clades, each of which includes a suite of lineages that utilize virtually the same set of 15 closely related host plant species. This pattern of parallel insect-host plant radiation may be driven by cospeciation, host-shifting to the same set of host plants, or some combination of these processes. We used molecular-phylogenetic data on the two gall-thrips clades to analyze the degree of concordance between their phylogenies, which is indicative of parallel divergence. Analyses of phylogenetic concordance indicate statistically-significant similarity between the two clades. Their topologies also fit with a hypothesis of some degree of host-plant tracking. Based on phylogenetic and taxonomic information regarding the phylogeny of the Acacia host plants in each clade, one or more species has apparently shifted to more-divergent Acacia host-plant species, and in each case these shifts have resulted in notable divergence in aspects of the phenotype including morphology, life history and behaviour. Our analyses indicate that gall-thrips on Australian Acacia have undergone parallel diversification as a result of some combination of cospeciation, highly restricted host-plant shifting, or both processes, but that the evolution of novel phenotypic diversity in this group is a function of relatively few shifts to divergent host plants. This combination of ecologically restricted and divergent radiation may represent a microcosm for the macroevolution of host plant relationships and phenotypic diversity among other phytophagous insects.     

Water usage and diet preferences of free ranging kangaroos, sheep and feral goats in the Australian arid zone during summer

In much of the arid rangelands of Australia the common large mammalian herbivores are the native marsupials, the Red kangaroo ( Megalein rufa ) and the Euro ( Mucropus robustus ), and the introduced eutherian species, the domestic sheep ( Ovis aries ) and the feral goat ( Capra hircus ). In the north west of New South Wales a study was carried out to examine the patterns of water usage during summer of these species when they were free ranging in the same area. Drinking frequencies, water turnovers, electrolyte concentrations and diet preferences were determined and information obtained on movements and dispersal from watering points.
The marsupials had a much lower water usage than either of the eutherians. The tritiated water turnover of the goats was three times and that of the sheep four times the value obtained for kangaroos. While much of the difference between the marsupials and eutherians appeared to be due to fundamental physiological differences the high water usage of sheep was in part related to the high intake of halophytic plants in their diet.
The water turnovers of the Red kangaroos and Euros were not found to be different. Drinking studies and urine osmolalities suggested, however, that the open plains dwelling Red kangaroos had a higher water requirement than the hill inhabiting Euro.
The principal components of the diets of the Red kangaroo were grasses; of the Euro, grasses and shrubs; of goats, trees and shrubs; of sheep, halophytic shrubs.