Varying levels of clonality and ploidy create barriers to gene flow and challenges for conservation of an Australian arid-zone ecosystem engineer, Acacia loderi

Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern Australia, spans a persistent (\u3e 15 000 year) but poorly studied landscape feature, the Darling River. We investigated the genetic structure of 19 stands of eight to \u3e 1000 plants separated by \u3c 300 km to test for variation in life histories between semi-arid and arid stands to the east and west of the Darling River, respectively. Eight of nine stands east of the Darling were exclusively sexual, whereas most of those to the west were clonal. Three western stands were monoclonal, two were polyploid, and one was a diverse mix of diploid and triploid phenotypes. Bayesian analysis revealed a complex genetic structure within the western stands, whereas the eastern stands formed only two genetic clusters. Conservation of small stands may require augmentation of genotypic diversity. However, most genotypic diversity resides within the eastern stands. Although arid zone stands of A. loderi are not always clonal, clonality and polyploidy are more common in the arid west. Clear demarcation of life histories either side of the Darling River may reflect ancient or contemporary effects of physical disturbance associated with the river channel, or cryptic environmental differences, with sexual and asexual reproduction, respectively, at a selective premium in the semi-arid east and arid west. The restricted distribution of clones and variation in clonality and polyploidy suggests that smaller stands may be vulnerable and warrant individual management

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements

Reproduction of threatened, long lived semi arid Acacia within highly fragmented stands in far western NSW

The contraction and aging of stands of overstory tree species in rangelands is well documented worldwide and largely reflects anthropogenic pressures such as agricultural land clearing and increased grazing leading to increased mortality and reduced recruitment. Without recruitment, stands that largely comprise old and senescent plants may soon go locally extinct. Complicating assessments of plant population health however, is the diversity of dynamics in populations of plant species; what constitutes reproductive failure and population contraction in one species can simply represent a natural cycle in another. In far western New South Wales (NSW), several Acacia species subject to intense grazing by domestic and feral herbivores display prolonged recruitment failure. Surveys over the past two decades have also failed to detect fruit set suggesting they are trending to extinction. Hypotheses explaining the failure of these fragmented populations to reproduce sexually have included restrictions to mating systems, insufficient genetic diversity, prolonged drought period, and the widely supported claim that extant plants are senescent. In stark contrast, some shorter lived co-occurring Acacia species such as A. ligulata and A. victoriae are thriving and reproducing regularly under the same conditions. It is not understood why this difference exists. Reproductive effort has not yet been monitored outside a prolonged period of drought, demographic surveys to date have only been qualitative, and little is known about their mating systems. Without this information it is impossible to know which of the competing hypotheses explain their decline, or to recommend conservation strategies for the future. Here I use a multidisciplinary and comparative approach combining surveys, genetic analysis and manual pollination and growth experiments to gain this information

Microsatellite primers for vulnerable and thriving acacia (Fabaceae) species from Australia\u27s arid zone

Premise of the study: Microsatellite markers were developed for the common arid Australian shrub Acacia ligulata (Fabaceae) and the threatened overstory trees A. melvillei and A. pendula. Methods and Results: DNA sequence data generated by 454 sequencing were used to identify microsatellite nucleotide repeat motifs. Including previously developed primer sets, we report on the development of 10 polymorphic microsatellite loci for each species. Six of these were novel for A. melvillei and A. ligulata, and five were novel for A. pendula, while five more each were transferred from primers developed for related species (A. carneorum and A. loderi). We found three to 17 alleles per locus for each species, with high multilocus genotypic diversity within each of two A. ligulata and A. pendula stands, and one A. melvillei population. A second A. melvillei stand appeared to be monoclonal. Conclusions: These markers will allow assessment of population genetics, mating systems, and connectedness of populations of these and possibly other arid-zone acacias

Isolation and Lack of Potential Mates may Threaten an Endangered Arid-Zone Acacia

Clonality may provide reproductive assurance for many threatened plants while limiting sexual reproductive success either through energetic tradeoffs or because clones are self-incompatible. Most stands of the Australian arid-zone plant Acacia carneorum, flower annually but low seed set and an absence of sexual recruitment now suggest that this species and other, important arid-zone ecosystem engineers may have low genotypic diversity. Indeed, our recent landscape-scale genetic study revealed that stands are typically monoclonal, with genets usually separated by kilometers. An inability to set sexually produced seed or a lack of genetically diverse mates may explain almost system-wide reproductive failure. Here, using microsatellite markers, we genotyped 100 seeds from a rare fruiting stand (Middle-Camp), together with all adult plants within it and its 4 neighboring stands (up to 5 km distant). As expected, all stands surveyed were monoclonal. However, the Middle-Camp seeds were generated sexually. Comparing seed genotypes with the single Middle-Camp genotype and those of genets from neighboring and other regional stands (n = 26), revealed that 73 seeds were sired by the Middle-Camp genet. Within these Middle-Camp seeds we detected 19 genotypes in proportions consistent with self-fertilization of that genet. For the remaining 27 seeds, comprising 8 different genotypes, paternity was assigned to the nearest neighboring stands Mallee and Mallee-West, approximately 1 km distant. Ironically, given this species\u27 vast geographic range, a small number of stands with reproductively compatible near neighbors may provide the only sources of novel genotypes

Data from: Varying levels of clonality and ploidy create barriers to gene flow and challenges for conservation of an Australian arid-zone ecosystem engineer, Acacia loderi

Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern Australia, spans a persistent (> 15 000 year) but poorly studied landscape feature, the Darling River. We investigated the genetic structure of 19 stands of eight to > 1000 plants separated by < 300 km to test for variation in life histories between semi-arid and arid stands to the east and west of the Darling River, respectively. Eight of nine stands east of the Darling were exclusively sexual, whereas most of those to the west were clonal. Three western stands were monoclonal, two were polyploid, and one was a diverse mix of diploid and triploid phenotypes. Bayesian analysis revealed a complex genetic structure within the western stands, whereas the eastern stands formed only two genetic clusters. Conservation of small stands may require augmentation of genotypic diversity. However, most genotypic diversity resides within the eastern stands. Although arid zone stands of A. loderi are not always clonal, clonality and polyploidy are more common in the arid west. Clear demarcation of life histories either side of the Darling River may reflect ancient or contemporary effects of physical disturbance associated with the river channel, or cryptic environmental differences, with sexual and asexual reproduction, respectively, at a selective premium in the semi-arid east and arid west. The restricted distribution of clones and variation in clonality and polyploidy suggests that smaller stands may be vulnerable and warrant individual management

Acacia loderi microsatellite genotypes and spatial coordinates

This file contains microsatellite genotypes and corresponding spatial coordinates for Acacia loderi plants

Research and conservation initiatives for the vulnerable purple-wood wattle : a model for plant species conservation in Australia?

Research on rare and threatened plants is a major focus of conservation biology. We want to know why species are rare or declining, how best to arrest that decline and what is lost when species become locally extinct. Occasionally, understanding decline is straightforward - e.g. if the species is restricted to fertile soils that are desirable for cultivation. However, managing declining populations is more complex and requires knowledge of genetic diversity and interspecific interactions

Tests for inbreeding and outbreeding depression and estimation of population differentiation in the bird-pollinated shrub Grevillea mucronulata

Background and Aims: Plants show patterns of spatial genetic differentiation reflecting gene flow mediated by pollen and seed dispersal and genotype × environment interactions. If patterns of genetic structure are determined largely by gene flow then they may be useful in predicting the likelihood of inbreeding or outbreeding depression but should be less useful if there is strong site-specific selection. For many Australian plants little is known about either their population genetics or the effects on mating systems of variation in pollen transfer distances. Experimental pollinations were used to compare the reproductive success of bird-adapted Grevillea mucronulata plants mated with individuals from a range of spatial scales. A hierarchical survey of microsatellite DNA variation was also conducted to describe the scale of population differentiation for neutral markers. Methods: The effects of four pollen treatments on reproductive performance were compared. These treatments were characterized by transfer of pollen from (a) neighbouring adults; (b) an adjacent cluster of adults (30-50 m distant); (c) a distant cluster (>5 km distant); and (d) open pollination. Sets of 17.9 ± 3·3 leaves from each of 15 clusters of plants were genotyped and spatial autocorrelation and F statistics were used to describe patterns of genetic structure. Key Results: Grevillea mucronulata displayed evidence of both inbreeding and outbreeding depression, with 'intermediate' pollen producing consistently superior outcomes for most aspects of fitness including seed set, seed size, germination and seedling growth. Significant genotypic structuring was detected within clusters (spatial autocorrelation) and among adjacent clusters and clusters separated by >5 km distance (F ST = 0.07 and 0·10). Conclusions: The superior outcome of intermediate pollen transfer and genetic differentiation of adjacent clusters suggests that G. mucronulata selection disfavours matings among closely and distantly related neighbours. Moreover, the performance of open-pollinated seedlings was poor, implying that current mating patterns are suboptimal