Extensive long-distance pollen dispersal and highly outcrossed mating in historically small and disjunct populations of Acacia woodmaniorum (Fabaceae), a rare banded iron formation endemic

Long-distance gene flow in Acacia senegal: Hope for disturbed and fragmented populations

Even though pollen and seed dispersals are some of the important factors that determine tree species survival across landscapes, gene dispersal data of important tropical dryland tree species such as Acacia senegal that are undergoing various population disturbances remain scarce. Understanding patterns of gene dispersal in these ecosystems is important for conservation, landscape restoration and tree improvement. We investigated pollen and seed mediated gene flow in two A. senegal populations of contrasting state (less disturbed and heavily undisturbed) using nine microsatellites and 128 genotyping-by-sequencing single nucleotide polymorphism (SNPs) multilocus genotypes of two growth stages (juvenile and adult trees) and their spatial locations. We performed parentage assignments using likelihood approach and undertook spatial genetic structure (SGS) analyses for the two growth stages through correlation among kinship coefficients and geographical distances between pair of individuals. The SNPs showed higher resolving power and assignment rates than microsatellites; however, a combination of the two marker-types improved the assignment rate and provided robust parentage assessments. We found evidence of long-distance (up to 210 m) pollination events for both populations; however, the majority of seed dispersal was found closer to the putative maternal parent. On average, parentage analysis showed high amounts of pollen (40%) and seed (20%) immigration in both populations. Significant positive SGS was found only for the adult cohorts in the less disturbed population for distance classes 20 and 40 m, indicating historical short-distance seed dispersals. Our results suggest long-distance gene flow within the species and we recommend conservation of remnant and isolated populations or individual trees to promote genetic connectivity.

Mating Systems of Single Families and Population Genetic Diversity of Endangered Ormosia hosiei in South China

Ormosia hosiei is a tree species native to China that has been extensively used for ornamental and furniture purposes due to its valued timber. The mating system has substantial impact on genetic diversity and structure of plant natural population. Such information should be considered when planning tree planting for forest restoration. Here we used 12 microsatellite markers and described the mating system of single families and the population genetic diversity of O. hosiei. A high level of genetic diversity was observed in both adults and progenies, although slight differences existed among populations and their progenies, with the expected heterozygosity ranging from 0.763 to 0.794. Overall, O. hosiei displayed a predominantly outcrossed mating. The estimate of multi-locus outcrossing rate (tm) was high with low variations among families, ranged from 0.997 to 1.000. The value of tm-ts, ranged from 0.000 to 0.139, indicated that biparental inbreeding occurred in progenies. Therefore, to obtain a reasonable genetic representation of native tree species and prevent problems associated with inbreeding depression, we suggested effective in situ conservation by replanting seedlings, but seedling production for restoration purposes may require a much larger sampling effort than is currently used. Moreover, it is necessary to conduct further multiple population and multi-year experiments to verify our conclusions.

Different landscape effects on the genetic structure of two broadly distributed woody legumes, Acacia salicina and A. stenophylla (Fabaceae)

Restoring degraded landscapes has primarily focused on re-establishing native plant communities. However, little is known with respect to the diversity and distribution of most key revegetation species or the environmental and anthropogenic factors that may affect their demography and genetic structure. In this study, we investigated the genetic structure of two widespread Australian legume species (Acacia salicina and Acacia stenophylla) in the Murray-Darling Basin (MDB), a large agriculturally utilized region in Australia, and assessed the impact of landscape structure on genetic differentiation. We used AFLP genetic data and sampled a total of 28 A. salicina and 30 A. stenophylla sampling locations across southeastern Australia. We specifically evaluated the importance of four landscape features: forest cover, land cover, water stream cover, and elevation. We found that both species had high genetic diversity (mean percentage of polymorphic loci, 55.1% for A. salicina versus. 64.3% for A. stenophylla) and differentiation among local sampling locations (A. salicina: ΦPT = 0.301, 30%; A. stenophylla: ΦPT = 0.235, 23%). Population structure analysis showed that both species had high levels of structure (6 clusters each) and admixture in some sampling locations, particularly A. stenophylla. Although both species have a similar geographic range, the drivers of genetic connectivity for each species were very different. Genetic variation in A. salicina seems to be mainly driven by geographic distance, while for A. stenophylla, land cover appears to be the most important factor. This suggests that for the latter species, gene flow among populations is affected by habitat fragmentation. We conclude that these largely co-occurring species require different management actions to maintain population connectivity. We recommend active management of A. stenophylla in the MDB to improve gene flow in the adversity of increasing disturbances (e.g., droughts) driven by climate change and anthropogenic factors.

Genetic analysis suggests extensive gene flow within and between catchments in a common and ecologically significant dryland river shrub species; Duma florulenta (Polygonaceae)

AIM

The conservation of plant species biodiversity has been identified as a crucial factor for the resilience of dryland ecosystems in the face of climate change and desertification. Duma florulenta (lignum) is a keystone species that facilitates biodiversity in the floodplains and wetlands of Australia's dryland river systems. This paper explores spatial genetic structure of lignum and investigates factors influencing dispersal and gene flow within and among river catchments of the northern Murray-Darling Basin.

LOCATION

Northern Murray-Darling Basin, eastern Australia.

METHODS

A total of 122 individual plants from subpopulations located on rivers in four adjacent catchments were genotyped using 10 microsatellite markers. Microsatellite data were then analyzed using population genetic techniques to evaluate levels of gene flow and genetic structure and identify factors influencing dispersal.

RESULTS

Results suggest high levels of gene flow between lignum subpopulations of the northern Murray-Darling Basin. AMOVA revealed small but significant differences between subpopulations, and STRUCTURE analysis did not detect meaningful structure when sampling information was not provided. However, when sampling information was supplied using the LOCPRIOR model, three genetic clusters were identified. All Lower Balonne subpopulations were assigned to cluster 1 while a number of the other subpopulations showed mixed ancestry. Weak relationships were identified between pairwise genetic distance and geographic as well as river distance, although the R 2 value of the former was only half that of the latter.

MAIN CONCLUSIONS

Patterns of genetic variation suggest frequent long-distance overland gene flow largely as a result of the movement of seeds via floodwater. Therefore, maintenance of natural variability in flow regime is key both to maintain conditions favorable to recruitment and to promote dispersal and gene flow across the landscape. However, given future climate change projections persistence may be more reliant on the species ability to endure long periods of drought between flood events.

Recovery of threatened plant species and their habitats in the biodiversity hotspot of the Southwest Australian Floristic Region

The Southwest Australian Floristic Region (SWAFR) is a global biodiversity hotspot with high plant diversity and endemism and a broad range of threatening processes. An outcome of this is a high proportion of rare and threatened plant species. Ongoing discovery and taxonomic description of new species, many of which are rare, increases the challenges for recovery of threatened species and prioritisation of conservation actions. Current conservation of this diverse flora is based on integrated and scientific evidence-based management. Here we present an overview of current approaches to the conservation of threatened flora in the SWAFR with a focus on active management through recovery and restoration that is integrated with targeted research. Key threats include disease, fragmentation, invasive weeds, altered fire regimes, grazing, altered hydro-ecology and climate change. We highlight the integrated approach to management of threats and recovery of species with four case studies of threatened flora recovery projects that illustrate the breadth of interventions ranging from In situ management to conservation reintroductions and restoration of threatened species habitats. Our review and case studies emphasise that despite the scale of the challenge, a scientific understanding of threats and their impacts enables effective conservation actions to arrest decline and enhance recovery of threatened species and habitats.

Persistence and stochasticity are key determinants of genetic diversity in plants associated with banded iron formation inselbergs

The high species endemism characteristic of many of the world's terrestrial island systems provides a model for studying evolutionary patterns and processes, yet there has been no synthesis of studies to provide a systematic evaluation of terrestrial island systems in this context. The banded iron formations (BIFs) of south-western Australia are ancient terrestrial island formations occurring within a mosaic of alluvial clay soils, sandplains and occasional granite outcropping, across an old, gently undulating, highly weathered, plateau. Notably, these BIFs display exceptionally high beta plant diversity. Here, we address the determinants and consequences of genetic diversity for BIF-associated plant species through a comprehensive review of all studies on species distribution modelling, phylogenetics, phylogeography, population genetics, life-history traits and ecology. The taxa studied are predominantly narrowly endemic to individual or a few BIF ranges, but some have more regional distributions occurring both on and off BIFs. We compared genetic data for these BIF-endemic species to other localised species globally to assess whether the unique history and ancestry of BIF landscapes has driven distinct genetic responses in plants restricted to this habitat. We also assessed the influence of life-history parameters on patterns of genetic diversity. We found that BIF-endemic species display similar patterns of genetic diversity and structure to other species with localised distributions. Despite often highly restricted distributions, large effective population size or clonal reproduction appears to provide these BIF-endemic species with ecological and evolutionary resilience to environmental stochasticity. We conclude that persistence and stochasticity are key determinants of genetic diversity and its spatial structure within BIF-associated plant species, and that these are key evolutionary processes that should be considered in understanding the biogeography of inselbergs worldwide.

Looking for the right mate in diploid species: How does genetic dominance affect the spatial differentiation of a sexual trait?

Divergence between populations for a given trait can be driven by sexual selection, interacting with migration behaviour. Mating preference for different phenotypes may lead to specific migration behaviour, with departures from populations where the preferred trait is rare. Such preferences can then trigger the emergence and persistence of differentiated populations, even without any local adaptation. However the genetic architecture underlying the trait targeted by mating preference may have a profound impact on population divergence. In particular, dominance between alleles encoding for divergent phenotypes can interfere with the differentiation process. Using a diploid model of a trait determining both mating success and migration rate, we explored differentiation between two connected populations, assuming either co-dominance or strict dominance between alleles. The model assumes that individuals prefer mating with partners displaying the same phenotype and therefore tend to move to the other population when their own phenotype is rare. We show that the emergence of differentiated populations in this diploid moded is limited as compared to results obtained with the same model assuming haploidy. When assuming co-dominance, differentiation arises only when migration is limited compared to the strength of the preference. Such differentiation is less dependent on migration when assuming strict dominance between haplotypes. Dominant alleles frequently invade populations because their phenotype is more frequently expressed, resulting in higher local mating success and a rapid decrease in migration. However, depending on the initial distribution of alleles, this advantage associated with dominance (i.e. Haldane's sieve) may lead to fixation of the dominant allele throughout both populations. Depending on the initial distribution of heterozygotes in the two populations, persistence of polymorphisms within populations can also occur because heterozygotes displaying the predominant phenotype benefit from high mating success. Altogether, our results highlight that heterozygotes' behaviour has a strong impact on population differentiation and highlight the need for diploid models of differentiation and speciation driven by sexual selection.

Pollinator identity and spatial isolation influence multiple paternity in an annual plant

The occurrence and extent of multiple paternity is an important component of variation in plant mating dynamics. However, links between pollinator activity and multiple paternity are generally lacking, especially for plant species that attract functionally diverse floral visitors. In this study, we separated the influence of two functionally distinct floral visitors (hawkmoths and solitary bees) and characterized their impacts on multiple paternity in a self-incompatible, annual forb, Oenothera harringtonii (Onagraceae). We also situated pollinator-mediated effects in a spatial context by linking variation in multiple paternity to variation in plant spatial isolation. We documented pronounced differences in the number of paternal sires as function of pollinator identity: on average, the primary pollinator (hawkmoths) facilitated mating with nearly twice as many pollen donors relative to the secondary pollinator (solitary bees). This effect was consistent for both isolated and nonisolated individuals, but spatial isolation imposed pronounced reductions on multiple paternity regardless of pollinator identity. Considering that pollinator abundance and pollen dispersal distance did not vary significantly with pollinator identity, we attribute variation in realized mating dynamics primarily to differences in pollinator morphology and behaviour as opposed to pollinator abundance or mating incompatibility arising from underlying spatial genetic structure. Our findings demonstrate that functionally distinct pollinators can have strongly divergent effects on polyandry in plants and further suggest that both pollinator identity and spatial heterogeneity have important roles in plant mating dynamics.

Parent-parent and parent-offspring distances inSpondias radlkoferiseeds suggest long-distance pollen and seed dispersal: evidence from latrines of the spider monkey

Pollen and seed dispersal are key ecological processes, directly impacting the spatial distribution, abundance and genetic structure of plant populations; yet, pollen- and seed-dispersal distances are poorly known. We used molecular markers to identify the parental origin (n = 152 adult trees) of 177Spondias radlkoferi(Anacardiaceae) seeds deposited by the spider monkey (Ateles geoffroyi) in latrines located beneath 17 sleeping-trees in two continuous forest sites (CF) and two forest fragments (FF) in the Lacandona rain forest, Mexico. We estimated mean parent-offspring (PO) distances per latrine and, for those seeds (54% of seeds) with more than one candidate parent (i.e. the potential maternal and parental parents), we also estimated parent-parent (PP) distances per latrine, and tested if PO and PP distances differed between forest types. Global PO and PP distances per latrine averaged 682 m (range = 83–1741 m) and 610 m (range = 74–2339 m), respectively, and did not differ significantly between CF and FF. This suggests that pollen dispersal is extensive in both forest types and that long seed dispersal distances (>100 m) are common, thus supporting the hypothesis that the spider monkey is an effective seed disperser ofS. radlkoferiin continuous and fragmented forests.

Native seed for restoration: a discussion of key issues using examples from the flora of southern Australia

Land clearing across southern Australia since European settlement has fundamentally changed the amount and distribution of native vegetation; it has also substantially reduced genetic diversity in plant species throughout Australia, especially in agricultural regions. The most recent State of the Environment report indicates that Australian biodiversity continues to decline. Many approaches to restoration are used in Australia including re-establishing plant populations using tube stock or by direct seeding. Native seed for these projects is often assumed to be plentiful and available for the majority of species we wish to restore but these assumptions are rarely true. We also rely on a small number of species for the majority of restoration projects despite the vast number of species required to fully restore complex plant communities. The majority of seed for restoration is still primarily collected from native vegetation despite longstanding concerns regarding the sustainability of this practice and the globally recognised impacts of vegetation fragmentation on seed production and genetic diversity. Climate change is also expected to challenge seed production as temperatures rise and water availability becomes more limited; changes to current planting practices may also be required. Until now native seed collection has relied on market forces to build a strong and efficient industry sector, but in reality the Australian native seed market is primarily driven by Federal, State and Territory funding. In addition, unlike other seed-based agri-businesses native seed collection lacks national industry standards. A new approach is required to support development of the native seed collection and use sector into an innovative industry.

The critical role of ants in the extensive dispersal of Acacia seeds revealed by genetic parentage assignment

Ants are prominent seed dispersal agents in many ecosystems, and dispersal distances are small in comparison with vertebrate dispersal agents. However, the distance and distribution of ant-mediated dispersal in arid/semi-arid environments remains poorly explored. We used microsatellite markers and parentage assignment to quantify the distance and distribution of dispersed seeds of Acacia karina, retrieved from the middens of Iridomyrmex agilis and Melophorus turneri perthensis. From parentage assignment, we could not distinguish the maternal from each parent pair assigned to each seed, so we applied two approaches to estimate dispersal distances, one conservative (CONS), where the parent closest to the ant midden was considered to be maternal, and the second where both parents were deemed equally likely (EL) to be maternal, and used both distances. Parentage was assigned to 124 seeds from eight middens. Maximum seed dispersal distances detected were 417 m (CONS) and 423 m (EL), more than double the estimated global maximum. Mean seed dispersal distances of 40 m (±5.8 SE) (CONS) and 79 m (±6.4 SE) (EL) exceeded the published global average of 2.24 m (±7.19 SD) by at least one order of magnitude. For both approaches and both ant species, seed dispersal was predominantly (44-84% of all seeds) within 50 m from the maternal source, with fewer dispersal events at longer distances. Ants in this semi-arid environment have demonstrated a greater capacity to disperse seeds than estimated elsewhere, which highlights their important role in this system, and suggests significant novel ecological and evolutionary consequences for myrmecochorous species in arid/semi-arid Australia.

Combining Niche Modelling, Land-Use Change, and Genetic Information to Assess the Conservation Status ofPouteria splendensPopulations in Central Chile

To assess the conservation status of a species with little ecological information is usually a challenging process.Pouteria splendensis an endemic shrub of the coastal range of Central Chile currently classified as lower risk (LR) by IUCN (version 2.3). Knowledge about this species is extremely limited. CurrentlyP. splendensis only found in two small and isolated populations, which are thought to be remaining populations of an originally large metapopulation. However, there is no evidence to support this hypothesis, limiting our ability to gauge the real current conservation status of this species. In this study we combine niche modelling, land-use information, and genetic techniques to test the metapopulation hypothesis and reassess the conservation status ofP. splendensusing the IUCN criteria. We also evaluated the potential effects of climate change in the species distribution. Our results support the hypothesis of a large metapopulation that was recently fragmented. Future climate could increase the range ofP. splendens; however the high level of fragmentation would preclude colonization processes. We recommend reclassifyingP. splendensas Endangered (EN) and developing strategies to protect the remaining populations. Similar approaches like the presented here could be used to reclassify other species with limited ecological knowledge.