Genetic diversity and structure of the globally invasive tree, <Emphasis Type="Italic">Paraserianthes lophantha</Emphasis> subspecies <Emphasis Type="Italic">lophantha</Emphasis>, suggest an introduction history characterised by varying propagule pressure

An emerging insight in invasion biology is that intra-specific genetic variation, human usage, and introduction histories interact to shape genetic diversity and its distribution in populations of invasive species. We explore these aspects for the tree species Paraserianthes lophantha subsp. lophantha, a close relative of Australian wattles (genus Acacia). This species is native to Western Australia and is invasive in a number of regions globally. Using microsatellite genotype and DNA sequencing data, we show that native Western Australian populations of P. lophantha subsp. lophantha are geographically structured and are more diverse than introduced populations in Australia (New South Wales, South Australia, and Victoria), the Hawaiian Islands, Portugal, and South Africa. Introduced populations varied greatly in the amount of genetic diversity contained within them, from being low (e.g. Portugal) to high (e.g. Maui, Hawaiian Islands). Irrespective of provenance (native or introduced), all populations appeared to be highly inbred (F _IS ranging from 0.55 to 0.8), probably due to selfing. Although introduced populations generally had lower genetic diversity than native populations, Bayesian clustering of microsatellites and phylogenetic diversity indicated that introduced populations comprise a diverse array of genotypes, most of which were also identified in Western Australia. The dissimilarity in the distribution and number of genotypes in introduced regions suggests that non-native populations originated from different native sources and that introduction events differed in propagule pressure.     

Glacial oceanographic contrasts explain phylogeography of Australian bull kelp

The evolutionary effects of Southern Hemisphere Pleistocene oceanographic conditions — marked by fluctuations in sea levels and water temperatures, and redirected currents — are poorly understood. The southeastern tip of Australia presents an intriguing model system for studying the biological impacts of palaeoceanography. In particular, contrasting oceanographic conditions that existed on eastern vs. western sides of the Bassian Isthmus during Pleistocene glacial periods allow for natural comparisons between putative refugial vs. re-invading populations. Whereas many western Tasmanian marine taxa were likely eliminated by cold subantarctic water during the last glacial period, eastern Tasmanian populations would have persisted in relatively warm temperatures mediated by the ongoing influence of the East Australian Current (EAC). Here we test for the effects of contrasting palaeoceanographic conditions on endemic bull kelp, Durvillaea potatorum , using DNA sequence analysis (COI; rbc L) of more than 100 individuals from 14 localities in southeastern Australia. Phylogenetic reconstructions reveal a deep (maximum divergence 4.7%) genetic split within D. potatorum , corresponding to the 'eastern' and 'western' geographical regions delimited by the Bassian Isthmus, a vicariant barrier during low Pleistocene sea levels. Concordant with the western region's cold glacial conditions, samples from western Tasmania and western Victoria are genetically monomorphic, suggesting postglacial expansion from a mainland refugium. Eastern samples, in contrast, comprise distinct regional haplogroups, suggesting the species persisted in eastern Tasmania throughout recent glacial periods. The deep east–west divergence seems consistent with earlier reports of morphological differences between 'western' and 'eastern' D. potatorum , and it seems likely that these forms represent reproductively isolated species.     

Extrinsic and intrinsic influences on the phylogeography of the Austrocochlea constricta species group

Although extrinsic factors, such as oceanic currents and isolation induced by sea level maxima during Plio-Pleistocene glacial cycles, are often suggested as principal determinants of marine phylogeography, they are not always complete explanations. The counterexamples to predominant phylogeographic patterns in southeastern Australia suggest for example, that intrinsic factors such a habitat preference or reproductive mode can have significant influence.We collected DNA sequences from mitochondrial cytochrome c oxidase I (COI) and two nuclear gene introns from the Austrocochlea constricta species group to determine whether its porcata and constricta phenotypes are genetically distinguishable, to examine the phylogeographic effects of the Bassian Isthmus landbridge formed between Tasmania and Victoria during glacial maxima, and to investigate the importance of intrinsic factors in structuring its genetic variability.No fixed genetic differences between the porcata and constricta phenotypes were identified in any gene so the number of species comprised by the group cannot yet be determined. The two major clades recovered in COI analyses were respectively found principally east or west of the Bassian Isthmus. A. constricta is the first lecithotrophic or estuarine invertebrate known to show this pattern. There were no fixed differences, for any of the three genes, between specimens from estuarine and marine populations within either the eastern or western COI clades. Other intrinsic factors such as breeding period (possibly) and larval type (probably) may play roles in modulating phylogeographic patterns.     

Microsatellite markers and mtDNA data indicate two distinct groups in dwarf galaxias, Galaxiella pusilla (Mack) (Pisces: Galaxiidae), a threatened freshwater fish from south-eastern Australia

Galaxiella pusilla is a small, non-migratory freshwater fish, endemic to south-eastern Australia and considered nationally threatened. To assist in the conservation of the species, microsatellite markers were developed and used to characterize genetic variation in 20 geographically distinct populations across its range. Substantial genetic differentiation was found between an eastern (Victoria east of the Otway Ranges and Tasmania) and western (South Australia and Victoria west of, and including, the Otway Ranges) region. This major separation was also observed in data from a mitochondrial gene and supports a previously proposed split. Populations from the eastern region had overall lower genetic diversity for both the microsatellite and mtDNA markers. There was substantial genetic differentiation between populations within the two regions, suggesting that gene flow is limited by the isolation of freshwater streams. Genetic structure, consistent with an isolation-by-distance model, was also evident in both regions. Patterns of genetic variation in this threatened species are compared to those obtained for other taxa across the same region. The need to consider separate conservation strategies for the two sets of populations is emphasized.     

Isolation and genetic diversity of endangered grey nurse shark (Carcharias taurus) populations

Anthropogenic impacts are believed to be the primary threats to the eastern Australian population of grey nurse sharks (Carcharias taurus), which is listed as critically endangered, and the most threatened population globally. Analyses of 235 polymorphic amplified fragment length polymorphisms (AFLP) loci and 700 base pairs of mitochondrial DNA control region provide the first account of genetic variation and geographical partitioning (east and west coasts of Australia, South Africa) in C. taurus. Assignment tests, analysis of relatedness and Fst values all indicate that the Australian populations are isolated from South Africa, with negligible migration between the east and west Australian coasts. There are significant differences in levels of genetic variation among regions. Australian C. taurus, particularly the eastern population, has significantly less AFLP variation than the other sampling localities. Further, the eastern Australian sharks possess only a single mitochondrial haplotype, also suggesting a small number of founding individuals. Therefore, historical, rather than anthropogenic processes most likely account for their depauperate genetic variation. These findings have implications for the viability of the eastern Australian population of grey nurse sharks.     

High microsatellite diversity and differential structuring among populations of the introduced common brushtail possum, Trichosurus vulpecula, in New Zealand

An understanding of genetic variation and structure of pest populations has the potential to improve the efficiency of measures to control them. Genetic analysis was undertaken at five microsatellite loci in four native Australian and 14 introduced New Zealand populations of the common brushtail possum Trichosurus vulpecula in order to document these parameters. Genetic variation in New Zealand populations, and phylogenetic relationships among Australian and New Zealand populations, were largely predicted by the recorded introduction history. Populations on the two main islands of New Zealand had only slightly lower genetic diversity than did Australian populations, except that allelic richness on the South Is. was significantly lower. Diversity was higher in North Is. than in South Is. populations (although not significantly so) and mainland New Zealand populations as a group were significantly more diverse than offshore islands that represented secondary population size bottlenecks. In phylogenetic analyses South Is. and offshore island populations grouped with Tasmania, while North Is. populations grouped either with mainland Australia or were intermediate between the two Australian sources. This scheme was supported by admixture coefficients showing that North and South Is./offshore island populations were largely mainland Australian and Tasmanian in origin, respectively. Population structure differed markedly between the North and South Islands: populations were typically more genetically differentiated on the former than the latter, which also showed significant isolation-by-distance. Substantial linkage disequilibrium in most sampled New Zealand but no Australian population between microsatellite loci Tv16 and Tv27 suggests they may be physically linked.     

Land barriers and open oceans: effects on gene diversity and population structure in Avicennia germinans L. (Avicenniaceae)

Avicennia germinans L. is a widespread mangrove species occupying the west coast of Africa and the Atlantic and Pacific coasts of the Americas from the Bahamas to Brazil and Baja California to Peru. An amplified fragment length polymorphism (AFLP) molecular analysis was carried out to assess genetic architecture within this species and to evaluate the effects of the Atlantic Ocean and the Central American Isthmus (CAI) on population and regional genetic diversity and differentiation. In total, 349 polymorphic AFLP fragments were identified among 144 individuals from 14 populations from the east Atlantic, west Atlantic and east Pacific. Levels of genetic diversity varied considerably among populations, but were generally higher in populations from the east Atlantic. Regional differentiation between the Pacific coast and Atlantic populations was greater than between east and west Atlantic populations, suggesting that the CAI has had an important influence on population genetic structure in this species. The lower level of divergence of east Atlantic from west Atlantic populations suggests some dispersal across the Atlantic Ocean, although migration rates are probably low; Nm from GST equal to 0.41 and accumulation of private and rare alleles in the east Atlantic. Population differentiation did not appear to follow an isolation by distance model and has probably resulted from complex patterns of population bottlenecks, and founder events due to landscape changes during the Pleistocene, particularly in the west Atlantic. The molecular data provide no support for the treatment of east Atlantic populations as a separate species A. africana.     

Phylogeography and population structure of the endangered Tehuantepec jackrabbit <Emphasis Type="Italic">Lepus flavigularis</Emphasis>: implications for conservation

The Tehuantepec jackrabbit (Lepus flavigularis) is an endangered species restricted to a small area in the Isthmus of Tehuantepec, Oaxaca, Mexico. To evaluate its phylogeographic structure, population genetics, and demographic history we sequenced the mitochondrial Control Region hypervariable domain (CR-1) for 42 individuals representing the entire species range. Phylogenetic patterns indicated that this species is subdivided into two highly divergent clades, with an average nucleotide genetic distance of 3.7% (TrN) between them. Clades A and B are geographically distributed in non-overlapping areas to the west and to the east of the Isthmus of Tehuantepec, respectively. Genetic diversity indices showed reduced genetic variability in L. flavigularis when compared to other species of Lepus within main clades and within populations. This low genetic diversity coupled with the restricted distribution to very small areas of occurrence and limited gene flow suggest that genetic drift has played an important role in the evolution of this species. Historical demographic analysis also pointed out that these two clades underwent a recent population expansion that started about 9,000 years ago for clade A and 3,200 years ago for clade B during the Holocene. Consequently, from the conservation perspective our results suggest that populations included in clades A and B should be regarded as distinct evolutionary lineages.     

Mitochondrial DNA variation in Indo-Pacific populations of the giant tiger prawn,Penaeus monodon

Surveys of mitochondrial DNA (mtDNA) variation in the giant tiger prawn, Penaeus monodon, using restriction fragment length polymorphisms have provided the first clear evidence that the Indo-West Pacific region is a site of accumulation of genetic diversity rather than a site of origin of genetic diversity. No haplotyes were found in common between a group of five southeast African populations and a group of five Australian (including Western Australia) and three southeast Asian populations. The dominant haplotype was different in the Australian and southeast Asian population groups. Genetic diversity (pi) was greatest in Indonesia (pi averaged 0.05), less in the Philippines and Australia (pi averaged 0.01), and markedly less in the southeast African and the West Australian populations (pi averaged 0.003). The high diversity of the southeast Asian populations resulted from the occurrence in those populations of a set of haplotypes found only in southeast Asia but derived from the southeast African haplotypes. These genetic variants therefore evolved in the Indian Ocean and later migrated into the Indo-West Pacific region. Low genetic variation in the geographically marginal populations in southeast Africa and Western Australia is considered to be the result of bottlenecks, but mismatch distributions suggest that large population sizes have been maintained in Indonesian populations for long periods.     

Sex-linked and autosomal microsatellites provide new insights into island populations of the tammar wallaby

The emerging availability of microsatellite markers from mammalian sex chromosomes provides opportunities to investigate both male- and female-mediated gene flow in wild populations, identifying patterns not apparent from the analysis of autosomal markers alone. Tammar wallabies (Macropus eugenii), once spread over the southern mainland, have been isolated on several islands off the Western Australian and South Australian coastlines for between 10 000 and 13 000 years. Here, we combine analyses of autosomal, Y-linked and X-linked microsatellite loci to investigate genetic variation in populations of this species on two islands (Kangaroo Island, South Australia and Garden Island, Western Australia). All measures of diversity were higher for the larger Kangaroo Island population, in which genetic variation was lowest at Y-linked markers and highest at autosomal markers (θ=3.291, 1.208 and 0.627 for autosomal, X-linked and Y-linked data, respectively). Greater relatedness among females than males provides evidence for male-biased dispersal in this population, while sex-linked markers identified genetic lineages not apparent from autosomal data alone. Overall genetic diversity in the Garden Island population was low, especially on the Y chromosome where most males shared a common haplotype, and we observed high levels of inbreeding and relatedness among individuals. Our findings highlight the utility of this approach for management actions, such as the selection of animals for translocation or captive breeding, and the ecological insights that may be gained by combining analyses of microsatellite markers on sex chromosomes with those derived from autosomes.     

Genetic variation in central and peripheral populations of Excoecaria agallocha from Indo-West Pacific

Genetic diversity and differentiation were studied in Excoecaria agallocha L., a mangrove species growing on the coastlines of the Indo-West Pacific region. Twenty natural populations of E. agallocha were sampled from the Malay Peninsula (central population), and in Southern China, North Australia, Sri Lanka and Southern Japan (peripheral populations). Our results showed that central populations from Malay Peninsula possessed significantly higher genetic diversity than the peripheral ones (P < 0.05). Analysis of molecular variation (AMOVA) revealed that genetic variability was partitioned at 22.9% among regions, 23.6% among populations within regions, and 53.5% within populations. Genetic differentiation (G_ST = 0.300) among the six central populations was stronger than those from peripheral regions. Populations from North Australia clustered closely together in the dendrogram and were distinct from the rest of the populations. Those from Southern Japan, Southern China and Sri Lanka also clustered closely together, respectively. However, populations from Malay Peninsula did not cluster by region. The east coast populations of Malay Peninsula (including Pasir population) were more genetically similar to the populations from Southern China than those from the west coastline of Malay Peninsula. Our study suggests that ocean currents, land barriers, limited dispersal ability of seeds, and founder effect may play important roles in the distribution of genetic diversity in E. agallocha.     

Genetic structure,diversity and distribution of a threatened lizard affected by widespread habitat fragmentation

Understanding the demographic consequences of habitat loss on populations is essential for the conservation of threatened species. The threatened swamp skink (Lissolepis coventryi) is restricted to fragmented wetland habitats in Victoria and southeast South Australia. It has experienced significant habitat loss in the last 150 years, particularly around the Melbourne metropolitan area, where several small and isolated populations remain. Using mtDNA and nuDNA SNPs, we examined distribution patterns and population structure to infer evolutionary history and genetic distinctiveness of populations throughout the species’ range. For populations in the Melbourne metropolitan area, we examined genetic diversity. We found the species to be highly divergent, separating into two distinct lineages to the east and west of Melbourne, likely due to geological and climate influences causing isolation of populations. Species’ detectability was low, particularly in the far east despite relatively intact habitat and presumed higher abundance. Melbourne populations showed signs of limited genetic diversity. We suggest that translocations to promote gene diversity amongst these populations, together with habitat restoration and protection, present an important management strategy for L. coventryi.

     

Marine biogeographical disjunction in temperate Australia: historical landbridge,contemporary currents,or both?

Marine biogeographers have long recognized broad east–west differentiation of marine communities across southern Australia, but few studies have explicitly assessed the site of disjunction or the factors potentially underlying this biodiversity. A recent, detailed phylogeographical and distributional study of the dispersive gastropod genus Nerita revealed an abrupt shift in species abundance across mainland Australia, apparently correlated with the site of an historical vicariant barrier: the Bassian Isthmus. In the current study I provide an independent assessment of this vicariant hypothesis by morphologically analysing over 3000 intertidal Nerita specimens from eight coastal sites around Tasmania. Consistent with the Bassian Isthmus hypothesis, the study reveals a dramatic east–west disjunction across north-east Tasmania. A survey of marine biogeographical literature reveals several additional examples supporting the east–west species turnover detected in Nerita . I discuss the role of contemporary oceanographic factors in preserving the biogeographical signature of marine vicariance, even in highly dispersive taxa. Based on recent marine connectivity data, the east–west disjunction in Nerita taxa can be interpreted as an historic vicariant pattern perpetuated by contemporary oceanographic conditions. The results of this study emphasize the potential importance of considering relative abundance data – rather than just species range data – in marine biogeographical analyses. As the observed disjunction is likely to have broad implications for Australia's marine biodiversity, it is imperative that conservation biologists incorporate such data in the design of marine protected areas.     

Phylogeography of the olive sea snake, Aipysurus laevis (Hydrophiinae) indicates Pleistocene range expansion around northern Australia but low contemporary gene flow

Pleistocene sea-level fluctuations profoundly changed landmass configurations around northern Australia. The cyclic emergence of the Torres Strait land bridge and concomitant shifts in the distribution of shallow-water marine habitats repeatedly sundered east and west coast populations. These biogeographical perturbations invoke three possible scenarios regarding the directions of interglacial range expansion: west to east, east to west, or bidirectional. We evaluated these scenarios for the olive sea snake, Aipysurus laevis, by exploring its genetic structure around northern Australia based on 354 individuals from 14 locations in three regions (Western Australia, WA; Gulf of Carpentaria, GoC; Great Barrier Reef, GBR). A 726-bp fragment of the mitochondrial DNA ND4 region revealed 41 variable sites and 38 haplotypes, with no shared haplotypes among the three regions. Population genetic structure was strong overall, phiST=0.78, P<0.001, and coalescent analyses revealed no migration between regions. Genetic diversity was low in the GBR and GoC and the genetic signatures of these regions indicated range or population expansions consistent with their recent marine transgressions around 7000 years ago. By contrast, genetic diversity on most WA reefs was higher and there were no signals of recent expansion events on these reefs. Phylogenetic analyses indicated that GBR and GoC haplotypes were derived from WA haplotypes; however, statistical parsimony suggested that recent range expansion in the GBR-GoC probably occurred from east coast populations, possibly in the Coral Sea. Levels of contemporary female-mediated gene flow varied within regions and reflected potential connectivity among populations afforded by the different regional habitat types.     

Invasion history of Lycium ferocissimum in Australia: The impact of admixture on genetic diversity and differentiation

Aim

We investigated the invasion history of Lycium ferocissimum, a spine-covered shrub native to South Africa that was introduced to Australia in the mid-1800s, and has since developed into a damaging invasive plant of undisturbed landscapes and pastures. In addition to identifying the provenance of the Australian plants, we tested for evidence of admixture, and contrasted genetic diversity and structuring across the native and introduced ranges.

Location

Samples were collected across South Africa (24 localities) and Australia (26 localities).

Methods

We used genotyping-by-sequencing (3117 SNPs across 381 individuals) to assess population genetic structuring in L. ferocissimum across Australia and South Africa. Coalescent analyses were used to explicitly test contrasting invasion scenarios.

Results

Clear geographic genetic structuring was detected across South Africa, with distinct clusters in the Eastern and Western Cape provinces. The L. ferocissimum plants in Australia form their own genetic cluster, with a similar level of genetic diversity as plants in South Africa. Coalescent analyses demonstrated that the lineage in Australia was formed by admixture between Eastern Cape and Western Cape plants, with most of the genetic material from the Australian lineage originating from the Western Cape. Our analyses suggest that L. ferocissimum plants were originally introduced to South Australia, though it is unclear whether admixture occurred before or after its introduction to Australia. We detected little evidence of geographic genetic structure across Australia, although many of the populations were genetically distinct from one another.

Main Conclusions

Our results illustrate how admixture can result in genetically diverse and distinct invasive populations. The complex invasion history of L. ferocissimum in Australia poses particular challenges for biological control. We suggest potential biological control agents should be screened against admixed plants (in addition to plants from the Eastern and Western Cape) to test whether they provide effective control of the genetically distinct invasive lineage.     

Hierarchical metapopulation structure in a highly mobile marine predator: the southern Australian coastal bottlenose dolphin (<Emphasis Type="Italic">Tursiops</Emphasis> cf. <Emphasis Type="Italic">australis</Emphasis>)

Little is known about the population ecology of the recently described bottlenose dolphin species Tursiops australis. The classification of this species is still under debate, but this putative species is thought to be comprised of small and genetically distinct populations (including sub-populations under increasing anthropogenic threats) and is likely endemic to coastal southern Australia. Mitochondrial DNA (mtDNA) control region sequences and microsatellite loci were used to assess genetic variation and hierarchical population structure of coastal T. cf. australis across a range of spatial scales and environmental discontinuities between southern Western Australia (WA) and central South Australia (SA). Overall, genetic diversity was similar to that typically found for bottlenose dolphins, although very low mtDNA diversity was found in Gulf St. Vincent (GSV) dolphins. We found historical genetic subdivision and likely differences in colonisation between GSV and Spencer Gulf, outer- and inner-gulf locations, and SA/WA and previously identified Victorian/Tasmanian populations. A hierarchical metapopulation structure was revealed along southern Australia, with at least six genetic populations occurring between Esperance, WA and southern Tasmania. In addition, fine-scale genetic subdivision was observed within each SA/WA population. In general, contemporary migration was limited throughout southern Australia, but an important gene flow pathway was identified eastward along the Great Australian Bight. Management strategies that promote gene flow among populations should be implemented to assist with the maintenance of the inferred metapopulation structure. Further research into the population ecology of this species is needed to facilitate well-informed management decisions.     

Evolutionary history and genetic connectivity across highly fragmented populations of an endangered daisy

Conservation management can be aided by knowledge of genetic diversity and evolutionary history, so that ecological and evolutionary processes can be preserved. The Button Wrinklewort daisy (Rutidosis leptorrhynchoides) was a common component of grassy ecosystems in south-eastern Australia. It is now endangered due to extensive habitat loss and the impacts of livestock grazing, and is currently restricted to a few small populations in two regions >500 km apart, one in Victoria, the other in the Australian Capital Territory and nearby New South Wales (ACT/NSW). Using a genome-wide SNP dataset, we assessed patterns of genetic structure and genetic differentiation of 12 natural diploid populations. We estimated intrapopulation genetic diversity to scope sources for genetic management. Bayesian clustering and principal coordinate analyses showed strong population genetic differentiation between the two regions, and substantial substructure within ACT/NSW. A coalescent tree-building approach implemented in SNAPP indicated evolutionary divergence between the two distant regions. Among the populations screened, the last two known remaining Victorian populations had the highest genetic diversity, despite having among the lowest recent census sizes. A maximum likelihood population tree method implemented in TreeMix suggested little or no recent gene flow except potentially between very close neighbours. Populations that were more genetically distinctive had lower genetic diversity, suggesting that drift in isolation is likely driving population differentiation though loss of diversity, hence re-establishing gene flow among them is desirable. These results provide background knowledge for evidence-based conservation and support genetic rescue within and between regions to elevate genetic diversity and alleviate inbreeding.Subject terms: Ecological genetics, Population genetics     

Population structure of the yellow-footed rock-wallaby Petrogale xanthopus (Gray, 1854) inferred from mtDNA sequences and microsatellite loci

The yellow-footed rock-wallaby Petrogale xanthopus is considered to be potentially vulnerable to extinction. This wallaby inhabits naturally disjunct rocky outcrops which could restrict dispersal between populations, but the extent to which that occurs is unknown. Genetic differences between populations were assessed using mitochondrial DNA (control region) sequencing and analysis of variation at four microsatellite loci among three geographically close sites in south-west Queensland (P. x. celeris) and, for mtDNA only, samples from South Australia (P. x. xanthopus) as well. Populations from South Australia and Queensland had phylogenetically distinct mtDNA, supporting the present classification of these two groups as evolutionarily distinct entities. Within Queensland, populations separated by 70 km of unsuitable habitat differed significantly for mtDNA and at microsatellite loci. Populations separated by 10 km of apparently suitable habitat had statistically homogeneous mtDNA, but a significant difference in allele frequency at one microsatellite locus. Tests for Hardy-Weinberg equilibrium and micro-geographical variation at microsatellite loci did not detect any substructuring between two wallaby aggregations within a colony encircling a single rock outcrop. Although the present study was limited by small sample sizes at two of the three Queensland locations examined, the genetic results suggest that dispersal between colonies is limited, consistent with an ecological study of dispersal at one of the sites. Considering both the genetic and ecological data, we suggest that management of yellow-footed rock-wallabies should treat each colony as an independent unit and that conservation of the Queensland and South Australian populations as separate entities is warranted.     

Genetic consequences of isolation: island tammar wallaby (<Emphasis Type="Italic">Macropus eugenii</Emphasis>) populations and the conservation of threatened species

Isolation and restricted gene flow can lead to genetic deterioration in populations. Populations of many species are increasingly becoming fragmented due to human impacts and active management is required to prevent further extinctions. Islands provide an ideal location to protect species from many mainland threatening processes such as habitat loss and fragmentation, disease and competition/predation from introduced species. However their isolation and small population size renders them prone to loss of genetic diversity and to inbreeding. This study examined two endemic and one introduced population of tammar wallaby (Macropus eugenii) on three islands in the Houtman Abrolhos Archipelago, Western Australia: East Wallabi (EWI), West Wallabi (WWI) and North Islands (NI). Nine autosomal and four Y-linked microsatellite loci, and sequence data from the mitochondrial DNA (mtDNA) control region were used to examine the impact of long-term isolation (EWI and WWI) and small founder size (NI) on genetic diversity and inbreeding. This study found all three populations had low genetic diversity, high levels of effective inbreeding and increased frequency of morphological abnormalities. Isolation has also led to significant inter-population genetic differentiation. These results highlight the importance of incorporating genetic management strategies when utilising islands as refuges for declining mainland populations.     

The invasion of <Emphasis Type="Italic">Senecio pterophorus</Emphasis> across continents: multiple,independent introductions,admixture and hybridization

Senecio pterophorus (Compositae) is a perennial shrub native to eastern South Africa that was introduced into the Western Cape in South Africa and Australia approximately 100 years ago and into Europe (Italy and Spain) more than 25–30 years ago. In this study, the aims were to unravel the putative sources of the introduced populations and identify the changes in genetic diversity after invasion using molecular markers and phylogeographic and population genetic analyses. We sampled the entire area of distribution for S. pterophorus extensively. Based on the results, three lineages were established along a latitudinal and climatic gradient in the native range (south, central, central/north) with high levels of admixture. Multiple, independent introductions occurred in the four invaded ranges. The central/northern lineage (humid climate) was the primary source for all of the invaded regions (with drier climates), although a secondary role was revealed for the southern lineage in the Western Cape and the central/northern lineage in Australia and Spain. The genetic diversity was slightly lower in the Spanish and Australian populations than that in the native populations. A variety of demographic and genetic processes affected the amount and structure of genetic diversity in the invaded areas, including multiple introductions and admixture (Western Cape, Australia and Spain) as well as pre-invasive hybridization (Italy). The patterns of dispersion support a hypothesis of rapid evolution of S. pterophorus after invasion in response to novel climatic conditions.