Disjunct Regions Research Articles

Habitat suitability and the constraints of migration in New World warblers

Identifying the factors that influence geographic range limits can illustrate the various ecological, physiological, and evolutionary constraints imposed on a species. The range limits of migratory birds are particularly challenging to study as they occur in disjunct regions at different times of the year, which can impose different constraints. Travel between breeding and wintering regions poses a significant energetic and navigational challenge to birds, although it is not clear how these movements influence breeding dispersal and range expansion. Here I ask whether the possible costs of migration limit the breeding ranges of wood warblers, a group of birds with an extensive history of ecological and evolutionary studies. I used occurrence records for multiple wood warbler species, breeding primarily in the boreal forest of North America, to generate environmental niche models. I tested for over‐prediction of habitat suitability into the western boreal forest, where most these species do not have occurrence records but where there is presumably suitable habitat. I found that some of these vagile taxa, primarily found east of the Rocky Mountains, also have predicted habitat suitability that extends into the north and west, where they have little to no occurrence records. I discuss several possible explanations for this discordance. In particular, the patterns are consistent with the costs of a long‐distance migration limiting the benefits of range expansion, as migration may become too onerous as the distance between breeding and wintering areas increases. These results speak to the process of niche filling more generally and call attention to an under‐appreciated explanation for why migratory species may not fully occupy their fundamental niche.

Allo-allo-triploid Sphagnum × falcatulum: single individuals contain most of the Holantarctic diversity for ancestrally indicative markers.

Allopolyploids exhibit both different levels and different patterns of genetic variation than are typical of diploids. However, scant attention has been given to the partitioning of allelic information and diversity in allopolyploids, particularly that among homeologous monoploid components of the hologenome. Sphagnum × falcatulum is a double allopolyploid peat moss that spans a considerable portion of the Holantarctic. With monoploid genomes from three ancestral species, this organism exhibits a complex evolutionary history involving serial inter-subgeneric allopolyploidizations. Studying populations from three disjunct regions [South Island (New Zealand); Tierra de Fuego archipelago (Chile, Argentina); Tasmania (Australia)], allelic information for five highly stable microsatellite markers that differed among the three (ancestral) monoploid genomes was examined. Using Shannon information and diversity measures, the holoploid information, as well as the information within and among the three component monoploid genomes, was partitioned into separate components for individuals within and among populations and regions, and those information components were then converted into corresponding diversity measures. The majority (76%) of alleles detected across these five markers are most likely to have been captured by hybridization, but the information within each of the three monoploid genomes varied, suggesting a history of recurrent allopolyploidization between ancestral species containing different levels of genetic diversity. Information within individuals, equivalent to the information among monoploid genomes (for this dataset), was relatively stable, and represented 83% of the grand total information across the Holantarctic, with both inter-regional and inter-population diversification each accounting for about 5% of the total information. Sphagnum × falcatulum probably inherited the great majority of its genetic diversity at these markers by reticulation, rather than by subsequent evolutionary radiation. However, some post-hybridization genetic diversification has become fixed in at least one regional population. Methodology allowing statistical analysis of any ploidy level is presented.

Wheelerodemus muhlenbergiae Henry and Sweet (Hemiptera: Lygaeoidea: Blissidae): Distribution, Host Plants, and Seasonality

Abstract. The chinch bug Wheelerodemus muhlenbergiae Henry and Sweet was described as a new species in 2015 based on collections from disjunct regions of Oklahoma (Arbuckle Mountains and nearby areas) and Texas (eastern Edwards Plateau). Adults are short winged (micropterous) and flightless. The known host plants are two species of the grass genus Muhlenbergia: M. lindheimeri in Texas and M. reverchonii in Oklahoma and Texas. The present paper provides additional information on the study sites and host plants, adds collection sites not included in the original description, and gives notes on seasonality. Adults overwintered and first instars were observed as early as late April. Second instars were present in late May, third instars in early to mid-June, and fourth and fifth instars in early July. The bug might be univoltine, but the adults observed in late October probably represented those of a second generation. Vascular plants and other insect groups with similar Arbuckle Mountains-Edwards Plateau ran...

Species delimitation and phylogeography of the studfishFundulus catenatusspecies group (Ovalentaria: Cyprinodontiformes)

The Central Highlands of North America have an old and complex geological and biological history, with extensive unexplored cryptic diversity. We examined the species limits of the Fundulus catenatus species group (F. catenatus, Fundulus bifax, and Fundulus stellifer) using two phylogenetic approaches. Fundulus catenatus was densely sampled from five geographically disjunct regions across the eastern USA. We sequenced four nuclear introns and used species tree analyses and two species delimitation methods to determine historical relationships and investigate species diversity within the group. Both methods strongly supported the presence of two reciprocally monophyletic species within F. catenatus. Species tree analysis of four nuclear introns (stx5a, ncl1, rpsa, and rps3) from the F. catenatus species group (including a tip for F. sp. cf. catenatus) recovered the two Mobile Basin species as sister to a strongly supported clade of F. catenatus and F. sp. cf. catenatus. Cytochrome b sequences were used in phylogeographical analyses of the two putative species. In one species we identified signatures of population expansion whereas the other exhibited genetic structure consistent with isolation of populations.

Complex patterns of global spread in invasive insects: eco-evolutionary and management consequences

The advent of simple and affordable tools for molecular identification of novel insect invaders and assessment of population diversity has changed the face of invasion biology in recent years. The widespread application of these tools has brought with it an emerging understanding that patterns in biogeography, introduction history and subsequent movement and spread of many invasive alien insects are far more complex than previously thought. We reviewed the literature and found that for a number of invasive insects, there is strong and growing evidence that multiple introductions, complex global movement, and population admixture in the invaded range are commonplace. Additionally, historical paradigms related to species and strain identities and origins of common invaders are in many cases being challenged. This has major consequences for our understanding of basic biology and ecology of invasive insects and impacts quarantine, management and biocontrol programs. In addition, we found that founder effects rarely limit fitness in invasive insects and may benefit populations (by purging harmful alleles or increasing additive genetic variance). Also, while phenotypic plasticity appears important post-establishment, genetic diversity in invasive insects is often higher than expected and increases over time via multiple introductions. Further, connectivity among disjunct regions of global invasive ranges is generally far higher than expected and is often asymmetric, with some populations contributing disproportionately to global spread. We argue that the role of connectivity in driving the ecology and evolution of introduced species with multiple invasive ranges has been historically underestimated and that such species are often best understood in a global context.

Geographic independence and phylogenetic diversity of red shiner introductions

Identifying areas at risk of invasion can be difficult when the distribution of a non-native species encompasses geographically disjunct regions. Understanding genealogical relationships among native and non-native populations can clarify the origins of fragmented distributions, which in turn can clarify how fast and far a non-native species may spread. We evaluated genetic variation across the native and invasive ranges of red shiner (Cyprinella lutrensis), a minnow known to displace and hybridize with native species, to reconstruct invasion pathways across the United States (USA). Examination of mitochondrial cytochrome-b variation found that native range populations of red shiner fall into four highly divergent lineages that likely warrant species recognition. Introduced red shiner populations in the eastern and western USA are derived from only two of these lineages. Western USA populations originate from the mid-western and western genetic lineages, whereas eastern introductions derive only from the mid-western lineage. Western USA invasive populations exhibit fewer, but more diverse haplotypes compared to eastern USA invasive populations. We also recovered an undescribed, divergent lineage of Cyprinella that has been cryptically introduced into the western USA, which raises the possibility that hybridization has proceeded following secondary contact between previously allopatric lineages. Approximate Bayesian Computation modeling suggests that the disjunct distribution of red shiner across North America is an agglomeration of independent regional invasions with distinct origins, rather than stepwise advance of an invasion front or secondary introductions across regions. Thus localized control may be effective in managing non-native red shiner, including further spread to areas of conservation concern.

Pleistocene climatic fluctuations explain the disjunct distribution and complex phylogeographic structure of the Southern Red-backed Salamander, Plethodon serratus

The southeastern United States (U.S.) has experienced dynamic climatic changes over the past several million years that have impacted species distributions. In many cases, contiguous ranges were fragmented and a lack of gene flow between allopatric populations led to genetic divergence and speciation. The Southern Red-backed Salamander, Plethodon serratus, inhabits four widely disjunct regions of the southeastern U.S.: the southern Appalachian Mountains, the Ozark Plateau, the Ouachita Mountains, and the Southern Tertiary Uplands of central Louisiana. We integrated phylogenetic analysis of mitochondrial DNA sequences (1399 base pairs) with ecological niche modeling to test the hypothesis that climate fluctuations during the Pleistocene drove the isolation and divergence of disjunct populations of P. serratus. Appalachian, Ozark, and Louisiana populations each formed well-supported clades in our phylogeny. Ouachita Mountain populations sorted into two geographically distinct clades; one Ouachita clade was sister to the Louisiana clade whereas the other Ouachita clade grouped with the Appalachian and Ozark clades but relationships were unresolved. Plethodon serratus diverged from its sister taxon, P. sherando, ~5.4 million years ago (Ma), and lineage diversification within P. serratus occurred ~1.9–0.6 Ma (Pleistocene). Ecological niche models showed that the four geographic isolates of P. serratus are currently separated by unsuitable habitat, but the species was likely more continuously distributed during the colder climates of the Pleistocene. Our results support the hypothesis that climate-induced environmental changes during the Pleistocene played a dominant role in driving isolation and divergence of disjunct populations of P. serratus.

Phylogeographic inference using Bayesian model comparison across a fragmented chorus frog species complex.

Fragmented species complexes provide an interesting system for investigating biogeographic history and the present distribution of genetic variation. Recent advances in sequencing technology and statistical phylogeography enable the collection and rigorous analysis of large multilocus data sets, but designing studies that produce meaningful phylogeographic inferences remains challenging. We implemented a Bayesian model comparison approach to investigate previous biogeographic hypotheses while simultaneously inferring the presence of genetic structure in a chorus frog species complex. The Illinois chorus frog (Pseudacris illinoensis), originally described as a subspecies of the broadly distributed Strecker's chorus frog (Pseudacris streckeri), occurs in small, disjunct regions associated with scarce sand prairie habitats that have been impacted by human development. We used high-throughput sequencing to develop and collect a multitiered genetic data set comprised of three different marker types (23 anonymous nuclear sequence loci, four mitochondrial genes and 14 microsatellite loci) designed to address questions across different evolutionary timescales. Phylogenetic analyses uncovered a deep divergence between populations in the Edwards Plateau of central Texas and all other P.streckeri/P. illinoensis populations, but suggest the disjunct distribution of P.illinoensis occurred more recently. Our best-supported migration model is consistent with the hypothesis that central Texas represented a refugium from which populations expanded via multiple routes. This model also indicates that disjunct northern and southern regions of P.illinoensis should be considered genetically distinct management units. Our study provides an evolutionary context for future studies and conservation efforts in P.illinoensis and demonstrates the utility of model-based approaches for phylogeographic inference.

Thriving in the Cold: Glacial Expansion and Post-Glacial Contraction of a Temperate Terrestrial Salamander (Plethodon serratus).

The dynamic geologic history of the southeastern United States has played a major role in shaping the geographic distributions of amphibians in the region. In the phylogeographic literature, the predominant pattern of distribution shifts through time of temperate species is one of contraction during glacial maxima and persistence in refugia. However, the diverse biology and ecology of amphibian species suggest that a “one-size-fits-all” model may be inappropriate. Nearly 10% of amphibian species in the region have a current distribution comprised of multiple disjunct, restricted areas that resemble the shape of Pleistocene refugia identified for other temperate taxa in the literature. Here, we apply genetics and spatially explicit climate analyses to test the hypothesis that the disjunct regions of these species ranges are climatic refugia for species that were more broadly distributed during glacial maxima. We use the salamander Plethodon serratus as a model, as its range consists of four disjunct regions in the Southeast. Phylogenetic results show that P. serratus is comprised of multiple genetic lineages, and the four regions are not reciprocally monophyletic. The Appalachian salamanders form a clade sister to all other P. serratus. Niche and paleodistribution modeling results suggest that P. serratus expanded from the Appalachians during the cooler Last Glacial Maximum and has since been restricted to its current disjunct distribution by a warming climate. These data reject the universal applicability of the glacial contraction model to temperate taxa and reiterate the importance of considering the natural history of individual species.

Evolutionary Migration of the Disjunct Salt Cress Eutrema salsugineum (= Thellungiella salsuginea, Brassicaceae) between Asia and North America.

Eutrema salsugineum (= Thellungiella salsuginea Brassicaceae), a species growing in highly saline habitats, is a good model for use in salt-stress research. However, its evolutionary migrations and genetic variations within and between disjunct regions from central Asia to northern China and North America remain largely unknown. We examined genetic variations and phylogeographic patterns of this species by sequencing ITS, 9 chloroplast (cp) DNA fragments (4379 bp) and 10 unlinked nuclear loci (6510 bp) of 24 populations across its distributional range. All markers suggested the high genetic poverty of this species and the limited number of genetic variations recovered was congruently partitioned between central Asia, northern China and North America. Further modelling of nuclear population-genetic data based on approximate bayesian computation (ABC) analyses indicated that the long-distance dispersals after the recent origin of E. salsugineum may have occurred from central Asia to the other two regions respectively within 20000 years. The fast demographic expansions should have occurred in northern China in a more recent past. Our study highlights the importance of using ABC analyses and nuclear population genetic data to trace evolutionary migrations of the disjunct distributions of the plants in the recent past.

Large divergence and low diversity suggest genetically informed conservation strategies for the endangered Virgin Islands Boa (Chilabothrus monensis)

The Virgin Islands boa (Chilabothrus monensis) was listed as critically endangered by the U.S. Fish and Wildlife Service in 1979, and is presently known to occur in two disjunct regions: Isla de Mona and the eastern Puerto Rico Bank. Populations of the species are highly vulnerable and are hypothesized to have contracted considerably from their former range. Here we conduct intraspecific genetic analyses for this species using mitochondrial and nuclear loci as well as population genetic simulations. In so doing, we characterize nine microsatellite markers for C. monensis and demonstrate their potential usefulness for in situ or ex situ conservation genetic analysis. We find that populations on the Puerto Rico Bank are highly divergent (3.03% sequence divergence; 2.10 Mya temporal divergence) from Isla de Mona animals and that little genetic diversity exists within or among these sampling sites. Furthermore, we provide recommendations and an assessment of translocation/reintroduction potential for this species based on the genetic data presented herein. Our study also highlights the usefulness of simulations for assessing small sample size in conservation genetic studies. We anticipate that these results and genetic tools will be useful in formulating a comprehensive conservation genetic approach for Virgin Island boas.

Localized habitat change near Churchill, Manitoba and the decline of nesting Whimbrels (Numenius phaeopus)

Whimbrels (Numenius phaeopus) are large shorebirds that breed in two geographically disjunct regions in the North American Subarctic and Arctic. Since the early 1970s, the nesting distribution of Whimbrels in the Subarctic near Churchill, Manitoba, Canada has changed, and an area of historic breeding importance was no longer used as nesting habitat in 2008. We compared aerial photography of the 2.55 km2 area from 1973 to 1986, to high-resolution satellite imagery from 2006 to assess structural habitat change. Comparison of the three time-period imagery showed that over the 33-year span shrubs and trees increased in cover by 12.6 and 6.9 %, respectively, whereas other vegetation, including lichen, decreased by 19.1 %. This localized evidence of shrub and tree encroachment is accompanied by a decline in Whimbrel nesting densities from 17–19 pairs (max. 7.45 pairs/km2) in 1973 and 1974, to 1–2 pairs (max. 0.78 pairs/km2) in 2007, and 0 pairs in 2008. Change in vegetation structure has important implications for the long-term viability of Subarctic and Arctic breeding shorebird populations.

Pleistocene survival, regional genetic structure and interspecific gene flow among three northern peat‐mosses: Sphagnum inexspectatum, S. orientale and S. miyabeanum

AbstractAimArctic plant species are often characterized by a complex genetic structure because of changes in their population size, the fragmentation of metapopulation systems, extensive hybridization and allopolyploidization, and survival in disjunct refugia, historical features associated with Pleistocene glaciation. We assessed the biogeographical and genetic patterns in three closely related northern species of peat‐moss (Sphagnum inexspectatum, S. orientale and S. miyabeanum), especially interspecific hybridization, infraspecific geographical differentiation and Pleistocene survival in one or more refugial areas. We tested alternative hypotheses of refugial survival in three widely disjunct regions: eastern Asia, Alaska and Greenland.LocationNorth America (Canada, western USA and Greenland), China, Japan and Russia.MethodsFour hundred and forty‐three plants were genotyped at 12 microsatellite loci. Nucleotide sequences from 130 accessions for two plastid and two nuclear loci were used to reconstruct haplotype relationships. Population genetic analyses produced estimates of genetic diversity, levels of interspecific gene flow and rates of infraspecific intercontinental migration. Approximate Bayesian computation was used to test alternative biogeographical scenarios.ResultsWe found evidence of hybridization between two of the three species, but phylogenetic patterns are predominantly divergent rather than reticulate. Disjunct populations of one species, S. orientale, in Greenland, Alaska and China are genetically differentiated, but migration has occurred among all three metapopulation systems. Divergence‐time analyses strongly support the hypothesis that S. orientale survived the Last Glacial Maximum in Beringia and also in Greenland.Main conclusionsOur results indicate that Beringia served as a refugium for peat‐mosses, and therefore peatlands, which are currently extensive at high latitudes of the Northern Hemisphere. Sphagnum orientale also appears to have survived the Last Glacial Maximum in Greenland, indicating that the species persisted in multiple Pleistocene refugia. Phylogenetic patterns are relatively simple in these mosses compared with those commonly encountered in Arctic angiosperms.

Development and characterization of 21 microsatellite loci for the Pine Barrens treefrog (Hyla andersonii)

Twenty-one polymorphic microsatellite loci were developed and characterized for the rare Pine Barrens treefrog (Hyla andersonii). This species is found in three disjunct regions of the eastern United States and is con- sidered threatened by each state in which it occurs. In order to elucidate population structure and identify possible declines in this treefrog we designed primers that amplify across all three regions. Loci were isolated from a genomic library enriched for a variety of repetitive elements. The number of alleles ranged from 2 to 15, the observed het- erozygosity ranged from 0.17 to 0.93, and the expected heterozygosity ranged from 0.38 to 0.95 using only 15 individuals. These microsatellite markers will address a deficiency of genetic data for H. andersonii by assessing differences among the three regions and describing popu- lation structure within each region in order to inform conservation efforts.

Long-term persistence and vicariance within the Australian Monsoonal Tropics: the case of the giant cave and tree geckos (Pseudothecadactylus)

The Australian Monsoonal Tropics (AMT) are one of the largest unbroken areas of savannah woodland in the world. The history of the biota of this region is poorly understood; however, data from fossil deposits indicate that the climate was more mesic in the past, and that biodiversity has been shaped by attenuation and turnover as arid conditions expanded and intensified through the Miocene and Plio-Pleistocene. The giant cave and tree geckos (Pseudothecadactylus) are distributed across three disjunct regions of relatively high rainfall in the AMT (the north-west Kimberley, the ‘Top End’, and Cape York). We present an analysis of the diversity and biogeography of this genus based on mitochondrial (ND2) and nuclear (RAG-1) loci. These data indicate that the three widely allopatric lineages of Pseudothecadactylus diverged around the mid-Miocene, a novel pattern of relatively long-term persistence that has not previously been documented within the AMT. Two Pseudothecadactylus species endemic to sandstone scarps in the west Kimberley Region and ‘Top End’ also include divergent mitochondrial lineages, indicative of deep intraspecific coalescence times within these regions. Pseudothecadactylus is a highly relictual lineage with an extant distribution that has been shaped by a history of attenuation, isolation and persistence in the face of increasingly arid conditions. The low ecological and morphological diversity of Pseudothecadactylus also contrasts with its diverse sister lineage of geckos in New Caledonia, further underlining the relictual nature of standing diversity in the former.

Gleichenia inclusisora, a new and uncommon tangle fern from New Zealand

Gleichenia inclusisora is described here as a new and uncommon fern endemic to New Zealand. Several morphological features readily distinguish G. inclusisora from other Gleichenia species, and in the context of New Zealand species these features include: sori embedded in the lamina; bicolorous, orbicular to ovate, peltate scales on abaxial surfaces of the ultimate segments; glabrous stipes and glabrescent proximal costae; and unpouched and abaxially white ultimate segments. Phylogenetic analyses of New Zealand species using chloroplast DNA sequences support the distinctiveness of G. inclusisora. It is recorded from four disjunct regions, but no extant population is known for one of these. We suggest that G. inclusisora be treated in the threat classification system as Naturally Uncommon, with the Range Restricted qualifier.

Population genetic structure of in situ wild Sorghum bicolor in its Ethiopian center of origin based on SSR markers

In situ population studies of wild relatives of crops are crucial for the conservation of plant genetic resources, especially in regions with high genetic diversity and a risk of local extinction. Ethiopia is the center of origin for sorghum, yet little is known about the genetic structure of extant wild populations. Using 9 Simple Sequence Repeat loci, we characterized 19 wild populations from five regions, 8 local cultivar populations from three regions, and 10 wild sorghum accessions from several African countries. To our knowledge, this is the most comprehensive study to date of in situ wild sorghum populations in Africa. Genetic diversity corrected for sample size was significantly greater in the wild populations in situ than in local cultivars or the accessions. Approximately 41 % of the genetic variation in the wild plants was partitioned among populations, indicating a high degree of differentiation and potential value for germplasm conservation, and the average number of migrants (Nm) per generation was 0.43. Cluster analyses showed that some wild populations were grouped by geographic region, whereas others were not, presumably due to long-distance seed movement. Four wild populations from disjunct regions formed a unique cluster with an Ethiopian accession of subsp. drummondii and probably represent a weedy race. STRUCTURE and other analyses detected evidence for crop-wild hybridization, consistent with previous molecular marker studies in Kenya, Mali, and Cameroon. In summary, in situ wild sorghum populations in Ethiopia harbor substantial genetic diversity and differentiation, despite their close proximity to conspecific cultivars in this crop/wild/weedy complex.

Utilizing a multifaceted approach to assess the current distribution and conservation status of an uncommon species: the golden mouse (Ochrotomys nuttalli) in Florida

AbstractAimOur goal was to assess the conservation status of the understudied and naturally uncommon habitat specialist, the golden mouse (Ochrotomys nuttalli), at the edge of its range where its historically fragmented habitat has been subjected to severe loss.LocationPeninsular Florida, north of approximately 27° latitude, USA.MethodsWe used data gathered from museum collections, regional biologists, geographic information systems (GIS) layers, field surveys and DNA sequencing to determine the habitats that best explain the distribution of the species, examine changes in the geographic extent of both the species and its habitats, and compare genetic differentiation between populations occupying disjunct regions. The results from these multiple analyses were combined to assess the conservation status of the species.ResultsGolden mouse occurrence records align well with the distribution of hardwood habitats in Florida. These habitats occur naturally as ‘islands’, but have become increasingly fragmented by anthropogenic land use. Despite habitat loss, the location of the southern range periphery has remained relatively unchanged in location over the past century. Genetic analysis reveals a history of limited dispersal of females among habitat ‘islands’ that likely predates anthropogenic landscape fragmentation. This pattern suggests that isolated populations that are extirpated will have little to no chance of successful recolonization.Main conclusionsThe combined results from multiple analyses produced a more complete picture of the threats faced by this previously data‐deficient species than any single analysis would have. Although the species' southern range limit cannot be shown to have retracted in the face of human expansion, habitat fragmentation clearly has put the species at increased risk. Conservation and management of hardwood habitats are critical to the persistence of the golden mouse at the edge of its range.

Brazilian peppertree (Schinus terebinthifolius) in Florida and South America: evidence of a possible niche shift driven by hybridization

Brazilian peppertree (Schinus terebinthifolius Raddi, Anacardiaceae) was introduced into Florida from South America in the 1800s and commercialized as an ornamental plant. Based on herbaria records and available literature, it began to escape cultivation and invade ruderal and natural habitats in the 1950s, and is now considered to be one of Florida’s most widespread and damaging invasive plants. Historical records and molecular evidence indicate that two genetic lineages of Brazilian peppertree were established in Florida, one in Miami on the east coast and a second near Punta Gorda on the west coast. Since arriving, the distributions of these two types have greatly expanded, and they have extensively hybridized. Principal component analysis and reciprocal niche fitting were used to test the equivalency of climatic niches of the Florida populations with the climatic niches of the two South American chloroplast haplotype groups which established in Florida. Both approaches indicated a significant shift in niches between the parental populations in the native range and the invasive populations in Florida. The models, however, closely predicted the areas of initial establishment. We hypothesize that (1) Brazilian peppertree was able to gain an initial foothold in Florida due to niche similarity and (2) the current dissimilarity in native and exotic niches is due to hybridization followed by rapid selection of genotypes adapted to Florida’s climate. In addition, to examine the potential consequence of the introduction of additional genetic diversity from the native range on invasion success, a niche model constructed with occurrences of all native genotypes was projected onto the continental United States. The result of this test indicated that under such an event, the potential invasive range would greatly expand to cover most of the southeastern USA. Our study suggests that multiple introductions from disjunct regions in the native range can facilitate invasion success.

Historical population connectivity and fragmentation in a tropical freshwater fish with a disjunct distribution (pennyfish,Denariusa bandata)

Pennyfish, Denariusa bandata, are small freshwater fish widely distributed in northern Australia in 4 highly disjunct regions and in the Fly River and Bensbach River drainages in southern Papua New Guinea (PNG). Alternating phases of exposure of the Australia-New Guinea Continental Shelf (ANGCS) during stands of lowered sea levels during Pleistocene glacial phases created a land bridge and fresh/ brackish water habitats that intermittently connected Australia and PNG. Some biogeographic theories and empirical evidence for several freshwater crustaceans suggest that wetlands on the exposed ANGCS during the last glacial maximum were an important conduit for dispersal and gene flow in freshwater species between Australia and PNG and across northern Australia and that connectivity was severed by the most recent sea level rise in the region (,6-8 thousand years before present). We used mitochondrial deoxyribonucleic acid (mtDNA) sequence data to test phylogeographic hypotheses concerning the origin of the disjunct distribution in D. bandata in relation to dispersal-vicariant processes and exposure of the ANGCS during Pleistocene sea level changes. Rather than a late Pleistocene origin associated with the last glacial maximum, the coalescence of the regional populations was in the early- to mid-Pleistocene, and the molecular data indicated that the eastern regional populations split before the northern populations split (i.e., sequential vicariance), whereas the northern populations split contemporaneously (i.e., simultaneous vicariance). The complex mtDNA genealogy for D. bandata also indicated a phylogeographic history in which ancestral lineages were retained in the northwestern part of its distribution, and ancestral haplotype diversity was retained in the Fly River (PNG) population because several divergent clusters of PNG haplotypes were more closely related to Australian haplotypes than to each other.