Evidence Of Geographic Structure Research Articles

Population genetic structure and phenotypic diversity of Aspidodera raillieti (Nematoda: Heterakoidea), a parasite of Didelphini marsupials in Brazil’s South and Southeast Atlantic Forest

BackgroundThe population genetics of parasites may be influenced by host specificity, life cycle, host geographical range, evolutionary history, and host population structure. The nematode Aspidodera raillieti infects different marsupial and rodent hosts in the Nearctic and Neotropical regions, implying a gene flow among populations. However, niche diversification of the main hosts of A. raillieti in superimposed areas may provide conditions for population genetic structuring within this parasite species. We examined the genetic structuring of A. raillieti infecting three marsupial species co-occurring along the South and Southeast Brazilian Atlantic Forest, a hotspot of biodiversity.MethodsWe employed morphometric analyses and partial mitochondrial cytochrome c oxidase I gene sequences (MT-CO1) to characterize populations via phylogenetic and phylogeographic analyses.Results Among 175 A. raillieti specimens recovered from the marsupial hosts Didelphis aurita, D. albiventris, and Philander quica, we identified 99 MT-CO1 haplotypes forming four haplogroups and four clades in networks and phylogenetic trees, respectively. Clades I and II encompassed parasites of D. albiventris from the South region, clade III comprised parasites of D. aurita from the South and Southeast regions, and clade IV encompassed parasites of D. aurita and D. albiventris from the South and Southeast regions and parasites of P. quica from the South region. High genetic differentiation between clades, with a high fixation index and greater genetic variation in the analysis of molecular variance (AMOVA), indicated low gene flow between clades. Haplotypes shared among host species revealed a lack of host specificity. A significant correlation in the Mantel test suggested parasite isolation by distance, while there was no evidence of geographical structure between populations. Negative neutrality test values for clades III and IV suggested recent population expansion. Morphometric differentiation between A. raillieti specimens recovered from different host species, as well as from different localities, was more evident in males.ConclusionThe genetic structure of A. raillieti populations in the South and Southeast Atlantic Forest resulted from historical events rather than from current geographical distribution or host specificity. We also demonstrate morphometric variation associated with host species and localities, suggesting phenotypic plasticity to host attributes and to spatial variables.Graphical

Genetic diversity of Anopheles stephensi in Ethiopia provides insight into patterns of spread

BackgroundThe recent detection of the South Asian malaria vector Anopheles stephensi in the Horn of Africa (HOA) raises concerns about the impact of this mosquito on malaria transmission in the region. Analysis of An. stephensi genetic diversity and population structure can provide insight into the history of the mosquito in the HOA to improve predictions of future spread. We investigated the genetic diversity of An. stephensi in eastern Ethiopia, where detection suggests a range expansion into this region, in order to understand the history of this invasive population.MethodsWe sequenced the cytochrome oxidase subunit I (COI) and cytochrome B gene (CytB) in 187 An. stephensi collected from 10 sites in Ethiopia in 2018. Population genetic, phylogenetic, and minimum spanning network analyses were conducted for Ethiopian sequences. Molecular identification of blood meal sources was also performed using universal vertebrate CytB sequencing.ResultsSix An. stephensi COI-CytB haplotypes were observed, with the highest number of haplotypes in the northeastern sites (Semera, Bati, and Gewana towns) relative to the southeastern sites (Kebridehar, Godey, and Degehabur) in eastern Ethiopia. We observed population differentiation, with the highest differentiation between the northeastern sites compared to central sites (Erer Gota, Dire Dawa, and Awash Sebat Kilo) and the southeastern sites. Phylogenetic and network analysis revealed that the HOA An. stephensi are more genetically similar to An. stephensi from southern Asia than from the Arabian Peninsula. Finally, molecular blood meal analysis revealed evidence of feeding on cows, goats, dogs, and humans, as well as evidence of multiple (mixed) blood meals.ConclusionWe show that An. stephensi is genetically diverse in Ethiopia and with evidence of geographical structure. Variation in the level of diversity supports the hypothesis for a more recent introduction of An. stephensi into southeastern Ethiopia relative to the northeastern region. We also find evidence that supports the hypothesis that HOA An. stephensi populations originate from South Asia rather than the Arabian Peninsula. The evidence of both zoophagic and anthropophagic feeding support the need for additional investigation into the potential for livestock movement to play a role in vector spread in this region.Graphical

Genetic diversity and structure of Taxus baccata from the Cantabrian-Atlantic area in northern Spain: A guide for conservation and management actions

The maintenance of biological diversity at ecosystem, species and intraspecific levels is essential to ensure the survival of forests. The palaeartic yew Taxus baccata is part of a number of threatened forest types with prioritized conservation value in Europe. We investigated the spatial distribution of microsatellite genetic diversity in forty-six T. baccata populations (1,054 trees) spanning the Cantabrian-Atlantic Region (CR) in Northern Spain, framed within a conservation and restoration plan of the species in that region. Different layers of genetic structure were detected, with low structure at a global scale, suggesting historical connectivity, and a complex structure at smaller spatial scales. A low but significant regional genetic variation was also identified associated with biogeographical groups within CR, of potential interest to assist conservation and restoration programs. These genetic differences were reflected on a heterogeneous contribution to the total heterozygosity and allelic richness by the different regions. Data were contextualized within the Iberian Peninsula using previous data in this species (totaling 2,731 trees from 128 populations) after genotype standardization for a common set of seven microsatellites, confirming higher genetic diversity and more homogeneous structure in CR than in central and southeastern Iberian regions. Evidence of geographical structure between eastern (Betic Range, Catalonian Ranges, Pyrenees) and western (Cantabrian Range, Central System Range, Iberian System Range) populations was detected. This study deepens into the spatial distribution of genetic diversity in T. baccata through an intensive survey in CR as a basis for different in situ and ex situ conservation actions in the region aimed to conserve the genetic resources of this species and improve protected yew-associated natural habitats.

Species delimitation based on mtDNA genes suggests the occurrence of new species of Mesocestoides in the Mediterranean region

BackgroundThis study is the first contribution to the molecular taxonomy of Mesocestoides spp. from domestic and wild carnivores in the Mediterranean area. A total of 13 adult worms and 13 larval stages of Mesocestoides spp. were collected from domestic and wild carnivore hosts in Italy and Tunisia. Samples collected in the Slovak Republic were used as comparative samples from outside the Mediterranean. The genes cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunit 1 (nad1) of the mitochondrial genome were used as molecular markers to investigate the presence of cryptic Mesocestoides species in the area analysed.ResultsResults were consistent in showing three well-supported clusters of Mesocestoides spp. in southern Italy and Tunisia, which were strongly divergent from Mesocestoides litteratus, M. corti and M. lineatus. High levels of genetic variation and no evidence of geographical structuring was found between the clusters.ConclusionsConsidering the low dispersal capability of the intermediate hosts of Mesocestoides spp., the lack of geographical structuring among the Mediterranean regions could be due to a high potential for dispersion of the definitive hosts. This study provides a foundation for future formal descriptions of new species of the genus Mesocestoides in the Mediterranean area.

High connectivity in Rastrelliger kanagurta: influence of historical signatures and migratory behaviour inferred from mtDNA cytochrome b.

Phylogeographic patterns and population structure of the pelagic Indian mackerel, Rastrelliger kanagurta were examined in 23 populations collected from the Indonesian-Malaysian Archipelago (IMA) and the West Indian Ocean (WIO). Despite the vast expanse of the IMA and neighbouring seas, no evidence for geographical structure was evident. An indication that R. kanagurta populations across this region are essentially panmictic. This study also revealed that historical isolation was insufficient for R. kanagurta to attain migration drift equilibrium. Two distinct subpopulations were detected between the WIO and the IMA (and adjacent populations); interpopulation genetic variation was high. A plausible explanation for the genetic differentiation observed between the IMA and WIO regions suggest historical isolation as a result of fluctuations in sea levels during the late Pleistocene. This occurrence resulted in the evolution of a phylogeographic break for this species to the north of the Andaman Sea.

Stable Isotope Analysis of Fall Migration Stopover by Six Passerine Species in an Inland Pitch Pine-Scrub Oak Barren

Abstract We conducted mist-net surveys of migrating songbirds during fall migration 2007–2009 on the 1,300-ha Albany Pine Bush Preserve (APBP), a fire-managed inland pitch pine–scrub oak (Pinus rigida–Quercus spp.) barren in east-central New York. We banded 244 migrating passerines from 32 non-resident species in 8,610 net/m/hr documenting use of northeastern pine barrens as stopover sites for passerines with diverse breeding ecologies. We estimated the breeding site origin of six species (a kinglet, four warblers, and a sparrow) using stable hydrogen isotope measurements from flight feathers. There was a broad range of isotope ratios within each species indicating a large catchment area extending several hundred kilometers north and west of the stopover site. Over half the birds originated >750 km from the APBP. We found no evidence for geographical structure of the timing of migration through APBP; slopes of regression lines for capture date versus hydrogen isotope ratio from feathers (δDf) were not sta...

Evidence of geographical structuring in the Malaysian Snakehead, Channa striata based on partial segment of the CO1 gene

Channa striata, locally known as “haruan”, is economically important in fisheries and aquaculture industries in several Asian countries. DNA sequencing, based on a partial segment of the Cytochrome oxidase c subunit 1 (CO1) gene, was used to determine genetic variation in C. striata samples from four different populations on the west coast of Peninsular Malaysia. The highest nucleotide and haplotype diversities were observed in the Linggi population (π = 0.0067, h = 0.835), and the lowest in the Timah Tasoh population (π = 0.0008, h = 0.286). Apart from Kajang-Linggi, which was insignificant, FST values were significant (p < 0.05) in all pairwise-population comparisons. Consequently, it is inferred that genetic structuring C. striata populations in this region was largely shaped by a common origin, with secondary influences from geographical factors and isolation.

Phylogeography of the blue land crab,Cardisoma guanhumi(Decapoda: Gecarcinidae) along the Brazilian coast

Several crab species are important fishery resources in Brazil and their overexploitation has lead to severe population declines in some regions. The management of populations of these species should take into account the degree of gene flow among populations in different estuaries. The goal of the present study is to assess the degree of geographical structure in the genetic diversity of the blue land crab,Cardisoma guanhumi, along the Brazilian coast. A fragment of the control region of the mtDNA (750 bp) was sequenced for 95 specimens collected across 5 Brazilian states. Analyses using F-statistics failed to indicate any evidence of geographical structure, a result that was corroborated by a nested clade analysis of the same dataset. Mismatch distribution analyses indicated that populations of the blue land crab have experienced an expansion during their recent evolutionary past. The obtained results are similar to those recently described for another sympatric crab,Ucides cordatus, particularly with respect to the extensive degree of gene flow. However, populations ofC. guanhumiseem to be older than those ofU. cordatusand do not show the north–south expansion found in that species.

Population genetics of steelhead (Oncorhynchus mykiss) in the Klamath River

An analysis of population structure and genetic diversity was conducted on samples of Oncorhynchus mykiss (steelhead/rainbow trout) from 33 sites in the Klamath–Trinity River basin. Genotype data from 16 microsatellite loci in almost 1,700 fish revealed genetic differentiation between most sampled locations. Two pairs of samples from the same sites in different years were not significantly different, indicating stability of population structure, at least on a short time scale. Most sampling sites were genetically distinct from all other sampling sites, and there was an evidence of geographic structure within the Klamath–Trinity River basin, although populations from tributaries within the watershed (e.g. Salmon River, Scott River, Clear Creek) did not always constitute distinct genetic lineages. Population structure was evident using phylogeographic trees, isolation by distance analyses and individual assignment tests, which all found a relationship between geographic and genetic distance. Populations in the lower Klamath region, below the confluence with the Trinity River, consistently clustered together in phylogeographic analyses and had patterns of genetic diversity that suggest reduced gene flow between these sites and sites above the confluence. Finally, in an analysis that included data from other coastal California rivers, the populations closest to the mouth of the Klamath River appeared intermediate between populations from adjacent watersheds and the lineage formed by the other populations in the Klamath–Trinity basin.

Genetic variation and geographical structure of five mouse‐sized opossums (Marsupialia, Didelphidae) throughout the Guiana Region

AbstractAim and location To study the patterns of genetic variation and geographical structure of five forest‐dwelling didelphid species distributed throughout the Guiana Region (Marmosops parvidens, M. pinheiroi, Monodelphis brevicaudata, Marmosa murina, Micoureus demerarae) and place the results for wide‐ranging species (M. murina, M. demerarae) in the broader geographical context of the rest of the taxon ranges based on published data.Methods Variation in the mitochondrial cytochrome b gene were analysed in order to assess intra‐specific sequence divergence as well as haplotypic and nucleotide diversity among populations. Relationships between haplotypes were inferred by cladistic (maximum parsimony) and probabilistic (maximum likelihood) approaches, allowing comparisons between tree topologies and patterns of populations geographical distribution.Results Phylogenetic analysis of the Guiana Region populations suggest the lack of common patterns of geographical structure among mouse‐sized opossums except for both Marmosops species. Marmosops parvidens and M. pinheiroi showed individuals from Surinam strongly related with those from Guyana, and haplotypes from French Guiana having a basal position. Concerning Micoureus demerarae, haplotypes from Venezuela were positioned as ancestral, in contrast with Monodelphis brevicaudata, whose French Guiana haplotypes were clustered in a basal position. No evidence of geographical structure was observed for Marmosa murina. Genetic variation within Guiana Region populations fluctuated between 1% for M. murina and 7% in the case of M. brevicaudata. Regarding the widely distributed species, phylogeographical structure at the scale of the Amazon Basin suggests that Guiana Region populations are the sister group of south‐eastern Amazonian and Atlantic Forest populations, thus resulting in an eastern clade well separated from the western Amazonian regions.Main conclusions Monophyly of mouse‐sized opossums haplotypes over the Guiana Region confirms the presence of a well‐differentiated zoogeographical area relative to other Amazonia bioregions. Low genetic diversity among Guiana Region samples suggests a relatively recent origin of populations dating from later Miocene and Pleistocene periods. Moreover, nucleotide and haplotypic diversity values suggest an evolutionary scenario of rapid population growth and dispersal over the Guiana territory, from an ancestral population with small effective size. Dispersal events – rather than vicariance – seem to be responsible for the present genetic and phylogeographical patterns observed in the Guiana Region.

Morphological Adaptation with No Mitochondrial DNA Differentiation in the Coastal Plain Swamp Sparrow

-We estimated genetic differentiation between morphologically distinct tidal marsh populations of Swamp Sparrows (Melospiza georgiana nigrescens) and the more widespread inland populations (M. g. georgiana and M. g. ericrypta). The tidal marsh populations are consistently grayer with more extensive black markings (particularly in the crown), and their bills are larger. These differences are variously shared with other species of salt marsh birds and small mammals. We analyzed mitochondrial DNA sequences (5' end of control region, COII/ t-lys /ATPase8, and ND2) of Swamp Sparrows and found low levels of genetic variation and no evidence of geographic structure. These results suggest a rapid and recent geographic expansion of Swamp Sparrows from restricted Pleistocene populations. Morphological differentiation has occurred without long-term genetic isolation, suggesting that selection on the divergent traits is intense. The grayer and more melanistic plumage is probably cryptic coloration for foraging on tidal mud, which tends to be grayish as a result of the formation of iron sulfides, rather than iron oxides, under anaerobic conditions. Received 14 May 1997, accepted 9 January 1998. VERTEBRATES SHOW CONSPICUOUS ADAPTATIONS to the distinct environment of tidal marshes. For example, diurnal terrestrial species tend toward grayish or blackish coloration (Grinnell 1913, Von Bloeker 1932, Greenberg and Droege 1990). In addition, emberizid finches often have relatively large bills compared with non-tidal populations (Greenberg and Droege 1990). Tidal marsh populations often are small and geographically restricted compared with inland populations. This leads to the question of how distinct morphological features evolve in these populations in the face of potential gene flow from larger inland populations. Few studies have addressed the degree of geographic genetic structuring in species with tidal and inland forms. Swamp Sparrows (Melospiza georgiana) breed in tidal marshes of Delaware and Chesapeake bays and in inland fresh water wetlands within formerly glaciated areas and occur only sporadically south of the glacial line, inhabiting the few suitable postglacial bogs, brushy marshes, 4E-mail: antwren@erols.com 5Present address: Deptartemento de Ecologia y Evolutia, Museo Nacional de Ciencias Naturals, C.S.I.C., Jose Gutierrez Abascal 2 28006, Madrid, Spain. and wet meadows. Except for a few scattered populations, a hiatus extends between the inland and coastal Swamp Sparrow populations through the Piedmont of Maryland and Pennsylvania, leaving the only potential area of significant contact in northern New Jersey and southern New York State (Greenberg and Droege 1990: figure 1). Coastal Plain Swamp Sparrows (M. g. nigrescens) have more extensive black coloration (e.g. almost three times the area of black in the crown), are generally grayer, and have bills that average 29% greater in overall volume than Swamp Sparrows from inland populations (Greenberg and Droege 1990). In contrast to the morphological differentiation between the estuarine and the closest freshwater populations, the interior subspecies (M. g. ericrypta and M. g. georgiana) are morphologically quite uniform across their ranges, with the two recognized subspecies exhibiting only slight differences in the degree of pale markings on the back. Three possible scenarios can account for the evolution of the nigrescens subspecies: (1) tidal marsh populations have been genetically isolated from other populations for a substantial period of time; (2) selective pressures differ and are of sufficient magnitude to cause strong and rapid morphological divergence in the face

GENE FLOW AND MITOCHONDRIAL DNA VARIATION IN THE KILLIFISH,FUNDULUS HETEROCLITUS

Two subspecies of killifish, Fundulus heteroclitus, inhabit the Atlantic coast of the United States. The contact zones between them are typified by morphological, physiological, nuclear gene, and mitochondrial DNA clines. Considerable debate exists about the importance of restricted gene flow and natural selection in maintaining these clines. To evaluate the relative importance of these two evolutionary forces we employed analysis of mtDNA as an independent measure of gene flow. Solutions of equilibrium diffusion equations suggested that killifish dispersal must be less than 2 km to maintain previously observed allozyme frequency clines in the absence of strong selection. To determine whether populations separated by distances greater than 2 km accumulate significant genetic differences we examined a total of N = 480 individuals from five killifish populations spanning a continuous shoreline distance of 8.4 km. Distribution of the 25 detected haplotypes indicated that most of the variation was within rather than between sampling locations. No evidence of geographic structure was detected, nor were there any significant genetic differences between killifish populations. With these data, gene flow was evaluated by estimating effective migration rate (Ne m) between the populations. Ne m was estimated from Gst (Ne m = 49.4), from Fst (Ne m = 24.1), by the private alleles approach (Ne m = 18.5) and via four phylogenetic analyses (Ne m ranged from 11.4 to 16.9). Regardless of the analysis, Ne m was greater than one; the threshold level at which gene flow is strong enough to prevent differentiation due to genetic drift. This suggests that while the characteristics that distinguish Fundulus subspecies may have arisen in isolation, the current clinal distributions exhibited along the Atlantic coast are most likely maintained by selection.