Environmental transition zone and rivers shape intraspecific population structure and genetic diversity of an Amazonian rain forest tree frog

Diversification processes acting across geographically continuous populations have been rarely documented in Amazonia, because of the lack of fine-scale sampling over extensive areas. We aimed to determine the geographic effects of an environmental transition zone and large rivers on the intraspecific population structure of the Manaus slender-legged tree frog (Osteocephalus taurinus) along a ~ 900 km transect of tropical rain forest. Using one mitochondrial (16S), two nuclear genes (TYR, POMC) and three microsatellites, we estimated the population structure, phylogenetic relationships and geographic variation of 262 O. taurinus and 5 O. oophagus (a close relative) along the Purus–Madeira interfluve (PMI) and opposite banks of the central Amazon and upper Madeira rivers, at central-southern Amazonia, Brazil. Six genetic clusters were identified: two corresponding to sympatric populations of O. taurinus and O. oophagus from their type locality, north of Amazon river. Within PMI, there were three distinct O. taurinus genetic clusters distributed along the geographic gradient with one main phylogeographic break found (concordant between 16S and TYR), that corresponds to a transition zone (ecotone) between dense and open rain forest ecotypes. The sixth cluster was an O. taurinus population isolated at the east bank of the upper Madeira river. In addition, restricted haplotype sharing was identified from the west to east banks at upper Madeira river. Within PMI, parapatric genetic structure is explained by a potential association of the genetic clusters to the different forest ecotypes they inhabit coupled with isolation by distance, thus supporting the gradient hypothesis for diversification. Differentiation of populations that are external to the PMI is most likely explained by the barrier effect of the Madeira and Amazon rivers. Our findings provide new evidence on diversification processes across continuous Amazonian landscapes; however, the specific mechanisms underlying the origin and maintenance of the identified phylogeographic break need to be further studied.     

Current known range of the Platte River caddisfly, Ironoquia plattensis, and genetic variability among populations from three Nebraska Rivers

The Platte River caddisfly (Ironoquia plattensis Alexander and Whiles 2000) was recently described from a warm-water slough along the Platte River in central Nebraska and was considered abundant at the type locality. Surveys of 48 sites in 1999 and 2004 found eight additional sites with this species on the Platte River. The caddisfly was not found at the type locality in 2004 and one additional site in 2007, presumably because of drought conditions. Because of its apparent rarity and decline, the Platte River caddisfly is a Tier I species in Nebraska. For this project, surveys for the caddisfly were conducted at 113 new and original sites primarily along the Platte, Loup, and Elkhorn Rivers between 2009 and 2011. These surveys identified 30 new sites with the caddisfly. Larval densities were quantified at a subset of inhabited sites, and there was a large variation of densities observed. Seven sites on other Nebraska drainages were found to support morphologically similar caddisflies, presumably the Platte River caddisfly. Because of the discovery of populations outside the Platte River drainage, amplified fragment length polymorphism (AFLP) was used to determine the amount of genetic variability and breeding among sites on the Platte, Loup, and Elkhorn Rivers. Analysis of molecular variance (AMOVA) suggested moderate gene flow among the three river systems and that there was more genetic variation within populations than between populations. Differentiation, but not total divergence, was exhibited by the northernmost population from the Elkhorn River. Because it may be considered an indicator species and is vulnerable to ongoing habitat loss and degradation, all Platte River caddisfly populations should be conserved.     

Systematics, biogeography, and evolution of the Neotropical peacock basses Cichla (Perciformes: Cichlidae)

To investigate forces influencing diversification in Neotropical fishes, the phylogenetic relationships among species and populations of the cichlid genus Cichla were examined. Mitochondrial DNA was sequenced for 454 individuals of the 5 nominal Cichla species and several putative undescribed species. Phylogenetic analyses support the distinction of two major clades of Cichla. Clade A includes C. temensis and two undescribed species from the lower Amazonas and Xingu Rivers. Clade B includes C. orinocensis, C. monoculus, C. ocellaris. C, intermedia, and an undescribed species from the upper Madeira River. Species boundaries were relatively well-circumscribed for clade B, while incomplete lineage sorting was inferred for clade A. Three probable instances of introgression were observed, including a regional population of C. orinocensis from the Negro River that shows a history of introgression. Biogeographic patterns from Cichla are partially congruent with those seen in several other Neotropical fish clades, and the diversification of Cichla species is inferred to result from both vicariance and sympatric divergence.     

Looking to the past and the future: were the Madeira River rapids a geographical barrier to the boto (Cetacea: Iniidae)?

In the present study we tested if a series of 18 rapids on the upper Madeira River form an effective barrier to gene flow, and in particular if they delimit the distribution of the boto Inia boliviensis—which it is believed to occurs only in the Bolivian sub-basin, above the rapids—and I. geoffrensis, which occurs throughout the Amazon basin and below the upper Madeira River rapids. We analyzed 125 individuals from the Madeira River basin sampled from upstream and downstream of the rapids. As the two species are morphologically similar, we used diagnostic molecular characters from known reference specimens to assign individuals to species. We observed that all individuals of Inia from the Bolivian sub-basin up to almost the mouth of the Madeira River belong to the species I. boliviensis. Therefore we concluded that the rapids do not delimit the distribution of I. boliviensis upstream and I. geoffrensis downstream of the rapids as previously hypothesized. Since we registered I. boliviensis along almost the entire length of the Madeira River, we estimated gene flow, time of divergence and effective population sizes of the upstream (Bolivian) and downstream (Madeira River) groups of I. boliviensis using IMa2. We concluded that gene flow is uni-directional from the upstream to the downstream group. Divergence time between the two groups was estimated to have occurred ~122 thousand years ago. The coalescent effective population size for the upstream group was estimated at ~131 thousand individuals, while for the downstream group it was estimated at ~102 thousand individuals. Recently two dams have been constructed in the region of the rapids; neither has a mechanism that will maintain connectivity between the upstream and downstream regions, and together with anthropogenic alterations to the hydrodynamic regime and ecology of the river will likely pose serious long-term and short-term consequences for I. boliviensis and other aquatic taxa.     

Invasion genetics of nutria (<Emphasis Type="Italic">Myocastor coypus</Emphasis>) in Okayama,Japan, inferred from mitochondrial and microsatellite markers

Nutria (Myocastor coypus) is a large semi-aquatic rodent native to South America, introduced worldwide for fur farming in the early twentieth century. In Japan, 150 individuals were introduced from the USA in 1939, and their feral populations are currently causing serious problems to aquatic ecosystem and agriculture. Okayama Plain is the largest habitat of nutria in Japan, established by the escapees from breeding farms around the middle of the 1940s. Here, we examined genetic structure of Okayama population and inferred gene flow among populations, using mtDNA and ten microsatellite markers (MS), to estimate eradication units for the effectiveness of population control. For mtDNA, two haplotypes (A and B) were detected in cytochrome b region. Haplotype A was widely distributed in Okayama Plain, while haplotype B was mainly observed around Yoshii River. For MS, Okayama population showed high genetic diversity, comparable to USA and Argentine populations. Genetic differentiation was recognized among drainages with a significant isolation-by-distance pattern. Multivariate analyses and Bayesian clustering method suggested two genetic clusters and radial dispersal around the coast of the Kojima Bay, while these clusters did not necessarily concord with mtDNA haplotypes in distribution. Genetic heterogeneity tended to be higher in males than in females, and females exhibited a higher relatedness than males in Asahi River. These results suggest that nutria in Okayama Plain originated from farming sites downstream in Yoshii and Takahashi Rivers and have expanded its distribution along rivers via tributaries. Mitochondrial-nuclear discordance seems to be due to male-biased dispersal in nutria.     

Conservation genetics of the yellow-blotched sawback Graptemys flavimaculata (Testudines: Emydidae)

Turtles within the genus Graptemys are increasingly becoming a group of conservation priority due to (1) the number of species endemic to single Gulf of Mexico rivers and (2) human alterations of riverine habitat. The yellow-blotched sawback (Graptemys flavimaculata) is a federally threatened species that is endemic to the Pascagoula River system of southeastern Mississippi, USA. Currently, there is nothing known about genetic variation and population structure in G. flavimaculata. We used microsatellite data to analyze population genetic structure, assess historical demography, and determine effective population size at six sites throughout the Pascagoula River system. Considerable genetic diversity was found within each site (mean allelic richness: 6.65–8.08) and two analyses found no evidence of genetic bottlenecks. All of the pairwise F _ST values, while low (average = 0.026), were significant, with most sites possessing one or more private alleles. Pairwise F _ST values with the Escatawpa River site were larger (0.030–0.047), which likely reflect its historical isolation. Genetic distance was correlated to geographic distance between sites, with the exception of the Escatawpa River site; a similar pattern was also found with estimates of recent rates of migration among sites. While an analysis of molecular variance indicated that most variation was partitioned within rather than among sites, STRUCTURE analysis strongly supported the recognition of two distinct groups (mainstem Pascagoula vs. Escatawpa), with the possibility of additional substructure within the mainstem Pascagoula.     

Genetics and telemetry indicate unexpected movements among structured populations for Brachyplatystoma platynemum in the Amazon

The genetic analysis of Brachyplatystoma platynemum individuals sampled from the lower Madeira River reinforces the existence of two structured populations in the Amazon Basin (Madeira and Amazon populations). However, the recapture of an individual from the Amazon population in the Solimões River, which was telemetry-tagged in the Madeira River after the damming, indicates that fish from the Amazon population move between the two river systems. This has not yet been observed, however, in the Madeira River population, which is currently divided and isolated in the lower and upper Madeira River by the construction of two dams.     

Phylogenetic and taxonomic assessment of the endangered Cumberland bean, <Emphasis Type="Italic">Villosa trabalis</Emphasis> and purple bean, <Emphasis Type="Italic">Villosa perpurpurea</Emphasis> (Bivalvia: Unionidae)

Inadequate understanding of the phylogeography, taxonomy, and historical distribution of two critically imperiled freshwater mussels, Cumberland bean, Villosa trabalis, and purple bean, Villosa perpurpurea, has hindered management and recovery actions related to population restoration within their extant ranges. For more than 100 years, the purple-to-pink nacre of V. perpurpurea and white nacre of V. trabalis have been the only defining phenotypic characteristics used to distinguish each species. Genetic samples were analyzed from 140 individuals collected from 10 streams located in Virginia, Tennessee, and Kentucky, representing all known extant populations of each species. A 784-bp section of the mitochondrial DNA ND1 region was sequenced to assess the phylogeography and taxonomic validity of these taxa. Results of our phylogenetic analyses showed 100 % Bayesian posterior support for two distinct clades, one occurring in the Cumberland River basin and the other in the Tennessee River basin, separated by a mean genetic distance of 4 %. Mean genetic distances between haplotypes within each clade was <1 %. Among individuals from the Cumberland River basin, the nacre of shells was white to bluish-white, but in the Tennessee River basin, nacre graded from white to pink to dark purple; thus, nacre color is a variable and inconsistent character in nominal V. trabalis and V. perpurpurea occurring in the Tennessee River basin. Our data suggest that these morphologically similar species do not co-occur, as was previously believed. Instead, we conclude that the two species most likely share a common ancestor, but became isolated within each basin and experienced allopatric speciation. Updates to nomenclature, taxonomic placement, and recovery plans for the investigated species are needed.     

A New Subspecies of <Emphasis Type="Italic">Saguinus fuscicollis</Emphasis> (Primates,Callitrichidae)

Saddleback tamarins (Saguinus fuscicollis, S. melanoleucus, and S. tripartitus) occur in the upper Amazon, west of the rios Madeira and Mamoré–Guaporé to the Andes. They currently comprise 13 species and subspecies in Bolivia, Brazil, Colombia, Ecuador, and Peru. Here we report on a previously undescribed subspecies of Saguinus fuscicollis from the interfluvium of the lower rios Madeira and Purus in the central Amazon of Brazil. It is a distinct form with a very pronounced mottling on the back giving the appearance of a saddle, a characteristic shared by the 3 species, and the reason for their collective common name. The lack of a white superciliary chevron and its highly mottled ochraceous-dark brown to black saddle that extends from the scapular region to the base of the tail distinguish the new taxon from Saguinus fuscicollis weddelli. The latter characteristic also distinguishes it from another saddleback tamarin (Saguinus fuscicollis ssp.) that has been reported immediately to the south of its range in the same interfluvium. We compare pelage coloration, external characters and craniometric measurements with its geographically closest relatives, Saguinus fuscicollis weddelli and S. f. avilapiresi, and indicate its probable geographic distribution in a small area between the rios Madeira and Purus, just south of the Rio Amazonas.     

Microsatellite DNA analysis of spatial and temporal population structuring of <Emphasis Type="Italic">Phragmites australis</Emphasis> along the Hudson River Estuary

Phragmites australis is a perennial grass that has invaded wetlands of the northeastern United States over the past century. The Hudson River Estuary and surrounding watersheds are no exception in that populations of P. australis have spread dramatically along its shores and tributaries in the past 40 years. Recent studies have shown that genetically variable populations of P. australis can spread by seed dispersal in addition to clonal mechanisms. It is important to characterize the genetic variation of Hudson River populations as part of a management strategy for this species to determine the mechanisms by which its spreads and colonizes new habitats, particularly those with frequent anthropogenic disturbances. The goals of this study were to quantify levels of genetic variation and structuring in Hudson River populations of P. australis using microsatellite DNA analysis. A total of 354 culms of P. australis were collected from nine locations ranging from Albany, New York to Staten Island, New York in the summers of 2004 (N = 174) and 2011 (N = 180). Microsatellite data from eight loci indicated that the Hudson River Estuary has some of the highest levels of genetic variation of all U. S. Atlantic Coast regions containing P. australis. Gene diversity (Hs) across all loci in the 2004 collection was 0.45 (±0.02) and that of the 2011 collection was 0.47 (±0.07). Patches within sample sites were rarely monoclonal and had multiple genetic phenotypes. Moran’s Identity tests indicated that individuals within a patch were closely related, whereas little genetic relatedness was evident among individuals from sample sites >1 km apart. Spatial structuring was also not evident in autospatial correlation and principle coordinate analyses. These findings suggest that genetic diversity is maintained within stands by sexual reproduction and that seeds are important in dispersal of P. australis across the Hudson River Estuary. Ample habitats are available for establishment of new Phragmites stands due to high levels of anthropogenic disturbance from populations living along the Estuary. Wildlife managers should focus on monitoring habitats that provide seedbed for Phragmites and promote land use practices that prevent soil disturbance and establishment of new stands.     

Historic speciation and recent colonization of Eurasian monkey gobies (Neogobius fluviatilis and N. pallasi) revealed by DNA sequences,microsatellites, and morphology

Aim Hidden diversity within an invasive ‘species’ can mask both invasion pathways and confound management goals. We assessed taxonomic status and population structure of the monkey goby Neogobius fluviatilis across Eurasia, comparing genetic variation across its native and invasive ranges. Location Native populations were analysed within the Black and Caspian Sea basins, including major river drainages (Dnieper, Dniester, Danube, Don and Volga rivers), along with introduced locations within the upper Danube and Vistula river systems. Methods DNA sequences and 10 nuclear microsatellite loci were analysed to test genetic diversity and divergence patterns of native and introduced populations; phylogenetic analysis of mtDNA cytochrome b and nuclear RAG‐1 sequences assessed taxonomic status of Black and Caspian Sea lineages. Multivariate analysis of morphology was used to corroborate phylogenetic patterns. Population genetic structure within each basin was evaluated with mtDNA and microsatellite data using F_ST analogues and Bayesian assignment tests. Results Phylogenetic analysis of mitochondrial and nuclear sequences discerned a pronounced genetic break between monkey gobies in the Black and Caspian Seas, indicating a long‐term species‐level separation dating to c. 3 million years. This pronounced separation further was confirmed from morphological and population genetic divergence. Bayesian inference showed congruent patterns of population structure within the Black Sea basin. Introduced populations in the Danube and Vistula River basins traced to north‐west Black Sea origins, a genetic expansion pattern matching that of other introduced Ponto‐Caspian gobiids. Main conclusions Both genetic and morphological data strongly supported two species of monkey gobies that were formerly identified as subspecies: N. fluviatilis in the Black Sea basin, Don and Volga Rivers, and the Kumo‐Manych Depression, and Neogobius pallasi in the Caspian Sea and Volga River delta. Genetic origins of introduced N. fluviatilis populations indicated a common invasion pathway shared with other introduced Ponto‐Caspian fishes and invertebrates.     

Molecular phylogeographic analyses of the loach Oxynoemacheilus bureschi reveal post‐glacial range extensions across the Balkans

Rivers on the Balkan Peninsula can be separated into ichthyofaunistic areas with different endemic fish species. The Vardar River contains a particularly large number of endemics, indicating its complete and long‐term isolation from neighbouring river systems. One of the few species shared with other rivers is the loach species Oxynoemacheilus bureschi. In this study, the genetic analyses of 175 individuals of O. bureschi from 17 sites, covering the entire distribution of the species, including the Rivers Vardar (= Axios), Struma (= Strymon), Mesta (= Nestos) and Danube, were performed using one mitochondrial and one nuclear marker. Genetic differentiation among populations was in general low. Shared haplotypes were common and occurred even between distant localities and different river systems. This points to a high degree of gene flow among populations and rejects the hypothesis that the population in the Vardar River represents a relict from an early colonization of the Balkan Peninsula. In contrast, the results suggest that populations in the Vardar River, as well as those in the Danube River, are of recent origin, and a human‐mediated introduction cannot be excluded. On the other hand, the populations in the Aggitis River, a left tributary of the lower Struma River, were clearly separated from the rest of the species and represent a long‐term isolated lineage. Demographic analyses suggest a recent population expansion for O. bureschi, in which the population in the Aggitis River was not involved.     

Mitochondrial D-loop nucleotide diversity in Astyanax (Osteichthyes, Characidae) from the upper Paraná and upper Paraguay River basins

The morphological discrimination between the species Astyanax altiparanae and A. asuncionensis of the upper Paraná River and Paraguay River basins, respectively, has always been difficult. Two D-loop haplogroups of A. altiparanae are known, one with the presence (AltoPR) or the absence (AltoPR-D) of a 32-bp block similar to that in A. asuncionensis. We examined these samples to characterize A. altiparanae and verify whether A. asuncionensis occurred in the upper Paraná River prior to the submergence of the Sete Quedas Falls when Itaipu reservoir was impounded. D-loop sequences were analyzed in A. altiparanae of the upper Paraná and Igua?u Rivers and those of A. asuncionensis of the upper Paraguay River. The haplogroup AltoPR was found at all sites of the upper Paraná and Igua?u Rivers, whereas AltoPR-D occurred in the Itaipu reservoir, floodplain and in the Tietê and Grande Rivers. Two haplogroups of A. asuncionensis were identified and both did not have the 32-bp block. However, AltoPR and AltoPR-D differed from one another in 5.1% of their bases and between 8.9 and 12.5% with regard to the haplogroups of the upper Paraguay basin. Further, AltoPR-D occurred in the Grande River upstream the Marimbondo Falls and other older reservoirs than Itaipu. The results reject the hypothesis of the establishment of A. asuncionensis and suggest that the haplogroup AltoPR-D existed in the upper Paraná River before the impounding of the Itaipu reservoir. Moreover, morphological similarity and high genetic variation within the altiparanae/asuncionensis group suggest the existence of a cryptic species complex.     

After 100 years: hydroelectric dam-induced life-history divergence and population genetic changes in sockeye salmon (<Emphasis Type="Italic">Oncorhynchus nerka</Emphasis>)

Understanding the impact of barriers and habitat fragmentation on the ecology and genetics of species is of broad interest to many biologists. In aquatic systems, hydroelectric dams often present an impenetrable barrier to migratory fish and can have negative effects on their persistence. Hydroelectric dams constructed in the Coquitlam and Alouette Rivers in the Fraser River drainage (British Columbia, Canada) in the early 1900s were thought to have led to complete loss of anadromous sockeye salmon from both rivers. For both reservoirs, recent water release programs resulted in the unexpected downstream migration of juvenile sockeye salmon and the subsequent upstream migration of adults towards the reservoir 2 years later. Here we investigate the evolutionary impact of dams on the sockeye salmon migration behavior by investigating the genetic distinction between migratory and non-migratory individuals within the Alouette and Coquitlam reservoirs. We also compare historical and contemporary genetic connectivity among 11 Lower Fraser River sockeye sites to infer recent population connectivity changes that might have been influenced by anthropogenic activities. Our molecular genetic analyses show a genetic distinction between the sea-run and resident individuals from the Coquitlam reservoir and population splitting time estimates suggest a very recent divergence between them. These results indicate a genetic component to migration behavior. For our broader survey from 11 sites, our comparisons suggest a general decline in gene flow, with a few interesting exceptions. In summary, our results suggest (i) early stage divergence between life history forms of sockeye salmon within one reservoir, and (ii) recent changes in genetic connectivity among Lower Fraser River populations; both of these results have potential recovery implications for historically migratory populations that were affected by anthropogenic barriers such as hydroelectric dams.     

Geographic differentiation of <Emphasis Type="Italic">Cobitis shikokuensis</Emphasis> inferred from mtDNA RFLP analysis

Mitochondrial DNA divergence among populations of the Japanese spinous loach Cobitis shikokuensis, endemic to Shikoku Island, was investigated by restricted fragment length polymorphism analysis. A total of 68 restriction sites on DNA fragments from the cytochrome b to D-loop regions and from the 12S rRNA to 16S rRNA regions, amplified by PCR, were analyzed. A total of 12 haplotypes (plus 6 in outgroups) were detected in 268 specimens collected from 19 localities in seven rivers (and 41 specimens from four localities in three rivers in outgroups). Three of the seven river populations of C. shikokuensis were shown to have unique haplotypes, and four of the seven river populations were monomorphic. The nested structure of the haplotype network for populations of C. shikokuensis exhibited two large clades corresponding to (1) populations from the Shimanto River and its neighbors and (2) two genetically divergent populations in the Shigenobu and Iwamatsu Rivers. The population from the Shimanto River, the largest river inhabited by C. shikokuensis, maintains great haplotype diversity as well as the allozyme diversity previously reported. On the other hand, populations from the Hiji River, the second largest river, which exhibited the highest allozyme diversity, were monomorphic in their mtDNA. The nested clade analysis (NCA) revealed that past fragmentation between the above two clades could occur in the initial distribution process of C. shikokuensis. The large genetic divergence of two river populations from the Shigenobu and Iwamatsu Rivers was inferred to be caused by a process of long distance colonization and fragmentation. MtDNA introgression into the Hiji River population from southern river populations was suggested. Taking genetic divergence into consideration, each river population of C. shikokuensis should be conserved separately as like a distinct species, and conservation programs for the small populations showing less genetic variability should be invoked as soon as possible.     

Near absence of hybridization between sauger and introduced walleye despite massive releases

We analyzed 11 microsatellite loci to determine the genetic population structure of saugers and to describe the amount and pattern of hybridization with widely introduced walleyes in the upper Missouri River drainage. We detected significant genetic differentiation among saugers spawning upstream and downstream of the confluence of the Bighorn and Yellowstone Rivers. Samples from upstream of the confluence had significantly lower heterozygosity and allelic richness. We suspect this reflects isolation at the periphery of the species’ range and possibly genetic drift resulting from recent population contractions due to dams, diversions, and water development. We detected only eighteen hybrids out of 925 individuals analyzed. Hybridization appeared recent, as nearly 50% of the hybrids showed significant evidence for having a non-hybrid ancestor within two generations. All but one hybrid were detected in the Yellowstone River drainage, despite a substantially higher rate of walleye stocking in the Missouri River drainage, suggesting conditions in the Yellowstone may be more conducive to hybridization. Rarity of hybridization is unexpected, given both massive walleye releases and previous findings of more frequent hybridization in the study area. Introgression of walleye genes into native saugers does not appear to be an immediate threat.     

Genetic analysis reveals two distinct Sacramento splittail (<Emphasis Type="Italic">Pogonichthys macrolepidotus</Emphasis>) populations

The Sacramento splittail is an endemic cyprinid fish of the San Francisco estuary and its tributaries, which is a highly manipulated, constantly changing ecosystem. Splittail is the only extant member of its genus and is listed as a federal and California Species of Special Concern due to uncertainties regarding long-term abundance trends. Determining population structure for splittail is important because unique populations may contain different adaptive genetic variation, which can allow one population to persist through future environmental or demographic stochasticity while others become extirpated. To assess splittail population structure, 13 microsatellite markers were used to genotype 489 young-of-year splittail from five major rivers draining into the estuary: Cosumnes, Napa, Petaluma, Sacramento, and San Joaquin Rivers. Two genetically distinct populations were found to exist within our study region; one largely comprised of splittail collected from the Petaluma and Napa Rivers and the second comprised of splittail collected from tributaries in Californiaȁ9s Central Valley: Cosumnes, Sacramento, and San Joaquin Rivers. These results were replicated in two consecutive years with both distance and model-based algorithms. The genetic distinction between these two populations appears correlated with salinity differences between migratory regions and spawning grounds. Splittail from the Petaluma River exhibited a significantly higher degree of differentiation from the Central Valley population than did Napa River splittail. Our results suggest on-going monitoring programs are probably highly biased towards sampling splittail from the Central Valley population. Understanding population dynamics of splittail could be improved if monitoring programs were expanded to include all splittail populations.     

Homegardens on Amazonian Dark Earths,Non-anthropogenic Upland,and Floodplain Soils along the Brazilian Middle Madeira River Exhibit Diverging Agrobiodiversity<Superscript>1</Superscript>

Homegardens on Amazonian Dark Earths, Non-anthropogenic Upland, and Floodplain Soils along the Brazilian Middle Madeira River Exhibit Diverging Agrobiodiversity. We test the hypothesis that the agrobiodiversity associated with homegardens on three different soils—upland Amazonian Dark Earths (ADE) and Oxisols (OX), and Fluvent Entisols (FL)—commonly found along the middle Madeira River in the municipality of Manicoré, Amazonas State, Brazil, is different due to the contrasting biotic, abiotic, and cultural settings specific to each of these soils. Using data from interviews with 63 farmers about food and utility species, we compare structural and floristic characteristics of homegarden agrobiodiversity. The density of individuals is higher on ADE than on the other soils (mean ± standard deviation: 715 ± 363 on ADE, 474 ± 283 on OX, 642 ± 399 on FL). ADE and OX have higher species richness (28.2 ± 5.6 on ADE, 25 ± 3.7on OX, 23.6 ± 5 on FL), while ADE and FL have a greater degree of domestication (2 ± 0.6 on ADE, 1.3 ± 0.5 on OX, 2.3 ± 0.6 on FL). ADE and OX have greater proportions of richness, density, and coverage composed of South American species, while FL has greater proportions of richness and density composed of Old World species. ADE has higher proportions of density and coverage of Mesoamerican species. Floristic composition is also different between soils: ADE occupies an intermediate position, composed of species associated with each of the other soil types and species that are most common on ADE. These differences in agrobiodiversity emerge through the interaction of human agency, plant responses, and the unique properties of soils in relation to socioeconomic and historical trajectories over time.     

Geographic distribution of genetic diversity in populations of Rio Grande Chub <Emphasis Type="Italic">Gila pandora</Emphasis>

In the southwestern United States (US), the Rio Grande chub (Gila pandora) is state-listed as a fish species of greatest conservation need and federally listed as sensitive due to habitat alterations and competition with non-native fishes. Characterizing genetic diversity, genetic population structure, and effective number of breeders will assist with conservation efforts by providing a baseline of genetic metrics. Genetic relatedness within and among G. pandora populations throughout New Mexico was characterized using 11 microsatellite loci among 15 populations in three drainage basins (Rio Grande, Pecos, Canadian). Observed heterozygosity (H_O) ranged from 0.71–0.87 and was similar to expected heterozygosity (0.75–0.87). Rio Ojo Caliente (Rio Grande) had the highest allelic richness (A_R = 15.09), while Upper Rio Bonito (Pecos) had the lowest allelic richness (A_R = 6.75). Genetic differentiation existed among all populations with the lowest genetic variation occurring within the Pecos drainage. STRUCTURE analysis revealed seven genetic clusters. Populations of G. pandora within the upper Rio Grande drainage (Rio Ojo Caliente, Rio Vallecitos, Rio Pueblo de Taos) had high levels of admixture with Q-values ranging from 0.30–0.50. In contrast, populations within the Pecos drainage (Pecos River and Upper Rio Bonito) had low levels of admixture (Q = 0.94 and 0.87, respectively). Estimates of effective number of breeders (N _b ) varied from 6.1 (Pecos: Upper Rio Bonito) to 109.7 (Rio Grande: Rio Peñasco) indicating that populations in the Pecos drainage are at risk of extirpation. In the event that management actions are deemed necessary to preserve or increase genetic diversity of G. pandora, consideration must be given as to which populations are selected for translocation.     

Selenium and mercury concentrations in some fish species of the Madeira River, Amazon Basin, Brazil

Samples of 7 species of piscivorous, omnivorous, and herbivorous fish caught at 12 different sites on the Madeira River, Amazon Basin, were analyzed for selenium and mercury. Selenium was determined by anodic stripping voltammetry and mercury by cold vapor atomic absorption spectrophotometry. The means for selenium concentrations ranged from 0.49 to 3.11 nmol/g and for mercury from 0.41 to 6.66 nmol/g depending on the fish species. The molar ratios of Hg:Se increased according to the fish trophic level. Piscivorous species had the highest mean ratio (4.0) and herbivorous species the lowest (0.9). There was a positive and statistically significant correlation between selenium and mercury concentrations for the herbivorous species (r = 0.716;p = 0.0088) not seen for omnivororus and piscivorous species (r = -0.2032;p = 0.3407). These findings are significant for the fish-eating population of the Madeira River because the ingestion of mercury would always be in excess of selenium.