Genetic effects of habitat fragmentation and population isolation on Etheostoma raneyi (Percidae)

The use of genetic methods to quantify the effects of anthropogenic habitat fragmentation on population structure has become increasingly common. However, in today’s highly fragmented habitats, researchers have sometimes concluded that populations are currently genetically isolated due to habitat fragmentation without testing the possibility that populations were genetically isolated before European settlement. Etheostoma raneyi is a benthic headwater fish restricted to river drainages in northern Mississippi, USA, that has a suite of adaptive traits that correlate with poor dispersal ability. Aquatic habitat within this area has been extensively modified, primarily by flood-control projects, and populations in headwater streams have possibly become genetically isolated from one another. We used microsatellite markers to quantify genetic structure as well as contemporary and historical gene flow across the range of the species. Results indicated that genetically distinct populations exist in each headwater stream analyzed, current gene flow rates are lower than historical rates, most genetic variation is partitioned among populations, and populations in the Yocona River drainage show lower levels of genetic diversity than populations in the Tallahatchie River drainage and other Etheostoma species. All populations have negative F_IS scores, of which roughly half are significant relative to Hardy–Weinberg expectations, perhaps due to small population sizes. We conclude that anthropogenic habitat alteration and fragmentation has had a profoundly negative impact on the species by isolating E. raneyi within headwater stream reaches. Further research is needed to inform conservation strategies, but populations in the Yocona River drainage are in dire need of management action. Carefully planned human-mediated dispersal and habitat restoration should be explored as management options across the range of the species.     

THE ROLE OF INTROGRESSIVE HYBRIDIZATION IN THE EVOLUTION OF THE GILA ROBUSTA COMPLEX (TELEOSTEI: CYPRINIDAE)

Abstract The extent and impact of introgressive hybridization was examined in the Gila robusta complex of cyprinid fishes using mitochondrial DNA (mtDNA) sequence variation. Lower Colorado River basin populations of G. robusta, G. elegans, and G. cypha exhibited distinct mtDNAs, with only limited introgression of G. elegans into G. cypha. The impact of hybridization was significant in upper Colorado River basin populations; most upper basin fishes sampled exhibited only G. cypha mtDNA haplotypes, with some individuals exhibiting mtDNA from G. elegans. The complete absence of G. robusta mtDNA, even in populations of morphologically pure G. robusta, indicates extensive introgression that predates human influence. Analysis of the geographic distribution of variation identified two distinctive G. elegans lineages; however, the small number of individuals and localities sampled precluded a comprehensive analysis. Analysis of haplotype and population networks for G. cypha mtDNAs from 15 localities revealed low divergence among haplotypes; however, significant frequency differences among populations within and among drainages were found, largely attributable to samples in the Little Colorado River region. This structure was not associated with G. cypha and G. robusta, as morphotypes from the same location are more similar than conspecific forms in other locations. This indicates that morphological and mtDNA variation are affected by different evolutionary forces in Colorado River Gila and illustrates how both hybridization and local adaptation can play important roles in evolution.     

中间黄颡鱼群体遗传变异与亲缘生物地理

通过分析81尾采自华南西部12条水系的中间黄颡鱼(Pelteobagrus intermedius)mtDNA控制区435 bp的序列,研究其群体遗传变异及亲缘生物地理格局。结果显示,中间黄颡鱼群体间的遗传分化较小,核苷酸变异只有0.54%。12条水系的群体共有7个单倍型,其中一些现已相互隔离的水系中的群体共享同一个单倍型,提示这些水系曾经有非常密切的联系。根据嵌套进化支序分析,中间黄颡鱼可能起源于峒中河、北仑河、防城河所在的广西与越南交界地区,并通过两条途径向华南沿海西部诸独立水系和海南岛扩散,在演化过程中,曾发生片断化事件,长距离建群和持续的分布区扩张。     

华南沿海西部美丽小条鳅基于线粒体控制区的种群遗传变异及亲缘地理格局

为研究其种群遗传变异和亲缘地理格局,分析了107尾采自华南西部和海南岛的12条水系的美丽小条鳅(Micronoema-cheilus pulcher Nichols)控制区934-938 bp的序列,其中有79个核苷酸变异位点。分子变异分析(AMOVA)表明,种群间的遗传变异占46.88%,种群内的遗传变异占55.06%。基于36个单倍型的系统树显示,12条水系的种群聚成两支。其中,广西沿海诸独立水系(防城河、峒中河、北仑河、南流江)和西江水系与广东漠阳江和潭江水系关系密切,而海南岛万泉河和南渡江与广东鉴江水系关系密切。根据嵌套进化枝系地理分析(NCPA)推测,防城河周边地区可能是美丽小条鳅的扩散中心,该物种可由此区域通过两条途径扩散:(1)沿西江水系向广西沿海独立水系至广东漠阳江和潭江水系扩散;(2)向海南岛诸水系再至雷州半岛的鉴江水系扩散。在演化过程中,曾发生片断化事件、长距离建群和持续的分布区扩张。     

MITOCHONDRIAL DNA VARIATION WITHIN AND BETWEEN SPECIES OF THE PAPILIO MACHAON GROUP OF SWALLOWTAIL BUTTERFLIES

Species limits and phylogenetic relationships in the Papilio machaon species group are potentially confounded by a complex pattern of Pleistocene range fragmentation, hybridization, and ecological race formation. Mitochondrial DNA (mtDNA) restriction-site analysis has been used to define genetic affinities and genetic population structure within this species group. The distribution of mtDNA haplotypes generally confirms prior phylogenetic hypotheses and species delineations, but there is poor correspondence between ecological races and mtDNA haplotypes. The amount and distribution of mtDNA sequence variation within species vary among species, reflecting differences in current patterns of gene flow and/or historical population structure. In spite of wing pattern characters that ally them with P. polyxenes, both P. joanae and P. brevicauda have mtDNA that is closely related to that of P. machaon. We suggest that P. joanae and P. brevicauda are of hybrid origin.     

Molecular phylogenetics at the population/species interface in cave spiders of the southern Appalachians (Araneae:Nesticidae:Nesticus)

This paper focuses on the relationship between population genetic structure and speciation mechanisms in a monophyletic species group of Appalachian cave spiders (Nesticus). Using mtDNA sequence data gathered from 256 individuals, I analyzed patterns of genetic variation within and between populations for three pairs of closely related sister species. Each sister-pair comparison involves taxa with differing distributional and ecological attributes; if these ecological attributes are reflected in basic demographic differences, then speciation might proceed differently across these sister taxa comparisons. Both frequency-based and gene tree analyses reveal that the genetic structure of the Nesticus species studied is characterized by similar and essentially complete population subdivision, regardless of differences in general ecology. These findings contrast with results of prior genetic studies of cave-dwelling arthropods that have typically revealed variation in population structure corresponding to differences in general ecology. Species fragmentation through both extrinsic and intrinsic evolutionary forces has resulted in discrete, perhaps independent, populations within morphologically defined species. Large sequence divergence values observed between populations suggest that this independence may extend well into the past. These patterns of mtDNA genealogical structure and divergence imply that species as morphological lineages are currently more inclusive than basal evolutionary or phylogenetic units, a suggestion that has important implications for the study of speciation mechanisms.      

Repeated intraspecific divergence in life span and aging of African annual fishes along an aridity gradient

Life span and aging are substantially modified by natural selection. Across species, higher extrinsic (environmentally related) mortality (and hence shorter life expectancy) selects for the evolution of more rapid aging. However, among populations within species, high extrinsic mortality can lead to extended life span and slower aging as a consequence of condition‐dependent survival. Using within‐species contrasts of eight natural populations of Nothobranchius fishes in common garden experiments, we demonstrate that populations originating from dry regions (with short life expectancy) had shorter intrinsic life spans and a greater increase in mortality with age, more pronounced cellular and physiological deterioration (oxidative damage, tumor load), and a faster decline in fertility than populations from wetter regions. This parallel intraspecific divergence in life span and aging was not associated with divergence in early life history (rapid growth, maturation) or pace‐of‐life syndrome (high metabolic rates, active behavior). Variability across four study species suggests that a combination of different aging and life‐history traits conformed with or contradicted the predictions for each species. These findings demonstrate that variation in life span and functional decline among natural populations are linked, genetically underpinned, and can evolve relatively rapidly.     

INTRASPECIFIC PHYLOGEOGRAPHY OF NORTH AMERICAN HIGHLAND FISHES: A TEST OF THE PLEISTOCENE VICARIANCE HYPOTHESIS

The highland fish fauna of eastern North America consists of Appalachian and Ozark centers of endemism separated by the intervening Glacial Till Plains. Clades within these areas are more closely related phylogenetically to each other than to clades occurring in the intervening formerly glaciated region, suggesting that the Pleistocene glaciations fragmented a widespread highland region and its associated fauna. Alternatively, it is possible that these faunal assemblages predate the glaciations or that recent dispersals may have been more important than vicariance in determining faunal compositions. We examined the relationships among mitochondrial DNA (mtDNA) haplotypes within five clades of highland fishes, each with a distribution suggestive of a Pleistocene vicariance event. Darters of the subgenera Litocara and Odontopholis have distributions and mtDNA relationships that are consistent with the Pleistocene integration and burial of the Teays-Mahomet valley, a major drainage of the early Pleistocene. The distribution and mtDNA relationships among subspecies of Erimystax dissimilis are not consistent with Pleistocene vicariance, but relationships among Appalachian haplotypes are consistent with the late Pleistocene integration of the modern Ohio River system. Both Cottus carolinae and the Fundulus catenatus species group have representatives in the Mobile basin consistent with pre-Pleistocene divergences. Three haplotype clusters were found in C. carolinae, corresponding to the Appalachian, Ozark, and upper Kanawha River populations. However, Appalachian and Ozark F. catenatus populations are paraphyletic with respect to each other. This, coupled with a relatively low degree of sequence divergence, suggests that no long-term barriers to gene flow exist for C. carolinae and F. catenatus. These three distinct phylogeographic patterns indicate that Pleistocene vicariance is not the only explanation for the Appalachian-Ozark distribution of highland fish communities.     

EVIDENCE FOR MULTIPLE ORIGINS AND SYMPATRIC DIVERGENCE OF TROPHIC ECOTYPES OF SMELT (OSMERUS) IN NORTHEASTERN NORTH AMERICA

The rainbow smelt, Osmerus mordax (Mitchill), is an osmerid fish that exhibits extensive life-history diversity throughout watersheds of northeastern North America. There are both ???sea-run (anadromous) and lake-resident (lacustrine) populations and the latter have diversified further into “dwarf-” and “normal-sized” life-history types. Anadromous and lacustrine smelt may inhabit the same watershed and there are several instances where dwarf and normal populations reside within the same lake. We assayed variation among smelt for morphological traits linked to feeding performance in fishes to see if trophic ecology might promote life-history diversity in Osmerus. We also examined mitochondrial DNA (mtDNA) restriction site variation among forms to assess their evolutionary interrelationships. Dwarf smelt had significantly more gill rakers, larger eyes, but shorter upper jaws than normal lake and anadromous smelt. The populations clustered into two trophic “morphotypes”; an anadromous/normal lake group of populations and a group consisting only of dwarf smelt. The mtDNAs of 444 smelt from 16 populations were digested with 12 restriction enzymes revealing 93 composite mtDNA genotypes that clustered (UPGMA) into two major phylogenetic groups differing by 0.78% in sequence. Both genetic groups were present in dwarf and normal smelt as well as in anadromous fish. Further, geographic proximity, rather than trophic morphotype, appeared to be the major determinant of genetic affinities among populations. In two lakes, however, dwarf and normal smelt populations had significantly different mtDNA genotype frequency distributions indicating that the forms are reproductively isolated within both lakes. A clustering analysis of population affinities suggested that the divergence of sympatric dwarf and normal populations had occurred independently in the two lakes. We concluded (1) that trophic ecology is an important factor promoting differentiation in smelt life histories; (2) that smelt ecotypes are polyphyletic and there have been multiple, independent divergences of Osmerus life-history types throughout northeastern North America; and (3) that the biological and mtDNA differences between coexisting dwarf and normal lake smelt argue strongly that their genetic isolation may have developed sympatrically.     

The effect of deforestation on the genetic diversity and structure in <Emphasis Type="Italic">Acer saccharum</Emphasis> (Marsh): Evidence for the loss and restructuring of genetic variation in a natural system

The level and distribution of genetic diversity can be influenced by species life history traits and demographic factors, including perturbations that might produce population bottlenecks. Deforestation and forest fragmentation are common sources of population disturbance in contemporary populations of forest ecosystems. Although the genetic effects of forest fragmentation and deforestation have been examined by assessing levels of genetic variation in forest fragments that remain after logging, few considerations have been made of the populations that re-colonize once-cleared areas. Here we examine the effects of human-mediated population bottlenecks on the level and distribution of genetic diversity in natural populations of the long-lived forest tree species, Acer saccharum (sugar maple). We compared genetic variation and structure for populations of sugar maple found within old-growth forested area and in area that has re-colonized since logging. In this study the percent polymorphic loci and allelic richness estimates were reduced in the logged populations compared to old-growth populations. Jackknifed estimates of population genetic differentiation showed significantly higher differentiation among logged populations, with this result being consistently seen when individuals within populations were grouped according to diameter at breast height. The result of decreased genetic variation and higher levels of genetic structure among logged populations suggests that even one extensive bout of logging can alter the level and distribution of genetic variation in this forest tree species.     

SEX-BIASED GENE FLOW IN SPECTACLED EIDERS (ANATIDAE): INFERENCES FROM MOLECULAR MARKERS WITH CONTRASTING MODES OF INHERITANCE

Abstract Genetic markers that differ in mode of inheritance and rate of evolution (a sex‐linked Z‐specific micro‐satellite locus, five biparentally inherited microsatellite loci, and maternally inherited mitochondrial [mtDNA] sequences) were used to evaluate the degree of spatial genetic structuring at macro‐ and microgeographic scales, among breeding regions and local nesting populations within each region, respectively, for a migratory sea duck species, the spectacled eider (Somateria fisheri). Disjunct and declining breeding populations coupled with sex‐specific differences in seasonal migratory patterns and life history provide a series of hypotheses regarding rates and directionality of gene flow among breeding populations from the Indigirka River Delta, Russia, and the North Slope and Yukon‐Kuskokwim Delta, Alaska. The degree of differentiation in mtDNA haplotype frequency among breeding regions and populations within regions was high (φ_CT= 0.189, P < 0.01; φ_SC= 0.059, P < 0.01, respectively). Eleven of 17 mtDNA haplotypes were restricted to a single breeding region. Genetic differences among regions were considerably lower for nuclear DNA loci (sex‐linked: φ_ST= 0.001, P > 0.05; biparentally inherited microsatellites: mean θ= 0.001, P > 0.05) than was observed for mtDNA. Using models explicitly designed for uniparental and biparentally inherited genes, estimates of spatial divergence based on nuclear and mtDNA data together with elements of the species' breeding ecology were used to estimate effective population size and degree of male and female gene flow. Differences in the magnitude and spatial patterns of gene correlations for maternally inherited and nuclear genes revealed that females exhibit greater natal philopatry than do males. Estimates of generational female and male rates of gene flow among breeding regions differed markedly (3.67 × 10^‐4 and 1.28 × 10^‐2, respectively). Effective population size for mtDNA was estimated to be at least three times lower than that for biparental genes (30,671 and 101,528, respectively). Large disparities in population sizes among breeding areas greatly reduces the proportion of total genetic variance captured by dispersal, which may accelerate rates of inbreeding (i.e., promote higher coancestries) within populations due to nonrandom pairing of males with females from the same breeding population.     

Population genetics of the freshwater mussel, <Emphasis Type="Italic">Amblema plicata</Emphasis> (Say 1817) (Bivalvia: Unionidae): Evidence of high dispersal and post-glacial colonization

Over 70% of North American freshwater mussel species (families Unionidae and Margaritiferidae) are listed as threatened or endangered. Knowledge of the genetic structure of target species is essential for the development of effective conservation plans. Because Ambelma plicata is a common species, its population genetic structure is likely to be relatively intact, making it a logical model species for investigations of freshwater mussel population genetics. Using mtDNA and allozymes, we determined the genotypes of 170+ individuals in each of three distinct drainages: Lake Erie, Ohio River, and the Lower Mississippi River. Overall, within-population variation increased significantly from north to south, with unique haplotypes and allele frequencies in the Kiamichi River (Lower Mississippi River drainage). Genetic diversity was relatively low in the Strawberry River (Lower Mississippi River drainage), and in the Lake Erie drainage. We calculated significant among-population structure using both molecular markers (A.p. Φ_st = 0.15, θ_st = 0.12). Using a hierarchical approach, we found low genetic structure among rivers and drainages separated by large geographic distances, indicating high effective population size and/or highly vagile fish hosts for this species. Genetic structure in the Lake Erie drainage was similar to that in the Ohio River, and indicates that northern populations were founded from at least two glacial refugia following the Pleistocene. Conservation of genetic diversity in Amblema plicata and other mussel species with similar genetic structure should focus on protection of a number of individual populations, especially those in southern rivers.     

The effects of riverine impoundment on genetic structure and gene flow in two stream fishes in the Mobile River basin

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Associations between physical isolation and geographical variation within three species of Neotropical birds

We studied effects of physical isolation on geographical variation in mtDNA RFLP polymorphisms and a suite of morphological characters within three species of neotropical forest birds; the crimson-backed tanager Ramphocelus dimidiatus, the blue-gray tanager Thraupis episcopus, and the streaked saltator Saltator albicollis. Variation among populations within continuous habitat on the Isthmus of Panama was compared with that among island populations isolated for about 10000 years. Putative barriers to dispersal were influential, but apparent isolation effects varied by species, geographical scale, and whether molecular or morphological traits were being assessed. We found no geographical structuring among the contiguous, mainland sampling sites. Migration rates among the islands appeared sufficient to maintain homogeneity in mtDNA haplotype frequencies. In contrast, variation in external morphology among islands was significant within two of three species. For all species, we found significant variation in genetic and morphological traits between the island (collectively) and mainland populations. Interspecific variation in the effects of isolation was likely related to differential vagility. These data generally corroborate other studies reporting relatively great geographical structuring within tropical birds over short distances. Behaviourally based traits - low vagility and high ‘sensitivity’ to geographical barriers - may underlie extensive diversification within neotropical forest birds, but more extensive ecological and phylogeographic information are needed on a diverse sample of species.     

SPECIES RECOGNITION AND PATTERNS OF POPULATION VARIATION IN THE REPRODUCTIVE STRUCTURES OF A DAMSELFLY GENUS

The selection pressures imposed by mate choice for species identity should impose strong stabilizing selection on traits that confer species identity to mates. Thus, we expect that such traits should show nonoverlapping distributions among closely related species, but show little to no variance among populations within a species. We tested these predictions by comparing levels of population differentiation in the sizes and shapes of male cerci (i.e., the clasper structures used for species identity during mating) of six Enallagma damselfly species. Cerci shapes were nonoverlapping among Enallagma species, and five of six Enallagma species showed no population variation across their entire species ranges. In contrast, cerci sizes overlapped among species and varied substantially among populations within species. These results, taken with previous studies, suggest that cerci shape is a primary feature used in species recognition used to discriminate conspecific from heterospecifics during mating.     

Population structure and genetic variation in the endangered Giant Kangaroo Rat (<Emphasis Type="Italic">Dipodomys ingens</Emphasis>)

Populations of the endangered giant kangaroo rat, Dipodomys ingens (Heteromyidae), have suffered increasing fragmentation and isolation over the recent past, and the distribution of this unique rodent has become restricted to 3% of its historical range. Such changes in population structure can significantly affect effective population size and dispersal, and ultimately increase the risk of extinction for endangered species. To assess the fine-scale population structure, gene flow, and genetic diversity of remnant populations of Dipodomys ingens, we examined variation at six microsatellite DNA loci in 95 animals from six populations. Genetic subdivision was significant for both the northern and southern part of the kangaroo rat’s range although there was considerable gene flow among southern populations. While regional gene diversity was relatively high for this endangered species, hierarchical F-statistics of northern populations in Fresno and San Benito counties suggested non-random mating and genetic drift within subpopulations. We conclude that effective dispersal, and therefore genetic distances between populations, is better predicted by ecological conditions and topography of the environment than linear geographic distance between populations. Our results are consistent with and complimentary to previous findings based on mtDNA variation of giant kangaroo rats. We suggest that management plans for this endangered rodent focus on protection of suitable habitat, maintenance of connectivity, and enhancement of effective dispersal between populations either through suitable dispersal corridors or translocations.     

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.     

PHYLOGEOGRAPHY OF THE SPOTTED SAND BASS, PARALABRAX MACULATOFASCIATUS: DIVERGENCE OF GULF OF CALIFORNIA AND PACIFIC COAST POPULATIONS

Abstract Have the warm tropical waters and currents of the southern Gulf of California, Mexico (also known as the Sea of Cortez), formed a barrier to gene flow, resulting in disjunct populations in the upper gulf that are isolated from the outer Pacific Coast? Phylogeographic and genetic divergences of the spotted sand bass, Paralabrax maculatofasciatus, from three Gulf of California and two outer Pacific coastal locations were tested using mitochondrial DNA (mtDNA) control region sequences. Sequence data from two congeners that are sympatrically distributed along the outer Pacific Coast, the barred sand bass, P. nebulifer, and the kelp bass, P. clathratus, were used to gauge the levels of genetic divergences. Differences among the three species and between the northern gulf and outer Pacific coastal populations of P. maculatofasciatus also were analyzed using 40 allozymic presumptive gene loci. Allozyme and mtDNA analyses each revealed many fixed differences among the species. Three significant allozymic frequency differences and two fixed mtDNA substitutions differentiated the gulf and outer Pacific coastal populations of P. maculatofasciatus. Three unique mtDNA haplotypes and three unique allozyme alleles were identified from the outer Pacific coastal population. The gulf sites contained four unique mtDNA haplotypes and six unique allozyme alleles. Partitioning of the mtDNA variation revealed that 72% of the variance occurred between the gulf and outer Pacific Coast, 20% between sampling sites in the two regions, and 8% within the sites. There appears to be little gene flow across the waters of the southern Baja Penninsula, producing divergence estimated as 120,000 to 600,000 years between the outer Pacific coastal and the Gulf of California populations. This separation level may date to a hypothesized seaway closure near La Paz, Mexico, during the mid‐Pleistocene, and characterizes other fish populations. A second pattern of deeper allopatric species‐level divergences in some other fishes may date to a Pliocene closure of a mid‐Baja Penninsular seaway. Significant differences also were discerned in P. maculatofasciatus between the San Diego and central Baja California coastal sites and between the upper/central and the lower gulf locations. Variation between locations in the two regions may be indicative of larval retention and low adult migration, which needs to be tested further.     

Drought in an evolutionary context: molecular variability in Flannelmouth Sucker (Catostomus latipinnis) from the Colorado River Basin of western North America

Summary 1. Fishes can often rebound numerically and distributionally from short‐term (i.e. seasonal) drought, yet their capacity to recover from decades or centuries of drought is less apparent. An exceedingly warm and dry period swept the intermontane west of North America ca. 7500 years BP, concomitant with an abrupt extinction of >35 mammal species. Were larger fishes in mainstem rivers also impacted by this drought? 2. The Colorado River Basin encompasses seven states in western North America and drains 600 000 km². Its endemic mainstem fish community is ancient (i.e. Miocene) but depauperate. 3. We evaluated one widely distributed candidate species (flannelmouth sucker, Catostomus latipinnis) for basin‐wide genetic and geographic structure at three fast‐evolving mitochondrial (mt) DNA genes, ND2 with 589 bp and ATPase 8 and 6 with 642 bp. It is hypothesized that a concomitant signature would be present in the mtDNA of this species, if indeed it had been seriously bottlenecked by post‐Pleistocene drought. A total of 352 individuals were sequenced from 24 populations (4–40 individuals/population; average of 14.7). 4. Only 49 unique haplotypes were found, 53% of which represented single individuals. Haplotype diversity was high (0.905 ± 0.007) whereas nucleotide diversity was low (0.002 ± 0.000). 5. A significant and positive geographical cline (P < 0.001) in nucleotide diversity was observed as sampling locations progressed upstream from southwest to northeast. These results divided the Colorado River Basin into three reaches: the lower reach with six populations and 83 individuals; the upper reach with seven populations and 83 individuals; and the middle reach with 11 populations and 186 individuals. An analysis of molecular variance (amova ) revealed that 81.5% of the total genetic variation was within populations, 16% among populations within reaches and 2.5% among reaches. Only the last was significant. Populations from the three reaches diverged from one another by 3400–11 000 years BP. Haplotype distribution suggested populations in the upper Colorado River are expanding. 6. The lack of genetic variation and recent coalescence of lineages in C. latipinnis are unusual given its fossil history, broad geographical sampling, the rapid rate of mtDNA evolution and the number (and evolutionary rate) of the genes examined. The most parsimonious explanation for these data is a rapid expansion following a recent period of low effective population size at the end of the Pleistocene. 7. The intense drought is suggested at the end of the Pleistocene (late‐to‐mid‐Holocene), severely impacted not only large mammals but also larger fishes in western North American rivers. These perspectives have important implications for management of endangered and threatened species in this region.     

Recent,small beginnings: genetic analysis suggests Catostomus rimiculus (Klamath smallscale sucker) in the Smith River,California, are introduced

Identification of introduced species can be important to understanding ecological systems and meeting conservation and management goals, but the process can be surprisingly challenging. The Klamath smallscale sucker Catostomus rimiculus seems likely to be native to the Smith River because the drainage separates two basins believed to be within the fish's native range, the Rogue and Klamath rivers. Further, C. rimiculus is broadly distributed in the Smith River, and the indigenous Dee-ni’ People of the Smith River have a unique word for sucker. Nonetheless, a historical survey of fishes that described C. rimiculus from the Rogue and Klamath rivers did not include C. rimiculus among the fishes of the Smith River. To determine whether the genetic structure of the Smith River C. rimiculus reflects expectations for a native sucker population, the authors of this study examined variation in microsatellite and mitochondrial genetic markers from the Smith River and surrounding drainages. The genetic analyses revealed a pattern consistent with extreme founder effects in Smith River C. rimiculus, as would be expected from a single introduction of six or fewer effective individuals. The sharing of a high-frequency haplotype between the Smith River and Klamath River that is not detected in the Rogue River suggests the Klamath River as the likely source for the introduction. The findings highlight that local-scale introductions can be easily overlooked because the newly established populations can appear to be parts of contiguous natural distributions.