Spatial genetic variation and habitat association of <Emphasis Type="Italic">Rhinichthys cataractae</Emphasis>, the longnose dace,in the Driftless Area of the upper Mississippi River basin

The Driftless Area of the upper Mississippi River drainage is a unique geographic region because of its complex geological history and the influence of recent, intensive human activities. The longnose dace, Rhinichthys cataractae, is a relatively common, small freshwater fish that is distributed in swift, cool streams within the region. The aim of this study was to determine the spatial genetic differentiation of the longnose dace and define the broad scale environmental variables that shape the distribution of the species in the southwestern portion of the Driftless Area. Genotypic data from seven microsatellite loci were analyzed for 276 individuals from 15 localities representing major drainages within the region in northeast Iowa. Broad scale environmental variables including hydrologic, soil, and climatic factors were evaluated to construct an ecological niche model (ENM) to predict the suitability of habitat for the species within the region. Results of the genetic analyses revealed two distinct, but somewhat admixed genetic clusters of longnose dace in Iowa. The genetic differentiation between localities and between drainages was low to moderate with some evidence of isolation by distance. Most of the variation was observed by differences between individuals within local populations. The ENM generated largely reflected the known distribution of the species in Iowa with a decreasing probability of suitable habitat from northern to southern drainages. Geologic factors played a key role in the model. The distribution and population structure of the longnose dace in the northeast Iowa revealed that isolation by distance, historical processes and the underlying geology are primarily responsible for the observed spatial distribution of genetic variation.     

Morphological and genetic analysis of sympatric dace within the Rhinichthys cataractae species complex: a case of isolation lost

The Nooksack dace (Pisces: an undescribed putative taxon within Rhinichthys) and longnose dace (Rhinichthys cataractae) are two forms within the R. cataractae species complex that are distinguishable from one another by mitochondrial (mt) DNA divergence of 2–3%, as well as by subtle morphological differences. The two forms are found in allopatry in south‐eastern British Columbia (BC), Canada, and adjacent areas of western Washington, USA, and are sympatric in three streams in the lower Fraser River valley, BC, and may represent cryptic species. We assayed 12 morphometric traits and two meristic characters (N = 582; 23 sampling locations) to test for diagnosability of the two dace, as well as to test for morphological differentiation by mtDNA type in sympatry. We then employed a 10‐locus microsatellite DNA assay (N = 374; 12 sampling locations) to test for genetic distinction between Nooksack dace and longnose dace in sympatry. We found that the two dace could not be reliably differentiated morphologically: there was overlap in all characters measured, and sampling location had a much larger effect on morphology than mtDNA group. Microsatellite analysis showed no distinction by mtDNA type in localities with sympatric dace, indicating complete admixture between the sympatric Nooksack dace and longnose dace. The Nooksack dace and longnose dace provide an example of ‘ephemeral speciation’: two lineages that, despite an estimated 1.1 Myr of isolation, have developed no apparent barriers to reproduction and appear to have collapsed into a single interbreeding population where they come into secondary contact. Nonetheless, the zone of secondary contact and the diagnosability of the Nooksack dace in terms of mtDNA represent significant aspects of the evolutionary legacy within R. cataractae and support its conservation importance.     

Taxonomic status of the extinct Banff longnose dace,Rhinichthys cataractae smithi,of Banff National Park,Alberta

Synopsis Study of 314 specimens of Rhinichthys cataractae from British Columbia, Alberta, and Wyoming, lead to the following conclusions: (1) Rhinichthys cataractae smithi Nichols,1916, is a valid subspecies, endemic to Cave and Basin Hotsprings and distinguished by 48–58 as opposed to 58–74 lateral line scales; (2) between 1925 and 1971, R. c. smithi hybridized with the eastern subspecies R. c. cataractae (Valenciennes,1842) from the Bow River and by 1981 the former had undergone almost complete introgression and was virtually extinct; (3) probable factors leading to this are introduction of tropical fishes into the hotsprings and periodic reduction of inflow from the hotsprings; (4) the closest relative of R. c. smithi is R. c. cataractae, rather than the westslope longnose dace (without a scientific name) inhabiting the Pacific basin; (5) the low number of lateral line scales of R. c. smithi may be a pleomeristic response to dwarfing; (6) R. c. smithi develops breeding tubercles at sizes as small as 21.1 mm SL, whereas R. c. cataractae develop them at 36.3 mm SL in Alberta; (7) introductions should not be made into a body of water prior to the study of its native fishes and consultation with experts in taxonomy and distribution of rare fishes. R. c. smithi is illustrated for the first time.     

Biogeography of ‘Cyprinella lutrensis’: intensive genetic sampling from the Pecos River ‘melting pot’ reveals a dynamic history and phylogenetic complexity

Thorough sampling is necessary to delineate lineage diversity for polytypic ‘species’ such as Cyprinella lutrensis. We conducted extensive mtDNA sampling (cytochrome b and ND4) from the Pecos River, Rio Grande, and South Canadian River, New Mexico. Our study focussed on the Pecos River due to its complex geological history and potential to harbour multiple lineages. We used geometric–morphometric, morphometric, and meristic analyses to test for phenotypic divergence and combined nucDNA with mtDNA to test for cytonuclear disequilibrium and combined our sequences with published data to conduct a phylogenetic re‐assessment of the entire C. lutrensis clade. We detected five co‐occurring mtDNA lineages in the Pecos River, but no evidence for cytonuclear disequilibrium or phenotypic divergence. Recognized species were interspersed amongst divergent lineages of ‘C. lutrensis’. Allopatric divergence among drainages isolated in the Late Miocene and Pliocene apparently produced several recognized species and major divisions within ‘C. lutrensis’. Pleistocene re‐expansion and subsequent re‐fragmentation of a centralized lineage founded younger, divergent lineages throughout the Rio Grande basin and Edwards Plateau. There is also evidence of recent introductions to the Rio Grande, Pecos and South Canadian Rivers. Nonetheless, deeply divergent lineages have coexisted since the Pleistocene.     

Phylogeography and post-glacial colonization patterns of the rainbow darter, Etheostoma caeruleum (Teleostei: Percidae)

Aim To examine the effects of historical climate change and drainage isolation on the distribution of mitochondrial DNA cytochrome b genetic variation within the rainbow darter, Etheostoma caeruleum (Percidae: Etheostomatinae). Location Eastern North American streams including tributaries to the Mississippi River, Great Lakes, Potomac River and Hudson Bay drainages. Methods Parsimony analyses, Bayesian analyses and haplotype networks of mitochondrial DNA sequences. Results Four major clades were recovered from sampled populations of E. caeruleum. Three of four clades are distributed in the western portion of the species’ range (primarily west of the Mississippi River). Samples from this region do not form a monophyletic group, and sequences often vary greatly between samples from adjacent stream systems (up to 7.2% divergence). A basal clade includes samples from the White River system in the Ozark Highlands. The northern Ozarks–upper Midwest clade includes samples from Missouri River tributaries and the upper Midwest (Hudson Bay, upper Mississippi River, and western Lake Michigan drainage). The eastern clade is composed of individuals from the Ohio River, Great Lakes and Potomac River. The Mississippi River corridor clade includes samples from middle and lower Mississippi River tributaries. Main conclusions The four major clades of E. caeruleum are deep allopatric lineages with well‐defined boundaries and have additional phylogeographical structure within each clade. The Ozark Highlands have the greatest levels of diversity relative to distributional area, with marked cytochrome b subdivisions between adjacent stream systems. Samples from previously glaciated areas do not have a subset of the cytochrome b diversity found in unglaciated areas, but four separate source areas are identified based on phylogenetic analyses. Dispersal into previously glaciated areas followed several known glacial outlets and, based on sequence divergence between populations, may have occurred during different glacial or interglacial stages. The disjunct distribution and cytochrome b pattern of E. caeruleum in the Mississippi River corridor clade is consistent with late Pleistocene and Recent changes in the course and characteristics of the middle and lower Mississippi River. Phylogeographical boundaries between clades of E. caeruleum correspond to independent sources of biogeographical information and provide insight into historical stream drainage relationships, post‐glacial colonization and drainage isolation patterns.     

Evaluation of swimming performance for fish passage of longnose dace Rhinichthys cataractae using an experimental flume

The swimming performance of longnose dace Rhinichthys cataractae, the most widely distributed minnow (Cyprinidae) in North America, was assessed in relation to potential passage barriers. The study estimated passage success, maximum ascent distances and maximum sprint speed in an open‐channel flume over a range of water velocities and temperatures (10·7, 15·3 and 19·3° C). Rhinichthys cataractae had high passage success (95%) in a 9·2 m flume section at mean test velocities of 39 and 64 cm s^–1, but success rate dropped to 66% at 78 cm s^–1. Only 20% of fish were able to ascend a 2·7 m section with a mean velocity of 122 cm s^–1. Rhinichthys cataractae actively selected low‐velocity pathways located along the bottom and corners of the flume at all test velocities and adopted position‐holding behaviour at higher water velocities. Mean volitional sprint speed was 174 cm s^–1 when fish volitionally sprinted in areas of high water velocities. Swimming performance generally increased with water temperature and fish length. Based on these results, fishways with mean velocities <64 cm s^–1 should allow passage of most R. cataractae. Water velocities >100 cm s^–1 within structures should be limited to short distance (<1 m) and structures with velocities ≥158 cm s^–1 would probably represent movement barriers. Study results highlighted the advantages of evaluating a multitude of swimming performance metrics in an open‐channel flume, which can simulate the hydraulic features of fishways and allow for behavioural observations that can facilitate the design of effective passage structures.     

Characterization of microsatellite loci in longnose dace (Rhinichthys cataractae) and interspecific amplification in five other Leuciscinae species

The longnose dace (Rhinichthys cataractae) appears as a relevant model to address environmental and ecological issues in an evolutionary perspective. Eleven microsatellite markers were characterized for this species. Eight of these loci were highly polymorphic for populations of this species. Between four to 10 loci were also successfully amplified in five closely related species. These markers are believed to be valuable tools for genetic analysis of populations of longnose dace and other Leuciscinae species.     

Inter‐basin exchange and repeated headwater capture across the Sierra Madre Occidental inferred from the phylogeography of Mexican stonerollers

Aim Geomorphic evolution of river basins can shape the structure and diversity of aquatic communities, but understanding the biological significance of basin evolution can be challenging in semi‐arid regions with ephemeral or endorheic conditions and complex drainage configurations such as the Sierra Madre Occidental (SMO) in North America. In this study, we characterized range‐wide patterns of genetic variation in the Mexican stoneroller (Campostoma ornatum) to infer how orogenic and erosional influences on river basin connectivity have given rise to the diverse and largely endemic freshwater communities across the SMO region. Location Twelve drainage basins across northern Mexico and the south‐western United States, centred on the SMO. Methods  We collected 202 specimens from 98 localities across the range of C. ornatum. We performed phylogenetic analyses of DNA sequences from one mitochondrial (cytochrome b) and one nuclear (intron S7) gene. Phylogenetic trees were estimated for each data set using maximum likelihood and Bayesian inference. Results Phylogenetic analyses consistently resolved a monophyletic C. ornatum composed of multiple evolutionary lineages within two markedly divergent clades that differentiate northern drainages from southern drainages in the SMO region. Within‐clade patterns of divergence corresponded to fine‐scale geographic structure within and among SMO drainage basins. However, the geographic distribution of evolutionary lineages within the northern and southern clades did not always correspond to the geographic configuration of drainage basins. Some subclades encompassed multiple drainages, and individuals from a single drainage were sometimes recovered in multiple subclades. Main conclusions Our findings indicate that a common ancestor of Mexican Campostoma is likely to have entered north‐west Mexico through an ancient Rio Grande system that extended as far south as the Rio Nazas and Rio Aguanaval. The geographic orientation of the two strongly divergent clades recovered within C. ornatum provides evidence of long‐standing isolation of southern basins from northern basins within the ancestral Rio Grande system, possibly due to the combined influence of tectonic events and increasing regional aridity. Geographic patterns of genetic variation also provide evidence of range expansion from Atlantic to Pacific drainages due to drainage evolution and river capture events, as well as further inter‐basin exchange via more recent headwater capture events, hydrological connections and possible anthropogenic introductions.     

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.     

Population structure and genetic management of Rio Grande cutthroat trout (Oncorhynchus clarkii virginalis)

The Rio Grande cutthroat trout, Oncorhynchus clarkii virginalis, has declined precipitously over the past century, and currently exhibits a highly fragmented distribution within the Canadian, Pecos and Rio Grande river systems of the western United States. The relationships between populations in the three river drainages, and between O. c. virginalis and the closely related taxa O. c. pleuriticus and O. c. stomias, are not well understood. In order to guide management decisions for the subspecies, we investigated the distribution of variation at 12 microsatellite loci and two regions of the mitochondrial genome. We observed a high level of genetic differentiation between O. c. virginalis populations occupying different headwater streams (global F_st = 0.41). However, we found evidence for previous gene flow within the Rio Grande drainage, indicating that inter-population differentiation may have been exacerbated by the recent effects of population fragmentation. Despite large-scale anthropogenic movement of individuals from the Rio Grande into the Canadian and Pecos, the genetic signature of long-term evolutionary independence between the three drainages has been retained.     

Phylogeography of the bigeye chub Hybopsis amblops (Teleostei: Cypriniformes): early Pleistocene diversification and post‐glacial range expansion

The bigeye chub, Hybopsis amblops, is a member of the Central Highlands ichthyofauna of eastern North America. Phylogenetic analyses of the H. amblops species group based on a 1059 bp fragment of the mitochondrial DNA cytochrome b gene did not recover a monophyletic group. The inclusion of Hybopsis hypsinotus in the species complex is questionable. Within H. amblops, five strongly supported clades were identified; two clades containing haplotypes from the Ozark Highlands and three clades containing haplotypes from the Eastern Highlands and previously glaciated regions of the Ohio and Wabash River drainages. Estimates of the timing of divergence indicated that prior to the onset of glaciation, vicariant events separated populations east and west of the Mississippi River. East of the Mississippi River glacial cycles associated with the blocking and rerouting of the Teays River system caused populations to be pushed southward into refugia of the upper Ohio River. Following the most recent Wisconsinan glaciation, populations expanded northward into previously glaciated regions and southward into the Cumberland River drainage. In the Ozarks, west of the Mississippi River, isolation of clades appears to be maintained by the lack of stream capture events between the upper Arkansas and the White River systems and a barrier formed by the Arkansas River.     

Past climate change drives current genetic structure of an endangered freshwater mussel species

Historical‐to‐recent climate change and anthropogenic disturbance affect species distributions and genetic structure. The Rio Grande watershed of the United States and Mexico encompasses ecosystems that are intensively exploited, resulting in substantial degradation of aquatic habitats. While significant anthropogenic disturbances in the Rio Grande are recent, inhospitable conditions for freshwater organisms likely existed prior to such disturbances. A combination of anthropogenic and past climate factors may contribute to current distributions of aquatic fauna in the Rio Grande basin. We used mitochondrial DNA and 18 microsatellite loci to infer evolutionary history and genetic structure of an endangered freshwater mussel, Popenaias popeii, throughout the Rio Grande drainage. We estimated spatial connectivity and gene flow across extant populations of P. popeii and used ecological niche models (ENMs) and approximate Bayesian computation (ABC) to infer its evolutionary history during the Pleistocene. structure results recovered regional and local population clusters in the Rio Grande. ENMs predicted drastic reductions in suitable habitat during the last glacial maximum. ABC analyses suggested that regional population structure likely arose in this species during the mid‐to‐late Pleistocene and was followed by a late Pleistocene population bottleneck in New Mexico populations. The local population structure arose relatively recently, perhaps due to anthropogenic factors. Popenaias popeii, one of the few freshwater mussel species native to the Rio Grande basin, is a case study for understanding how both geological and anthropogenic factors shape current population genetic structure. Conservation strategies for this species should account for the fragmented nature of contemporary populations.     

Patterns of population differentiation in annual killifishes from the Paraná–Uruguay–La Plata Basin: the role of vicariance and dispersal

Aim To elucidate the role of vicariance versus dispersal at the microevolutionary scale in annual killifish populations belonging to the Austrolebias bellottii species complex (Rivulidae). Within this complex, A. bellottii and A. apaii have low vagility and occur widely within the study area, making them excellent models for testing biogeographic hypotheses of differentiation. Location South America, in the Paraná–Uruguay–La Plata river basin. Methods Molecular data and morphometric analyses were used to reconstruct the phylogeographic history and morphological variation of 24 populations of two taxa of the A. bellottii species complex. Phylogenetic analyses using maximum likelihood (ML) and Bayesian inference (BI) model‐based methods, estimates of clade divergence times implemented in beast , non‐metric multidimensional scaling, analysis of molecular variance results, and morphological analyses elucidated the role of vicariance versus dispersal hypotheses in population differentiation in the aforementioned river basin. Results In the A. bellottii species complex from the Paraná–Uruguay–La Plata river basin, past allopatric fragmentation from vicariance events seems to be the most plausible scenario for diversification since the Late Miocene and more recently since the Plio‐Pleistocene. The Plio‐Pleistocene vicariance produced the differentiation of three major clades in A. bellottii populations. One clade from the eastern Uruguay River drainage was separated from another in western Uruguay and the Paraná–La Plata River drainages. A later vicariance event split populations to the south (lower Paraná–La Plata Basin) and north (middle Paraná) of the western Paraná River drainage. However, our results do not exclude the possibility of dispersal events among A. bellottii populations from both the Uruguay and Paraná river drainages, which could occur in these river basins during hypothesized connectivity cycles of the Late Pliocene and Pleistocene. Main conclusions Past allopatric fragmentation caused by different vicariance events seems to be the main driver of diversification in the A. bellottii species complex since the Plio‐Pleistocene. However, the current molecular data suggest that populations from both drainages of the Paraná–Uruguay rivers may have experienced cycles of connectivity during the Pleistocene, perhaps including multiple vicariance or dispersal events from populations located in the western lower Uruguay River drainage, which encompassed climatic and geological changes in the Paraná–Uruguay–La Plata Basin.     

Conservation and management implications of fine-scale genetic structure of Gulf sturgeon in the Pascagoula River, Mississippi

The anadromous Gulf sturgeon occurs along the north central coast of the Gulf of Mexico and is federally listed as threatened. We analyzed fine‐scale patterns of Gulf sturgeon population structure, focusing on the Pascagoula River drainage of Mississippi, in reference to movement patterns as determined via telemetry and capture data. We genotyped 361 Gulf sturgeon using eight microsatellite loci including samples from the Pascagoula, Pearl, Escambia, Yellow, Choctawhatchee, and Apalachicola river drainages. Pairwise F_ST estimates indicated that genetic structure occurs at least at the drainage level. The Pascagoula and Pearl rivers form a western group, demonstrating 100% bootstrap support for a division with drainages to the east. Assignment tests detected non‐natal genotypes occurring in all drainages. According to assignment tests, the Pascagoula supports an admixture of individuals, containing minimal influence from drainages to the east (2%) and substantial interaction with the Pearl River (14.1%). The occurrence of Pascagoula River fish in the Pearl was non‐reciprocal, observed at 1.1%. After accounting for non‐natal genetic diversity within the Pascagoula, there remained a disparity between a pooled Pascagoula group and the only documented spawning site within the drainage located in the Bouie River. We interpret this as an indication of a second genetic stock within the Pascagoula River drainage. Radio telemetry data suggest that spawning likely occurs in the Chickasawhay River, in areas isolated from the Bouie River spawning site by about 350 river kilometers. We emphasize the utility of integrating field and molecular approaches when delineating fine‐scale patterns of population structure in anadromous fishes.     

Morphological and molecular variation in the least madtom Noturus hildebrandi (Siluriformes: Ictaluridae), a Mississippi Embayment endemic: evidence for a cryptic lineage in the Hatchie River

Sheared principal component analysis of 40 morphometric characteristics measured for 146 individuals and relative frequencies of pigmentation patterns scored for 980 individuals of the least madtom Noturus hildebrandi, a diminutive catfish endemic to eastern lowland drainages of the Mississippi Embayment region of North America, suggested a clinal pattern of morphological variation extending across the range from north to south. DNA sequence data representing 90 individuals from the mitochondrial gene cytochrome b (cytb) analysed using Bayesian phylogenetic methods recovered four major haplotype clades, suggestive of a high degree of isolation by drainage. Individual gene trees of cytb and four additional nuclear loci as well as trees based on concatenated datasets of these genes consistently recovered a cryptic lineage of individuals from the Hatchie River drainage that is morphologically indistinguishable from surrounding populations. Gene‐tree analyses failed to recover a monophyletic N. hildebrandi with respect to Noturus baileyi. A coalescence‐based species tree analysis, however, did recover N. hildebrandi monophyly with high support, suggesting that relationships reflected in individual gene trees and concatenated datasets are in part artefacts of incomplete lineage sorting or an ancient introgressive event. Results are consistent with the hypothesis of an ancient connection between the Hatchie and Tennessee River systems. Current subspecific designations are of limited utility as they reflect morphological variation and are not entirely consistent with phylogeny. Discrepancies between the pattern of variation observed in the morphological and molecular data may be explained by recent local adaptation to individual stream conditions that masks deeper evolutionary divergences.     

Morphological differences between the Teleosts Couesius plumbeus (Lake chub) and Rhinichthys cataractae (Longnose dace) and their hybrids from Alberta

Marked external and osteological differences exist between the related cyprinids Couesius plumbeus and Rhinichthys cataractae. C. plumbeus differs from R. cataractae in several external features, such as eye size and mouth shape, any one of which permits identification of individuals. C. plumbeus has postcleithral and nasal bones while R. cataractae does not. Many differences in bone shape also exist. Natural hybrids between the two species from Upper and Lower Kananaskis reservoirs, southwestern Alberta, are intermediate in the average of their external and osteological characters. Some characters in the hybrids, however, are so variable that they fall within the range of both parental species. An individual hybrid may resemble one parental species in one diagnostic character and the other parental species in another. The largest individuals known of the three forms from the Kananaskis system are hybrids.     

Disentangling the divergence and cladogenesis in the freshwater crab species (Potamonautidae: Potamonautes perlatus sensu lato) in the Cape Fold Mountains,South Africa,with the description of two novel cryptic lineages

River networks of major drainages can form barriers that shape the phylogeography of freshwater organisms, particularly those with low dispersal capabilities. Freshwater crab species' distributions can be used to examine hydrological patterns to expose historical drainage interconnectivity. We used molecular sequence data (mitochondrial and nuclear DNA) and divergence time estimations to determine the phylogeography of the freshwater crab, Potamonautes perlatus sensu lato, from six drainage systems along the Cape Fold Mountains, South Africa. Two major clades were detected: clade 1 comprised two geographically discrete haploclades occurring in southern flowing drainages, whereas clade 2 included specimens from western flowing drainages. Divergence time estimations suggested a Pleistocene (c. 2.61 Mya) divergence of P. perlatus s.l. The Pleistocene was associated with arid conditions and drainage contractions. However, it is likely that during the mesic conditions of the Pleistocene, P. perlatus s.l. migrated and diverged into contemporary patterns. We conclude that three lineages are nested within P. perlatus s.l., two representing novel species. Potamonautes perlatus sensu stricto is confined to western flowing drainages. The two novel species both occurring in southern flowing drainages are described here: P otamonautes barbarai sp. nov. occurs in the Gamtoos and Gourits Rivers and P otamonautes barnardi sp. nov. in the Breede River. © 2014 The Linnean Society of London     

Differences in morphological growth trajectories between greenside darter Etheostoma blennioides populations from two distinct drainages

The greenside darter Etheostoma blennioides is a small-bodied benthic stream fish that occurs in multiple drainages of the eastern USA. Previous studies have revealed some morphological differentiations among greensides from isolated drainage systems but growth relationships among functional morphological characteristics have not been examined within and between populations. Specifically, we tested for differences in functional morphology and allometric distinctions in morphological growth trajectories between greenside populations from two drainages, the Osage River and White River. Morphological differences between individuals of the two drainages included more dorso-ventrally compressed bodies, longer snouts and larger jaw features in White River darters. Furthermore, body depth, snout length and jaw width grow at significantly different trajectories in individuals of the two drainages. Individuals of the White River drainage (generally a higher gradient stream system) become comparatively more streamlined and develop proportionately larger feeding related traits during growth. These results suggest that individuals of both drainages share a similar morphology during early life but deviate during continued development and this may be partially due to environmentally induced plastic response. This study represents a novel approach for comparing morphological development among fish populations and presents environmental factors (e.g., stream gradient and elevation) that potentially influence functional characteristics.     

Evaluating the genetic status of a Great Basin endemic minnow: the relict dace (<Emphasis Type="Italic">Relictus solitarius</Emphasis>)

The relict dace (Relictus solitarius) is an endemic minnow restricted to isolated spring systems within Butte, Goshute, Ruby and Steptoe valleys in the eastern Nevada portion of the Great Basin. It is the only native fish in these basins, but speckled dace (Rhinichthys osculus) have been introduced into some localities in Ruby Valley and, based on morphology, the two species are believed to have hybridized in those areas. We used DNA sequence data from one mitochondrial gene (cytochrome b) and one nuclear intron (S7) to determine if putative relict dace populations in Ruby Valley share mtDNA haplotypes with speckled dace, or show signs of hybridization. Results of our analyses show that 11 of 16 Ruby Valley populations sampled contain only speckled dace, and one speckled dace population exhibited signs of limited introgressive hybridization. The remaining five Ruby Valley populations that were sampled contain relict dace that remain genetically distinct from speckled dace. The integrity of the Ruby Valley relict dace populations should be actively protected, particularly in the area surrounding Ruby Lake where speckled dace have been widely introduced.     

Cyprinid assemblages,and the physical and chemical characteristics of small northern Ontario lakes

Synopsis The cyprinid species, and physical and chemical characteristics were recorded from 58 small lakes in the Algoma district of northern Ontario. A group of typical stream-dwelling lithophilous species, which included common shiner, Notropis cornutus, creek chub, Semotilus atromaculatus, and blacknose dace, Rhinichthys atratulus, tended to occupy lakes of larger than average drainage areas. Phoxinus spp., pearl dace, Semotilus margarita, and fathead minnow, Pimephales promelas, occurred commonly in lakes with small drainage areas, and the average drainage area of lakes they occupied was near or below the overall average. Lakes without stream cyprinids were discriminated from lakes with them on a combination of chemical variables, including pH, alkalinity and calcium, which indicated that they were more susceptible to anthropogenic acidification.