Dace Populations Research Articles

Conservation Genetics of Clinch Dace Chrosomus sp. cf. saylori

Clinch Dace (Chrosomus sp. cf. saylori) is a newly recognized and yet-undescribed species of minnow with a restricted and fragmented distribution in the upper Tennessee River basin in southwestern Virginia, USA. We collected Clinch Dace from seven streams and observed variations at nine selectively neutral microsatellite DNA loci to infer population genetic processes and identify units for conservation management. Bayesian cluster analysis showed that three of the seven surveyed populations were genetically distinct, while the other four populations showed signs of recent admixture. Estimated effective population sizes and m-ratios were low within most populations, suggesting loss of alleles due to recent genetic drift. Positive FIS values, high average individual inbreeding coefficients, and high degrees of inferred relatedness among individuals suggested that inbreeding is taking place in some populations. FST values were high, and analysis of molecular variance indicated genetic divergence among populations. These indicators suggest that Clinch Dace populations are subject to the genetic processes that are characteristic of small and isolated populations.

Taxonomy of the Speckled Dace Species Complex (Cypriniformes: Leuciscidae, Rhinichthys) in California, USA

The Speckled Dace, Rhinichthys osculus (Girard), is a small species of fish (Cypriniformes, Leuciscidae) that has the widest geographic range of any freshwater dispersing fish in western North America. The dynamic geologic history of the region has produced many isolated watersheds with endemic fish species. However, Speckled Dace from these watersheds cannot be differentiated readily by morphometrics and meristics. This has led to the widely accepted hypothesis that the dace's adaptability and ability to cross geologic barriers has resulted in interbreeding among neighboring populations, maintaining the dace as a single species. We investigate this hypothesis by looking at Speckled Dace populations in California which are the result of at least three separate colonization events of isolated watersheds. We synthesize results from taxonomic, genetic, and zoogeographic studies in combination with the findings of a recent genomics study, to show that there are distinctive evolutionary lineages within the Speckled Dace complex. These lineages are used to designate multiple species and subspecies. We back up these designations by examining how well these lineages fit with the geologic history of the isolated basins they inhabit and with the presence of other endemic fishes. We conclude the following nine taxa can be recognized within the Speckled Dace complex in California.

Thermal tolerance of cyprinids along an urban-rural gradient: Plasticity, repeatability and effects of swimming and temperature shock.

Urbanization changes the thermal profile of streams in much the same way that climate change is predicted to with higher temperatures, more varied flow and rapid temperature pulses with precipitation events. Whether exceptional tolerance to these altered thermal conditions is a pre-requisite for a fish species to inhabit urban streams or if urbanization has changed the thermal physiology of those fish species that persist in urban streams is unknown, but could help predict the outcome of future climate disruption. To test whether residence in urban streams is associated with altered thermal tolerance, we compared thermal tolerance (CTMax) and phenotypic plasticity of thermal tolerance (ΔCTMax/Δ acclimation temperature) in five populations of an urban-tolerant cyprinid, the blacknose dace (Rhinichthys atratulus), from multiple watersheds along an urban/rural gradient. Thermal tolerance of these stream fish was tested while swimming at 10cm*s-1 but also in static water and after thermal shocks of 4°-6°C simulating precipitation events. To test whether blacknose dace as a species has unusual thermal tolerance or thermal plasticity, we also compared two blacknose dace populations with two co-resident, co-familiars (creek chub (Semotilus atromaculatus) and rosyside dace (Clinostomus funduloides), that don't persist in urban streams at three different acclimation temperatures. Thermal tolerance of blacknose dace, as measured by a critical thermal maximum test (CTMax), was independent of size and activity level, i.e. individuals had identical thermal tolerance whether swimming or resting and CTMax was significantly repeatable across two levels of activity. Although there was some variance among populations, blacknose dace from streams of varied urbanization generally exhibited comparable thermal tolerances, ability to acclimate to different temperatures and were unaffected by thermal shocks. Rosyside dace had significantly lower thermal tolerance than the other two species but plasticity of thermal tolerance was uniform across the three cyprinid species. Our conclusions are that exceptional thermal tolerance or ability to thermally acclimate are not pre-requisite characters for a given cyprinid species to survive in urban streams, nor has thermal tolerance undergone directional selection in this urban environment.

Are Road Crossings Fragmenting Populations of Clinch Dace?

Chrosomus sp. cf. saylori (Clinch Dace) is a newly recognized species of minnow with a restricted distribution in southwestern Virginia. We analyzed genetic variation and abundance at paired sites above and below road crossings. Road crossings did not have a strong effect on presence, abundance, or genetic differentiation of Clinch Dace. Of all sites where Clinch Dace were found, only 1 perched culvert presented a barrier to upstream migration; however, no genetic differentiation was found between collections above and below that or any other culvert. Distribution and abundance of Clinch Dace populations were not influenced by habitat variables measured at the site level. Low abundance in small headwaters, nest association, and high mobility appear to be characteristics of this species of Chrosomus.

Conservation genetics of redside dace (Clinostomus elongatus): phylogeography and contemporary spatial structure

Redside dace Clinostomus elongatus (Teleostei: Cyprinidae) is a species of conservation concern that is declining throughout its range as a result of habitat fragmentation, degradation and loss. We characterized the genetic structure and diversity of redside dace populations across the species range using mitochondrial and microsatellite data to inform conservation efforts and assess how historical and recent events have shaped genetic structure and diversity within and among populations. Phylogeographic structure among 28 redside dace populations throughout southern Ontario (Canada) and the United States was assessed by sequence analysis of the mitochondrial cytochrome b and ATPase 6 and 8 genes. Populations were also genotyped using ten microsatellite loci to examine genetic diversity within and among populations as well as contemporary spatial structuring. Mitochondrial DNA sequence data revealed three geographically distinct lineages, which were highly concordant with groupings identified by microsatellite analysis. The combined genetic data refute published glacial refugia hypotheses of a single Mississippian refugium or of two lineages associated with Mississippian and Atlantic refugia. Secondary contact between the two eastern groups was documented in the Allegheny River drainage and tributaries to Lake Ontario. With the exception of several allopatric populations within the Allegheny watershed, high genetic structuring among populations suggests their isolation, indicating that recovery efforts should be population-based.

Densities and Population Sizes of Clinch DaceChrosomussp. cf.sayloriin the Upper Clinch River Basin in Virginia

Estimates of abundance and density for the imperiled Clinch Dace (Chrosomus sp. cf. saylori) are needed across its range to indicate where populations exist and estimate their long-term viability. We generated estimates of population extent, measured in km of potentially occupied habitat, based on 206 site visits from four fish surveys since 1999 within the Clinch Dace's putative range. Next, we used mark–recapture surveys to estimate Clinch Dace densities in five occupied streams. A linear regression model generated from these data was used to transform single-pass count data into estimated abundance with 90% prediction intervals (PI) for Clinch Dace in sampled reaches. We combined estimates of individual population sizes to estimate global abundance. Finally, we examined the correlation between habitat variables and Clinch Dace abundance in occupied streams. Clinch Dace populations at low densities potentially occupy 31.5 km of the approximately 351 km of 2nd- and 3rd-order streams in northern Russell a...

Pluvial Drainage Patterns and Holocene Desiccation Influenced the Genetic Architecture of Relict Dace, Relictus solitarius (Teleostei: Cyprinidae).

Changing drainage patterns have played a significant role in the evolution of western North American aquatic taxa. Relict dace, Relictus solitarius, is a Great Basin endemic cyprinid with a native range that is restricted to four valleys in eastern Nevada. Relictus solitarius now occupies spring systems that are the remnants of Pleistocene-era pluvial lakes, although it may have occurred in the area for much longer. Here we use mitochondrial DNA sequence data to assess range-wide genetic diversity of R. solitarius, and to estimate divergence times to determine whether pluvial drainages played an important role in shaping intraspecific genetic diversity. Genetic diversification within R. solitarius began during the early to mid-Pleistocene, separating populations within two sets of valleys (Butte/Ruby and Goshute/Steptoe). Additional diversification in each of the two sets of valleys occurred more recently, in the mid- to late-Pleistocene. Holocene desiccation has further isolated populations, and each population sampled contains unique mtDNA haplotypes. Pluvial drainage patterns did contribute to the genetic structure observed within R. solitarius, but most of the intraspecific diversification does not appear to be associated with the Last Glacial Maximum. Holocene desiccation has also contributed to the observed genetic structure. The relict dace populations we sampled are all unique, and we recommend that future management efforts should strive to preserve as much of the genetic diversity as possible.

Repeatability and phenotypic plasticity of fish swimming performance across a gradient of urbanization

How phenotypic plasticity of locomotor performance varies among populations in nature is poorly known. Swimming ability of blacknose dace (Rhinichthys atratulus) from eight different watersheds had previously been shown to depend upon watershed impervious surface cover (ISC) and stream base-flow. Keeping these populations of stream fish under low flow conditions produced changes in locomotor capacity suggestive of phenotypic plasticity varying among the populations. The present experiments were conducted to better understand the plasticity of swimming performance in dace and how urbanization affects dace biology. Two experimental approaches were used: 1) laboratory training of dace populations at two levels of flow for 6 weeks; and, 2) exploring in situ training by capturing fish from relatively fast and slow reaches of three different streams and comparing their swimming abilities at three different scales. Individual sprint and endurance (modified Ucrit) swimming were significantly repeatable across a laboratory training regimen; sprint performance had previously been shown to not be repeatable when dace were held in static water. Both of our approaches suggested that sprint and endurance swimming ability significantly respond to changes in environmental flow. Although there was no evidence for a different magnitude of phenotypic plasticity among populations, urban populations that experience more stochastic flow regimes had more consistent plasticity. Phenotypic plasticity of locomotor performance in response to variable flow appears to be an important characteristic of blacknose dace biology, yet we did not uncover sufficient evidence to suggest that it is under selection in fish adjusting to urban stream habitats.

An Ecohydraulic Model to Identify and Monitor Moapa Dace Habitat

Moapa dace (Moapa coriacea) is a critically endangered thermophilic minnow native to the Muddy River ecosystem in southeastern Nevada, USA. Restricted to temperatures between 26.0 and 32.0°C, these fish are constrained to the upper two km of the Muddy River and several small tributaries fed by warm springs. Habitat alterations, nonnative species invasion, and water withdrawals during the 20th century resulted in a drastic decline in the dace population and in 1979 the Moapa Valley National Wildlife Refuge (Refuge) was created to protect them. The goal of our study was to determine the potential effects of reduced surface flows that might result from groundwater pumping or water diversions on Moapa dace habitat inside the Refuge. We accomplished our goal in several steps. First, we conducted snorkel surveys to determine the locations of Moapa dace on three warm-spring tributaries of the Muddy River. Second, we conducted hydraulic simulations over a range of flows with a two-dimensional hydrodynamic model. Third, we developed a set of Moapa dace habitat models with logistic regression and a geographic information system. Fourth, we estimated Moapa dace habitat over a range of flows (plus or minus 30% of base flow). Our spatially explicit habitat models achieved classification accuracies between 85% and 91%, depending on the snorkel survey and creek. Water depth was the most significant covariate in our models, followed by substrate, Froude number, velocity, and water temperature. Hydraulic simulations showed 2–11% gains in dace habitat when flows were increased by 30%, and 8–32% losses when flows were reduced by 30%. To ensure the health and survival of Moapa dace and the Muddy River ecosystem, groundwater and surface-water withdrawals and diversions need to be carefully monitored, while fully implementing a proactive conservation strategy.

Changes in Fish Community Structure and Effects on Blackside Dace (Chrosomus cumberlandensis) Populations Following Beaver Colonization in Davis Branch, Cumberland Gap National Historical Park, Bell County, Kentucky

Davis Branch in Cumberland Gap National Historical Park was considered important for the recovery of the Federally threatened Chrosomus cumberlandensis (Blackside Dace). Monitoring of the Davis Branch population began in 1990. Castor canadensis (North American Beaver) colonization was reported in 1994, and a series of dams have persisted in the upper section of the stream. The pervasive effects of Beavers on Blackside Dace populations were unknown. Our goals were: 1) to characterize the fish community structure and relative abundance of Blackside Dace within the assemblage, 2) to determine the direct and indirect effects of beaver dams on the fish community, and Blackside Dace population, 3) to monitor the age structure of the Blackside Dace population, and 4) to recommend management actions that will enhance the Blackside Dace population within Davis Branch. Fishes were collected from eight stations annually from 1990–2010, except for 2003–2005. Stations were delineated within downstream and upstream sections based on Beaver presence, and within three periods, prior (1990–1993), post (1994–2002), and recent (2006–2010). Fish community structure indicated distinct downstream and upstream assemblages prior to Beaver colonization, with the relative abundance of Blackside Dace approximately 6% and 18%, respectively. The fish assemblage and relative abundance of Blackside Dace shifted over time, with the relative abundance of Lepomis gulosus (Warmouth), Lepomis auritus (Redbreast Sunfish), and Chrosomus erythrogaster (Southern Redbelly Dace) increasing, and Blackside Dace decreasing; only 25 Blackside Dace were encountered from 2006–2010. Comparison of Blackside Dace age classes between the 3 periods indicated the 0 age class decreased over time and 1 and 2 age classes increased initially but eventually declined within both the downstream and upstream sections. It is speculated that the continued presence of beaver dams increased stream temperatures downstream and upstream, altered the flow regime, and changed the available habitat, thus creating conditions more suitable for centrarchid species and Southern Redbelly Dace, which probably preyed upon and out-competed Blackside Dace, respectively. It is recommended that the National Park Service and its partners 1) develop a Beaver management program, 2) return Davis Branch to its free-flowing, pre-Beaver condition, 3) significantly decrease nonnative species and decrease native centrarchid species to abundances prior to Beaver colonization, and 4) establish a Davis Branch Blackside Dace propagation and reintroduction program.

Histopathological Analysis of Fish from Acorn Fork Creek, Kentucky, Exposed to Hydraulic Fracturing Fluid Releases

Fracking fluids were released into Acorn Fork, KY, a designated Outstanding State Resource Water, and habitat for the threatened Chrosomus cumberlandensis (Blackside Dace). As a result, stream pH dropped to 5.6 and stream conductivity increased to 35,000 µS/cm, and aquatic invertebrates and fish were killed or distressed. The objective of this study was to describe post-fracking water quality in Acorn Fork and evaluate if the changes in water quality could have extirpated Blackside Dace populations. Semotilus atromaculatus (Creek Chub) and Lepomis cyanellus (Green Sunfish) were collected from Acorn Fork a month after fracking in lieu of unavailable Blackside Dace. Tissues were histologically analyzed for indicators of stress and percent of fish with lesions. Fish exposed to affected Acorn Fork waters showed general signs of stress and had a higher incidence of gill lesions than unexposed reference fish. Gill lesions observed were consistent with exposure to low pH and toxic concentrations of heavy metals. Gill uptake of aluminum and iron was demonstrated at sites with correspondingly high concentrations of these metals. The abrupt and persistent changes in post-fracking water quality resulted in toxic conditions that could have been deleterious to Blackside Dace health and survival.

Evaluating the genetic status of a Great Basin endemic minnow: the relict dace (Relictus solitarius)

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.

Estimating local and regional population sizes for an endangered minnow, redside dace (Clinostomus elongatus), in Canada

ABSTRACTThe Laurentian Great Lakes have undergone drastic declines in freshwater fishes, with 22 species having become extinct in the past century and many more currently at risk. One such species is the endangered minnow, the redside dace (Clinostomus elongatus), which is undergoing severe declines across its entire range.Depletion and mark–recapture surveys were used to quantify population estimates of redside dace at several spatial scales (pool, reach and catchment) across several Great Lakes tributaries in Canada.There was large variation in the local population estimates and the rate of occurrence of redside dace populations. In some cases, such as Gully Creek, a Lake Huron tributary, redside dace were widespread (9/10 of pools) but in low abundances (13.5 individuals per pool ± 5.09 ). In other cases, such as in the Don River, redside dace were highly localized (2/27 pools) but in relatively high abundance (99.2 individuals/pool ± 18.1).Extrapolated population estimates at the catchment scale showed that three of the five study populations were below conservative estimates needed for long‐term population viability.Differences in redside dace populations were driven by adjacent land‐use. Post‐hoc analyses revealed strong negative associations between population estimates and impervious land‐use (i.e. urbanization) at both the pool and sub‐catchment level.Immediate recovery actions that will focus on eliminating chronic and episodic impacts of adjacent land‐use and improve connectivity are needed to help ensure redside dace, like many freshwater species in the Laurentian Great Lakes, remain a species at risk of – rather than facing – extinction.Copyright © 2012 John Wiley & Sons, Ltd.

The Functional Gene Diversity in Natural Populations over Postglacial Areas: The Shaping Mechanisms Behind Genetic Composition of Longnose Dace (Rhinichthys cataractae) in Northeastern North America

The diversity of functional genes and the related processes are important issues for conservation biology. This is especially relevant for populations that have suffered from demographic reduction as a consequence of the processes of postglacial colonization. In this perspective, the aims of the present study are (1) to quantify the genetic diversity of functional genes and (2) to disentangle the long- and short-term effects of natural selection that shapes genetic diversity from those of drift, mutation, and allopatric fragmentation. This research was conducted using an extensive genetic polymorphism analysis of populations of longnose dace (Rhinichthys cataractae) living over an area once covered by Pleistocene glaciations. The sequence and diversity of one exon of three genes (MHC IIβ, growth hormone, and trypsin) were jointly analyzed with non-coding nuclear loci from 27 populations; these populations were sampled over four major basins of northeastern North America. The survey revealed a surprisingly low allelic richness, especially for the MHC gene, considering the number of individuals and populations sampled. The results suggest that there is a complex mixture of different evolutionary processes shaping the level of polymorphism among longnose dace. While our study underlines the importance of the short-term effects of neutral processes and the major impact of post-glacial colonization on gene diversity, locally dependent balancing selection was detected on MHC. From this perspective, our results support an understanding of the importance of drift on functional gene diversity but also highlight the transient effects of natural selection on allelic composition, even in populations that show drastic reduction of genetic diversity.

Presence of natural and anthropogenic organic contaminants and potential fish health impacts along two river gradients in Alberta, Canada

In the current study, 28 organic contaminants were measured, many with estrogen-like activity, in water collected from 16 sites on two rivers in the South Saskatchewan River Basin, Alberta, Canada. The compounds detected included synthetic estrogens (birth control pill compounds and hormone therapy drugs) downstream of municipal wastewater effluents and natural hormones downstream of municipal wastewater effluents and in agricultural areas. Greater concentrations of cholesterol and derivatives, phytosterols, and fecal sterols were measured at the most downstream sites, which indicates cumulative inputs of such compounds in these rivers. A native minnow (longnose dace, Rhinichthys cataractae) was sampled to assess pathophysiological responses to exposure to compounds with estrogen-like activity. Hepatic vitellogenin protein was detected in at least one adult male longnose dace from 14 of 15 sites sampled for fish. Vitellogenin was negatively correlated with hepatosomatic (r = -0.47, p < 0.001) and gonadosomatic (r = -0.44, p < 0.003) indices, which suggests potential health impacts in male longnose dace in the South Saskatchewan River Basin. The current study demonstrates that organic contaminants, many with estrogen-like activity, are distributed over hundreds of kilometers throughout the South Saskatchewan River Basin and not just downstream of major point-sources. Therefore, many activities within these basins impact water quality in the South Saskatchewan River Basin and affect endemic longnose dace populations.

Evidence for host variation in parasite tolerance in a wild fish population

Hosts can protect themselves against parasites by actively reducing parasites burden (i.e. resistance) or by limiting the damages caused by parasites (i.e. tolerance). Disentangling between tolerance and resistance is important for predicting the evolutionary outcomes of host-parasite interaction. Dace (Leuciscus leuciscus) are often parasitized by the ectoparasite Tracheliastes polycolpus which feeds on (and destroys) fins, reducing thus the host’s condition. We tested the hypothesis that genetically-based variation in ectoparasite tolerance exists in a wild dace population. We found that moderately heterozygous dace, which are less resistant than highly heterozygous or homozygous dace, tolerated better the effect imposed by T. polycolpus for a given parasite burden. However, tolerance also varied upon environmental conditions, suggesting that genetic and environmentally-based variation exists for both resistance and tolerance in this natural host-parasite system. Moreover, a negative genetic correlation may exist between tolerance and resistance, and hence several evolutionary outcomes are possible in this interacting system.

Basin‐wide impacts of compounds with estrogen‐like activity on longnose dace (Rhinichthys cataractae) in two prairie rivers of Alberta, Canada

Environmental compounds with estrogen- or antiestrogen-like activity can enter rivers from multiple sources, including municipal wastewater and agricultural runoff. We used longnose dace (Rhinichthys cataractae) to investigate exposure to compounds with estrogen-like activity, which we measured in water at multiple sites in the Oldman and Bow rivers (AB, Canada). We evaluated changes in vitellogenin mRNA with quantitative reverse transcription-polymerase chain reaction, then compared vitellogenin levels to sex ratios and fish performance indices to assess how exposure to compounds with estrogen-like activity affects longnose dace populations. Vitellogenin levels were elevated at least 59 to 110 km downstream of municipalities. In the Oldman River, increased vitellogenin expression and female-biased sex ratios suggest severe endocrine disruption, likely resulting from the combined impacts of municipal wastewater, agriculture, and large cattle operations within the basin. In the Bow River, municipal wastewater may be the major source of compounds with estrogen-like activity that affect longnose dace. The sex ratios were not heavily skewed, as in the more agriculturally influenced Oldman River. We detected organic contaminants in river samples at every site, but the highest concentrations were found downstream of municipalities and in areas with intense agriculture. Vitellogenin levels and sex ratios of longnose dace suggest basin-wide exposure to compounds with estrogen-like activity. Our results demonstrate that it is important to assess rivers at large spatial scales to detect fully the impacts of municipal wastewater and agriculture on fish populations.

Changes in Population, Growth, and Physiological Indices of Longnose Dace (Rhinichthys cataractae) in the Red Deer River, Alberta, Canada

The Red Deer River, Alberta, Canada is a prairie river that is impacted by the point-source input of Red Deer's municipal wastewater effluent and non-point- source agricultural runoff. We used population, growth, and physiological performance end points in longnose dace (Rhinichthys cataractae), an endemic and abundant minnow, to evaluate changes in fish health over a 220 km section of the Red Deer River. Longnose dace immediately downstream of Red Deer had elevated catch per unit effort with larger body and liver sizes compared to upstream of Red Deer sites, likely due to elevated riverine productivity from Red Deer's wastewater effluent. Longnose dace immediately downstream of Red Deer showed depressed testosterone production capacity and elevated ethoxyresorufin-O-deethylase (EROD) activity, which is consistent with exposure to endocrine-disrupting compounds and aromatic hydrocarbons, respectively. Longnose dace 150-180 km downstream of Red Deer had reduced liver and gonad sizes, elevated EROD, and increased 11-ketotestosterone production capacity compared to upstream of Red Deer sites, possibly related to a non-point-source agricultural influence on water quality. Longnose dace populations at the most downstream sites were missing the oldest age classes and might reach sexual maturity faster than at upstream sites, which is consistent with a younger age structure. Our results highlight the importance of assessing multiple performance end points to reveal physiological or reproductive effects in natural fish populations. We have demonstrated how longnose dace populations change over a river impacted by municipal wastewater and agricultural runoff; further studies are required to determine if these changes will influence the long-term viability of longnose dace in the Red Deer River.

Environmental Correlates, Plasticity, and Repeatability of Differences in Performance among Blacknose Dace (Rhinichthys atratulus) Populations across a Gradient of Urbanization

Urbanization alters stream and watershed hydrology so that fish from urban stream systems are confronted with extreme flows during storms and runoff events. To test whether residence in urban streams is associated with altered swimming ability, we compared sprint and endurance swimming performances of eight populations of blacknose dace (Rhinichthys atratulus) from different watersheds along an urban/rural gradient. Watershed impervious surface cover, a measure of urbanization, was significantly correlated with sprint performance in dace from all stream types and endurance swimming performance (U(crit)) when only fish from urban streams were analyzed. Three estimators of water flow in a stream system, watershed area, mean annual discharge, and base-flow current speed, were all related to U(crit) in fish from nonurban streams. The U(crit) was significantly repeatable after 6 mo in the laboratory, but dace populations with exceptional U(crit) values lost ability under no-flow, "detraining" conditions. Sprint performance changed substantially in individual dace after 10 wk under no-flow conditions and was a significant function of the animal's original performance. Animals with high sprint performance tended to lose ability, whereas those with poor performance gained ability. Interpopulation differences in both sprint and endurance swimming were robust over multiple years of collection from the same sites.

The impact of postglacial marine invasions on the genetic diversity of an obligate freshwater fish, the longnose dace (Rhinichthys cataractae), on the Quebec peninsula

Postglacial seas are expected to have had significant effects on the genetic structure of populations of obligate freshwater fishes. To assess this influence, mitochondrial DNA variability was evaluated in 32 populations of longnose dace (Rhinichthys cataractae) of the Quebec peninsula located within and outside of the maximum extent of marine invasions of the Champlain and Laflamme seas. Three clades of haplotypes diverging from one to two mutations were defined. Despite this low divergence, a clear and significant spatial genetic structure was observed outside of the extent of marine invasions. However, a higher genetic diversity was observed in populations located within the extent of marine invasions because of the admixture of these clades with an additional lineage restricted almost exclusively to those areas. The low genetic divergence between the main haplotypes suggests a single origin, despite the known presence of this species in various refuges. Marine invasions preventing entry to the peninsula, especially from Atlantic refuge, are proposed as a possible explanation to this particular result. This study is a relevant argument for integrating postglacial marine invasions into postglacial colonization models of freshwater species in the northeastern part of North America.