Microsatellite DNA markers for the rainbow darter,Etheostoma caeruleum (Percidae), and their potential utility for other darter species

The rainbow darter Etheostoma caeruleum is a small fish in the perch family (Percidae) that is adapted to fast‐flowing streams in eastern North America. It is relatively sensitive to habitat degradation and is widely used as a sentinel of stream condition. To provide a complementary tool for assessing the integrity of stream ecosystems, 16 highly polymorphic tetranucleotide microsatellite markers were identified for these darters. Between four and 16 loci were found to be useful in five congeneric species. These markers will be useful for characterizing population genetic structure and diversity of rainbow darters and related fishes.     

Creation and maintenance of habitat downstream from a weir for the greenside darter, Etheostoma blennioides – a rare fish in Canada

The biology, microhabitat use and migratory behaviour of the greenside darter, Etheostoma blennioides, was studied at the Mannheim Weir on the Grand River, Ontario during the summer of 1995 and 1996. Officially listed as vulnerable in Canada, greenside darters reached maturity at age 1 and lived up to 4 years. They were found in riffle habitats that consisted of cobble and loose boulders, with large mats of Cladophora. This type of unembedded substrate is uncommon in the Grand River watershed. However, local abundance of greenside darters immediately downstream from the Mannheim Weir was likely due to high water velocities from weir discharge, freshets and ice scour which help maintain unembedded riffle areas. Trap data indicated that greenside darters temporally partition this habitat with the stonecat, Noturus flavus. Other darter species were not commonly found in areas with greenside darters, whose depth selection and habitat choices were influenced by predators and morphology. Denil fishways at the Mannheim Weir rarely passed greenside darters due to prohibitively high water velocities and exclusion by larger fish. This revised version was published online in August 2006 with corrections to the Cover Date.     

Modelling patterns of coexistence of three congeneric headwater fishes

1. Mechanisms driving patterns of occurrence and co-occurrence among North American freshwater fishes are poorly understood. In particular, the influence of biotic interactions on coexistence among stream reaches and their effects on regional species distribution patterns is not well understood for congeneric headwater fishes.
2. Occupancy models provide a useful framework for examining patterns of co-occurrence while also accounting for imperfect detection. Occupancy models may be extended to test for evidence that a dominant species influences the occurrence of a subordinate species and thus evaluate support for the hypothesis that species interactions drive patterns of coexistence.
3. We examined patterns of occurrence and co-occurrence at the stream-reach scale among three species of darters (Percidae: Etheostomatinae) that occupy headwater streams within a Gulf Coastal Plain drainage in the south-eastern U.S.A. We assessed species occurrences at 97 sites in first- to third-order streams on one occasion each and used data from four sub-reaches sampled with equal effort at each site to estimate species-specific detection probabilities. Following sampling, a suite of habitat variables was collected at three equidistant points along each of the three transects established within a sub-reach. Coarse (stream-segment, catchment, network) scale variables were also incorporated using geospatial data. Single-species and two-species occupancy models were used to examine patterns of occupancy and coexistence.
4. The occupancy of each species was influenced by distinct habitat variables. Goldstripe darters (Etheostoma parvipinne) were constrained by a stream size gradient, groundwater input appeared to influence the occurrence of Yazoo darters (Etheostoma raneyi), and local habitat heterogeneity (e.g. variation in depth and current velocity) appeared to influence the occupancy of redspot darters (Etheostoma artesiae).
5. We found no evidence that the presence of one species influenced the occurrence of another within a stream-reach based on two-species occupancy models. Rather, species co-occurrences were best explained as independent occurrences within a stream-reach according to species-specific habitat associations.
6. Occupancy modelling may provide a suitable framework for evaluating the influence of biotic interactions among congeneric stream fishes along species-specific habitat gradients at the stream reach scale. Our study offers insight into how habitat variation can influence coexistence of potential competitors across a large river system.

     

Habitat Use of Fish Communities in A Virginia Stream System

Fish habitat use during summer was examined at micro- and meso-levels, to determine species associations in the upper Roanoke River watershed, Virginia. Based on multivariate-mesohabitat analysis and examination of mean microhabitat use, seven habitat-use guilds were apparent. These included four rheophilic (fast-riffle, riffle/run, fast-generalist, and shallow-rheophilic) and three limnophilic guilds (pool/run, open-pool, and pool-cover) that were reasonably robust across two river segments and two years. Although simple-hydraulic, bottom-topographic, and turbulence variables all segregated fish habitat-use guilds, turbulence variables were redundant with simple-hydraulic variables, substratum use by limnophilic fishes was related to availability, and only one guild consistently selected high cover levels. At the family level, suckers, darters, and especially minnows were notable for occupying several habitat-use guilds, because of species differences in habitat preferences. Such formulation of guilds can simplify habitat-impact analyses in biodiverse, warmwater streams, via focus on habitat needs of guilds rather than on individual species.     

Comparative Microhabitat Use of Ecologically Similar Benthic Fishes

Although benthic insectivorous fishes such as darters and sculpins represent a significant component of riffle communities, few studies have compared the habitat use of these non-related but ecologically similar fishes. The objectives of this study were to examine the habitat use of Etheostoma olmstedi (tessellated darter) compared to Cottus bairdi (mottled sculpin) in Nescopeck Creek and Cottus cognatus (slimy sculpin) in Jack's Creek, Pennsylvania through underwater observation. Etheostoma olmstedi occupied habitats with significantly deeper waters than those available, whereas adult and young of the year Cottus occupied habitats with significantly faster water velocities than those available. Canonical discriminant analysis revealed microhabitat partitioning between E. olmstedi and each Cottus species. Cottus bairdi and C. cognatus occupied significantly shallower habitats with faster water velocities than E. olmstedi. Sculpin species were observed most frequently under substrate whereas E. olmstedi occurred most frequently on the top surface of the substrate. Hurlbert's standardized niche breadth values indicated that C. bairdi and C. cognatus were habitat specialists with regard to water velocity measures, but exhibited generalistic patterns of depth and substrate size use. Etheostoma olmstedi was a habitat specialist with respect to depth, but exhibited generalistic patterns of resource use for substrate size. Differential habitat use by these benthic fishes is consistent with the hypothesis that resource partitioning facilitates species coexistence among stream fishes.     

Indirect food web interactions increase growth of an algivorous stream fish

1. We tested the hypothesis that indirect food web interactions between some common, invertivorous fishes and their prey would positively affect growth of an algivorous fish species. Specifically, we predicted that orangethroat darter (Etheostoma spectabile) would increase periphyton biomass via a top‐down pathway, indirectly enhancing growth of the algivorous central stoneroller minnow (Campostoma anomalum). Moreover, we predicted that sand shiner (Notropis stramineus) would increase periphyton biomass via a bottom‐up pathway and indirectly enhance growth of the stoneroller minnow. 2. In an 83‐day experiment in large, outdoor, stream mesocosms, we stocked two fish species per mesocosm (stoneroller and either darter or shiner), estimated the effects of the invertivorous and grazing fishes on periphyton biomass and estimated growth of the algivorous fish. 3. The darter consumed grazing invertebrates, indirectly increasing periphyton biomass. The shiner consumed terrestrial insects as predicted, but it did not affect periphyton biomass. 4. In support of our hypothesis, the darter indirectly enhanced stoneroller growth. As predicted, stonerollers consumed the increased periphyton in streams with darters, resulting in greater growth, condition and gut fullness compared to streams without darters. No indirect interaction was observed between stonerollers and shiners. 5. Our study suggests that some invertivorous fish species can positively affect growth of algivorous fishes through indirect food web interactions. Thus, in stream communities, it is possible that the loss of a single, invertivorous fish taxon could have negative consequences on algivorous fish populations via the removal of positive indirect food web interactions.     

Population genetic structure and conservation genetics of threatened Okaloosa darters (Etheostoma okaloosae)

Imperiled Okaloosa darters (Etheostoma okaloosae) are small, benthic fish limited to six streams that flow into three bayous of Choctawhatchee Bay in northwest Florida, USA. We analyzed the complete mitochondrial cytochrome b gene and 10 nuclear microsatellite loci for 255 and 273 Okaloosa darters, respectively. Bayesian clustering analyses and AMOVA reflect congruent population genetic structure in both mitochondrial and microsatellite DNA. This structure reveals historical isolation of Okaloosa darter streams nested within bayous. Most of the six streams appear to have exchanged migrants though they remain genetically distinct. The U.S. Fish and Wildlife Service recently reclassified Okaloosa darters from endangered to threatened status. Our genetic data support the reclassification of Okaloosa darter Evolutionary Significant Units (ESUs) in the larger Tom??s, Turkey, and Rocky creeks from endangered to threatened status. However, the three smaller drainages (Mill, Swift, and Turkey Bolton creeks) remain at risk due to their small population sizes and anthropogenic pressures on remaining habitat. Natural resource managers now have the evolutionary information to guide recovery actions within and among drainages throughout the range of the Okaloosa darter.     

Patterns of change over time in darter (Teleostei: Percidae) assemblages of the Arkansas River basin,northeastern Oklahoma,USA

Rivers and streams are among the most threatened ecosystems worldwide, and their fish assemblages have been modified by anthropogenic habitat alteration and introductions of non‐native species. Consequently, two frequently observed patterns of assemblage change over time are species loss and biotic homogenization. In the present study, we compared contemporary (2006–2007) and historical (1948–1955) assemblages of darters, a group of small benthic fishes of the family Percidae, in the Arkansas River drainage of northeastern Oklahoma, USA. Results showed species loss between the two sampling periods, with historical estimates of overall species diversity across the study area exceeding contemporary estimates by five to eight species. Assemblages showed a low degree of darter similarity based on species presence and absence, with pairwise site comparisons (Jaccard's similarity index) between historical and contemporary samples averaging < 0.35. No significant homogenization or differentiation of assemblages occurred. Range expansion of widespread species, one of the primary mechanisms of biotic homogenization, was not observed; rather, all species occurred at a smaller proportion of sites in contemporary samples. Our results highlight the threat posed by anthropogenic habitat alteration to taxonomic groups such as darters, most of which are habitat specialists. However, our results suggest that biotic homogenization is unlikely to occur in the absence of immigration, especially if assemblages are subjected to ‘novel disturbances’ such as dam construction and watershed‐scale habitat degradation which negatively affect all components of the assemblage.     

Ecological constraint and the evolution of sexual dichromatism in darters

It is not known how environmental pressures and sexual selection interact to influence the evolution of extravagant male traits. Sexual and natural selection are often viewed as antagonistic forces shaping the evolution of visual signals, where conspicuousness is favored by sexual selection and crypsis is favored by natural selection. Although typically investigated independently, the interaction between natural and sexual selection remains poorly understood. Here, we investigate whether sexual dichromatism evolves stochastically, independent from, or in concert with habitat use in darters, a species‐rich lineage of North American freshwater fish. We find the evolution of sexual dichromatism is coupled to habitat use in darter species. Comparative analyses reveal that mid‐water darter lineages exhibit a narrow distribution of dichromatism trait space surrounding a low optimum, suggesting a constraint imposed on the evolution of dichromatism, potentially through predator‐mediated selection. Alternatively, the transition to benthic habitats coincides with greater variability in the levels of dichromatism that surround a higher optimum, likely due to relaxation of the predator‐mediated selection and heterogeneous microhabitat dependent selection regimes. These results suggest a complex interaction of sexual selection with potentially two mechanisms of natural selection, predation and sensory drive, that influence the evolution of diverse male nuptial coloration in darters.     

Niche partitioning and the effect of interspecific competition on microhabitat use by two sympatric galaxiid stream fishes

1. Numerous interacting abiotic and biotic factors influence niche use and assemblage structure of freshwater fishes, but the strength of each factor changes with spatial scale. Few studies have examined the role of interspecific competition in structuring stream fish assemblages across spatial scales. We used field and laboratory approaches to examine microhabitat partitioning and the effect of interspecific competition on microhabitat use in two sympatric stream fishes (Galaxias‘southern’ and Galaxias gollumoides) at large (among streams and among sites within streams) and small (within artificial stream channels) spatial scales. 2. Diurnal microhabitat partitioning and interspecific competition at large spatial scales were analysed among three sympatry streams (streams with allotopic and syntopic sites; three separate catchments) and four allopatry streams (streams with only allotopic sites; two separate catchments). Electro‐fishing was used to sample habitat use of fishes at 30 random points within each site by quantifying four variables for each individual: water velocity, depth, distance to nearest cover and substratum size. Habitat availability was then quantified for each site by measuring those variables at each of 50 random points. Diet and stable isotope partitioning was analysed from syntopic sites only. Diel cycles of microhabitat use and interspecific competition at small spatial scales were examined by monitoring water velocity use over 48 h in artificial stream channels for three treatments: (i) allopatric G. ‘southern’ (10 G. ‘southern’); (ii) allopatric G. gollumoides (10 G. gollumoides) and (iii) sympatry (five individuals of each species). 3. One hundred and ninety‐four G. ‘southern’ and 239 G. gollumoides were sampled across all seven streams, and habitat availability between the two species was similar among all sites. Galaxias‘southern’ utilised faster water velocities than G. gollumoides in both the field and in channel experiments. Both species utilised faster water velocities in channels at night than during the day. Diet differences were observed and were supported by isotopic differences (two of three sites). No interspecific differences were observed for the other three microhabitat variables in the field, and multivariate habitat selection did not differ between species. Interspecific competition had no effect on microhabitat use of either species against any variable either in the field (large scale) or in channels (small scale). 4. The results suggest that niche partitioning occurs along a subset of microhabitat variables (water velocity use and diet). Interspecific competition does not appear to be a major biotic factor controlling microhabitat use by these sympatric taxa at any spatial scale. The results further suggest that stream fish assemblages are not primarily structured by biotic factors, reinforcing other studies de‐emphasising interspecific competition.     

Reproductive Behavior, Captive Breeding, and Restoration Ecology of Endangered Fishes

Species recovery efforts generally focus on in situ actions such as habitat protection. However, captive breeding can also provide critical life history information, as well as helping supplement existing or restoring extirpated populations. We have successfully propagated nine species in captivity, including blackside dace, spotfin chubs, bloodfin darters, and boulder darters. Threatened blackside dace, Phoxinus cumberlandensis, were induced to spawn in laboratory aquaria by exposing them to milt from a reproductively mature male stoneroller, Campostoma anomalum or river chub, Nocomis micropogon. The latter are nest-building minnows, with which Phoxinus may spawn in nature. Eggs are broadcast among gravel and pebbles. Blackside dace individuals reared in captivity were used for translocation. Threatened spotfin chubs, Cyprinella monacha, fractional crevice spawners, deposited eggs in laboratory aquaria in the spaces created between stacks of ceramic tiles. Captively produced spotfin chubs were used as part of a larger stream restoration and fish reintroduction project in the Great Smoky Mountains National Park. The bloodfin darter, Etheostoma sanguifluum, was first used as a surrogate to develop techniques for spawning a closely related species, the endangered boulder darter, E. wapiti. Both darter species mated in a wedge created between two ceramic tiles. Our efforts have had variable but generally high success, with survival rates of 50–90% of eggs deposited. Captive production of nongame fishes can aid recovery of rare species or populations, aid in watershed restoration, and can help to refine water quality standards. In addition, captive breeding allows discovery of important behavioral or life history characteristics that may constrain reproduction of rare species in altered natural habitats.     

Patterns of shield darter, <Emphasis Type="Italic">Percina peltata</Emphasis>, distribution in the Eastern Piedmont of Maryland,USA

Detailed analyses of habitat associations with rare species are typically constrained by limited sample size and the availability of habitat data. The dense spatial coverage of stream sampling by the Maryland Biological Stream Survey provides ample data to quantitatively examine correlations between habitat and rare species distributions. The shield darter, Percina peltata, has a widespread distribution on the Atlantic Slope of the United States, but is uncommon throughout its range in Maryland. Associations of in situ physical habitat, water chemistry, and alterations in landscape with shield darter presence in the Eastern Piedmont physiographic province in Maryland were examined. Shield darter occurrence was associated with larger sized streams in concordance with the species’ known ecology. Shield darter distribution was further associated with stream segments with deep riffle habitats with diverse velocities, low concentrations of chloride and sulfate, low levels of urbanization in upstream catchments, and several pollution intolerant fish species. Although the exact mechanism of the effects is not clear, results indicate that the shield darter is sensitive to urban development and habitat and water quality alteration that typically accompanies urbanization. Shield darter conservation in Maryland necessitates the protection and restoration of minimally urbanized watersheds where they are known to occur. The results from this study indicate that habitat information on rare species may be important in elucidating important habitat associations that are not evident via examination of community level data.     

Selective predation by four darter (Percidae) species on larval chironomids (Diptera) from a Mississippi stream

We determined seasonal foraging modes of four sympatric darter species, Etheostoma lynceum, E. stigmaeum, E. swaini and Percina nigrofasciata, from Beaverdam Creek, Mississippi (USA) at two scales of taxonomic resolution: (1) chironomid prey identified to family and (2) chironomid prey identified to genus/species. When chironomids were identified to family, high proportional similarity (PS) and low niche breadth (NB) values suggested the darters fed opportunistically on a relatively small number of available prey taxa. In contrast, when chironomids were identified to genus/species, concordant low PS and NB values suggested the darters fed like classic specialists, selecting a small number of prey taxa relative to prey availability in the resource base. The darters selected just one to four chironomid taxa from 52 available taxa across seasons. Our study shows that the scale of taxonomic resolution used to identify darter prey may influence the characterization of darter foraging modes.     

Linking microhabitat availability and local density of rainbow trout in low-gradient Japanese streams

Quantification of reach-based microhabitat availability for rainbow trout (Oncorhynchus mykiss), considering their microhabitat requirements in two low-gradient streams, northern Japan, was attempted to test for habitat space limitation of local trout density. Underwater observations revealed that fish selected microhabitats of moderate current velocity, relatively greater depth and shorter distance to overhead cover in both streams, although habitat features used and available differed slightly between the streams. Habitat space for fish potentially available in the channel environment was evaluated using principal component analysis (PCA) of both available and used microhabitat. A close relationship was evident in both streams between reach-based microhabitat availability and fish density, which was assessed by a three-pass removal method. Direct estimates of fish microhabitat availability using PCA can contribute to accurate predictions of local fish density and provide insight into the mechanisms responsible for fish–habitat relationships in streams.     

Seasonal changes in low oxygen tolerance of fantail,Etheostoma flabellare,rainbow, E. caeruleum,and greenside,E. blennioides,darters

Synopsis The tolerance of fantail, rainbow, and greenside darters to low oxygen was determined by exposing fish to conditions of progressively decreasing oxygen levels and recording the oxygen concentration at which loss of equilibrium occurred. The greenside darter was least tolerant to low oxygen levels in summer, with loss of equilibrium occurring at a mean O₂ concentration of 3.39 mg l⁻¹. Tolerances then increased through spring. A similar trend was observed for the fantail darter, with the lowest tolerance occurring in summer (2.36 mg ⁻¹). and greatest tolerance in spring (2.03 mg l⁻¹). The rainbow darter exhibited its greatest tolerance to low oxygen in summer and spring (1.64 and 1.93 mg l⁻¹, respectively). Interspecific differences were greatest in summer, with greenside darters being the least tolerant to low oxygen levels and the rainbow darter being the most tolerant. No differences in tolerance among the species were noted in winter. The low oxygen tolerance exhibited in summer by the greenside darter may be due to a higher metabolic cost and a higher critical oxygen tension at maximal stream temperatures (>25° C). The observed differences in oxygen tolerance may influence the longitudinal distribution and habitat selection of darters, especially in the summer months.     

Similarities in Behavioral Ecology among Amphidromous and Catadromous Fishes on the Oceanic Islands of Hawai'i and Guam

About seven families of fishes occur routinely in fresh water on oceanic high islands of the tropical Pacific; others (sharks, jacks, bonefish, etc.) are occasional visitors. However, amphidromous fishes (freshwater adults, marine larvae) of the families Gobiidae and Eleotridae are predominant in island streams. Hawai'i, representing the northernmost extent of Polynesia, has five species of gobioid fishes whose adults are limited to fresh water, but Guam, in the Mariana Islands of the far Western Pacific, has more than four times that number. Hawaiian stream fishes are strikingly similar to their Guamanian relatives in their distribution, ecology, and behavior. At both localities, these fishes typically exhibit strong species specificity in the section of stream inhabited by adults, in the microhabitat selected, and in their food and feeding. Although incompletely understood, aspects of the life cycles of amphidromous island fishes (spawning, migrations into and from the sea, and others) are cued by seasonal and short-term changes in stream flow. In the Hawaiian Islands, water-use decisions based on the imperatives of allowing no net loss of habitat for aquatic animals and maintaining stream-ocean pathways for migrating animals have facilitated both management and conservation of diversity in island streams.     

The ecological drivers of nuptial color evolution in darters (Percidae: Etheostomatinae)

Closely related animal lineages often vary in male coloration, and ecological selection is hypothesized to shape this variation. The role of ecological selection in inhibiting male color has been documented extensively at the population level, but relatively few studies have investigated the evolution of male coloration across a clade of closely related species. Darters are a diverse group of fishes that vary in the presence of elaborate male nuptial coloration, with some species exhibiting vivid color patterns and others mostly or entirely achromatic. We used phylogenetic logistic regression to test for correlations between the presence/absence of color traits across darter species and the ecological conditions in which these species occur. Environmental variables were correlated with the presence of nuptial color in darters with colorful species tending to inhabit environments that would support fewer predators and potentially transmit a broader spectrum of natural light compared to species lacking male coloration. We also tested the color preferences of a common darter predator, largemouth bass, and found that it exhibits a strong preference for red, providing further evidence of predation as a source of selection on color evolution in darters. Ecological selection therefore appears to be an important factor in dictating the presence or absence of male coloration in this group of fishes.     

Population Dynamics and Spatial Distribution of Coral Reef Fishes: Comparison Between Continuous and Isolated Habitats

Recent studies have shown that there are high degrees of spatial and temporal stability in coral reef fish assemblage structures in a continuous habitat, in contrast to results of observations in isolated habitats. In order to determine the reason for the difference in temporal stability of fish assemblage structures in a continuous habitat site and an isolated habitat site, population dynamics and spatial distributions of coral reef fishes (six species of pomacentrids and two species of apogonids) in the two habitat site were investigated over a 2-year period in an Okinawan coral reef. The population densities of pomacentrid and apogonid species increased in juvenile settlement periods at both sites, but the magnitude of seasonal fluctuation in population density was significantly greater at the isolated habitat site, indicating that the rate of juvenile settlement and mortality rate in the isolated habitat were greater than those in the continuous habitat. The magnitude of aggregation of fishes, which affects density-dependent biological interactions that modify population density such as competition and predation, was also significantly greater at the isolated habitat site, especially in the juvenile settlement season. Most of the fishes at the isolated habitat site exhibited more generalized patterns of microhabitat selection because of less coral coverage and diversity. The seasonal stability in the species composition of fishes was greater at the continuous habitat site than that at the isolated habitat. Our findings suggest that the relative importance of various ecological factors responsible for regulation of the population density of coral reef fishes (e.g., competition, predation, microhabitat selection and post-settlement movement) in a continuous habitat site and the isolated habitat site are different.     

Microsatellite markers for the endangered Roanoke logperch, Percina rex (Percidae) and their potential utility for other darter species

The Roanoke logperch (Percina rex Jordan and Evermann), an endangered fish, occurs in only six watersheds in the Roanoke and Chowan river drainages of Virginia, USA. The species’ population genetic structure is poorly known. We developed 16 microsatellite markers that were reliably scorable and polymorphic P. rex. Markers were also screened in seven other darter species of the genus Percina. Most markers exhibited successful amplification and polymorphism in several species. These markers may therefore prove useful for population genetic studies in other darters, a diverse but highly imperiled group.