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East Chattanooga, TN, United States

Fluker B.L.,University of Alabama | Kuhajda B.R.,University of Alabama | Kuhajda B.R.,Tennessee Aquarium Conservation Institute | Harris P.M.,University of Alabama
Freshwater Biology | Year: 2014

Riverine impoundments (reservoirs) are thought to impede natural migration in small-stream-inhabiting fishes, resulting in spatially and genetically fragmented populations. However, this hypothesis remains poorly tested, and the genetic consequences of riverine impoundment for stream fishes with differing dispersal capabilities are not well understood. This study utilised a combination of microsatellite DNA loci from 479 individuals and the mitochondrial (mt) DNA cytochrome b gene (810-1140 bp) from 83 individuals from eight streams to compare genetic structure and diversity between reservoir-fragmented and non-fragmented groups of two species of stream fishes with differing dispersal capabilities in the Mobile River basin of the south-eastern United States. For both species, analysis of microsatellite loci revealed genetic discontinuities between neighbouring tributaries that have been fragmented by reservoir construction. This finding was in stark contrast to the high degree of continuity for both species between reference tributaries in a natural river setting. Results from mtDNA revealed no significant genetic structure within reservoir-fragmented or non-fragmented groups, indicating a lack of historical genetic structure (i.e. prior to reservoir construction). Microsatellite-based estimates of genetic diversity and migration were differentially affected in the two species, indicating that stream fishes with relatively high dispersal abilities may be equally or more susceptible to reservoir fragmentation when compared to species with relatively low dispersal abilities. Collectively, our data revealed that riverine impoundment and reservoir-induced habitat fragmentation adversely affect genetic characteristics in small-stream-inhabiting fishes. This is of particular interest in biodiversity hotspots such as the south-eastern United States where hydroelectric and recreational reservoirs restrict connectivity in aquatic systems. © 2013 John Wiley & Sons Ltd. Source


Ennen J.R.,Tennessee Aquarium Conservation Institute | Lindeman P.V.,Edinboro University of Pennsylvania | Lovich J.E.,U.S. Geological Survey
Ecology and Evolution | Year: 2015

Coloration can play critical roles in a species' biology. The allometry of color patterns may be useful for elucidating the evolutionary mechanisms responsible for shaping the traits. We measured characteristics relating to eight aspects of color patterns from Graptemys oculifera and G. flavimaculata to investigate the allometric differences among male, female, and unsexed juvenile specimens. Additionally, we investigated ontogenetic shifts by incorporating the unsexed juveniles into the male and female datasets. In general, male color traits were isometric (i.e., color scaled with body size), while females and juvenile color traits were hypoallometric, growing in size more slowly than the increase in body size. When we included unsexed juveniles in our male and female datasets, our linear regression analyses found all relationships to be hypoallometric and our model selection analysis found support for nonlinear models describing the relationship between body size and color patterns, suggestive of an ontogenetic shift in coloration traits for both sexes at maturity. Although color is critical for many species' biology and therefore under strong selective pressure in many other species, our results are likely explained by an epiphenomenon related to the different selection pressures on body size and growth rates between juveniles and adults and less attributable to the evolution of color patterns themselves. © 2015 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. Source


Ennen J.R.,Tennessee Aquarium Conservation Institute | Kalis M.E.,Maryville College | Patterson A.L.,Maryville College | Kreiser B.R.,University of Southern Mississippi | And 3 more authors.
Biological Journal of the Linnean Society | Year: 2014

Widely distributed species often display intraspecific morphological variation due to the abiotic and biotic gradients experienced across their ranges. Historically, in many vertebrate taxa, such as birds and reptiles, these morphological differences within a species were used to delimit subspecies. Graptemys nigrinoda is an aquatic turtle species endemic to the Mobile Bay Basin. Colour pattern and morphological variability were used to describe a subspecies (G.n. delticola) from the lower reaches of the system, although it and the nominate subspecies also reportedly intergrade over a large portion of the range. Other researchers have suggested that these morphological differences merely reflect clinal variation. Our molecular data (mtDNA) did not support the existence of the subspecies, as the haplotypes were differentiated by only a few base pairs and one haplotype was shared between the putative subspecies. While there were significant morphological and pattern differences among putative specimens of G.n. nigrinoda, G.n. delticola and G.n.nigrinoda × delticola, these differences probably represent clinal variation as they were also related to environmental variables [i.e. cumulative drainage area and drainage (categorical)]. Specimens occupying slow-current, high-turbidity river reaches (e.g. the Tensaw River) exhibited greater relative carapace heights and more dark pigmentation, while specimens occupying fast-current, clearer rivers (e.g. the upper Alabama, Cahaba and Tallapoosa rivers) exhibited lower carapace heights and more yellow pigmentation. Given the absence of clear molecular and morphological differences that are related to drainage characteristics, we suggest that there is not sufficient evidence for the recognition of G.n. delticola as a distinct subspecies. © 2014 The Linnean Society of London. Source


Venarsky M.P.,University of Alabama | Venarsky M.P.,U.S. Geological Survey | Huntsman B.M.,West Virginia University | Huryn A.D.,University of Alabama | And 2 more authors.
Oecologia | Year: 2014

Energy limitation has long been the primary assumption underlying conceptual models of evolutionary and ecological processes in cave ecosystems. However, the prediction that cave communities are actually energy-limited in the sense that constituent populations are consuming all or most of their resource supply is untested. We assessed the energy-limitation hypothesis in three cave streams in northeastern Alabama (USA) by combining measurements of animal production, demand, and resource supplies (detritus, primarily decomposing wood particles). Comparisons of animal consumption and detritus supply rates in each cave showed that all, or nearly all, available detritus was required to support macroinvertebrate production. Furthermore, only a small amount of macroinvertebrate prey production remained to support other predatory taxa (i.e., cave fish and salamanders) after accounting for crayfish consumption. Placing the energy demands of a cave community within the context of resource supply rates provided quantitative support for the energy-limitation hypothesis, confirming the mechanism (limited energy surpluses) that likely influences the evolutionary processes and population dynamics that shape cave communities. Detritus-based surface ecosystems often have large detrital surpluses. Thus, cave ecosystems, which show minimal surpluses, occupy the extreme oligotrophic end of the spectrum of detritus-based food webs. © 2014, Springer-Verlag Berlin Heidelberg. Source


Chen X.-Y.,CAS Kunming Institute of Zoology | Neely D.A.,California Academy of Sciences | Neely D.A.,Tennessee Aquarium Conservation Institute
Zootaxa | Year: 2012

Schistura albirostris, a new species of nemacheiline loach, is described from the Longchuanjiang, a tributary of the Irrawaddy River of Tengchong County, southwestern Yunnan, China. It differs from all congeners in the combination of an extremely slender body; a distinctive rectangular unpigmented area on the snout, ethmoid region and anterior rostral barbels; 5-7 dark dorsal saddles that are confluent with 5-8 lateral bars; lacking a suborbital flap in males; and possessing an incomplete lateral line with 27-51 pores, and a weakly-developed processus dentiformis. Copyright © 2001-2012 Magnolia Press. Source

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