An Ecohydraulic Model to Identify and Monitor Moapa Dace Habitat

<div><p>Moapa dace (<em>Moapa coriacea</em>) 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.</p> </div

Random sample locations used for model development inside and outside of occupied dace patches in Plummer Springbrook.

<p>Snorkel surveys in the spring of 2009 were conducted to determine the locations of Moapa dace (shown in red), while absence locations were generated randomly outside of known dace sites with a GIS (309 absences and 141 presences).</p

The relationship between Moapa dace density and four probability classes in Plummer Creek, as output by Model 2.

<p>Probability classes are 1 (0–20%), 2 (20.1–40%, 3 (40.1–60%), and 4 (>60%). Dace densities were obtained by averaging three back-to-back snorkel surveys (spring of 2009), counting the number of dace within each probability class, and dividing by the number of cells (0.0144 m²) found within each probability class.</p

Model results for univariate and multivariate logistic regression, listed from best to worst according to AIC score (<i>n</i> = 450; 309 absences and 141 presences).

<p>Statistics presented are twice the negative log-likelihood value (−2L), the number of parameters (NPar), change in AIC score when compared to the best model (ΔAIC), AIC model weight (w), Hosmer-Lemeshow goodness-of-fit statistic (Ĉ), Nagelkerke pseudo R-squared (R²), overall classification accuracy (OA), ROC area-under-the-curve (AUC), and the principal variables in each model (higher-order terms not shown. For variable descriptions, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055551#pone-0055551-t001" target="_blank">Table 1</a>; * denotes the variable that had the greatest influence on the model’s log likelihood. Quadratic terms are not shown in the Variables field.</p

Predictor variables used for Moapa dace habitat modeling.

<p>Predictor variables used for Moapa dace habitat modeling.</p

Model parameters and coefficients for Model 1 (top) and Model 2 (bottom): outputs were obtained from multiple logistic regression on Plummer Creek, with samples collected in the spring of 2009 (<i>n</i> = 450; 309 absences and 141 presences).

<p>See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0055551#pone-0055551-t001" target="_blank">Table 1</a> for variable definitions; variables with an underscore (e.g., Dep_2) are squared terms.</p

Habitat-discharge relations among Plummer, Pedersen, and Apcar creeks, in 10% flow increments.

<p>In panel A, the amount of predicted habitat by flow is presented after standardizing the data by stream length. In panel B, the relative change in habitat in relation to baseflow was calculated in 10% flow increments.</p

A map of the project area with the three spring-fed creeks displayed inside the Refuge boundary.

<p>Culverts route the springbrooks under the road located on the Refuge boundary.</p

Complex cellular phenotype of V644del mutant channel.

<p><b>(A)</b> Cellular localization of YFP-tagged wild-type canine CNGA3 and CNGA3-V644del mutant in HEK tsA201 cells. Cells transfected with the wild-type construct showed specific fluorescence pattern of expression limited to the plasma membrane and Golgi-like organelles (arrow); an evident increase in intracellular aggregates was observed in cells transfected with V644del mutant construct consistent with abnormal trafficking and potential ER retention. Scale bar: 10μm. <b>(B)</b> cGMP- and cAMP-activated currents recorded from CNGA3-WT and a responsive patch expressing V644del mutant channels. Approximately 40% of V644del mutant patches had no cGMP-activated currents, in contrast to 100% responsive patches from the CNGA3-WT-transfected cells. This partial loss of channel activity might reflect incomplete subunit assembly associated with disruption of the coiled-coil structure as depicted in the simulation studies. The responsive patches showed cyclic nucleotide-activated currents with similar characteristics to WT channels. <b>(C)</b> Histograms of subcellular localization patterns monitored in HEK tsA201 cells co-transfected with V644del and CNGA3-WT cDNA constructs. Cells were transfected with either CNGA3-WT or CNGA3-V644del or both constructs at the indicated ratios. Each cell count represents >300 cells from at least 2 transfections (mean% ± SD).</p

R424W mutation disrupts salt bridge interaction and destabilizes the open state of pore in a homotetrameric CNGA3 model.

<p><b>(A)</b> Schematic representation of CNGA3 subunit consisting of six transmembrane (TM) spanning segments (S1-S6) and a pore domain between S5 and S6. The highlighted last residue of S6 (blue) is the site of canine CNGA3-R424W mutation; its predicted partner, glutamic acid E306, is the first residue of S4-S5 linker. <b>(B)</b> Amino acid sequence alignment of the S4-S5 linker and S6 segment of selected shaker K^<b>+</b> channel superfamily members. The TM regions of the CNG channel family were assigned using the crystal structure of the chimeric voltage-gated potassium channel Kv1.2/2.1 (PDB ID: 2R9R). Sequence alignments of S5 domain and pore region were omitted for clarity. The R424 residue is shown in blue and its interacting partner, E306 in red. The conserved salt bridges in the Kv channels show opposite charges at these positions. c = canine, b = bovine, h = human, r = rat, m = mouse. <b>(C)</b> Side view of the wild-type CNGA3 homotetramer model and the CNGA3-R424W mutant channel equilibrated in its environment. The voltage-sensing domain (S1-S4) is presented in green, the S4-S5 linker in purple and the pore-forming region (S5-S6) in grey. The residues E306 and R424 are shown as red and blue rods, respectively. The E306:R424 interaction (wild-type) or its loss (R424W mutant) is demonstrated on the higher magnification images. Carbon atoms are labeled in cyan, nitrogens in blue and oxygens in red. Other side chains were omitted for clarity. Note that R424 forms a salt bridge with the E306 molecule in three subunits out of four. <b>(D)</b> Bottom views of the wild-type CNGA3 and CNGA3-R424W mutant channels. S6 is represented as a grey solid surface highlighting the partial closure of the pore in the R424W mutant model.</p