Habitat-Morphotype Associations of Pecos Pupfish (Cyprinodon pecosensis) in Isolated Habitat Complexes
Alterations to the Pecos River in New Mexico and Texas, USA, including damming and river channelization, plus water extraction and diversion from, and pollution of associated habitats during the 19th and 20th centuries have greatly impacted many fish species. The Pecos pupfish (Cyprinodon pecosensis) is one species that was heavily impacted, especially because introduction of a congener, the sheepshead minnow (C. variegatus), to the Pecos River in the 1980s eliminated pure C. pecosensis from most of its range via hybridization. Currently, C. pecosensis is restricted to generally small isolated habitats, although historically this species had a large metapopulation with a large geographic range. The current study was an initial survey of morphological variation within different isolated habitat complexes to determine if there were habitat-morphotype distinctions. We used analysis of convex hull coverage (ACHC) with geometric morphometric data to assess whether morphotypes were distinct. ACHC results confirmed that three morphotypes were evident in the Bitter Lake National Wildlife Refuge: deep sinkhole, riverine, and marshland morphotypes. Alternatively, connectivity between a deep sinkhole and marshland habitat in the Bottomless Lakes State Park appeared to produce non-extreme body shapes with little variation, suggesting gene flow mitigates morphological divergence. Results from this study highlight that disruption of gene flow in metapopulations can spur divergent evolutionary trajectories in isolated populations. For species with conservation concern, like C. pecosensis, it is not clear if re-establishing gene flow would be beneficial or detrimental for populations that are potentially adapted to their local environments.
Sampling locations. Sampling locations are marked on the map of New Mexico, but are mostly too clustered to discern. The smaller maps on the right zoom in on specific locations. These maps are not equally scaled, but are intended to show the geographical relationships among habitats. Abbreviations are for Pecos River (PR), Delaware River (DR), deep sinkholes (SH), Bitter Lake (BL) marshland, Waterfowl impoundments (WF), and Bureau of Land Management (BLM) outflow marsh from Lea Lake. Symbols indicate precise locations (as best ascertained from collection notes) and correspond to the same graphical symbols used in Figure 3. As some sites were sampled multiple times, the number of sites shown is less than the number of samples in the analyses.
Anatomical landmarks for geometric morphometric analyses. The larger landmarks are “fixed” and represent junction of premaxilla and cranium, center of eye, insertion points for dorsal, caudal, anal, and pectoral fins, base of the preopercle where it intersects the interopercle, and dorsal margin of the operculum. The smaller points are the sliding semilandmarks used to estimate curvature of the fish body and operculum.
Principal component (PC) plot indicating shape variation among and within morphotypes. Morphotypes include Pecos River (PR), upper Bitter Lake (BL), Waterfowl impoundments (WF), deep sinkholes (SH), and Lea Lake and BLM outflow marsh (BLM). The sample means for these morphotypes are indicated by symbols, and convex hulls are shown to indicate the most extreme values. Hulls with solid lines are for habitats within BLNWR, differentiated by color. Hulls with small and large dashed black lines represent PR and BLM, respectively. Additionally, sample means from SH 1, Figure Eight Lake North (F8LN), and the Pecos River at its confluence with the Delaware River (PR@DR) are indicated. PC axes were obtained from a covariance matrix among the 56 sample means that comprised the seven morphotypes. The amount of among-sample mean variation explained by each axis is indicated. Transformation grids are shown to facilitate an understanding of shape variation. These grids represent the transformation of the mean shape (origin) associated with their location in the PC plot.
Results of analysis of convex hull coverage (ACHC). The plot on the left represents the relative frequency distribution of convex hulls found for 3,318 uniform points covering the represented PC space (inset upper right). The points of this uniform grid are colored corresponding to the number of hulls found at each point. The relative frequency of the number of hulls at each point is shown as the solid black line in the relative frequency distribution; dotted lines indicate 95% confidence bands, from 1,000 random permutations. The plot on the right indicates the position of the observed standard deviation of relative frequencies (probabilities) of convex hull number (from left plot) in the sampling distribution of 1,000 random standard deviations, found in the permutation procedure. The probability of finding a greater value, by chance, is indicated.
Contributor Notes
Associate Editor: J. F. Schaefer.