Phenotypic Variation in Brook Trout Salvelinus fontinalis (Mitchill) at Broad Spatial Scales Makes Morphology an Insufficient Basis for Taxonomic Reclassification of the Species
It was recently proposed that there are three new species of Salvelinus with microendemic distributions in the Great Smoky Mountains National Park, Tennessee, USA. The three species of Salvelinus were hypothesized to be distinct from their congener Brook Trout S. fontinalis based on three meristic traits—pored lateral-line scales, vertebral counts, and number of basihyal teeth. After analyses that included specimens sampled from a larger portion of the geographic range of S. fontinalis, we conclude that the three populations of Salvelinus recently described as new species are not morphometrically distinct from Brook Trout and consider all three to be synonyms of S. fontinalis. Moreover, the low number of specimens originally examined conflates morphological differences among populations with sexual dimorphism and/or phenotypic plasticity, both of which are documented extensively in Brook Trout but were not controlled for in the species descriptions. While there is currently insufficient phenotypic or genotypic evidence to support the hypothesis of three new species that are distinct from S. fontinalis, we acknowledge the need to understand the unique selection pressures that shape evolutionary trajectories in small, isolated populations of Brook Trout and to conserve evolutionarily significant sources of genotypic and phenotypic diversity. To that end, we provide comments on research opportunities to support Brook Trout conservation, including the importance of collaborative, range-wide phylogenetic studies to identify the most appropriate scales of management efforts.
Native distribution of Brook Trout (shaded gray area) in the United States and Canada, with Brook Trout used in our comparative analyses originating from survey locations located in panels A and B. The three streams in Long Island, NY, surveyed by Stauffer and King (2014) are shown in panel A. Panel B shows streams from the Great Smoky Mountains National Park (GSMNP) surveyed by Weathers et al. (2019; circles) and Stauffer (2020; diamonds), with the three streams included in both studies symbolized with matching colors (Cosby Creek: yellow; Greenbrier Creek: green; Indian Camp Creek: blue). Streams included in Weathers et al. (2019) but not included in Stauffer (2020) are shown in gray circles.
First two dimensions of principal components analysis (PCA) of ten meristic traits for five populations of Salvelinus. The populations analyzed included the three surveyed by Stauffer (2020) and Weathers et al. (2019) from Cosby (yellow), Greenbrier (green), and Indian Camp (blue) Creeks, collections from Weathers et al. (2019) for 35 additional streams in the Great Smoky Mountains National Park (GSMNP; gray), and three populations from Long Island, NY described by Stauffer and King (2014; red). Ellipses envelop 95% of variation for each population, and population centroids are indicated by a triangle.
Comparison of pored lateral-line scale counts for specimens collected from (A) 38 streams in the Great Smoky Mountains National Park (GSMNP) by Weathers et al. (2019) and (B) three streams surveyed by Stauffer (2020) and three populations described by Stauffer and King (2014) in Long Island, NY. Individual-level data collected by Weathers et al. (2019) are displayed with violin plots, with the width of the violin plot for each stream demonstrating the density of the distribution for a given value and the minimum and maximum values indicated by the tails of the distribution. Due to discrepancies between published and raw data, values from Stauffer (2020) and Stauffer and King (2014) are shown using two methods. Data from the publication appear as the mode(s) (circle) and range (lines), and the raw, individual-level data appear as violin plots. Streams appear on the x-axis by ascending average trait value, and streams included in both Weathers et al. (2019) and Stauffer (2020) are plotted with the same color (Cosby Creek [CS]: yellow; Greenbrier Creek [GB]: green; Indian Camp Creek [ICC]: blue). Data from populations in NY are shown in red and all other sites from GSMNP, TN in gray.
The number of vertebrae (A) and basihyal teeth (B) reported by Stauffer (2020) for Cosby (CS; yellow), Indian Camp (ICC; blue), and Greenbrier (GB; green) Creeks. Vertebrae counts from peer-reviewed literature are also shown (see the supplement for sources), and, where appropriate, mean (triangle), mode (circle), and/or range (line) are indicated. The dashed line in panel B reflects values that were reported for basihyal tooth count from Cosby Creek in Stauffer (2020) but which were inconsistent with the requested data.
Representative examples of diverse morphology, particularly in mouth shape and position, observed within a single stream-dwelling Brook Trout population. Fish on the first row display more inferior mouth positions, whereas fish on the last row show more isognathous and prognathic jaws with a terminal/superior mouth position. All fish were captured from Crabtree Creek in the Savage River Watershed of western Maryland (39°27′47.25″N, 79°12′36.08″W). Fish total length is noted in the upper right corner of each photograph. A full description of collection and photography protocols is provided in Kazyak et al. (2015).
Contributor Notes
Associate Editor: M. P. Davis.