Taxonomists currently recognize 16 cryptic species within the Plethodon glutinosus complex revealed by allozyme analysis but that typically do not differ in morphology or color pattern. Two putative species, P. grobmani and P. mississippi, are distributed across the Gulf Coastal Plain, with geographic ranges that are separated by Mobile Bay and the Alabama River. Character divergence is thought to distinguish the two species, with P. grobmani (east of Mobile Bay) having a short snout and extensive patches of white coloration, and P. mississippi (west of Mobile Bay) having an elongate snout and lacking extensive patches of white coloration. However, specimens used to characterize these two species were examined in life, were collected mainly from areas adjacent to Mobile Bay, and were evaluated by a single investigator. Additionally, the two traits (snout shape and color) were combined into a single variable, masking the contribution of each trait to individuating the two species. To test the utility of these characters, we applied identical measurements of the two traits to preserved specimens representing an east–west transect across the geographic ranges of the two putative species. Data were generated by three investigators who measured each specimen twice, a design that allowed examination of reproducibility within and among investigators. Traits were evaluated separately and as a combined score. Both snout shape and color were found to be traits that are reproducible for measurements within individual investigators and the measurement of these traits did not differ among investigators. Specimens from east of Mobile Bay had more extensive white coloration and higher total scores than those west of Mobile Bay; snout shape did not differ across Mobile Bay. Longitude was a significant correlate of color and total score, with the slope of the relationship differing on each side of Mobile Bay. Color and total score of specimens west of Mobile Bay had a positive association with longitude, while scores of specimens east of Mobile Bay had a negative association. Thus, rather than exhibiting character divergence across Mobile Bay, slimy salamanders converge on a phenotype with extensive white coloration at Mobile Bay. We find no color or morphological feature that distinguishes putative P. grobmani from putative P. mississippi, a line of evidence suggesting that those populations are a single species with regional change in color.
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Vol. 107 • No. 4