Two New Cryptic Endemic Toads of Bufo Discovered in Central Nevada, Western United States (Amphibia: Bufonidae: Bufo [Anaxyrus])
We describe two new cryptic species of Bufo within the subgenus Anaxyrus discovered in Central Nevada of the western United States. Our analyses revealed that these two localized endemic toads are genetically divergent and morphologically distinct, yet were concealed under the range of the broadly distributed western toad (Bufo boreas), which occurs throughout Nevada. The newly discovered species are close in geographic proximity to each other (albeit, in different hydrological basins) but have evolved unique morphological characters that are distinct from each other and distinctive from all allied taxa within the B. boreas species complex. The delimiting of these two rare toads emphasizes the link between taxonomic crypsis and inadequate conservation as these newly described species are vulnerable to extinction due to severely restricted geographic ranges, unknown population sizes, and dependency on rare, fragile wetland habitat, which is a limited resource within Nevada, the primary state that makes up the arid Great Basin. These two endemics join the Great Basin B. boreas species complex as imperiled new members, and our study demonstrates that our knowledge of anuran diversity is incomplete and that new discoveries can still be made, even in unlikely settings.
Sampling localities of congeneric taxa within the B. boreas species complex included for morphological (A) and DNA (B) collections within the hydrological Great Basin and surrounding states (Gordon et al., 2017). (A) Colors indicate species-specific populations measured for morphological analysis, with stars denoting new species. (B) Colors correspond with localized species and colors of B. boreas correspond with major mtDNA haplotype clades: W–Oregon and Western Great Basin (yellow), HL–Humboldt-Lahontan (blue), S–Mojave (aqua), and stars denote new species, which comprise the Eastern Great Basin clade (E). Maps created using ArcGIS software by ESRI (Environmental Systems Research Institute, 2011, ArcGIS Desktop: Release 10. Redlands, CA).
Discriminant function analysis (DFA). Cross validated DFA using 14 size-corrected morphological characters measured from 518 live adult toads (Fig. 1A) examined within the hydrological Great Basin B. boreas species complex. Species identified as B. boreas (red), B. nelsoni (brown), B. exsul (dark green), B. williamsi (light blue), B. nevadensis (light green), and B. monfontanus (dark blue).
Molecular examination of B. boreas species complex. (A) The TCS haplotype network was constructed using 257 sequences (1,622 bp) obtained from toad sampling (Fig. 1B) resulting in 62 unique haplotypes. Circle sizes correspond with the number of individuals of a particular haplotype. Major haplotype clades identified within B. boreas (W–Western Great Basin [yellow], HL–Humboldt-Lahontan [blue], and S–Mojave [aqua]) and to localized species (B. canorus [purple], B. exsul [tan], B. nelsoni [orange], B. williamsi [red]) and highlight the genetic divergence of both B. nevadensis (mauve) and B. monfontanus (brown). (B) Maximum likelihood tree derived from the control region of mitochondrial genome. Branches corresponding to partitions reproduced in less than 50% bootstrap replicates are collapsed. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches (Felsenstein, 1985). See Data Accessibility for tree file.
Molecular phylogenetic reconstruction of region-wide B. boreas species complex diversity. Tree reconstruction included sequence data (Table 3) from B. boreas outside the Great Basin to evaluate the relationships between toads from Hot Creek and Railroad Valley and Utah and Colorado toads using the maximum likelihood method. Minor and major groups identified. Terminal ends include haplotype number and locality of collection. Sequences of B. boreas from outside the Great Basin (Table 3) include this taxon name within terminal end identifier. Minor groups include localized species within the Great Basin: B. nelsoni (green), B. exsul (orange), B. canorus (purple), B. williamsi (red), and newly delimited species, B. monfontanus (mauve) and B. nevadensis (pink), of the major group identified as the Eastern Great Basin clade (black bar). Two haplotypes of the root are shown. See Data Accessibility for tree file.
Distribution of B. boreas and Great Basin B. boreas species complex. (A) The range-wide distribution of Bufo boreas shown in brown with hydrologic Great Basin outlined in black and hash mark interior within the western United States (Gordon et al., 2017). (B) Bufo boreas species complex and new species shown within hydrologic Great Basin, illustrating the small ranges of localized endemics. Spatial data for all toads except B. williamsi, B. nevadensis, and B. monfontanus provided by IUCN (2015). Images taken by M. R. Gordon except B. canorus, with photo credit to G. Nafis.
Photographs of Bufo (Anaxyrus) nevadensis, new species, holotype (CAS 259272). Female toad in life: (A) dorsal view and (B) ventral view; and in preservative: (C) dorsal view and (D) ventral view. Photographs taken by M. R. Gordon.
Photographs of Bufo (Anaxyrus) monfontanus, new species, holotype (CAS 259273). Male toad in life: (A) dorsal view and (B) ventral view; and in preservative: (C) dorsal view and (D) ventral view. Photographs taken by M. R. Gordon.
Contributor Notes
Associate Editor: B. Stuart.