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| Eleutherodactylus humboldti Devitt, Tseng, Taylor-Adair, Koganti, Timugura & Cannatella, 2023 DOI: 10.7717/peerj.14985 |
Abstract
Background:
The subgenus Syrrhophus (genus Eleutherodactylus) contains >40 species of small, direct-developing frogs that occur at low to moderate elevations from Texas through Mexico and into Guatemala and Belize, with two species in western Cuba. Morphological conservatism and phenotypic convergence have made species delimitation challenging and resulted in a complicated taxonomic history. Since 2015, molecular systematic work has uncovered eleven new species from western Mexico and one from eastern Mexico, but current taxonomy still underestimates species level diversity and there is confusion surrounding the validity and boundary of several species.
Methods:
We used phylogenetic analysis of 16S ribosomal RNA (rRNA) sequences, multivariate statistical analysis of morphological data, and bioacoustic analysis of male advertisement calls to discover two additional unnamed species of Eleutherodactylus from Central and Western Mexico. We describe those species here.
Results:
Eleutherodactylus (Syrrhophus) humboldti sp. nov. is described from the Quaternary Valle de Bravo volcanic field of the Eje Neovolcánico in Central Mexico. This species is sister to E. maurus and is 3% divergent in 16S. Eleutherodactylus (Syrrhophus) jamesdixoni sp. nov. is described from the Sierra Madre Occidental of western Mexico. This species is sister to E. nitidus and is 3% divergent. We provide color photographs, advertisement call recordings, and molecular diagnoses of these new species and their sister species to aid future workers.
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| Eleutherodactylus humboldti, sp. nov. in life (A) MZFZ 4505 (holotype); (B) MZFZ 4504 (paratype); (C and D) MZFZ 4506 (paratype); |
Eleutherodactylus (Syrrhophus) humboldti, new species
Suggested English name: Humboldt’s Peeping Frog
Suggested Spanish name: Rana fisgona de Humboldt
Diagnosis and comparisons:
Molecular synapomorphies for this species are (character: state change): 147: A => G, 204: C => T, 241: C => T, 243: A => T, 256: T => C, 279: C => A, 281: C => T, 292: G => A, 295: A => G and 358: G => C. Character numbers refer to the position in the alignment (Data S1).
Among species of the western clade of Syrrhophus, E. humboldti is most similar in appearance to E. maurus (Fig. 8); however, our sample sizes for each species are too small to make robust inter- or intrapopulation comparisons. These two taxa are very similar in having a triangular head with a sharp canthus rostralis with a black stripe on the lateral aspect. The stripe fades inferiorly into a grayish brown. This stripe seems to extend across the eye in the sense that the middle and lower part of the iris is black, whereas the upper part of the iris is gold. The stripe extends posterior to the eye across the tympanum (which is slightly paler in color) to the axilla. In the postorbital region, the stripe borders the sharp supratympanic fold.
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Etymology: We name this species in honor of German scientist Alexander von Humboldt, whose year-long exploration of south-central Mexico at the turn of the 19th century resulted in the first scientific account of the New World and whose writings continue to influence biogeographers, ecologists and evolutionary biologists seeking to understand the origin and maintenance of biodiversity in mountain regions (Rahbek et al., 2019b, 2019a).
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| Holotype of Eleutherodactylus jamesdixoni, sp. nov. (IBH 34852) in life. |
Eleutherodactylus (Syrrhophus) jamesdixoni, new species
Suggested English name: Dixon’s Peeping Frog
Suggested Spanish name: Rana fisgona de Dixon
Diagnosis and comparisons:
Molecular synapomorphies for this species are (character: state change) 204: C => T, 291: C => A, and 360: C => A. Character numbers refer to the position in the alignment (Data S1).
Among species of the western clade of Syrrhophus, E. jamesdixoni (Fig. 10) is most similar in appearance to E. nitidus (Fig. 11). We restrict our comparison to topotypic samples of E. nitidus. The two species are very similar in having a roughly triangular head with a gently angled canthus rostralis. The lateral aspect of the canthus is darker than the dorsal surface of the snout. In E. jamesdixoni a dark greenish black stripe is present, but in E. nitidus this stripe varies from very dark to barely differentiated from the color of the snout (Fig. 11). The stripe fades inferiorly in E. nitidus, but in E. jamesdixoni it is more distinct. This stripe seems to extend across the eye in that the middle and lower part of the iris is dark, whereas the upper part of the iris appears as densely packed gold flecks (this golden region is larger than in E. maurus and E. humboldti). In both, the stripe extends posterior to the eye across the tympanum (which is slightly copper-colored) to the axilla but is much less distinct than in E. maurus and E. humboldti. In the postorbital region the stripe becomes indistinct. The supratympanic fold is rounded but weakly developed.
Etymology: We name this species in honor of the late James R. Dixon, Professor Emeritus and Curator Emeritus of amphibians and reptiles at the Biodiversity Research and Teaching Collections at Texas A&M University. Dr. Dixon provided the first and most thorough statistical analysis to date of geographic variation among populations of the former genus Tomodactylus from western Mexico (Dixon, 1957).
Conclusions:
Here, we have delimited two new species of Syrrhophus using morphology, calls, and DNA-based diagnoses. These frogs are among the most ubiquitous and abundant of Mexican amphibians, yet remain among the least known. Exceptional microendemism typifies this group, with several species known only from the type locality. Their ubiquity, diversity, high endemism, and unusual reproductive mode (direct development) offer potential for addressing fundamental and emerging questions in ecology, evolution, and behavior. This potential has not yet been realized however, due to an inaccurate taxonomy that underestimates species-level diversity. Additional species await description; the need for this research is great, and the timing is urgent. Mexico is home to two Biodiversity Hotspots—the Madrean Pine Oak Woodlands and tropical lowlands of Mesoamerica—but high rates of deforestation and a general lack of conservation areas pose increasing threats to species survival there. Some 60% of Mexican amphibians are threatened with or have already been lost to extinction, including nine species of Syrrhophus that are classified as Endangered or Critically Endangered by the International Union for the Conservation of Nature (IUCN, 2021). Discovering and describing unrecognized species-level diversity and identifying areas of endemism will directly impact conservation prioritization in Mexico.
Thomas J. Devitt, Karen Tseng, Marlena Taylor-Adair, Sannidhi Koganti, Alice Timugura and David C. Cannatella. 2023. Two New Species of Eleutherodactylus from western and central Mexico (Eleutherodactylus jamesdixoni sp. nov., Eleutherodactylus humboldti sp. nov.) PeerJ. 11:e14985. DOI: 10.7717/peerj.14985