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| the Amolops marmoratus group from India A, B. Amolops afghanus. C. Amolops ammachi sp. nov.. D–F. A. assamensis. G–I. Amolops bella sp. nov.. J–M. A. gerbillus. N, O. A. indoburmanensis; A. Amolops indoburmanensis haplo 1. C. A. cf. indoburmanensis sp. 1. E. A. jaunsari. F, A. nepalicus. H. Amolops sendenyu sp. nov. Biju, Ellepola, Sarmah, Upadhyaya, Bisht, Tajo, Hanken & Garg, 2026 Photos: S. D. Biju. |
Abstract
The Cascade Frog genus Amolops, currently comprising 95 described species, is a taxonomically challenging group of Asian frogs. Although the genus has been studied extensively across most of its range, the Indian members remain poorly understood, with sporadic species descriptions and no comprehensive taxonomic revision to date. Additionally, the current taxonomy of Amolops in India remains in flux; the true species diversity is potentially underestimated due to insufficient sampling efforts, misidentifications arising from limited investigations, and lack of a comprehensive comparative framework. In this study, we addressed these gaps through extensive sampling of Amolops across their range in India and by using an integrative morphological and molecular approach to investigate existing diversity. By using a multilocus data set of mitochondrial (16S, CO1, ND2) and nuclear (RAG1, TYR) markers, we present the first comprehensive Amolops phylogeny, including all known Indian species, which enables us to confidently establish species boundaries and infer evolutionary relationships. By assigning available names to well-supported lineages and testing multiple species-delimitation hypotheses, we identified a high level of undescribed cryptic diversity in the genus. Integrative analyses confirm three distinct unnamed lineages, which are formally described here as Amolops ammachi sp. nov., Amolops bella sp. nov., and Amolops sendenyu sp. nov. In addition, we report five new country records for India: three genetically conspecific with Amolops afghanus, Amolops nepalicus, and Amolops wangyali, and two shallowly divergent populations of A. medogensis and A. bellulus. Conversely, five nominal species do not represent distinct taxa and are here treated as junior subjective synonyms: Amolops chanakya synonym of Amolops wangyali; Amolops mahabharatensis synonym of Amolops jaunsari; Amolops senchalensis synonym of Amolops formosus; Amolops shillong synonym of Amolops assamensis; and Amolops terraorchis synonym of Amolops gerbillus. Molecular species delimitation reveals six additional candidate species from India; these lineages are left unnamed due to shallow divergence from established species and warrant further taxonomic investigation. Our time-calibrated phylogenetic analyses suggest that Amolops diversification began around the Eocene-Oligocene boundary, with a mean age of 31.5 Mya (median age: 32.5 Mya; 95% highest posterior density: 28.12–36.67 Mya). The most recent common ancestor (MRCA) of extant Amolops was widely distributed across Southeast China, mainland Southeast Asia, and the Malayan Peninsula during the early Oligocene. Through subsequent range contraction, subdivision, and jump dispersal, they spread into adjacent regions with dramatic rapid diversification toward the late Miocene. Biogeographic analyses suggest multiple waves of east-to-west colonization and highlight the role of early Himalayan uplift in mediating a complex “into-and-out-of-Himalaya” dynamic in structuring the contemporary distribution and high cryptic diversity in the genus. Mitochondrial haplotypes also show strong geographic structuring, indicating historical allopatric divergence by secondary contact among regions. These findings additionally improve our broader understanding of diversification and distribution patterns in this unique group.
KEYWORDS: Amphibia, Anura, cryptic diversity, evolutionary history, Integrative taxonomy, Himalayas, South and Southeast Asia, species delimitation, monticola Group, viridimaculatus Group, marmoratus Group, tadpole morphology
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| Dorsolateral views of species within the Amolops marmoratus group from India, in life. A, B. A. afghanus (SDBDU 2023.6459 and SDBDU 2021.322, respectively). C. Amolops ammachi sp. nov. (ZSI A 16551). D–F. A. assamensis (SDBDU 2022.1100, SDBDU 2018.3843, and SDBDU 2025.6858, respectively). G–I. Amolops bella sp. nov. (SDBDU 2011.6959, SDBDU 2011.6913, and SDBDU 2011.6956, respectively). J–M. A. gerbillus (SDBDU 2024.6597, SDBDU 2024.6726, SDBDU 2021.1225, and SDBDU 2024.6598, respectively). N, O. A. indoburmanensis (SDBDU 2018.3870 and SDBDU 2022.5572, respectively). Photos: S. D. Biju. |
Amolops ammachi sp. nov.
Etymology. The species is named in honor of the late Ms. Padmini Varkey, a renowned social worker and philanthropist from Kerala, India. She is fondly referred to as “Ammachi,” meaning “mother” in Malayalam, the language of Kerala. Her unconditional love and readiness to help those in need were widely admired. The species epithet ammachi is a tribute to her life and spirit; it is treated as an invariable noun in apposition to the generic name.
Suggested Common Name. Ammachi's Cascade Frog.
Amolops bella sp. nov.
Etymology. The specific epithet bella is from the Latin word bellus, meaning beautiful, and referring to the beauty of the frog. The species epithet is considered an invariable noun in apposition.
Suggested Common Name. Beautiful Cascade Frog.
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| Dorsolateral views of species within the Amolops marmoratus group from India, in life. A. A. indoburmanensis haplo 1 (SDBDU 2024.6670). B. A. indoburmanensis haplo 2, (SDBDU 2021.4629). C. A. cf. indoburmanensis sp. 1 (SDBDU 2009.140). D, E. A. jaunsari (SDBDU 2012.6991 and SDBDU 2012.153, respectively). F, G. A. nepalicus (SDBDU 2026.6929 and SDBDU 2026.6928, respectively). H. Amolops sendenyu sp. nov. (SDBDU 2024.5438). I–K. A. siju (SDBDU 2023.457, SDBDU 2022.1468, and SDBDU 2025.6832, respectively). L. A. yarlungzangbo (SDBDU 2022.6141). Photos: S. D. Biju. |
Amolops sendenyu sp. nov.
Etymology. The species is named after Sendenyu Village, Nagaland State, where the type series was collected. The species epithet is considered an invariable noun in apposition.
Suggested Common Name. Sendenyu Cascade Frog.
S. D. Biju, Gajaba Ellepola, A. N. Dikshit Akalabya Sarmah, Radhakrishna Upadhyaya, Karan Bisht, Tage Tajo, James Hanken and Sonali Garg. 2026. Systematics, Molecular Phylogeny, Diversification, and Biogeography of Cascade Frogs (Ranidae: Amolops) from India: An Integrative Assessment with Description of Three New Species. Bulletin of the Museum of Comparative Zoology. 164(1); 1-144. DOI: doi.org/10.3099/MCZ88.1 (11 August 2026)
