Integrative revision splits Malayan dwarf toad into two species, including golden-crested toad from Thailand

An integrative taxonomic study found that the Malayan dwarf toad, Ingerophrynus parvus, consists of two genetically, morphologically and acoustically distinct lineages, and formally described the northern lineage as the new species Ingerophrynus chrysolophus. The revision was based on mitochondrial and nuclear DNA, external and skeletal morphology, male advertisement calls and species distribution models.

Researchers sampled the I. parvus species complex across Southeast Asia, collecting or examining specimens from Thailand, Malaysia, Myanmar and Indonesia and supplementing them with museum material and sequences available in GenBank. The mitochondrial analysis included 65 Ingerophrynus specimens, representing 10 of the genus’s 13 then-recognized species and 44 specimens assigned to the I. parvus complex. Bayesian inference and maximum-likelihood analyses used a combined alignment of up to 4,479 base pairs from the 12S rRNA, 16S rRNA and ND1 mitochondrial genes.

Both analyses recovered the northern and southern lineages as reciprocal sister lineages with strong support. The southern lineage, retained as I. parvus sensu stricto, included specimens from Sumatra, Peninsular Malaysia and the southernmost part of Peninsular Thailand south of the Kangar-Pattani Line. The northern lineage included populations from Peninsular Myanmar and Thailand north of that biogeographic boundary. In the 465-base-pair 16S rRNA fragment, uncorrected divergence between the lineages was 5.04%, compared with intraspecific distances of 1.54% in the northern group and 2.08% in the southern group.

The nuclear analysis also distinguished the lineages. Researchers sequenced POMC, BDNF and RAG1 in 16 specimens, eight representing each lineage, and constructed median-joining allele networks. The northern lineage had two unique POMC and two unique RAG1 haplotypes separated from southern haplotypes by seven and five mutation steps, respectively. Two unique BDNF haplotypes were separated from the closest southern haplotypes by one or two mutational steps. These results support marked evolutionary differentiation, although the nuclear sample was relatively small.

Morphological comparisons used adults in good condition from the two lineages: 10 southern-lineage specimens, comprising seven males and three females, and 28 northern-lineage specimens, comprising 18 males and 10 females. Southern-lineage females were larger than northern-lineage females, while principal component analysis separated adult males from the two lineages without overlap. The first two components accounted for 15.99% and 12.94% of total variation. The new species differs from I. parvus sensu stricto in body size, cranial and limb proportions, and coloration, including bright orange cranial crests rather than brown ones.

Ingerophrynus chrysolophus has a snout-vent length of 30.3–35.7 mm in males and 34.0–42.4 mm in females. Micro-computed tomography was used to examine the skull of one adult male and one adult female from the northern lineage. The scans documented a generally well-ossified cranium with traces of hyperossification in parts of the cranial roof and underossification in the otic region. Because the osteological comparison included only two individuals and no comparative dataset was available for the genus, the authors could not determine whether observed differences between the specimens reflect sexual dimorphism or individual variation.

Bioacoustic comparisons were based on 188 calls from three males at two localities: two males in Kedah, Peninsular Malaysia, representing the southern lineage, and one male in Ratchaburi, Thailand, representing the northern lineage. Southern-lineage advertisement calls were high-pitched rising trills, with 13–15 calls per series, call durations of 0.05–0.07 seconds, 6–9 pulses per call and peak frequencies of 2,438–2,625 Hz. Northern-lineage calls consisted of 8–10 calls per series, lasted 0.02–0.05 seconds, contained 5–6 pulses and had peak frequencies of 1,292–1,378 Hz. These measured differences support distinctiveness, but the recordings included only one male from the northern population, limiting how broadly the acoustic result can be generalized.

Species distribution modeling used 155 georeferenced localities and 19 bioclimatic variables, with models generated at 5-kilometre pixel size. Reported test-area AUC values were 0.980 for the northern lineage and 0.956 for the southern lineage. The models indicated almost completely non-overlapping climatic niches, with the predicted boundary broadly corresponding to the Kangar-Pattani Line. The northern lineage was associated with more seasonal tropical and subequatorial mountain-forest conditions, whereas the southern lineage was modeled in equatorial perhumid forest. These are model-based estimates of potential distributions, not direct measurements of complete population ranges or evidence that the boundary caused genetic divergence.

The revision restricted the recognized range of I. parvus sensu stricto to Sumatra, westernmost Java, the Malay Peninsula south of the Kangar-Pattani Line and offshore islands including the Seribuat Archipelago, and removed I. parvus from the documented faunas of Cambodia and Myanmar. Ingerophrynus chrysolophus was described from Thailand and recorded across southern, central, western and eastern Thailand, adjacent southern Myanmar and southwestern Cambodia. The authors proposed treating I. wangyingyongi and I. ledongensis as subspecies of I. galeatus pending further analysis, and proposed a preliminary conservation category of Least Concern for the new species while identifying habitat loss and degradation associated with logging and deforestation as potential threats.

Subject of Research: Integrative taxonomic revision of the Ingerophrynus parvus species complex, with a new toad species from Thailand

Article Title: A taxonomic revision of the Ingerophrynus parvus species complex ( Amphibia , Anura , Bufonidae ) with the description of a new species from Thailand

Article References: Arkhipov, D. V., Pawangkhanant, P., Sarker, G., Gorin, V. A., Bragin, A. M., Nguyen, T. V., Hamidy, A., Muin, M. A., Kurniawan, N., Brown, R. M., Suwannapoom, C., Smith, E., & Poyarkov, N. A. (2025). A taxonomic revision of the Ingerophrynus parvus species complex (Amphibia, Anura, Bufonidae) with the description of a new species from Thailand. Herpetozoa, 38, 271-297. https://doi.org/10.3897/herpetozoa.38.e165173

Image Credits: AI Generated

DOI: 10.3897/herpetozoa.38.e165173

Keywords: Ingerophrynus chrysolophus, Malayan dwarf toad, taxonomic revision, amphibian diversity, new species, Thailand, phylogenetics, bioacoustics, species distribution modeling, taxonomic, revision, Ingerophrynus