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| Ingerana occidens Naveen, 2026 |
ABSTRACT
I assessed morphological variation between two populations previously treated as Ingerana borealis, occurring allopatrically on either side of a prominent biogeographic barrier, the Brahmaputra River. Significant morphological differences were found between the population from the Garo and Khasi Hills (south of the Brahmaputra River) and the topotypic population of I. borealis from the Abor Hills (north of the river). Therefore, I provide a redescription of I. borealis based on topotypic material and restrict its distribution to regions north of the Brahmaputra. Based on a 16S rRNA gene fragment (446 bp), this lineage is found to be deeply divergent, showing 23.1–24.6% divergence from some sequences labelled and referred to as ‘true’ Ingerana tenasserimensis and 17.9 to 18.3% divergence from the Ingerana sp. occurring in the Khasi and Garo hill ranges south of the Brahmaputra. The Khasi and Garo hill populations also show 21.8 to 23.2% divergence from I. tenasserimensis and multiple morphological differences. Based on these differences between this distinct population and other known Ingerana species, I describe it as a new species here. The sequences of Ingerana species included in this study were not recovered as a monophyletic group in the phylogeny, suggesting that the genus-level taxonomy of this group may require further revision, or that some sequences may be misidentified. However, given the lack of information for some of these sequences, resolving this issue is beyond the scope of the present study; therefore, all taxa examined here are provisionally retained within Ingerana, following previous studies.
KEYWORDS: 16S rRNA, allopatry, Amphibia, biogeographic barrier, Brahmaputra River, Eastern Himalayas, Indo-Burma region, occidens, paraphyletic, systematics
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| Ingerana borealis in life. (A) Female topotype (BNHS 6842); (B) male topotype (BNHS 6844). |
Ingerana borealis (Annandale)
Diagnosis: A small-sized dicroglossid frog, distinguished by the following combination of characters: snout–vent length (SVL) ranging from 29.4 to 29.9 mm in adult males (n = 2) and 31.0 mm in a single adult female; head wider than long; supratympanic fold weakly developed; tympanum indistinct; thigh length greater than shank length (SHL/TL = 0.94); fingertips rounded to very small discs; dorsal surface prominently wrinkled; flanks wrinkled; ventral surface smooth; toe tips bearing small, rounded discs.
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| Ingerana occidens sp. n. in life. (A) Male holotype (BNHS 6845); (B) female referred material (PU RSN A27); (C) female paratype (BNHS 6847). |
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| Habitat of Ingerana occidens sp. n. (A) Type locality, a stream near Wari Chora, Agalgre, South Garo Hills; B) A stream near Mawlynnong village, East Khasi Hills. |
Ingerana occidens Naveen sp. n.
Definition: SVL 21.5–23.05 mm in adult males (n = 2) and 25.02–26.0 mm in females (n = 3); head wider than long; supratympanic fold well developed; tympanum distinct, circular, elevated in the centre to form a protrusion, more than half the diameter of the eye (VTYD/EL = 0.72–0.91) (n = 4); thigh length shorter than shank length; fingertips rounded to very small discs; dorsal surface weakly wrinkled; flanks wrinkled; ventral surface smooth; toe tips bearing small, rounded discs.
Etymology:
Ingerana borealis was named borealis based on the Latin word for ‘north’. Although Annandale (1912) did not provide an explicit reason, the epithet likely reflects the species’ range being farther north than the known distribution of the South Indian endemic genus Micrixalus Boulenger, 1888, to which it was originally assigned. And this reasoning also applies to Ingerana, as it remains the northernmost known member of the genus based on currently available data.
The new species described herein is named occidens, derived from the Latin term ‘occidens’, meaning ‘west’, in reference to its range occurring west of the ranges of the two other currently recognised congeners. The distribution of this species thus marks the westernmost known extent of the genus’ range. The specific epithet is used as a noun in apposition.
The recommended English common name is western trickle frog.
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| Map showing type localities and records from this study of the two Ingerana species from the Eastern Himalayas, separated by the Brahmaputra River. |
R. S. Naveen. 2026. A river in between: A New Species of Ingerana Dubois, (Anura: Dicroglossidae) from the Garo and Khasi Hills, with A Redescription of Ingerana borealis (Annandale) from the Abor Hills, India. Journal of Natural History. 60(17-20); 1105-1125. DOI: doi.org/10.1080/00222933.2026.2656411 [27 Apr 2026]
