Changing course of streams due to anthropogenic reasons is bad news for Adi cascade frogs
Making of check dams on streams and removal of boulders may wipe out the local population of Adi cascade frogs (Amolops adicola), a recently discovered species in Arunachal Pradesh, scientists claimed.
The nomenclature ‘cascade frogs’ draws on their preference for small waterfalls. Genus Amolops is among the largest groups of ranid frogs (family Ranidae) with 73 known species widely distributed across India’s North East and north, Nepal, Bhutan, China, the Indochina region and the Malaya Peninsula.
Cascade frogs, in general, depend on the flow of water. Both adults and tadpoles of Adi cascade frogs, the species in question, are particularly adapted to fast flowing sections of stream. As such, modification of stream channels may endanger them.
“One of the major threats to these animals is rapid change to their habitat; such as the construction of small dams on streams, altering stream-flow for agriculture and removal of boulders,” said Naitik G Patel from the Department of Endangered Species Management at Wildlife Institute of India (WII).
A team of Indian and American biologists from WII, University of Delhi and North Carolina Museum of Natural Science discovered the species at Arunachal’s Adi hills. They wrote about their research in the Journal of Natural History.
A typical fast flowing forest stream and associated moist habitat of the newly discovered Amolops adicola; photo: Dhritiman Mukherjee
Arunachal, a biodiversity hotspot, is home to many endemic, endangered and threatened species as well as to indigenous people who depend on its biological resources. Activities like habitat loss, deforestation and overexploitation have threatened the rich biodiversity. Construction of dams is among factors that have led to the destruction of forest cover.
The Forest Survey of India in 2019 estimated that Arunachal had 66,688 sq km of forests — 79.6 per cent of the state’s area. Global Forest Watch, hoewver, estimated the forests cover at 74 per cent of its total land area. The non-profit had also warned that 2,093 sq km of tree cover was lost from 2001-2019 — a 3.3 per cent decrease.
FSI has attributed the decline pressures of increasing population, developmental activities, and clearing for jhum agriculture. In lowlands, however, illegal tree-felling, expansion of roads and increasing plantations of cash crops are to be blamed too.
About Adi cascade
“The species was discovered while revisiting a century-old Adi expedition in 2018 and named after the land of the Adi tribe where the frogs dwell, particularly post-monsoon,” said Abhijit Das from WII.
The biologists were investigating a group of medium- to large-sized cascade frogs from the North East over five years. The new species was identified based on multiple criteria such as its external morphology, deoxyribonucleic acid (DNA) and calling patterns.
The study resolved century-old taxonomic confusions about the identity of another cascade frog species, Amolops monticola, which was described from the Sikkim Himalayas 150 years ago. The discoveries have important implications on the taxonomy and geographical distribution of several other members of this group found in India and the neighbouring regions of China.
The call of the frog is quite unique with continuous notes almost like a cricket, scientists said. They are delivered at very short intervals, not long call groups — giving an impression of being continuous: A typical call lasts 485.2 milliseconds.
The species is predominantly found in open riverine landscapes and human-inhabited rural areas. During October, calling activities started as early as 3 pm.
Calling individuals were located inside thick vegetation on roadside slopes facing the Mossing river by around 5 pm and the vocalisation continued until 10 pm.
Males were mostly observed on tree saplings, fern fronds and banana plants in and around the cultivated land. During peak activity, they were largely located among exposed roadside boulders below the slopes, closely by water.
The authors observed a similar-looking population of frogs in the Subansiri river basin, inhabiting rivers such as Ranganadi, Pare, Pati and Lichi in Arunachal’s Lower Subansiri district — 130-150 kilometres west of the type locality. Further studies are required to confirm their identity.
This frog — locally known as Juri (stream) Tatik (frog) — is considered a local delicacy. The authors observed bundles of smoked frogs being sold in the main Pasighat market.
High species diversity among A. monticola —evident from frequent new descriptions from neighbouring regions, integrating evolutionary histories and morphological diagnosability — makes it likely that more endemic taxa may be discovered from relatively unexplored forests in the Indian Himalayan biodiversity hotspot.
“This study is once again testament to how little is known about the most-threatened animal groups, frogs, in northeastern India,” saiud SD Biju, a professor in University of Delhi. Many frogs in the region reported to occur widely, in fact, have relatively small geographical ranges and need special attention to prevent extinction, he warned.
“The North East is a treasure house of species still unknown to science,” Biju added.
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