A new member of India's frog diversity with green blood and turquoise bones

Image: Gracixalus patkaiensis (Top). Gracixalus medogensis (Bottom). Image Credit: S D Biju, https://doi.org/10.11646/zootaxa.5659.4.3

Earth's biodiversity hotspots are places teeming with so much life that many have yet to be discovered or are under-investigated. The northeastern region of India, nestled within the majestic Himalayas and the Indo-Burma biodiversity hotspot, is one such place, with a vibrant ecosystem that continues to yield incredible biological surprises. 

A new study published in Zootaxa has shed new light on a group of tiny, enigmatic tree frogs, called Gracixalus frogs, revealing not only a new country record but also a truly astonishing biological trait: frogs with green blood and turquoise bones.The research was undertaken by researchers from the University of Delhi and Harvard University, led by Prof SD Biju from the University of Delhi.

Gracixalus frogs are relatively small tree frogs, with adults typically measuring between 20.0 and 43.0 millimeters (less than 2 inches) from snout to vent. They often live in dense forests, perching on bamboo culms, branches, or leaves high above the ground. Researchers conducted extensive field surveys in Arunachal Pradesh, India, specifically in the Tale Valley Wildlife Sanctuary, Tiwarigaon, and Namdapha National Park, to gain a deeper understanding of the elusive Gracixalus frogs. Their efforts, conducted primarily at night when these amphibians are most active, involved listening for their distinctive calls, photographing live specimens, and carefully collecting samples for detailed study. 

More crucially, they extracted DNA from tissue samples and sequenced a specific mitochondrial gene (16S rRNA). By comparing these genetic sequences with those of other known Gracixalus species, they were able to identify the Indian populations as G. medogensis definitively. The genetic data further revealed that these Indian populations are closely related to their Tibetan counterparts, showing a shallow divergence of only 1.2-1.8% in their genetic makeup, which supports the idea that they are the same species.

Beyond the identification of G. medogensis, the study delved deeper into its characteristics, providing the first detailed morphological redescription of the species using multiple specimens, rather than the single specimen on which its original description was based. 

They also offered the first insights into the male vocal repertoire of G. medogensis, documenting two distinct types of non-pulsatile, whistle-like calls and analyzing their duration, rise and fall times, and dominant frequencies. This bioacoustic data is crucial for understanding how these frogs communicate and for distinguishing them from other species. The research also expanded knowledge on Gracixalus patkaiensis, a species previously known from only one locality in India. New locality records for G. patkaiensis were documented in Namdapha National Park, and the study provided additional details on its morphology, color variations, natural history, and habitat use.

One of the most astonishing findings pertains to G. patkaiensis: the researchers documented the presence of green blood and turquoise bones in this species, a characteristic previously reported in only a few other Gracixalus species and one other rhacophorid genus, but never before in an Indian frog species. This unique trait, where the bones (including limbs, vertebral column, and skull) and blood appear distinctly colored through the translucent skin, adds a layer of mystery and wonder to these amphibians.

This work significantly improves upon previous research by providing the first confirmed record of Gracixalus medogensis in India, thereby expanding its known distribution. It offers a much-needed detailed redescription of this poorly understood species, moving beyond the limited information from its original discovery. The study also provides the first insights into the male calls of G. medogensis, a critical aspect of amphibian biology often used for species identification. Furthermore, the documentation of green blood and turquoise bones in G. patkaiensis is a novel discovery for an Indian frog, adding to the known instances of this rare biological phenomenon. 

However, the paper acknowledges certain limitations. The phylogenetic relationships of G. medogensis have remained largely unresolved in prior studies, and while this research clarifies its position as a deeply divergent lineage, the overall intra-genetic relationships among Gracixalus species still remain uncertain due to the use of a short mitochondrial DNA fragment. The authors suggest that future studies should incorporate multi-gene sequence data and more comprehensive sampling to fully resolve these evolutionary puzzles. Additionally, the unique green blood and turquoise bones observed in G. patkaiensis warrant further histological and functional studies to understand their evolutionary significance and purpose.

By documenting the presence of Gracixalus medogensis in India and expanding the known range of G. patkaiensis, this study contributes vital baseline data for biodiversity conservation efforts. Understanding the distribution and characteristics of species is the first step in protecting them, especially in biodiversity-rich but vulnerable regions like the Himalayas. This work highlights the immense, yet often hidden, diversity of life in these areas, underscoring the urgent need for continued exploration and research.

The research team included Tage Tajo, Radhakrishna Upadhyaya, A N Diskshit Akalabya Sarmah, and Sonali Garg under the guidance of Prof SD Biju. The research was supported by a combination of grants from the University of Delhi, Harvard University, University Grants Commission, and CSIR.

This article was written with the help of generative AI and edited by an editor at Research Matters.

The article has been edited to add the image caption and credits. The error is regretted.