ECR Feature: Arya Sidharthan on the cryptic diversity of mountain loaches

Arya Sidharthan is a PhD student at the Kerala University of Fisheries and Ocean Studies, India. She is a freshwater fish biologist, who uses molecular tools to study the ecology and evolution of fishes. Arya shares her recent work on unravelling the evolutionary history and cryptic diversity of mountain loaches in the Western Ghats.

It’s fun to be in the field early in the morning, when the mountain loaches are most active.

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Institute. Kerala University of Fisheries and Ocean Studies (KUFOS), India

Academic life stage. PhD candidate

Major research themes. Molecular Ecology, Biogeography, Freshwater Fish

Current study system. My research focuses on the molecular ecology of hillstream/mountain loaches on the Indian subcontinent. By understanding the phylogenetics and biogeography of this fascinating group of freshwater fishes, my work helps unravel the processes that have led to the amazing biodiversity in the Western Ghats mountain ranges, which is a global hotspot for endemic freshwater fish. Using genetic data, I try to decipher when and where different loach lineages originated, how they diversified, and the physical, geographic and climatic factors that influenced their speciation.

Recent paper in JBI. Sidharthan, A., Raghavan, R., Anoop, V. K., Philip, S., & Dahanukar, N. (2020). Riddle on the riffle: Miocene diversification and biogeography of endemic mountain loaches in the Western Ghats Biodiversity Hotspot. Journal of Biogeography, 47(12), 2741-2754. (Link)

Motivation behind this recent paper. The endemic loaches of genus Bhavania from the Western Ghats are poorly studied with respect to their systematics, evolutionary history and biogeography. Their morphological similarity to sucker-loaches of Indo-China and Sunda Islands has fuelled speculations that this group originated in South East Asia, and colonized the Western Ghats during the Pleistocene – but this has not been tested using molecular techniques. Also, the apparent wide distribution of the genus in Western Ghats from 9° to 13°N latitudes (an approximate south-north distance of 450 km), and the fact that only two species are currently known, encouraged me to investigate the true diversity within this genus.

The mountain loach, Bhavania australis is a “cryptic species complex” endemic to the Western Ghats Biodiversity Hotspot in India. Latin Name: Bhavania australis. (Photo credit: Beta Mahatvaraj)

Key methodologies. We carried out a multigene phylogenetic analysis of Bhavania specimens collected throughout their distribution range, using mitochondrial and nuclear markers. Subsequently, several species delimitation methods including the Automated Barcode Gap Analysis, Poisson Tree Process and Generalized Mixed Yule-Coalescent Model were used to understand the actual species diversity within the genus. A Bayesian chronogram was constructed to estimate the time elapsed since the most recent common ancestor of the distinct lineages of Bhavania. Ancestral ranges of distinct lineages of Bhavania were reconstructed using the dispersal–extinction–cladogenesis model to understand the historic factors (physical, geographic and climatic) that led to the current distribution pattern.

Typical mountain loach habitat in the Western Ghats! But finding my “freshwater nemo” is the toughest part of the job.

Major results. Our study suggested that the endemic Western Ghats mountain loach genus Bhavania originated in the early Neogene and diversified/radiated into cryptic lineages during the Miocene. This refuted the previously long-standing theory that the group arrived in India during the Pleistocene. It is likely that the Bhavania loaches dispersed across the Western Ghats mountains, expanding their range, with the help of intensified monsoonal rains during Miocene climatic changes. The current distribution of Bhavania loach lineages has been further shaped by events in the Miocene such as aridification and drying up of riverine connections, formation of land barriers and fragmentation of streams. Our results highlighted the first evidence that Cauvery, one of the largest eastward flowing rivers of Western Ghats, has acted as an east–west pathway for dispersal and diversification of an endemic fish lineage in the Western Ghats.

Unexpected challenges. The southern part of the Western Ghats where I carried out my field work was hit by two extreme climatic events resulting in catastrophic floods for over 4 months in the years 2018 and 2019 (coinciding with my main sampling period) cutting off all my field sites and making them inaccessible for months. Working closely with local fishers, we then managed to collect samples during weeks when there was some respite from the rains, in the most challenging of conditions.

One of my sampling sites is just below these majestic waterfalls.

Next steps? Collaborating with colleagues from across South and South East Asia, we plan to investigate the family-wide (global) phylogeny of mountain loaches. This work will not only improve our understanding of the current-day diversity and distribution patterns of this group of fishes, but also provide broader context of their evolutionary and biogeographical history in Asia.

If you could study any organism on Earth, what would it be? Penguins – because I just love them! Not just because they are adorable, but because they dwell in one of the most extreme climates on the planet, and still manage to be the best swimmers. Ah, and of course there are various misconceptions about their life history too (Happened to read this interesting book “The unexpected truth about animals” by Lucy Cooke. You must read it too!!! One of the interesting penguin facts highlighted in Cooke’s book is that penguins are often regarded as gentle, monogamous birds, when in reality, they are often the complete opposite: aggressive and highly promiscuous!  

Anything else to add? Studying freshwater biodiversity is monsoonal rivers, and particularly in tropical montane streams is challenging irrespective of gender due to the harsh and inaccessible terrain, and encounters with wild animals. But at the end of it, such studies give us a great satisfaction because of the way each study (however small) adds to the growing amount of knowledge required to conserve tropical freshwater biodiversity. In March 2020, I received an opportunity to present our work to the global conservation community at the Student Conference in Conservation Science at Cambridge. But Covid-19 dashed all my hopes. But now I am immensely happy that one of the world’s leading scientific journals has published and highlighted my work on their cover page, and through this blog! 

Published by jbiogeography

Contributing to the growth and societal relevance of the discipline of biogeography through dissemination of biogeographical research.

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