AN ECOLOGICAL THEATRE FOR STUDYING EVOLUTION AND CLIMATE IN ACTION

India is a home of extraordinary climatic variations, ranging from tropical (central plains and coastal) in the south to temperate in the north (Himalayas). Higher altitudes in the North receive ample winter snowfall (trans Himalayan regions of Uttarakhand, Himachal Pradesh, and Jammu & Kashmir), the Thar Desert in the west boils to 50°C in the summer (places like Phalodi) and drops to -2°C (places like Churu) during winter. The long coastal line has higher humidity. The monsoon works as a catalyst in the system. It rejuvenates life back on track after a long and stressful summer across the subcontinent. India’s climate is strongly dictated by the Himalayas and the Thar Desert.

Life interacts with the environment, and sometimes it unfolds in a graded fashion. In scientific terms, graded variations in traits are known as ‘clines’. These clines could be along long geographical ranges, including latitudinal and altitudinal variations. Clines are also good proxies for uneven climatic conditions across latitudes and altitudes, and their interaction with species. Across these graded environments, species act and variations appear at morphological, physiological, and behavioral levels. India is such an amazing ecological theatre where species show huge variations along its long latitudinal ranges and elevational gradients. In Darwinian language, selection (in the form of temperature, humidity, atmospheric pressure, etc.) operates on species, and species come up with modifications to cope with the prevailing conditions (or adapting). The clines are classic examples of evolution in action. Evolutionary processes maintain these variations along continuously changing climatic conditions (i.e., spatiotemporal variations).

According to a 2011 study, there are around 8.7 million species on this planet, and a large chunk of these are insects. Insects are also organisms that could possibly tolerate the widest thermal range. One such insect is the fruit-fly Drosophila melanogaster, an apple of scientists’ eyes. This tiny 2-3 mm long insect has told us way more than any other organism in the labs across the globe, particularly in the field of evolutionary biology. A large set of studies on clinal variations has been done on fruit-fly species across the globe. In India, it has been used for almost 2+ decades for ecological studies. This accounts for a dozen plus traits studied across geographical gradients (latitudes/altitudes) in more than 10 different fruit-fly species, including cosmopolitan Drosophila melanogaster.

Some of the most interesting trait patterns found along the Indian subcontinent are the presence of opposing clines in drought tolerance and starvation resistance. As you move from south to north, fruit flies get better at handling drought, whereas the opposite was observed for starvation resistance. These patterns could be dictated by seasonal variations, availability of resources, and interaction with other biotic components along the environmental gradients. The other interesting trait is body pigmentation in fruit flies. The cosmopolitan Drosophila melanogaster demonstrates a cline in body myelinization. These variations support the ‘thermal-melanism’ hypothesis, which suggests that insects living in colder climates need to warm up and cool down quickly than those living in warmer places. The ecophysiology traits studied so far have shown significant variations along the Indian latitudes, clearly highlighting their importance in tracking evolution in action.

Clines remains the most powerful tool for observing and assessing rapid evolutionary changes in populations along the environmental gradients, particularly in the context of climate change.  

To know more about some of the fundamental mechanisms covered in this piece, please refer to the following readings:

1. Mayekar H, Ramkumar DK, Garg D, Nair A, Khandelwal A, Joshi K, Rajpurohit S. 2022. Clinal variation as a tool to understand climate change. Frontiers in Physiology, 13:880728. https://doi.org/10.3389/fphys.2022.880728.

2. Rajpurohit S, Zhao X., and Schmidt PS. 2017. A resource on latitudinal and altitudinal clines of ecologically relevant phenotypes of the Indian Drosophila. Scientific Data, 4:170066. https://doi.org/10.1038/sdata.2017.66.

3. Rajpurohit S. and Nedved, O. 2013. Clinal variation in fitness related traits in tropical drosophilids of the Indian subcontinent. Journal of Thermal Biology, 38:345-354. https://doi.org/10.1016/j/jtherbio.2013.04.004.

4. Rajpurohit S, Nedved O. and Gibbs AG. 2013. Meta-analysis of geographical clines in desiccation tolerance of Indian drosophilids. Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 164:391-398.

author bio:

Subhash Rajpurohit is an evolutionary ecologist whose work bridges science and storytelling, exploring how life endures under heat, drought, and shifting climates. Blending research with creative expression, he transforms ecological insights into narratives that resonate beyond academia.