Small isolated populations are a raw material for speciation. Populations that get isolated from the main population are often small and soon begin evolving independently. However, small populations are prone to impacts of drifts and inbreeding which makes them vulnerable to extinction. With whole genome sequences of several endangered populations of tigers and rhinoceros we show that small isolated populations often purge some of their deleterious allele loads. However, whatever deleterious alleles remain in the population, are in high frequency and homozygosity. This might lead the population to extinction. We further observe with simulations and emperical observations that migrations from a different population although increases the deleterious allele load, also lead to decrease in the frequency of deleterious alleles and their homozygosity. Does this indicate that allopatric species also need mild gene flow from other populations?

 Long-term dynamism in forest vegetation composition has significant implications for biodiversity and conservation. In the mid-hills of Kumaon in the Western Himalaya (1500 m -2400 m asl), the expansion of pine into oak-dominated hardwood forest has been of concern, due to its possible impact on biodiversity and livelihoods. Yet this vegetational shift is poorly studied in terms of spatial extent, the underlying drivers or the ecological consequences. We used field-based and remote-sensing methods to quantify oak-to-pine transition over three decades and studied the effect of this shift on forest bird communities in a 1285 sq.km multiple-use forest landscape in Kumaon. Our analysis indicates a gradual replacement of hardwoods with pine over the period of study: specifically, 22% decline in dense (protected) oak, a 29% decline in degraded oak and 74% increase in pine- over their original extents respectively- from 1991 to 2017. We found significant roles for micro-scale spatial variation in habitat, topography and climate in driving the oak-to-pine transition. Spatial analysis of forest bird communities further suggests that the transition of hardwood forest to pine may result in significant defaunation over time. For instance, pine forests support 33-46% lower forest bird species richness than hardwood oaks. Hardwood forest specialists could be especially vulnerable to forest change, showing 93-97% lower abundance in pine forest sites in comparison to dense oak sites. Additional effects of warming and degradation may further intensify species losses at the regional scale, and require further study.

Altitudinal migration is the seasonal movement of organisms between higher-elevation breeding grounds and lower-elevation wintering grounds. Despite altitudinal migration being a common phenomenon (for instance, 70% of birds in the Himalayas migrate altitudinally), the abiotic and biotic drivers of altitudinal migration remain poorly understood. This is important because 85% of global terrestrial biodiversity is concentrated in mountains, and these species are vulnerable to the impacts of climate change. I propose to describe avian altitudinal migration in the Himalayas and determine the role of diet and thermal niche tracking in driving these seasonal movements.

The study site for my thesis is Eaglenest Wildlife Sanctuary, Arunachal Pradesh, which is part of the Eastern Himalayan Biodiversity Hotspot and is home to >350 breeding bird species. I first use a large open-source citizen science dataset to describe various altitudinal migration strategies across the Himalayas. I then go on to assess the various eco-morphological and functional traits as predictors of avian altitudinal migration. I then plan to determine whether migratory birds are tracking their thermal niche or dietary resource availability. For various species, I will assess and compare the degree of overlap in temperature and arthropod availability in their breeding and wintering grounds. Finally, I plan to investigate if diet can explain why certain birds migrate while others prefer to stay back in the harsh winter. I will determine bird diets using DNA metabarcoding on bird faecal samples. Given the various limitations of the DNA metabarcoding technique, I plan to use a complementary method to investigate diet – I will use stable isotope ratios of carbon and nitrogen in whole blood to compare the seasonal trophic niches of resident and altitudinal migrants in the eastern Himalayas. Results from this work will thus help improve our understanding of how and why birds migrate altitudinally, and will have implications for the conservation of montane biodiversity in the face of climate change.

A dramatic increase in global mean temperature and rapid thermal fluctuations are predicted to hit the earth in the coming decades. Anthropogenic activities are accelerating the thermal variations and it can have significant impacts on organisms worldwide. Tropical ectotherms are considered to be more vulnerable to climatic changes as they are adapted to relatively stable, aseasonal conditions of the tropics and are dependent on environmental temperature for all aspects of behaviour and physiology. While several studies have investigated the effect of climate warming on the behaviour and physiology of temperate ectotherms, studies on tropical ectotherms are lacking, though they’re predicted to be at high risk from global temperature increases. For my thesis, I propose to study the thermal responses of tropical agamid lizards in India. Furthermore, I propose predictions for organismal responses to future climate warming.

The first chapter looks at the effect of environmental temperature on the body colouration and regional heterothermy of P. dorsalis in a rural-urban context. The UV- visible colouration and body temperature patterns of both sexes will be measured on a range of temperatures (15, 20, 25, 30, 35 and 40 °C). The second chapter investigates the influence of environmental temperature on physiological and motor performances at a community level. The metabolic rate, sprint speed, endurance and bite force of the three species- P. dorsalis, P. blanfordanus and C. versicolor will be measured across the temperature range. In the third chapter, metabolic rate and motor performances of the three species will be used to predict how the species will respond to accelerated climate warming in the coming decades. The fourth chapter focuses on the developmental plasticity of thermal limits. The effect of thermal fluctuations experienced by the P. dorsalis eggs during the time of incubation on the thermal tolerance range of the hatchling will be examined. Overall, the thesis provides insight into the thermal ecology of tropical agamid lizards and the impact of climate change on their fitness.

Venom is a remarkable evolutionary innovation that has underpinned the successful survival of several animal lineages, including arthropods. Scorpions are one such charismatic arthropod group equipped with a potent venom arsenal that facilitates their predatory lifestyle. Interestingly, despite the evolutionary history of over 400 million years, the extant scorpions exhibit unparalleled morphological similarities with their fossil counterparts. With its diverse topographic and climatic conditions, India harbours a vast diversity of scorpion fauna.

Scorpion venoms are a treasure trove of bioactive components with remarkable target specificities optimised by natural selection for millions of years. These components have tremendous potential as prospective leads for developing venom-derived therapeutics. Despite being fascinating from an evolutionary venomics and biodiscovery perspective, Indian scorpions remain largely unexplored. Scorpion research in India has primarily focused on taxonomic investigations enumerating and describing novel species without appropriate validation with molecular phylogenetics. The Indian red scorpion (Hottentotta tamulus) is a cryptic group of medically relevant scorpions with a pan-India distribution. Historically, several subspecies were proposed that have been synonymised during taxonomic revisions without any molecular validation. Anecdotally, it is known that H. tamulus stings from specific locales are more potent than others. But despite the evident differences in clinical manifestations, very few studies have characterised their venom repertoire. Furthermore, our understanding of the influence of life history, population genetics structures, ecology, and environment in shaping scorpion venoms is also limited. As part of my PhD research, using a multifaceted approach integrating phylogenetics, population genetics, proteomics, transcriptomics, in vitro and biochemical characterisations, I propose to exhaustively characterise the venoms of geographically disparate populations of H. tamulus, unravel the influence of ecology and evolution on their venom arsenal, and investigate the evolutionary relationships of these arthropods within a phylogenomic framework to bridge the current knowledge gap.

Spiders of the family Theraphosidae, commonly known as tarantulas, represents the largest group within the infraorder Mygalomorphae. Tarantulas have a Gondwanan affiliation, more than 1000 species distributed worldwide and carry a repertoire of adaptive traits like urticating hairs, stridulatory setae, colour, and venom. All these features make them an exciting model system for evolutionary studies. Through my thesis, I will try to understand the macroevolutionary dynamics and historical biogeography of tarantulas at both broad and specific levels.

Widespread taxa of ancient origin represent ideal systems for studying continental scale biogeography. In the first chapter, using tarantulas as a model system, I aim to explore how the breaking up of Gondwana and subsequent tectonic activity of former Gondwanan landmasses have caused cladogenesis and shaped the modern-day distribution of these spiders.

The tree of life is highly asymmetrical in terms of species richness, and the theraphosid tree of life is no different. In the second chapter, I aim to investigate the causation of such disparity in clade sizes, i.e., why some clades are extremely specious while others are depauperate. Using an extensive time-calibrated phylogeny of tarantulas, I will test different macroevolutionary hypotheses. First, I will test the clade age hypothesis, which states that the bigger clades are older, so they have more time to diversify than younger clades. I will measure the net diversification, speciation, and extinction rates across the phylogeny. Using phylogenetic comparative methods, I will test the role of two potential candidate factors- microhabitat and defensive traits, which I suspect to have influenced the diversification dynamics and as potential explanations for this unevenness of diversity across clades.

The first two chapters will give us a broader picture, i.e., a zoomed-out view of the biogeography and diversification of the whole family. In the third chapter, I will zoom in on a particular subfamily Thrigmopoeinae, which represents an ancient endemic lineage restricted to the wet evergreen forests of Western Ghats. There is considerable taxonomic ambiguity in this subfamily. First, I will identify the species limits within this subfamily by employing a multicriteria approach using genetics, morphological and ecological data. Taking this result forward, I will explore the diversification and biogeography of this group. Being an ancient, niche conserved, and species-poor group, I hypothesize that the cretaceous volcanism which eventually wiped out all the wet evergreen forests of Northern and Central Western Ghats, as well as the topological discontinuity in the Western Ghats, might have played a significant role shaping the distribution and diversification of this lineage.

Assemblages of bat species are structured by the interplay of abiotic and biotic factors, which change dynamically across space and time. From the perspective of space, an assemblage is expected to uniquely correspond to a land-use type. Northeast India hosts two biodiversity hotspots and a variety of land uses, but ecological studies on bat assemblages are lacking. Bats make up the second most diverse mammalian order, with 1447 species, out of which 87% possess the ability to echolocate. Urban regions followed by rural regions represent the highest form of anthropogenic landscape modification, while natural regions like protected areas, reserve forests, etc. represent the least modified. This study aims to characterize the echolocating bat assemblages in the tropical lowlands of Assam and Arunachal Pradesh. I will investigate the response of foraging bat assemblages to different levels of landscape modification in terms of change in species diversity, species composition, and activity. Habitat, disturbance, roosts, and prey are known to be the key ecological drivers of assemblage change. Depending on the preferred foraging mode and morphology, a bat species is best adapted to a particular type of prey and foraging habitat/background. Therefore, whether the diversity of prey and spatial niches i.e., habitat are positively associated with species diversity will be examined. The temporal dynamics of disturbance and resource availability are expected to vary across the regions. On that account, I will determine if assemblage and species-wise bat activity patterns also differ in different regions. Detecting bat echolocation calls enables one to non-invasively monitor bats in the field. Since echolocation calls are mostly conserved and can be used for species identification, I will establish a regional call library by recording captured bats. Passive acoustic monitoring (PAM) methods will then be used to realise the above-mentioned objectives.

In highly biodiverse tropical mountains with thermally specialist biota, natural elevationally-linked temperature gradients strongly determine the distribution of species. In addition to this natural gradient, anthropogenic habitat change creates new abiotic conditions by (a) shifting existing thermal gradients upwards, and (b) through the creation of manmade habitats such as agriculture and degraded forest, which are hotter and climatically more variable than natural forest. Climate change is already causing rapid range shifts of many species to higher elevations, but how species adapt to changes in the abiotic environment because of the interactive effects of climate change and land-use change remains largely unknown. Recent evidence indicates that populations of some species undergo morphological changes over decades in response to warming temperatures. Further, in birds, environmental stressors (including thermal stress) trigger the hypothalamus-pituitary-adrenal axis (HPA axis) leading to the release of corticosterone, the primary stress hormone in birds. While blood corticosterone levels rise transiently in response to stress, feathers sequester corticosterone, providing a long-term picture of stress faced by birds. Prolonged stress also leads to an altered immune system, leading to changes in the composition of the gut, crucial for nutrient assimilation and detoxification. Unless morphological changes or range shifts minimise thermal stress, alterations in corticosterone levels and gut microbiota because of habitat degradation and climate change should affect fitness in birds. For three widely distributed bird species (abundant at all elevations and found in degraded forest; Schoeniparus castaneceps, Actinodura egertoni, and Trochalopteron erythrocephalum)that vary greatly in body size, I aim to understand how natural and man-made temperature gradients affect morphology, stress, the composition of gut microbiota, and survival in Eastern Himalayan montane bird species.

Species interactions are known to shape biological communities. While antagonistic interactions like competition and predation are well known, cooperative interactions have received comparatively less attention. Mixed-species foraging behaviour is a common phenomenon seen across various taxa, including fish, birds, and mammals, where different species form groups and forage together. Unlike symbiotic associations, these interactions are more dynamic and include a much larger subset of species of the community. We sampled mixed-species groups (MSG) of reef fish in the Lakshadweep islands, off the west coast of India. The data was gathered over four years following a mass-bleaching event which led to massive loss of coral in Lakshadweep in 2010. Though not widely reported, we discovered that mixed-species grouping is a common occurrence in the reef ecosystem. Around 130 of the 305 commonly observed species of fish in the Lakshadweep were seen participating in groups to some extent. Using a cluster analysis on species composition, we categorised the groups that were observed in Lakshadweep into nine compositional categories, which also exhibited variation in behaviour, habitat affinity and group cohesion. We then examined variation in grouping propensity, species richness, species evenness as well as species composition across space, time and habitat for the most commonly observed compositional categories. We found that invertivores tended to form smaller attendant groups, with clear nuclear-follower relationships, and likely form for direct foraging benefits. Herbivorous fish on the other hand formed large shoaling associations indicating benefits gained from increasing group size. We found evidence of the effect of the mass-bleaching event and subsequent ecosystem recovery on the formation of some groups. Reef fish MSGs are thus important components of these ecosystems and can both affect and be impacted by reef structure and function.

Honeybees are a well known example of self-organized collective systems. Individuals perform tasks and coordinate their behavior in a way that translates to the colony-level organization. Stressful situations such as high temperatures are common in the environment. Specifically, during heat stress periods individuals show enhanced behaviors such as fanning and spreading water. During such conditions, it is not understood how individuals in the colony vary in their behavior, what factors determine changes in behavior, and how these translate to the colonylevel response. We examine the honey bee heat stress response by introducing multiple agematched cohorts (i.e. several thousand tagged bees) into an observation hive, and analyzing their movement behavior. We use the behavior over time for each individual to extract the dominant modes of response, and furthermore ask how previous behavior predicts how an individual responds during heat stress. Broadly, such large scale colony-level analysis can reveal if there are general principles of reorganization that honeybees adhere to when encountered with sudden changes or stress.