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.

Venom research has focused on front-fanged venomous snakes with fewer than three percent of rear-fanged snake venom proteomes characterised. These venoms have been neglected due to difficulties obtaining venom for characterisation and a lack of toxin sequences in databases for proteomic identifications. We characterized venom gland transcriptomes, venom proteomes, and toxin biological activities, using both enzymatic and toxicity assays, for two Old World and two New World rear-fanged snake species. Venoms were dominated by either three-finger toxins (3FTxs) or metalloproteinases, paralleling the venom dichotomy of front-fanged venomous snakes. Rear-fanged snakes Boiga irregularis and Spilotes sulphureus had venoms dominated by 3FTxs, and shared similar heterodimeric 3FTxs with lizard specific toxicity. In addition, S. sulphureus venom contained a monomeric 3FTx with mammal specific toxicity, allowing this non-constricting snake to capture mammalian prey, whereas B. irregularis uses constriction. Metalloproteinase dominated venoms from Ahaetulla prasina and Borikenophis portoricensis rapidly degraded the alpha subunit of fibrinogen, and within five minutes A. prasina venom also degraded beta subunits. Beta subunit degradation rate for A. prasina was even faster than observed for the front-fanged rattlesnake Crotalus viridis viridis. The majority of bites from rear-fanged venomous snakes do not produce systemic effects in humans, however, these venoms provide insight into toxin binding selectivity and mechanisms of action, as well as predator-prey toxin evolution.

Heritable variation in traits that enhance dispersal rates can accumulate at population margins by spatial sorting. This mechanism of selection differs from natural selection as evolutionary change can ensue even in the absence of differential lifetime reproductive success. Although evidence suggests that populations are rapidly evolving at the margins due to global change pressures, such as invasions and range shifts, we lack a mathematical theory of spatial sorting to understand these evolutionary patterns. To this end, I present an algebraic theorem of evolution, which we call the sorting theorem, to elucidate the general mechanism of selection at margins. The sorting theorem suggests that at population margins, evolution can ensue by any biological mechanism that yields a statistical association between the number of offspring that individual leaves at the margin and the mean phenotype of those offspring. Thus, the sorting theorem can facilitate axiomatic development and criticism of spatial sorting theory. Its role in guiding research in this context is analogous to that of Price’s theorem in natural selection theory.

The evolution of morphological traits is often strongly influenced by functional and biomechanical demands. Perhaps the best example of this is the avian bill, a multifunctional appendage consisting of an inner bony core and an outer keratinous rhamphotheca, which presents a unique opportunity to study form-function relationships. Among the varied functions of the bill, certain groups of birds use their bills to excavate tree hollows for nesting, roosting, and feeding. The physical stresses experienced during this mechanically demanding task may be linked to bill shape and material properties, and also to broader factors like environmental conditions which influence the availability and mechanical properties of the substrate. Here, we examine these relationships in the frugivorous Asian and African barbets, which occupy diverse climatic regimes and excavate nest hollows in trees. Using micro-CT scans of museum specimens coupled with landmark-based geometric morphometrics, we find that bill shape diversity has accumulated gradually over time in both clades under allometric constraints, and exhibits a significant relationship with climatic variables. Secondly, using finite element analysis and beam theoretic approaches, we find that maxillary geometry trades off with excavation performance under different loading regimes. Our study thus aims for an integrative, interdisciplinary understanding of the evolution of morphological traits in birds.

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.

Collective behavior is observed at different scales, from cells to animal groups to societies. Recent technological advancements have enabled an unprecedented increase in our ability to collect data for how individuals behave in a group. I will show results from a long-term tracking study of honeybees, where 5000+ bees were individually tracked using barcodes over their entire lives. This data provides a detailed picture of daily behavioral differences, and reveals lifetime differences in motion and task-switching behavior among bees. Using the same framework we introduced reproductive male drones into the hive, and analysis of their in-nest motion reveals synchronized periods of high-speed “hyperactive” motion that coincide with trips outside. By comparing with other collective systems we have analyzed – including fish, rats, and cellular collectives – I will highlight basic ways how “big data” can be used to describe biological variation, and discuss ongoing work which seeks to connect observed differences to group function and environmental characteristics.