The cost-benefit framework forms the basis for current theories on the evolution of group living in animals. Much attention has been paid to drivers of intraspecific grouping in vertebrates, with recent emphasis on heterospecific groups. However, a disproportionately large fraction of vertebrate taxa choose to remain solitary at all times. Using a secondary dataset on extant species of fish, birds and mammals, the first part of this study aims to identify the suite of traits that these solitary taxa are typically associated with, and the possible benefits gained from choosing to remain solitary.

Heterospecific grouping is a widespread phenomenon because it allows animals to exploit benefits such as protection from predators or access to key resources in a manner that is more effective and energetically efficient, while simultaneously reducing the costs of competition associated with conspecific grouping.

Tropical reef fish are a system where both single- and multi-species groups are seen. The ecological significance of the latter is poorly understood when compared to other vertebrate taxa. It has been proposed that such groups might be capable of impacting the overall trophodynamics of the reef by influencing benthic invertebrate and algal community structure. Our study is aimed at understanding the different drivers that influence mixed-species grouping in reef fish. We intend on assessing factors like morphology, phenotype, resource availability and predation risk to determine their role in shaping association patterns of shoaling reef fish groups using primary and secondary data, and a combination of empirical and simulation-based approaches.

Alternative Reproductive Tactics (ARTs) refer to traits that allow individuals of a species to maximise their fitness in two or more ways. ARTs have been reported in many taxa and can manifest as discrete morphological, physiological, and behavioural differences among individuals of either sex. Various ecological contexts such as predation risk, spatial and demographic context can impact the fitness of ARTs and affect their persistence. Thus, studies on the effects of these contexts on the relative fitness of ARTS are essential, especially with respect to plastic, reversible ARTs that involve signalling. In this thesis, I will use an acoustically communicating, nocturnal species of tree cricket, Oecanthus henryi, to investigate how ecological context shapes the fitness of ARTs. Males of O. henryi can display ARTs such as calling, baffling, or acting as silent satellites to obtain copulations. Predation may affect the relative success of these ARTS by differentially affecting the mortality of males expressing these tactics. Furthermore, proximity to females may affect the relative efficacy of these tactics in attracting mates. Lastly, the interaction of demographic factors such as population density, frequency of tactic expression and sex ratio may affect the fitness outcomes of these ARTs. In this thesis, I propose to examine the effect of predation, spatial and demographic context on relative fitness benefits of different ARTs, using empirical and simulation-based approaches.

Venom is an adaptive trait that has propelled the expansion of snake lineages across diverse habitats. Natural selection optimises the potency, composition, and lineage-specificity of the snake venom arsenal for effective prey capture or deterrence of predators. Venoms of several closely related snake species that inflict life-threatening bites in humans have been documented to exhibit tremendous spatial and temporal venom variation. However, venom research in India has predominantly focussed on assessing the compositional variation among captive snake populations from restricted locales. Several questions pertaining to the evolutionary ecology of snake venoms remain unanswered. Therefore, studies integrating the knowledge on natural history and trophic interactions of medically important Indian snakes is warranted. 

As part of my PhD research, I propose to decipher the role of various ecological and environmental determinants on the diversification of Indian snake venoms. To understand the influence of the environment, I will sample snake venoms from the major biogeographic zones across the country. A multi-faceted approach involving proteomics, biochemical analysis, pharmacological assessment, and toxicity studies will be employed. Further, I will evaluate the role of ecological traits, such as ontogeny and gender, in shaping venoms by housing venomous snakes under captivity. The differences in their venom activities and toxic potencies will be evaluated. Moreover, as the feeding ecology of snakes plays a significant role in determining venom characteristics, the prey-specificity of these venoms will be determined using in vitro and in vivo experiments. Briefly, the kinetics of interaction between venom toxins and their target receptors (synthetic mimotopes) sequenced from various natural prey animals will be evaluated using bio-layer interferometry.  In vivo experiments will involve toxicity assays against diverse model systems including arthropods, amphibians, reptiles, birds, and mammals. These experiments will also shed light on the evolution of venom resistance in target organisms. Finally, the repercussions of venom variation at various levels on the snakebite treatment in India will be investigated by performing WHO-recommended preclinical assays. These studies will decipher the effectiveness of the currently employed conventional antivenom therapy in mitigating snakebite mortalities and morbidities across the country.

Microbial communities are highly dimensional, with many species and many variable environmental factors. Macroecology, which studies communities as statistical ensembles, is a promising way to connect these complex data to mechanistic models. In this talk, I will discuss a minimal set of macroecological patterns that characterize the statistical properties of species abundance fluctuations across communities and over time. A mathematical model based on environmental stochasticity quantitatively predicts these three macroecological laws, as well as non-stationary properties of community dynamics. Building on these results, it is possible to disentangle the (statistical) properties that determine ecosystems' stability over time and reproducibility across communities.

Understanding how species coexist despite competition is an enduring challenge in community ecology, with a rich history of theory, empirical work and controversy. In 2000 AD, Peter Chesson published a seminal paper in which he used Lotka-Volterra models of two-species interactions to derive the conditions for coexistence in terms of the relative strength of intra- vs. interspecific interactions. Modern coexistence theory or MCT, as this is termed, also incorporates the role of temporal and spatial factors on coexistence and offers a unifying theoretical framework to understand the processes that maintain diversity. In the years since, MCT has attracted much attention with key theoretical and empirical advances. It has been extended to multi-species systems and applied to questions of species distributions, invasive species, species persistence with climate change, and habitat fragmentation. MCT integrates previous work on species coexistence and is today a key paradigm in community ecology. In this lecture, we will go over the basic components of MCT, relate it to other theories of species coexistence, link to established frameworks of species interactions, and explore empirical applications and limitations. The goal of the lecture is to provide an overview of modern coexistence theory as a conceptual basis to contextualize questions regarding community assembly. 

We live in a human-dominated Earth. Human activities have broken up many once contiguous terrestrial habitats into smaller fragments—where ecological communities lose diversity. Patterns of diversity loss in forest fragments have been widely documented. Yet, we know surprisingly little about how the mechanisms that maintain diversity fare in fragments. Long-standing theory and growing empirical evidence indicate that in plant communities, pests and pathogens—natural enemies—help maintain diversity via negative feedbacks on host plant populations. The diversifying effects of enemies are especially strong during the early life-stages of seedling establishment and survival, but its imprint can last many generations. Could weaker enemy effects explain reduced plant diversity in forest fragments? In a human-modified forest, I found that enemies such as insects and fungi were less able to maintain diversity of tree seedlings near forest edges compared to interiors. Weaker effects of enemies also changed the functional characteristics of recruiting seedlings. Simulations using this field data show that changes to seedling dynamics can compromise the long-term ability of fragments to maintain diversity. Contrary to common expectation, canopy openness, a correlate of light availability, did not correlate with spatial variation in diversity of species or traits. With nearly 20% of the world’s forests being within 100 m of an edge, loss of cryptic biotic interactions may pose a widespread threat to plant diversity. In my future work, I will delve deeper into the mechanisms that link enemy-mediated feedbacks to species performance and diversity in forest edge vs. interior. Furthermore, I will expand on my ongoing work that examines how a changing climate (drought) will interact with edge effects to shape performance of tree species, and hence their fitness, in human-modified forests. Mechanistic insights that combine ecological theory with observation and experiment can help predict the trajectories of human-modified ecosystems in a fast-changing world.

TO BE UPDATED

As part of the initiative to have more conversations about mental health and wellbeing, the Workplace Wellbeing Committee would like to organise a talk and Q & A session with Dr. Vyjayanthi Subramaniyan, who serves as one of the two consulting psychiatrists at the IISc Wellness Centre. This session aims at addressing questions and concerns which are perhaps close to all our hearts- how do we recognise and ask for help in dealing with issues concerning mental health, for ourselves or for friends and loved ones. Dr. Vyjayanthi would like this to be a question & answer session so as to address our concerns better, in the limited time available.

Given India’s ancient association with Gondwana and subsequent separation from Africa and Madagascar, vicariance has often been invoked to explain the current distribution of some of its so-called Gondwanan biota. In this talk, I review phylogenetic studies and fossil data of Indian tetrapods to ascertain the relative contribution of dispersal and vicariance in shaping their distributions. Results indicate that Paleogene dispersal into India better explains the current distribution of most of the tetrapods in India. Vicariance is invoked for three fossorial groups, namely caecilians, frog family Nasikabatrachidae and blindsnake family Gerrhopilidae. It is plausible that much of India’s Late Cretaceous tetrapod fauna of Gondwanan origin went extinct due to Cretaceous-Paleogene mass extinction and Deccan volcanism. Subsequently, it was replaced by intrusive elements as India proceeded to dock with Asia in the Paleogene. In this regard, soil invertebrates might be a promising study system to understand the Gondwanan component of Indian biota.  

Genetic variability in an organism allows us to assess its ability to respond to changing environmental conditions or disease epidemics. Hence, preserving this genetic diversity is an essential aspect of conservation biology. Phylogenetic tools are often used to study this variation within and between groups and build strategies for management of Evolutionarily Significant Units. Population genetics, in addition, provides us information on the gene flow between populations, signatures of inbreeding and other aspects of their genetic condition. Studies in the past decade have brought up yet another angle of looking at biodiversity, in the form of the microbiome. Since microorganisms have a faster turnover than eukaryotic genes, the microbial diversity could potentially show signatures of change at much smaller time frames. For my PhD, I studied the variation in Antilope cervicapra or blackbuck across its range, both in terms of genetics of the animal and its gut microbial diversity.   

The first part of the study tries to clarify the phylogenetic position of Antilope cervicapra with respect to other antelope lineages. Both concatenated and coalescent based methods were used, on data from 12 nuclear markers, to resolve the phylogenetic relationships between multiple species of antelope belonging to the four genera, Gazella, Nanger, Eudorcas and Antilope. I find that both coalescent and concatenated based phylogenetic analyses consistently place A. cervicapra as sister to Gazella dorcas, thus making Gazella a paraphyletic group. Divergence dating using fossil calibrations and biogeographic analyses show that the Antilope lineage diverged around ~2 mya and dispersed from the Saharo-Arabian realm into India, post the expansion of grasslands. Unlike the gazelle found in India, A. cervicapra was better suited to grasslands and semi-arid conditions and did not extend their range beyond the Indian subcontinent.  

The next section looks at phylogeography and population genetics of A. cervicapra across its geographic range. Using both mitochondrial and microsatellite genetic information, I find that different markers shed light on different aspect of their evolutionary history. The blackbucks seem capable of travelling much longer distances than expected, although habitat fragmentation in recent times has probably restricted their movement, as seen by the lack of shared haplotypes between locations. Both microsatellite (nuclear) and mitochondrial data indicate that the population from the Eastern part of India is genetically distinct and the species as a whole shows signatures of having undergone a bottleneck and recent genetic expansion. Further the microsatellites indicate the presence of 3 genetic clusters in this species, pertaining to the Northern, Southern and Eastern regions of India. The study also indicates the most likely demographic scenario where an ancestral population separated into two groups that gave rise to the North and South clusters and the East population was derived from the South at a later time period.  

Finally, I compare the gut-microbiome of blackbucks from ten different locations, to understand what drives their alpha and beta diversity. Metagenome information from the V3-V4 region of 16S rRNA was used to delineate different taxonomic orders of gut bacterial communities, to determine whether host genetics or the host environment has a stronger influence in structuring gut microbial community. Results show that although distance to human settlement and precipitation affect species richness of gut microbes, the correlations between nucleotide diversity and Shannon and Simpson alpha diversities were significant. Further, the pairwise dissimilarity between the gut microbial composition increases with both increasing geographical distance as well as pairwise microsatellite distance. This study sets a baseline for further research on how animal gut microbiomes associate with host genes and potentially influence fitness. 

Largely, this thesis looks at diversity in an endemic ungulate from different angles and also tries to elucidate its taxonomic position among Antilopinae.