Organisms face the allocation problem of investing resources in different traits. Investment strategies are expected to maximise fitness by balancing the costs and benefits of investing in multiple traits used in diverse contexts, including acquiring territories, food, and mates. The trade-offs associated with trait investment are likely to be dynamic. For example, ecological factors, such as climate, temperature, and diet, and demographic factors, such as male and female densities and sex ratio, can affect trade-offs and, thereby trait investment. 

Many animals show strikingly exaggerated traits like antlers in Cervids. Such traits represent costly trade-offs because they decrease the residual resources available for allocation to other traits. Moreover, individuals within a population often exhibit variation in exaggerated traits, with relative trait sizes increasing with body size. This pattern of positive allometry where individuals ‘invest disproportionately more resources to traits as body sizes are larger’ has been proposed to be due to sexual selection. However, studies have also suggested that sexually selected traits might not universally display positive allometry; these studies provide examples of sexually selected traits that show slight negative to isometric scaling. More recent studies have proposed that whether sexually selected traits show positive allometry depends on the trait's behavioural context and functional relevance.   

A long history of examining resource investments using the approach of allometry has focused on quantifying how behaviours, morphology, and other traits scale with body size. Our understanding of the processes underlying the maintenance of positive allometry in a population is limited. Specifically, investigations of how dynamic changes in ecological and demographic factors affect positive allometry are few. Moreover, empirical studies investigating how trait allometries contribute to individual fitness are scarce. Such studies are necessary for deciphering the selective factors maintaining positive allometry in a population. 

Using the rupicolous agamid species Psammophilus dorsalis, we aim to understand how positive allometry in morphological traits is affected by dynamic variation in the selection environment. By employing microsatellite markers for genotyping and parentage analysis, we also propose to examine the contribution of positive allometry in morphological trait to reproductive fitness. Finally, in polygynous systems like P. dorsalis, males commonly use multiple traits in the competition for mates. We also aim to understand how investment patterns and relative scaling of the focal morphological traits affect the payoffs to other traits used in the competition for mates, including the diverse set of signals. The questions in the thesis will be answered using long-term morphology and demography datasets, together with behavioural observations and field experiments.

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.