Academic
Animal groups across taxa -- from insects and birds to fish and mammals -- exhibit a high degree of synchrony in their movement. Various empirical, computational and theoretical studies over the past two decades focus on how simple mechanisms produce these large-scale fascinating patterns. While a large number of empirical and theoretical studies examine the so-called proximate aspects of collective motion, only a few of them have investigated the functional or evolutionary significance. An important hypothesis for the function of group-living is that of reduced risks of predation. We hypothesise that not just group living but synchrony of group movement facilitates reduced risk of predation. For my PhD thesis, we will study this using theory and computational models in close collaboration with empirical work. We will employ empirically motivated computational spatial explicit models to study how anti-predatory behaviours at the level of individuals -- and crucially, flocking interactions among individuals -- result in collective escape dynamics of flocks. We will compute the effectiveness of information transfer via metrics such as spatial and temporal correlation measures or transfer entropy-based measures. We will compare how the efficiency of information transfer depends on the type of flocking interactions -- for example, when agents only interact stochastically with one of the near neighbours (as suggested by recent empirical studies) versus interaction with multiple neighbours (as suggested in classic physics-inspired modelling studies). These findings will later be compared with the results of empirical studies led by my colleagues in the lab to examine if the type of interaction (with just one neighbour or multiple neighbours) changes during collective escape dynamics. In summary, through this thesis, we will shed light on the functional importance of collective motion and the evolution of collective movement in both predators and prey. Through these models and empirical studies, we will gain insights on information transfer among collectively moving organisms, a topic with relevance in many ecological scenarios, ranging from foraging, predation to even human crowds.
Population biology is built on a strong mathematical foundation developed during the Modern Synthesis and encapsulated by the fields of theoretical population genetics, evolutionary game theory, and quantitative genetics. Historically, these formalisms have often worked with infinite populations, ignoring the effects of demographic stochasticity. Finite population models in population genetics usually assume a fixed population size and are of limited applicability in the real world, where population sizes routinely fluctuate. In this talk, I will outline how ideas from statistical physics can be used to analytically describe evolving populations from biological first principles. Starting from a density-dependent ‘birth-death process’ describing an arbitrary closed population of individuals with discrete traits, I derive a set of stochastic differential equations (SDEs) for how trait frequencies change over time. Along with recovering the effects of the standard evolutionary forces of selection, mutation, and drift, these SDEs also reveal a new directional evolutionary force, ‘noise-induced selection’, that is particular to finite populations and has been largely overlooked in standard mathematical formulations of evolution. Noise-induced selection can reverse the direction of evolution predicted by infinite-population frameworks, with implications for simulation studies and real world populations. Our equations also recover well-known results such as the replicator-mutator equation and Fisher’s fundamental theorem in the infinite population limit. I will try to stick to intuitive arguments and keep formal mathematics to a bare minimum in the talk.
Snakes are among the most notable reptilian lineages ubiquitous in several ecosystems across the globe. The innovation of the venom system has strongly underpinned their evolutionary success. Snake venoms are complex cocktails of toxins that collectively facilitate many ecological functions such as predation, defence, conspecific competition, or a combination thereof. Many of these venomous snakes can potentially inflict medically significant envenomation in humans. In India, the Indian spectacled cobra (Naja naja) is one of the “big four” medically relevant snake species that are responsible for most human envenomation and lethality. With a near-country-wide distribution, N. naja is a generalist snake that inhabits diverse ecological habitats. Geographically disparate populations of this species show observable differences in various phenotypic traits, including colouration, scalation, and hood markings, as well as in their venom composition. While the genus has garnered global taxonomic and venom research attention, detailed studies investigating molecular phylogenetics, the population genetic structures, and their influence on venom composition and potency are lacking for the Indian congener, N. naja. Taxonomic re-evaluations have led to the decomplexation of the N. naja complex into different Asiatic species of Naja. The nomen, ‘N. naja’, is retained for the populations present in the Indian subcontinent, with India Orientalis as its type locality. Based on morphological considerations, Deraniyagala (1960) proposed five subspecies of N. naja, which were subsequently rejected by researchers, clubbing them all as a monophyletic group. This synonymization, however, was without molecular evidence. The spatially disparate populations can also be structured into phylogenetic units corresponding to geographical regions and be closely associated with contemporary and historical population dynamics. Understanding the evolutionary relationships of these populations within a phylogenetic framework and assessing the genetic diversity would widen the understanding of the systematics of this medically important group. Even though the phylogenetic pattern by itself is not a good predictor for venom composition, phylogenetic studies can shed light on the underlying patterns of the evolution of the venom of the species. For my PhD, I aim to leverage an integrative approach involving phylogenetics, phylogeography, and population genetics to understand the evolution of N. naja across its range of distribution and the possible geological events responsible for its current distribution. Furthermore, the project will also evaluate the extent of gene flow between the populations and investigate the role of biogeographic conditions and population genetics on the venom composition and, consequently, venom potencies.
Forty years after the discovery of HIV as the causal agent of AIDS there is still no vaccine. Yet the COVID19 vaccine was designed and developed in less than 3 months. This scientific success has been largely recognized as a direct product of 25+ years investment in HIV research. Indeed, while the enormous antigenic diversity of HIV remains a major challenge, technological innovations in antibody discovery and development platforms allowed the discovery of a new generation of potent and broad neutralizing antibodies (bnAbs) which are not only being evaluated as prevention products but also used as template for vaccine design. The first approaches led to re-evaluation of partnership models to make antibody-based treatment more affordable and accessible. The second led to the development of novel vaccine concepts which successful evaluation in proof-of-concept Experimental Medicine Trials renewed hope that an HIV vaccine is achievable. Together with the establishment of global scientific and clinical capacities, these advances offer new opportunities way beyond HIV to address other Global Health challenges.
Sex-biased predation occurs when one sex of a prey species is consumed more than the other. Some of the potential factors leading to sex-biased predation are skewed natural sex-ratio and sex differences in morphology and/or behaviour of prey species. In the context of mate-finding, we often see sex-specific behavioural strategies, such as signalling and searching. The relative risk of predation on the two sexes during mate-finding depends on who signals, who searches, the risks associated with these behaviours, and the degree of involvement in these activities. Prey wing remains found in the roosts of a bat predator, Megaderma spasma, reveal interesting patterns for two katydid genera, Mecopoda and Onomarchus. Mecopoda sp. wing remains are male-biased in the breeding season and female-biased in the non-breeding season, while Onomarchus uninotatus wing remains are female-biased year-round. These two katydids differ in their mate-finding strategies: in Mecopoda sp., which are found close to the ground, males signal acoustically and females search silently to locate them. Onomarchus uninotatus is an arboreal katydid, that uses an acoustic-vibratory multimodal duet for mate-finding within trees, with both sexes signalling and searching to find mates.
To explore the factors driving the sex-biased predation by M. spasma on Mecopoda sp., we used a combination of field observations and enclosure experiments with wild-caught live animals. The males and females of Mecopoda sp. were compared with respect to (i) their availability, i.e., natural sex-ratio across the seasons, (ii) the predation risks associated with different behaviours, and (iii) the prevalence of their risky behaviours in the wild. We found that the relative availability of the sexes does not explain the male-biased predation on Mecopoda in the breeding season; whereas in the non-breeding season, very few males are available, which could lead to the female-biased predation. Males perform high-risk mate-finding behaviours, such as calling and flight, with a high prevalence in the wild. Although flight is equally risky for both sexes, females rarely fly.
To understand bat predation risk on male and female O. uninotatus and its possible role as a selection pressure driving the evolution of multimodal duetting, we performed outdoor enclosure experiments with live bats and katydids. Bat predation risks were compared (i) between the signalling and searching strategies of each sex, and (ii) between male and female signalling. We found that bat predation risk fails to explain the evolution of vibrational signalling in O. uninotatus females, as searching by walking is as safe as signalling, leading to an overall low predation risk on females within a tree. However, their duetting behaviour lowers the risk on males, who can shift from high-risk signalling to low-risk searching by walking, once females start signalling.
Finally, we focused on bat predation risk of searching behaviour in O. uninotatus, which potentially takes flights across trees. We compared (i) flight risks for O. uninotatus males and females in enclosure experiments and (ii) their across-tree movement pattern using radio-telemetry. We found that flight is equally risky for the sexes, but females move across trees 1.6 times more often and 1.8 times greater distances, which could make them more vulnerable to predation, explaining the female-biased prey remains found in M. spasma roosts.
Overall, this thesis provides a comprehensive examination of the predation risks associated with signalling and searching behaviours of katydids. The interplay between sex-specific behaviours and ecological factors, can explain sex-biased predation patterns.
Trait polymorphisms are widespread in nature, and explaining their stable co-existence is a central problem in ecology and evolution. Alternative reproductive tactics, in which individuals of one or more sex exhibit discrete, discontinuous traits in response to reproductive competition, represent a special case of trait polymorphism in which the traits are often complex, behavioral, and dynamic. Thus, studying how alternative reproductive tactics are maintained may provide general insights into how complex trait polymorphisms are maintained in populations. We construct a detailed individual-based model based on extensively collected empirical data to address the mechanisms behind the co-existence of three behavioural alternative reproductive tactics in males of a tree cricket (Oecanthus henryi). Our results show that the co-existence of these tactics over ecological time scales is facilitated by the spatial structure of the landscape they inhabit, which serves to equalize the otherwise unequal mating benefits of the three tactics. We also show that this co-existence is unlikely if spatial aspects of the system are not considered. Our findings highlight the importance of spatial dynamics in understanding ecological and evolutionary processes and underscores the power of integrative approaches that combine models with empirical data.
In December 2022 the 15th Conference of the Parties to the Convention on Biodiversity agreed a series of measures that requires ‘effective conservation and management’ of 30% of the world’s lands, waters and oceans. Determining where this attention should be directed – the exercise of conservation prioritisation – preoccupies many of the world’s leading conservation scientists. Conservation prioritisation is data hungry. It requires numerous data layers depicting land cover and land cover change, eco-region maps, agricultural activity, human populations, wealth, species distribution, predictions of how all these will change as the climate warms and so on. In this presentation I outline a new way of looking at the challenges of prioritisation by considering the data justice issues that it presents. I outline first why we need to think about data justice, and how it differs from other established concepts like epistemic justice. I then discuss what forms of data are being used in some conservation planning exercises and how using a data justice lens can help us better to understand the challenges they pose. I suggest practical ways of responding to some of the ethical challenges that arise.
Through the detailed unpacking of a colonial era fishing permit, known as the Boat License Certificate (BLC), operationalized in the Sundarbans National Park, this paper argues that some of the most exciting contributions of conservation work in India could be work that contends with the excruciatingly boring, bureaucratic, and pedantic work of paperwork. This would entail undoing an archaic set of fines, fishing licences and boat permits that have, over the years, generated a fearful regime that ‘incorporates illegality.’ BLCs not only convert the forest into a hostile environment, plunge Sundarbans fishers into new forms of inequality, but are also counterproductive to the goal of conserving the forest ecosystem. This ‘fishy’ business of fishing permits—closely interlinked to party politics and vote-bank politics—is something that all local, national, and international conservation organisations as well as the West Bengal Forest Department are aware of in the context of a global conservation hotspot. So why is it then that not a single conservation organisation is interested in tackling a regime of colonial licences that do not benefit the ecosystem or the fishing community? This paper suggests that conservation work in the Sundarbans, and in other national parks in India, is deeply depoliticized. In order for it to be genuinely transformative, it needs to contend with the boring work of paperwork.
Symposium highlighting work done at Prof. Rohini Balakrishnan's lab over the past 25 years.
Patterns of space use are key in understanding predator-prey interactions. The spatial overlap of predators with their prey influences their encounter rates, predation rates, and ultimately predator-prey dynamics. Animals engage in a dynamic behavioral response race, where prey actively try to avoid predators while predators seek out prey-rich spaces. Many extant studies fail to test for the emergent outcome of the dynamic space-use response race because they either fail to test for the dynamic responses of predator and prey when both are mobile or not addressing the underlying fine-scale behavioral mechanisms that drive space use in mobile predators and prey. In a qualitative literature survey, I examined how many studies report spatial and or temporal correlations between the distributions of mobile predator and prey and identified external constraints or ‘anchors’ that may influence the observed distributions. Anchors are defined as constraints like fixed resources or the presence of refuges that restrict free access to patches of choice. If only prey are constrained, predators can win the behavioral response race by achieving a positive spatial overlap with the prey, whereas a negative correlation may be seen if predators are constrained. Our results show that the presence of the identified anchors significantly influence the reported outcomes of the predator-prey space-use patterns. Such anchors can become important predictors of the emergent space-use patterns in predator-prey systems, making their identification vital in studies of predator-prey population dynamics and applied ecology. I then studied how predators from the African savanna choose home ranges based on the seasonal and yearly scales and how these timescales affect their choice of kill hotspots. I used movement data for tagged leopards and African wild dogs from the Karongwe Game Reserve in South Africa for this analysis. Our results show that the seasons affect where animals choose to hunt within their home range and that the choice of the home range itself may also change over seasons and years. There was also a difference in the space-use of leopards and wild dogs as expected from the differences in their behavioral mechanisms and hunting strategies. Overall, from movement data analysis, we conclude that a positive spatial overlap alone may not translate to uniform predation risk in the landscape as there are certain hotspots with higher encounters and predation activity that are riskier for prey. Future studies should focus on environmental constraints, intrinsic factors, and fine scale behavioral responses to explicate predation risk and ultimately its effect on predator-prey dynamics in a system.