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.  

Climate change factors, like elevated CO2 and high temperature, are expected to increase the frequency and severity of drought events thus affecting the processes of plant photosynthesis and productivity across both natural and crop ecosystems. Plant ecosystems are critical for sustaining a habitable climate and life on Earth. Hence, there has been a constant pressure to accurately predict plant ecosystem responses to climate change for effective management and use of the ecosystems and to develop climate-resilient crops. Stomata - the microvalves on leaf surfaces, dynamically regulate photosynthetic CO2-uptake and water-loss in response to changing environments. Consequently, stomata determine plant growth and productivity and exert a major influence on global climate by controlling about 95% of all the CO2 and water fluxes in terrestrial ecosystems. Hence, stomata are of central importance in attempts to accurately predict plant and ecosystem responses to climate change and develop climate-resilient crops.

In this talk, I will present my previous research on how stomatal traits (behavior and anatomy) vary among diverse plant groups and influence plant responses to changing environments. In addition, I will outline my future research plans to study stomatal traits in the grasses. Grasses form one of the most widespread biomes (grasslands) on Earth, can successfully thrive in extreme environments and are critical for global food security as they include cereal crops like wheat, rice, and sorghum. Despite the importance of grasses for both natural and agricultural ecosystems, surprisingly little is known about stomatal trait variation and the selective pressures giving rise to or maintaining this variation in grasses. In this talk I will specifically discuss my plans to (1) study the shift in stomatal traits that occurred during domestication of grasses (2) investigate changes in stomatal traits during evolution of grasses with different photosynthetic pathways and (3) investigate the role of stomatal traits in adaptation of grasses to diverse environments. Finally, I will highlight the implications of my research for improving representation of grasses in climate change models and for development of cereal crops that perform better under future climate.

Atmospheric [CO2] have been steadily rising due human activities like burning of fossil fuels and deforestations. The current atmospheric [CO2] have crossed already crossed the 400-ppm mark, highest is the past 700000 years, and projections by Intergovernmental Panel on Climate Change see atmospheric [CO2] to cross the 550-ppm mark by 2050. Elevated [CO2] are expected to increase the average global temperatures thus resulting in significant changes in wind and precipitation patterns and increased severity and frequency of droughts and floods. In addition to these effects on global climate, elevated [CO2] are likely to have profound and direct effects on the growth, physiology, and biochemistry of plants. These effects result from the central importance of [CO2] to plant metabolism. During the processes of photosynthesis plants take up atmospheric [CO2] and fix it into carbohydrate food with the help of sunlight, water and soil nutrients. This carbohydrate food is critical for plant growth and for survival of other life forms. Thus, photosynthesis is at the heart of plant metabolism and increasing the availability of CO2 for photosynthesis can have profound effects on many plant and ecosystem processes that depend on photosynthesis.

In today’s lecture we will see how elevated [CO2] affects the key process of photosynthesis in different plant types. We will particularly focus on understanding how plants belonging to different photosynthetic types, that is C3 and C4 species, respond to elevated [CO2] in terms of photosynthesis and productivity. And finally, we will see how techniques like free-air CO2 enrichment experiments have advanced our understanding of plant responses to elevated [CO2] in a more naturalistic way.

Urban lakes in India suffer from different types of problems. Lakes which are filled with sewage due to heavy inflows of wastewater through storm-water drains, lakes which remain dry due to a combination of diversion channels (bypass drains) and blocked storm-water drains and lakes which overflow and cause flooding, because they are already filled with partially treated sewage. Paradoxically, many cities in India have engaged citizen communities. Why then despite the considerable investment of money and citizen engagement do problems persist? The answer is quite complex. It has in equal parts to do with what we understand (and don't) about urban lakes, how government agencies work (and don't), and how citizens engage (and don't). In this talk, I will offer some lessons from having engaged with lakes for the last few years and a roadmap for change.

Phoresy is the dispersal of small organisms on larger ones to move out of an unfavourable habitat. Although these interactions are transient, they can form tight links with mutualistic interactions if the phoretic organisms are dependent on both mutualistic partners, one serving as a vehicle with the other providing a substratum for development. These linked tripartite interactions may further lead to increase in host specificity in phoretic organisms. Therefore, to understand the effects of phoretic interactions on the entire mutualistic system and factors that can help the phoretic organisms to gain host-specificity, I investigated the phoretic nematode community associated with the fig–fig wasp brood-site pollination mutualism. I chose Ficus racemosa, a wide-spread and a common tropical keystone fig species, which shows a mutualistic relationship with a unique pollinating fig wasp species and harbours a host-specific phoretic nematode community. Ficus racemosa has an Indo-Australian distribution and is known to be associated with several nematode species throughout its range. A few nematode species have also been reported from India, but they lacked comprehensive detail on their morphology and also molecular characterization, thus making it difficult to carry out further species-specific studies. Therefore, we firstly characterised the phoretic nematode community associated with the Ficus racemosa system in south India, using both morphological and molecular approaches and found a mixture of plant-parasitic, animal-parasitic and possibly omnivorous taxa. We found that the nematode community consisted of three new nematode species out of which one species showed phenotypic plasticity. The phylogenetic analysis based upon near-full-length small subunit (SSU) and D2–D3 expansion segments of large subunit (LSU) rRNA genes showed that the species have close affinities with sister nematode species reported from Ficus racemosa from other geographical locations outside India. To determine the effects of phoretic nematodes on the entire mutualism, we performed various bioassays and determined the fitness effects of phoretic organisms on both mutualistic partners, i.e., figs and pollinator fig wasps. We found that not only did the nematodes negatively affect the survival, flight ability, offspring number and predation risk faced by their fig wasp vehicles, but they also negatively impacted fruit seed number and size in a density-dependent manner. Furthermore, wasps arriving at their destinations carried lower phoretic nematode load compared to dispersing wasps suggesting that there is selection on hitchhiker numbers within a vehicle during the dispersal process. Using choice experiments with single nematodes and employing conspecific as well as heterospecific co-travellers, we showed that these phoretic organisms were able to distinguish between vehicles with different hitchhiker density and physiological states. Plant-parasitic nematodes preferred vehicles devoid of conspecifics and likely hitchhiked in pairs, while animal-parasitic nematodes preferred vehicles with conspecifics within a certain density range. Both types of nematodes were insensitive to the presence of heterospecific co-travellers. The nematodes used volatiles and carbon dioxide for this intra-specific vehicular discrimination. We also characterized the volatiles emitted by the pollinator wasps and identified the possible set of compounds that might elicit an attraction response in the nematodes towards their vehicles. Overall, we show that phoretic nematodes have a density-dependent negative effect on the mutualism between figs and their pollinating fig wasps and that they use parameters such as vehicle physiology and existing traveller load within the vehicle to select a vehicle for their dispersal.

https://teams.microsoft.com/l/channel/19%3abb4ece80bcaf4251a935efa618fc8...

Effective communication in animals comprise emission of a signal by a signaller and a response by a receiver, such that the interaction is beneficial to either only the signaller, or both the signaller and the receiver. Although animals often communicate using a single sensory modality, use of multimodal signals is very prevalent, possibly to increase the efficacy of communication. The evolution of signalling traits in new sensory modalities, in the presence of signals in pre-existing sensory channels is intriguing, as it requires co-evolution between signals and receiver psychology. Furthermore, environmental conditions and energetic constraints of signallers, may govern the type and intensity of signals, as well as, their efficacy in reaching the sensory systems of the receivers. 

In the first chapter, I studied the general ecology of a single species of a diurnal gecko in the genus Cnemaspis to understand its habitat use, activity patterns, and composition of population. I found that individuals of Cnemaspis mysoriensis are active throughout the day and found in areas with broad trees and numerous crevices. I also found that males of this species have colour morphs, which differ in their relative abundance in areas of high and low density. The population of this species has highly skewed adult to juvenile numbers in areas of high density. Finally, I found that individuals show low site fidelity and males avoid cohabiting. 

In the second chapter, I determined the presence of multimodal signalling and the relative importance of signal components in chemical and visual sensory modalities for intraspecific communication in a single species of Cnemaspis. I found that male and female receivers differed in responses to signal components. Chemical stimuli were necessary and sufficient for female receivers; however, male receivers required both the chemical and visual stimuli as a multimodal signal to elicit a response. 

In the third chapter, I determined whether complexity and elaboration of various components of a multimodal signal across multiple species of Cnemaspis were associated with environmental parameters. I also investigated whether components in different modalities had trade-offs in their expression and intensity, possibly due to constraints. I found that some visual and chemical traits of signallers were well-associated with the environment to either increase the conspicuousness of signallers to conspecifics (visual traits) or decrease the loss of signal in the environment (chemical traits). I also found some evidence for trade-offs between components of signals between the two sensory modalities. 

Finally in the fourth chapter, by comparing receiver responses of two closely related species of Cnemaspis, one with unimodal signals and another with multimodal signals, I investigated whether the evolution of receiver responses were associated with elaboration of traits in a new signal modality. I found that movement-based responses of male receivers of the species with multimodal signalling were highest towards multimodal signal, providing some support for the evolution of receiver response with trait elaboration. 

Overall, I found that in multiple diurnal gecko species, the elaboration of traits in the visual sensory channel shows some trade-off with chemical trait expression, and seems to have evolved to enhance interactions among males.