Latest Events

Topic: 
Resource allocation patterns and strategies in the mutualism between figs and fig wasps
Speaker: 
Manasa Kulkarni, CES, IISc
Date & Time: 
7 Oct 2020 - 3:00pm
Event Type: 
Comprehensive Examination
Venue: 
Online
Abstract:

Mutualisms are omnipresent across all life-forms; from prokaryotes to higher organisms. In a mutualistic interaction, one or both the partners provide services to the other, in exchange for which they receive rewards. Lately, mutualisms have also been considered as consumer–resource interactions, where, a host receives some service from its partner and provide resources in exchange as rewards. Resources, hence can be regarded as a currency in the operation of mutualism and are therefore central to the working of most mutualisms. However, resource allocation within a mutualism has rarely been studied. 

The Fig–Fig wasp interaction provides us with an excellent model system to study resource allocation in a mutualism. It is a typical example of an obligate brood-site pollination mutualism, wherein the pollinator wasps provide figs with pollination services in exchange for which the developing pollinator offspring receive nutrition.  

I aim to look at the patterns and strategies of resource allocation in the mutualism between figs and fig wasps. First, I will look into the patterns of resource allocation across the developmental phases of figs, and to the different occupants of the figs. I will then look at how different factors like position of the syconium and different occupants within the fig, that also include parasites, can influence resource allocation. I will also look into another potential, but completely unexplored factor, i.e. photosynthesis rate of the figs, which can also influence the amount of nutrition a fig can acquire.  

Topic: 
Diversity from the gut to species: Phylogeny, population genetics and microbiome of Antilope cervicapra
Speaker: 
Ananya Jana, CES, IISc
Date & Time: 
8 Sep 2020 - 3:00pm
Event Type: 
Thesis Colloquium
Venue: 
Online
Abstract:

https://teams.microsoft.com/l/team/19%3abfb48615d561409380167f6365cae6e5...

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 chapter 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 second chapter 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 have 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.

In the third chapter, 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 were 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, my thesis looks at diversity in an endemic ungulate from different angles and also tries to elucidate its taxonomic position among Antilopinae.

Topic: 
Through the looking glass: Phoresy as seen in the light of mutualism
Speaker: 
Satyajeet Gupta, CES, IISc
Date & Time: 
9 Sep 2020 - 3:00pm
Event Type: 
Thesis Colloquium
Venue: 
https://teams.microsoft.com/l/team/19%3aa3c31132fe2a479bb2d83130f1cf036b%40thread.tacv2/conversations?groupId=5c2352e4-0c3c-47be-b89a-154624566ba1&tenantId=6f15cd97-f6a7-41e3-b2c5-ad4193976476
Abstract:

Phoresy is the dispersal of small organisms on larger ones to move out of an unfavourable habitat. Although these interactions are transient, phoretic organisms can form tight associations with mutualistic systems if they 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 of the 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.

Topic: 
Collective escape dynamics of blackbuck herds during predation-like events
Speaker: 
Akanksha Rathore, CES, IISc
Date & Time: 
26 Aug 2020 - 3:00pm
Event Type: 
Thesis Colloquium
Venue: 
https://meet.google.com/nss-knzk-mvg
Abstract:

Collective movement is a fundamental process affecting the survival and reproductive success of group-living animals. Many of the hypothesized benefits of grouping such as predation evasion and foraging efficiency require the individuals in a group to move in a coordinated way. While moving in groups, animals are not only responding to the environment but also interacting with each other. These interactions give rise to emergent collective movement and behavioral patterns. A novel aspect of emergent behavior is that a group can exhibit properties that no individual displays on its own.

Most studies on emergent properties of collective behavior are conducted in controlled conditions. However, in natural settings, habitat is heterogeneous in terms of resource distribution, availability of hiding places and substrate for movement. Empirical studies have rarely investigated such fine-scale interactions (e.g. alignment, attraction among individuals) in their natural habitat. One reason for the dearth of such studies is the difficulty of data collection. Recent advances in techniques of aerial imagery allow us to observe and record such fine-scale data. For my PhD project, I studied collective behavior of blackbuck herds in their natural habitat. More specifically, I investigated the collective response of blackbuck herds during predation-like events. By analyzing multiple interactions among group members simultaneously, I aimed to understand the role of social interactions in shaping the collective response of blackbuck herds when faced with predation-like threats.

First, we overcome the difficulty of observing fine-scale interactions in animal groups (in their natural habitat) by using UAVs. We recorded blackbuck herding behavior at high spatio-temporal resolutions (30 frames per second). Using this technique we were able to record blackbuck herd’s collective escape behavior in the context of predation using controlled-simulated threats.

Tracking animals in the videos recorded in natural habitat is extremely difficult due to varying background and light conditions and clutter in the background. Relatively basic image processing methods and default tools don’t perform satisfactorily in such scenario.

Hence, we developed a machine learning method and GUI tool to extract the spatial locations and movement trajectories of all the individuals in a group from the videos recorded in natural field conditions.

Once we were able to obtain the movement trajectories from the videos, I then analysed these trajectories and interactions between individuals to explore - how the information about predatory risk spreads through a group in natural conditions. Broadly, our results suggest that transient leader-follower relationships emerge in these groups while performing high-speed coordinated movement. Also, males and females respond differently to the threat scenario: adult females are more likely to be the response initiators whereas adult breeding males are more likely to influence the group movement during the escape response. Our results indicate that in fission-fusion groups associations are likely to last for short time scales and spatial positions of the individuals only affect their response-time (vigilance behavior) but not their influence on the group.

Topic: 
Impact of the invasive shrub Lantana camara L. (Verbenaceae) on carbon and nitrogen stocks in a seasonally dry tropical forest
Speaker: 
Debarshi Dasgupta , CES, IISc
Date & Time: 
25 Aug 2020 - 3:00pm
Event Type: 
Thesis Defense
Venue: 
Microsoft Teams
Abstract:

The effects of invasive plant species on ecosystems are manifested in various ways which might often be counter-intuitive and confusing. Existing literature has largely stressed upon the negative impacts of invasive species on certain ecosystem properties, like suppression of growth of native seedlings. However, the holistic view of the effects of such species on ecosystems is still not clear. There is a need to understand that invasive species are a structural and functional part of invaded ecosystems. Studying ecosystem functions like nutrient cycling and regulation, in relation to invasion, is necessary because it directly linked to all organisms in an ecosystem and it is modified by the characteristics and abundance of the invasive species.

In this study, we aimed to understand the effects of plant invasion on nutrient stocks in biomass, litter and soil. First, we aimed to estimate for resident carbon and nitrogen pools, in a tropical dry deciduous forest (considered to be one of the most at-risk ecosystems in the world) in Mudumalai Tiger Reserve, India, over a period of one year. Then, we tried to understand how pools of these elements are modified under the influence of increasing abundance of the invasive shrub species Lantana camara.

This study reinforces the fact that it is difficult to predict the impacts of invasive plants on soil nutrient cycling processes. Through time, we see areas of higher density of Lantana camara showing more pronounced effects on parameters like soil microbial biomass carbon and nitrogen as compared to lower densities. In other parameters like litter carbon and nitrogen, soil carbon and nitrogen and biomass carbon and nitrogen, the results vary among the density categories through time. For most of the study, the carbon and nitrogen stock changes under different density of infestations did not vary significantly from the mean values of the forest. Expected patterns do emerge in certain cases, but do not remain consistent both throughout the course of study as well as the density categories. In many cases, places with low or intermediate levels of the shrub show more significant effects. These results validate the need of more consolidated research on such issues to gain in-depth understanding of ecosystem functions for better forest management and policy formulations.

Topic: 
Patterns and drivers of multimodal signalling in diurnal geckos
Speaker: 
Md Shakilur Kabir, CES, IISc
Date & Time: 
5 Aug 2020 - 3:00pm
Event Type: 
Thesis Colloquium
Venue: 
Microsoft Teams
Abstract:

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.

Topic: 
Patterns and drivers of multimodal signalling in diurnal geckos
Speaker: 
Md Shakilur Kabir, CES
Date & Time: 
5 Aug 2020 - 3:00pm
Event Type: 
Thesis Colloquium
Venue: 
CES Seminar Hall, 3rd Floor, Biological Sciences Building
Abstract:

TBA

Topic: 
Distribution, activity budget and feeding ecology of Himalayan gray langur in Kashmir Himalaya
Speaker: 
Mehreen Khaleel, CES, IISc
Date & Time: 
28 Jul 2020 - 11:00am
Event Type: 
Thesis Defense
Venue: 
Microsoft Teams
Abstract:

Colobines are group of primates known to inhabit different habitats. These habitats pose diverse challenges which they have coped up physiologically and behaviourally. Primates in such environments are subjected to prolonged scarcity of food due to phenological variations and low temperature in winters. They are expected to allocate their time to various activities optimally in order to balance their energy requirements. One such primate inhabiting the harsh weather condition of Himalaya is Himalayan gray langur. Himalayan gray langur, Semnopithecus ajax, is little-known endangered primate, initially reported to be present in few parts of north-western Himalaya. To understand their survival strategies in these habitats one must know about the whereabouts of this species.

Therefore, I first accessed the spatial distribution and occurrence of Himalayan gray langur in Kashmir region. This was achieved by using well-structured questionnaire and on-ground surveys in the region. It was followed by identifying sites which face human-langur conflict. My results suggest a wider range of Himalayan gray langur in Kashmir which was previously thought to be restricted in a small range. Langurs were found distributed in the protected mountainous forest areas of Kashmir by showing a preference for broad-leaved deciduous and coniferous habitat types within 1600-3000 m. Conflict in the form of crop raiding was found in the villages around protected areas.

Based on the knowledge of the distribution of these primates in forests, I tried to address how this primate survives the seasonality and cold temperatures of Himalaya in the next chapters of my thesis. I have addressed this by investigating the behaviour patterns and the strategies they have adopted to balance the energy requirements. I used observational methods of instantaneous scans for different behaviour categories. My results suggest Himalayan langurs spend more time feeding during lean winter when high-quality food is less available and rest more during hotter months. Moreover, they have greater home range sizes in winter than in summer. These results suggest an energy maximizing strategy by these primates when resources are scarce by feeding more on less profitable food sources and expanding their home range size.

I further investigated the diet and feeding behaviour of langurs. They were found to shift their diet with seasonality. They feed on a variety of plant items ranging from bark, buds, young leaves, mature leaves, ripe fruits and seeds. I used resource selection functions to test for plant species preference. A seasonal preference for certain plant species and plant parts suggest that availability of plant parts influences their choices. From these results one can conclude that Himalayan gray langur has adapted to explore a variety of food sources other than leaves. This study helps us in understanding the ability of colobines to explore such versatile diets which has helped them colonize many habitats, one of them being the Himalaya.

Overall, this study provides a baseline information for conserving Himalayan gray langur through comprehensive understanding of its distribution, activity budget, home range, diet and feeding preference in Kashmir Himalaya. The current distribution serves as a base-map for various management policies towards the conservation of this high-altitude primate. Moreover, insights about the conflict will help managers in developing ideas to reduce and prevent conflict. Due to the presence of this species in the broad-leaved deciduous and coniferous forests of Kashmir, it becomes important to preserve and protect these habitats for its survival. The key findings of this study are expected to benefit directly towards the conservation of this species and in understanding the survival strategies of these high-altitude primates.

Topic: 
Soil microorganisms and biogeochemical cycles in a grazing ecosystem: interactions between producers, consumers, and decomposers
Speaker: 
Shamik Roy, CES, IISc
Date & Time: 
17 Jul 2020 - 3:00pm
Event Type: 
Thesis Colloquium
Venue: 
Microsoft Teams
Abstract:

Microbial decomposers are the unseen majority that determine ecosystem processes, and perform biogeochemical functions which translate into essential services, and regulate global climate. In grazing ecosystems that represent over 40% of the terrestrial realm, soil microbes respond to aboveground interactions between plants and herbivores. In this thesis, I analyse different aspects of soil microbial functions in the high-altitude grazing ecosystem of the Trans-Himalaya, and quantify the implications for biogeochemical cycles and sustainability under climate change.

In the first chapter, I explore how large mammalian herbivores alter foraging strategies of soil microbial decomposers. Soil microbes forage by releasing extracellular enzymes (EE) into their environment to break down organic matter. Long-term herbivore-exclusion experiment revealed that herbivores improve quality of biomass-input to soil. This reduced microbial deployment of generic-depolymerizing EE relative to specialised-EE that release assimilable end-products. I validated the underlying role of quality of detrital input to soil by a reciprocal transplant experiment using laboratory incubations. I synthesised 860 soil-EE profiles from across the world to establish that this response to quality of detrital-input to is soil is both widespread and general. These observations provide evidence of a continuum between herbivores and decomposers that is relevant to global nutrient cycles and can also explain how microbes control soil-C sequestration in grazing ecosystems. In other words, soil microbial decomposers forage more efficiently in the presence of large mammalian herbivores.

In the second chapter, I explored how microbes alter the stability of the soil-carbon pool when humans replace wild-herbivores with livestock in grazing ecosystems. I found microbial-respiration was lower in soils under grazing by wild-herbivores than under livestock, with corresponding differences in fungal:bacterial ratio, microbial-biomass, and metabolic-quotient. Direction and magnitude of these inter-related microbial responses were driven by reduced soil microbial carbon use efficiency (CUE) under livestock. Since CUE is a fundamental microbial trait, wild-herbivores sequestered twice the soil-C than livestock despite comparable ecological settings. This implies that investments in wildlife conservation in multiple-use landscapes can help decarbonise the atmosphere to mitigate some of the negative environmental impacts of livestock-production.

In the third chapter, I addressed the relationship between functional diversity of decomposer functions in soil and the stability of ecosystem processes under land-use change. Unlike producers and consumers, decomposer functions are common between natural and agroecosystems. I take advantage of alternative land-use in the Trans-Himalaya where the native reference state with wild plants and wild herbivores is repurposed into two distinct agroecosystems—to grow livestock, or crops. I find that the extent of human-alteration of the reference state is reflected in the degree of homogenization of decomposer functions. Relative to the native state, magnitude of individual functions was often higher under crops but remained unchanged under livestock, such that land-use had no net effect on multifunctionality. However, univariate and multivariate measures of functional heterogeneity were lower under crops but were unaffected under livestock. Stability of decomposer biomass, measured as invariance through time, was comparable across land-use types. These results show that previous knowledge on diversity-relationships in producers and consumers are not easily extended to decomposers, and there are fundamental differences. Although agroecosystems in the Trans-Himalaya show remarkably high degree of ecological resistance, homogenization of their decomposer functions can make them susceptible to environmental fluctuations, such as those foreseen by future climate projections.

In summary, this thesis explains how soil microbes contribute to the functioning of grazing ecosystems.

Topic: 
Rules and roles in bird hunting parties: Understanding rules of assembly and species interactions in mixed-species bird flocks
Speaker: 
Priti Bangal, CES, IISc
Date & Time: 
16 Mar 2020 - 11:00am to 12:30pm
Event Type: 
Thesis Defense
Venue: 
CES Seminar Hall, 3rd Floor, Biological Sciences Building
Coffee/Tea: 
Before the talk
Abstract:

In mixed-species bird flocks (flocks hereafter), participants vary in their degree of similarity with each other. Flock participants can gain group size (supplementary) benefits by choosing similar flock partners, or complementary benefits from dissimilar partners. The nature of benefits, therefore varies based on overall similarity in the flock. Earlier research has shown that flocks world-over tend to be phenotypically clumped and that intraspecifically gregarious species are important benefit providers. In this thesis, I examine changing patterns of associations and species importance with respect to group size, in mixed-species bird flocks.

In my first chapter, I examine the relationship between flock size and phenotypic clumping. I find that small flocks are more phenotypically clumped than expected by chance but as flocks become larger, the phenotypic variation does not differ from what’s expected by chance. I also find that, at a global scale, flocks in regions with lower average flock size are more phenotypically clumped. In the second chapter, I examine the importance of intra-specifically gregarious species. I find that flocks with less than or equal to two gregarious species have lower richness of non-gregarious species than expected by chance. I also study traits of intra-specifically gregarious species that are linked to functional importance and find that individual behavioural traits are not directly correlated to species importance. In the third chapter, I construct emergent networks of flock participant species based on flock co-occurrence. I find that a few species are structurally important in flocks of all sizes, while a few are important only in networks of large flocks. I also find that flock components that are unconnected in smaller flock networks, merge in large flock networks. Overall, I find that species similarity and presence of important species is crucial in smaller flocks whereas large flocks are heterogenous groups that resemble random phenotypic assemblages of flocking birds.

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