Division of labour plays a very important role in social insects and could either be reproductive or non-reproductive in nature. The lack of morphological differences among individuals in primitively eusocial species lead to greater flexibility in their social roles making them very interesting model systems to study division of labour. Ropalidia cyathiformis, a primitively eusocial wasp was chosen as the model system for the study of reproductive and non-reproductive division of labour. One of the key findings reveals that while dominance behaviour is used as a mechanism for reproductive division of labour, age is used for non-reproductive division of labour. We also compared our findings with what is already known in a related conspecific, Ropalidia marginata. Our findings showed that R. cyathiformis maybe a more primitive species compared to R. marginata and provide a glimpse into the origin of eusocial insects.

Reproduction is the avenue for gaining direct fitness. But in certain
species some individuals do not reproduce to gain direct fitness, instead
gain indirect fitness by helping relatives to reproduce; the prime
examples for this come from the worker caste of social insects like ants,
bees and wasps. Indirect fitness has been in focus for explaining the
evolution of workers while overlooking the fact that workers can also gain
direct fitness. One of the avenues for gaining direct fitness by workers
is nest foundation and I have studied this phenomenon in a social wasp. I
found that workers prepare in several ways for nest foundation, like
enhancing nutrient reserve and engaging in dominant interactions, even
before leaving their natal nests. While investigating the emergence of
cooperation and division of labour in newly founded nests, I observed how
these affect the productivities of the new nests. Finally I found that it
is ageing and nutrition and not work done towards gaining indirect fitness
that affect workers’ potential of gaining future direct fitness by
independent reproduction.

It is often believed the ecological and evolutionary timescales are very different and that it is difficult to study ecological and evolutionary processes together in a
rigorous and controlled manner. However as the experience of the last few decades shows, experimental ecology and evolution studies in laboratory settings provide us with
the ability to rigorously examine such phenomena and test hypotheses about evolutionary and ecological mechanisms, and their interactions, in a manner that is not possible
in the wild. In this talk, I will discuss a few examples from work in my laboratory over the past twenty years to illustrate the power of this approach, and underscore the
point that the evolutionary process is far more subtle and responsive to minor changes in ecology than is often thought to be the case.

TBA

Tropical habitats face a number of threats as a result of human activities. Two common and important anthropogenic threats to tropical biodiversity are invasive species and roads. Roads can have negative ecological consequences by degrading and fragmenting habitat, causing edge-effects, and increasing the risk of road-related mortality, hunting, fire and spread of invasive species. Lantana camara (henceforth lantana), a widespread invasive plant, can form dense monoculture thickets covering large areas, and yet knowledge is rare about its impacts on higher trophic levels, especially insects. I studied impacts of these two important proximate drivers of habitat disturbance, namely lantana and roads, on habitat use by butterflies in a tropical moist deciduous forest in Western Ghats of India. Both are expected to modify micro-habitat structure, resources, micro-climate and other aspects of the ecology of butterflies and thereby influence how they use space (i.e., micro-habitats within the larger habitat). Because systematic ecological information on tropical butterflies is comparatively limited, I adopted a multi-species approach. I examined habitat use responses of butterflies to a gradient in lantana cover within the forest, and to an unpaved road passing through the forest. The abundance of a butterfly species in different micro-habitats was taken as a measure of its habitat use. Data was collected over two seasons and at two spatial scales. Road and lantana were found to influence habitat use by butterflies. While there was substantial difference in the kinds of butterflies encountered on the road vs. the forest interior, high lantana areas in the interior appeared to contain only a subset of species encountered in low lantana areas. At a smaller spatial scale, a different set of species was encountered on lantana plots as compared to non-lantana plots. I then correlated the responses of butterfly species to road and lantana with their functional traits, as a way to detect general patterns. For this, I built a traits’ database by measuring morphological traits in 254 butterfly species from India and classifying them according to their habitat preferences (based on expert opinion). I examined relationships between morphological traits, habitat preference and evolutionary relatedness in butterflies. I then examined patterns of correlation between these traits and responses to the two habitat disturbances and found that certain traits can help predict response.
To summarize, my study suggests that butterfly habitat use is influenced by forest disturbance due to roads and lantana, though the response varies across species. Species with
certain traits may be especially vulnerable to these disturbances. The behavioural habitat use responses observed in my study can have population or community-level consequences that need to be further examined.

TBA

Time for a little fun and frolic

Millennia of photosynthesis has resulted in substantial accumulation of carbon in terrestrial vegetation. This carbon sequestration is an ongoing process and forests sequester a major fraction of anthropogenic carbon emissions. However, due to vulnerability of these forests to ongoing climate change, they may sequester less carbon or may even become a carbon source. Among all forest types, tropical forests demonstrate greatest carbon accumulation rate per unit area; however there are high uncertainties in the estimates of their carbon stocks and fluxes. Understanding the the response of these forests to future climate warrants a detailed investigation.

For this thesis, I am studying spatial and temporal variations in biomass and its drivers in the tropical forests of the Western Ghats of India. The first chapter of the thesis aims to address methodological issues that affect estimates of above-ground biomass obtained using global biomass models. Specifically, I examine height-diameter allometric relationships of trees and their environmental correlates. In the second chapter, I investigate a relatively new technique of biomass estimation using texture analysis of high resolution satellite imagery. I used this technique to generate a spatial biomass map for Mudumalai Tiger Reserve, Tamil Nadu. Here, the map will be validated with data from permanent forest plots and a comparison will be made with traditional reflectance-based biomass estimation techniques, such as using normalized difference vegetation index (NDVI). In the third chapter, I identify the key environmental factors driving variability of tree biomass for Mudumalai forest focusing on tree mortality and growth. In the fourth chapter, I attempt to apply all findings from previous chapters to project future biomass under different climate change scenarios

In this thesis progress presentation, I will present the progress made towards achieving each of my thesis objectives. I hope to receive feedback and suggestions to improve this study further.

Cooperation is ubiquitous across taxa in the animal kingdom. For
example,
microbes cooperate in producing antibiotic-resistant biofilms, mammals and
birds collectively mob predators, and humans cooperate in utilization of
common resources. However, cooperation is a paradox: why does natural
selection favour a costly behaviour? One of the key mechanisms of
cooperation is a spatial structure with local clustering of cooperators
(and defectors). This exposes defectors to the consequences of their own
selfish behaviour, keeping them in check. However, a vast fraction of
cooperative species is mobile. Movement allows defectors to escape their
fate, destroying spatial structure and hindering cooperation. Therefore,
cooperation is typically thought to be difficult to evolve in mobile
organisms. In this thesis, we question this assumption, and using
simulation and analytical studies, show that coevolutionary mechanisms can
promote cooperation in mobile populations.

Species across taxa, ranging from cells and microbes to fish, birds and
ungulates, live in highly mobile groups that frequently merge and split,
called fission fusion groups. The dynamics of these groups is governed by
local cohesive interactions between individuals. In the first chapter,
using explicit spatial agent-based evolutionary simulations, we explore
the coevolution of cooperation and local cohesive tendencies as a possible
route to cooperation. We show that, mobility facilitates spatial
structuring of cooperators via a dynamically evolving difference in the
cohesive tendencies of cooperators and defectors. We use the ideas of
assortment (where cooperators interact more frequently with other
cooperators) and multilevel selection (where selection for cooperation
between groups outweighs selection against them within groups) to
understand the coevolutionary dynamics. We discover an interplay among
cooperation and grouping, where self-assorted groups favour cooperation,
and cooperative interactions in turn favour such groups. Our results
reveal the possibility of cooperation in fission-fusion populations that
are typically thought to inhibit cooperation.

In the second and third chapters, we generalize our coevolutionary model
by considering a generic coevolving phenotypic trait (or ‘tag’) that
mediates interactions. Evolution happens via two key processes: selection
and drift. Unlike typical models of evolution that often employ only one
of these, we develop an analytical model that combines both. Our model
employs techniques from statistical physics to derive coupled
Fokker-Planck and Langevin equations for a finite population of organisms.
Our main finding is that mutations and demographic noise can facilitate
the evolution of tag-based cooperation. Our results could provide insights
into cooperation among metastatic cancer cells, quorum sensing bacteria,
and early multicellular clusters.

In the final chapter, we study the coevolution of cooperation and mobility
itself, in the context of human cooperation. Humans cooperate in the
utilization of spatial ecological public goods, such as forest produce,
fisheries, and grazing lands. However, humans evolve their strategies via
social learning, by imitating more successful individuals. Here, apart
from mobility, space introduces other features like incomplete information
and eco-evolutionary feedbacks. We incorporate these features into a
minimal, agent-based, evolutionary model to study human harvesting and
dispersal strategies. We show that, as resource utility increases and
dispersal becomes cheaper, societies progress from a sedentary,
subsistence-oriented lifestyle, through a nomadic phase characterized by
efficient and equitable resource harvest, to eventual social
stratification and overexploitation of the resource. Our model can
qualitatively reproduce harvesting and dispersal patterns observed across
the world throughout human history, such as in equestrian cultures and
shifting cultivation. It also helps us develop policy insights on the
sustainability of global commons, such as timber and fisheries.

In conclusion, we investigated coevolutionary dynamics across a spectrum
of mobility (from highly mobile to almost sedentary populations), and
found that coevolutionary mechanisms can facilitate cooperation in mobile
organisms. In the process, we also obtained insights into the role of
other factors, such as demographic stochasticity, rapid evolution,
incomplete information and eco-evolutionary feedbacks, on spatial
evolutionary dynamics.

TBA