Thesis Defense at CES on 30 January 2018 at 3:00 pm titled "The spatial and coevolutionary dynamics of cooperation" by Jaideep Joshi from CES

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The spatial and coevolutionary dynamics of cooperation
Jaideep Joshi, CES
Date & Time: 
30 Jan 2018 - 3:00pm
Event Type: 
Thesis Defense
CES Seminar Hall, 3rd Floor, Biological Sciences Building
Before the talk

Cooperation is ubiquitous across taxa in the animal kingdom. For
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.