Found this via: https://twitter.com/globalfinprint/status/1242889032062971906
Our new paper in Nature Physics led by the recently minted PhD from our lab – Jitesh Jhawar & with a fabulous collaborative team of Richard Morris, Danny Raj, Amith-Kumar, Harikrishnan & Tim Rogers!
Here is the link to read the paper (FREE): https://rdcu.be/b2pgG
Some background: We have seen collective motion in birds, mammals, fish, insects, microbes, etc – all fascinating patterns.
Each individual has only limited local information about surroundings. Yet they show these fascinating patterns. 2/n
So a question that many of us are interested is: what types of interactions produce these fascinating patterns?
This has been a question of substantial work over the last few decades, and we provide some new insights here. 3/n
To answer this broad question, physicists and computer scientists have built mathematical and computational models since 1980’s.
They show that organisms don’t need complex rules to exhibit collective motion. 4/n
For example, in the classic Vicsek model (PRL 1995), particles follow a simple rule: move in the average direction of their neighbours. This simplistic rule produces a highly-ordered collective motion.
[Pic below is Fig 1 of Vicsek et al 1995 PRL]
The first main result from our study is related to the above context — whats the rule that fish follow? We show that in a species called karimeeen (Etroplus suratensis) (i) fish just copy the direction of a (nearby) random fish, or (ii) they turn a bit randomly. 6/n
We call this rule a ‘pairwise copying’ — which is relatively simpler than the Vicsek-class of models which assume that organisms average the direction of neighbours and turn towards them. 7/n
Ours is not the first paper to show that real organisms behave differently compared to Vicsek-like models. In fact, fish school studies by @JHerbertread, @GTheraulaz etc also show a similiar simpl rule of interactions in other fish species. 8/n
That brings me to the second main result- also the title of the paper: We show that schooling in this fish is a rare empirical example of a phenomenon well studied in non-equilibrium stat physics: ‘noise-induced phase transitions’. But what is this? Let’s dig in a bit 9/n
So this is what we do in terms of experiments and analyses to make the connection with the physics theory. We use karimeen (Etroplus suratensis) — a popular edible fish in western coast of southern India and put them in a fish tank.111
So this is what we do in terms of experiments and analyses to make the connection with the physics theory.
We use karimeen (Etroplus suratensis) — a popular edible fish in western coast of southern India and put them in a fish tank.
We maintain shallow water, so that fish are effectively in a two-dimensional system. This makes tracking of fish movement relatively easy.
[This is from fig 1 of our paper.]
Here is a short video showing fish in the tank. Our experiments has 15 and 60 fish.
From video tracks of how fish, we calculate “polarisation M” – which measures how well aligned are fish with each other.
We then plot this quantity as a function of time. Crucially, we retain all information — not just mean but also how fluctuations are occurring over time.
From such a time series of the polarisation, we construct a stochastic differential equation!!!
I think this is one of the coolest part of the paper – because unlike most papers that intuitively derive a model or equation, here we let the data talk!
In simple words, this equation tells that i. when fish are ordered, even random things that they do, like copy one other, doesn’t change the overall behaviour very much ii. when the fish are moving in a misaligned state, the fluctuations are actually high.214
Therefore, when the fish are not well aligned with group members, the noise grows larger, eventually ‘kicking’ the group from one state — random swimming — to a different state — schooling!!!
This video (based on simulation of the model) makes the point on how noise is high in the disordered state, and pushes the group towards higher alignment.
I will stop here!! There is quite a bit of technical stuff in Methods and Supplementary Materials.
Jitesh Jhawar — a recently minted PhD from our lab — has just begun a postdoctoral research position at the Department of Collective Behavior, Max Planck Institute of Animal Behavior and the Centre for the Advanced Study of Collective Behavior at University of Konstanz, at Konstanz, Germany.
In his new position, he will work on an interdisciplinary project examining ‘collective sensing and group behaviour in epithelial cells and honey bees’.
During his PhD, Jitesh made some fundamental contributions to the lab — publishing our first experimental work which was also hugely collaborative and investigated the role of stochasticity in collective behaviour, leading to following several important publications (see publications page). He will be badly missed in the lab.
We wish him all the best in his endeavours!
Congratulations to Jitesh Jhawar, the newly minted PhD from our lab!!!! He defended his thesis in December 2019.
Jitesh defended his thesis titled “Intrinsic noise in collective dynamics” – where he theoretically and empirically investigated how stochasticity plays a very counter-intuitive role and creates order!
The thesis was reviewed by Prof Martin Evans (Dept of Physics, Edinburgh, UK) and Prof Malay Banerjee (Dept of Math, IIT Kanpur)! We thank them for their very constructive comments and their valuable time.
As you can see, although this work is from CES and we look at fish schools, it was reviewed by physicists/mathematicians! This is because there are lots of links between physics and schooling fish.
You can read the synopsis of his thesis here.
Here are three papers arising out his thesis (and two more are expected):
1) Jitesh Jhawar, Richard G. Morris, U. R. Amith-Kumar, M. Danny Raj, Harikrishnan R., Vishwesha Guttal, Noise-Induced Schooling of Fish, arXiv:1903.12132
2) Jitesh Jhawar and Vishwesha Guttal, 2019, Noise-induced Effects in Collective Dynamics and Inferring Local Interactions from Data, https://arxiv.org/abs/1911.09376
3) Jitesh Jhawar, Richard Morris, and Vishwesha Guttal, 2019, Deriving mesoscopic models of collective behaviour for finite populations, In Handbook of Statistics Vol 40: Integrated Population Biology and Modeling (edited by Arni Srini Rao and C R Rao), Part B, 551-594. DOI: https://doi.org/10.1016/bs.host.2018.10.002; Pre-print from Arxiv; Codes and data on GitHub. Download PDF
Jitesh is continuing as a short-term post-doctoral fellow in the lab. He will soon join Max Planck Institute for Collective Behaviour in Konstanz for his postdoctoral work on honey bees and collective cell migration.
Hearty congratulations to Dr. Sabiha Majumder who is all set to join ING in Amsterdam on a new exciting career path of banking/finance.
Sabiha got a PhD from the Physics department of IISc in 2017/18, working jointly with me and Sriram Ramaswamy. Her thesis applied ideas from nonequilibrium statistical physics and stochastic systems to analyse risks of ecological collapse. She published a number of excellent papers on this topic, in prestigious ecology journals. After her PhD, she joined ETH-Zurich for a postdoc, where she continued for two years.
In her new job, Sabiha will be employing her interdisciplinary skills as a Risk analyst in the banking/finance sector!
This shows how skills learnt in PhD are highly transferable. One need not continue in the traditional academic set up after PhD — something that a lot of PhD aspirants are unaware of. There are a large number of opportunities outside the academic set up where skills of PhD are going to be extraordinarily useful.
I receive a very large number of applications for summer internships from all over India (and occasionally one or two from abroad). I usually take 2-4 students every year.
Unfortunately, this year (2020), I have decided not to take any summer interns due to a rather hectic schedule I have in summer.
I had informed many students to contact me in early February to know about my decision on interns this year. If you see this message, I know this will be disappointing, but I hope we will find ways to work together later. I wish you all the best in finding alternative internships.
I am on the core-committee of KVPY from July this year and got an opportunity invite speakers for the KVPY Vijyoshi camp.
I (and everyone else involved) was thrilled that Prof Marlene Zuk accepted the invitation! She visited India to deliver spectacular talks at KVPY-2019 on sexual selection. She also attended and gave a talk at a mini-symposium/discussion on animal signals in CES.
Here is a picture of her with our lab:
During the visir of Guy Theraylaz, our lab members (Pritha, Jitesh, Akanksha) and collaborator Dr Danny Raj organized an interdisciplinary one-day symposium titled Collective behaviour at CES, IISc. Here is the full schedule:
Around 10 faculty members from IISc and other institutions gave presentations. Prof Theraulaz also gave a fascinating special seminar at the Collective behaviour symposium on self-organized nest architecture.
There was also a very lively poster session where a number of students presented their work.
The symposium was very well attended, including two IT folks who saw the notice on Twitter and joined the entire day of talks!
During the visit of Prof Theraulaz, we organized an intense workshop on collective behaviour at Valparai, Tamil Nadu from 08.09.2019 to 10.09.2019.
Many students working on collective behaviour from our lab and our collaborator Dr Danny Raj attended the workshop. The workshop focused on the discussion of existing research in the field of collective behaviour and potential future advances in the same.
The team also did a number of field visits to observe wildlife, assisted by extraordinary scientists and staff from Nature Conservation Foundation.