Our campus recently hosted a conference on Conflict and Cooperation in Cellular Populations (CCCP), featuring a wonderfully diverse set of talks and participants alike. Kruttika presented a poster summarizing her results on the bacterial communities of butterflies, and Laasya put up a last-minute poster on the benefits of altered initiator tRNA content in E. coli. We’re very happy that both of them won prizes for their posters! Congratulations!
I am pleased to announce a symposium on the genetic bases of adaptation and evolution, co-organized with my colleagues Gaiti Hasan and Krushnamegh Kunte. The meeting (28 Nov – 2 Dec at NCBS) will bring together evolutionary and development biologists, geneticists and theoreticians. Together, we will aim to synthesize current understanding of and future goals for determining the genetic bases of adaptation and evolution. This is an exciting time for such a synthesis!
We have a terrific lineup of speakers, and we hope to have equally amazing contributed talks and posters from advanced PhD students, postdocs, and young faculty. Applications for oral and poster presentations are due by 15 Sep 2016. More information
Gaurav’s analysis of the occurrence of Shine-Dalgarno-like motifs in prokaryotic coding regions has just been published in GBE. This is the first bioinformatics analysis we’ve done, and we are pretty pleased with the paper!
Bioinformatics analyses of bacterial genomes have uncovered interesting patterns of specific sequence features. Although it is tempting to invoke selection, it is important to distinguish the effects of selection from genetic drift, biophysical constraints, or indirect selection. For instance bacterial translation initiation usually requires ribosomal binding to the Shine-Dalgarno (SD) sequence in a gene’s 5′ untranslated region. Previous analyses showed that SD-like motifs are rare within protein coding genes of Escherichia coli and Bacillus subtilis (Li et al 2012, Nature). These authors suggested that because ribosomes pause at internal SD-like motifs, selection against them also explains codon bias across bacteria. However, it is important to consider alternative hypotheses. The SD sequence is GC-rich and well conserved across bacteria; hence its occurrence will vary simply as a function of genomic GC% (which ranges from 13-75% across bacteria). Experimental evidence also suggests positive selection on SD-like motifs: “programmed” internal ribosomal pauses are critical for proper folding and targeting of some proteins (e.g. Fluman et al 2014, Elife). We found that after accounting for the genomic GC content, ~50 out of 284 prokaryotic genomes showed no evidence of selection against internal SD-like motifs. Furthermore, selection on these motifs seems to vary according to their location. For instance, the C-terminal ends of genes are relatively enriched in SD-like motifs, potentially to initiate translation of the downstream gene. In contrast, the N-terminal ends of genes are depleted in SD-like motifs, perhaps due to their deleterious effects on local mRNA structure (known to affect gene expression). Our work thus highlights the complicated nature of selection acting on sequence elements and motifs, and the importance of accounting for genome-wide features such as GC content.
We’ve been busy! Here is some good news and fun plans for the summer. Many of us will be zipping across the world to present our work at conferences. If you happen to spot us, do come up to chat!
Gaurav, Vrinda and Saurabh successfully defended their thesis proposals and are now officially stamped and certified PhD students doing important thesis work. Hooray!
Laasya has been nominated for a Young Scientist Medal from the Indian National Science Academy (INSA). Good luck for the final presentation!
Arjit Jere (Garware College, Pune) finished his Master’s thesis working on ant lion pits (I served as Arjit’s thesis guide). Well done, Arjit!
Nilima Walunjkar (IISER Pune) has joined us again, this time for her Master’s thesis project. She will be working on the fitness effects of codon use in Methylobacterium. Welcome!
Aparna and I will be at the Evolution meetings in Austin, USA in June. Aparna will be partly funded by an Infosys Travel Award. Congratulations!
Mrudula and I will be at the SMBE meeting in Gold Coast, Australia in July. This is our first trip to the continent; we can’t wait to see Koalas and Kangaroos!
Gaurav and Laasya will be at an EMBO conference on Ribosome Structure and Function in Strasbourg, France, in July. Gaurav will be partly supported by a travel grant from DBT. Congratulations!
Laasya will also attend the Gordon Conference on Microbial Stress response in South Hadley, USA, in July 2016.
Finally, Gaurav Agavekar (MSc Wildlife student; I am serving as his thesis guide) received an Infosys travel award to attend the 2016 Ant course in Mozambique, Africa, in July. Congratulations!
Ashwin’s Master’s thesis work on the gut bacterial communities of dragonflies has been published in Current Science. The paper is highlighted in the “In this issue” section of the journal and supported by a Cover image of a Globe Skimmer (Pantala flavescens) by Shantanu. Good work, both!
In this paper, we describe culturable gut bacterial communities of eight species of dragonflies collected from three different locations in South India. We found that the bacterial communities are largely host-specific, which is a bit surprising since dragonflies are thought to be generalist predators. We also found weaker effects of sampling location and season, suggesting that dragonflies might indeed specialize on different prey leading to variable gut bacterial communities. At the moment these are interesting results that lead us to new hypotheses; we are now testing these ideas with larger datasets and more comprehensive sampling of microbial communities of dragonflies.
You can access the paper here.
Update: Here is a really nice graphic that Kruttika and Gaurav made, that captures some of the fun results from this work.
Our work showing rapid, parallel adaptation in Methylobacterium extorquens is now out online on the MBE website. The work represents a huge team effort from members of my former postdoctoral lab and my current lab at NCBS- Mrudula, Kruttika, Gaurav and Alefiyah. We are very excited about this paper, partly because of the surprisingly large adaptive benefits of synonymous mutations, and also because we show that no single mechanism underlies these fitness effects. Our understanding of the evolution of codon bias just got murkier, but also that much more interesting- we need new hypotheses!
Aparna Agarwal, Kruttika Phalnikar and Deepa Agashe
This article originally appeared in the 2016 edition of IMPRINT, the science magazine of the Dept of Zoology, St. Xavier’s College, Mumbai. The issue focused on life in the dark, and we wrote about evolutionary adaptations to darkness. We thought we would share it with others.
Look into the deepest caves
Or remember the darkest hour you’ve seen
Float in the midnight zones of the sea
Or visit the deepest pits your mind has been…
Humans have a strange connection with darkness. Technically, darkness is just the absence of light; yet our language is strewn with examples of how we both fear and are fascinated by the dark at the same time. The parts of the universe that cannot be observed are composed of dark matter. The devil lurks in the dark, while heaven is the light at the end of a tunnel. What we do not understand are the dark arts, while discovering the truth brings facts to light. This obsession with the dark is not unreasonable. As humans – just like many other animals – we rely heavily on our visual system for information about the world we live in. However, many animals have moved away from such a visual bias, and understanding the evolutionary processes that drive this change has enriched our understanding of evolution itself. In the next page or two, we will highlight some of these patterns that dark-adapted organisms have revealed. Continue reading
Imroze and Arun’s paper describing immunosenescence in flour beetles will be out in the January 2016 issue of the Journal of Animal Ecology! You can find the paper here.
Here’s a brief summary of the work described in the paper. In many animals, immune function decreases with age so that older animals are more likely to die from infections. We found that this pattern is also true for flour beetles (Tribolium castaneum): older beetles are more susceptible to infection by Bacillus thuringiensis. Oddly though, individual components of innate immune function (such as phenoloxidase activity) did not decrease with age. This mismatch could arise due to tradeoffs with other fitness components (e.g. fecundity or external antibacterial secretions). If young beetles invested in other aspects of fitness, they may not be able to invest more in immune function, and hence the levels of innate immune components may be lower than optimal. However, we did not find evidence for such a tradeoff. Another possibility is other factors affecting immune function end up muddying the expected relationship between immune components and age. Indeed, we found that a beetle’s sex and mating status also affect its immune function, and complex interactions between these factors determine immune function. The molecular mechanisms mediating these effects remain unclear and it is likely that we are missing other important factors that alter immune function. However, our work shows that a deeper understanding of life history, tradeoffs and fitness is necessary to understand how and why animals become more susceptible to infections as they age.
We presented three posters and a talk in the second edition of the Bacterial Expressions conference at NCBS, and Laasya won a best poster prize for her poster on bacterial stress response via tRNA levels. Congratulations Laasya!
Together with colleagues from various institutes, I am organizing the first Indian conference on Behaviour, Ecology, and Evolution at the Corbett National Park in March 2016. We hope to gather critical mass to discuss new work in these fields at a level that is currently missing. This should be an exciting meeting, and we hope you will present your work. Abstracts are due 20 Dec 2015. Check out the website for more information.
Please help us spread the word by email or print a copy of the poster and put it up on your notice board.