The American Society of Naturalists (ASN) conferred its prestigious 2018 Presidential Award to evolutionary biologists from the National Centre for Biological Sciences (NCBS) of the Tata Institute of Fundamental Research, based in Bangalore, India. The ASN Presidential Award honors an outstanding research article from among all the papers published in the society’s journal, The American Naturalist, in the preceding calendar year. ‘Am. Nat.’ is a prominent scientific journal that publishes research papers in frontier areas of evolutionary biology and ecology. This year’s award was given to the NCBS team for their research paper in the April 2017 issue of Am. Nat., which “… provided an original synthesis of the evolutionary origins and assembly of butterfly mimicry rings,” noted Prof. Sharon Strauss, President of the ASN, while announcing the award.
Considering the volume of high-quality research findings that Am. Nat. publishes each year, this is a significant achievement for the NCBS researchers Dr. Jahnavi Joshi, Ms. Anupama Prakash and Dr. Krushnamegh Kunte. The authors are also the first Asian researchers to receive this award. On winning the award, Dr. Kunte, who led the research project, said, “This is a terrific recognition for my research group, and a great personal honour.”
The genesis of the study took place in the cold stillness of the Christmas break way back in 2010, when Dr. Kunte was a Post-doctoral Research Fellow at Harvard University in Boston. Thinking about how ecological pressures and co-evolutionary dynamics may shape the formation of animal communities, Dr. Kunte turned to what seemed to be remote at the time: his favourite organisms—tropical butterflies. Some butterfly species are unpalatable to their predators, usually owing to the toxins they accumulate as caterpillars from the plants on which they feed. Hundreds of palatable butterfly species that are not related to these toxic species have come to closely resemble them over evolutionary time. This type of mimicry fools predators, who avoid these perfectly palatable butterflies because they look like toxic butterflies with which the predator had a prior unpleasant experience. Thus, there is a parasitic relationship between the toxic models and their palatable mimics. Together, these butterfly species form clearly defined ecological communities called ‘mimicry rings’. Dr. Kunte decided to look closely at how convergent evolution and biogeographic processes shape the formation, diversity and composition of these butterfly mimicry rings. However, data on tropical butterfly mimicry rings was limited, and rigorous phylogenetic methods to study convergent evolution in biological communities did not exist at that time.
Upon joining NCBS in 2012 as a faculty member, Dr. Kunte’s team started the hard work of sampling mimetic butterfly communities of the Western Ghats of India, which had never been studied and characterised properly. The NCBS research team turned out to be a perfect blend, with Dr. Kunte’s intimate knowledge of evolutionary theory and tropical butterflies and Dr. Joshi’s skills at advanced phylogenetic methods, supplemented by Ms. Prakash’s analysis of the diversity of mimicry rings. The team first built a molecular phylogeny (species tree) of the Western Ghats mimicry rings, and then used evolutionary models to study how butterfly wing patterns had changed over time in a convergent manner to form these mimetic butterfly communities. By then, new phylogenetic methods had been developed to probe community assembly in an evolutionary framework, which Dr. Joshi applied to this problem in novel ways. Contrary to the widespread belief that mimicry rings are formed from convergent evolution between highly dissimilar butterflies, the NCBS team discovered that toxic models in the Western Ghats mimicry rings are closely related, sharing their ancestral, warning wing colour patterns even when new species are formed. Thus, the toxic models do not show convergence, but have similar wing patterns because of a shared ancestor. The mimics, however, join the mimicry rings after remarkable bouts of convergent evolution, sometimes separated by tens of millions of years.
Interestingly, the peculiar geography of the Western Ghats also appears to have influenced species diversity in these butterfly mimicry rings. Evergreen forests of SE Asian tropics and the eastern Himalaya—part of the Asian mainland—support very diverse mimicry rings. On the other hand, mimicry rings in the Western Ghats—a young, isolated mountain chain that acts as a habitat island—are species-poor. Ecological theory has long posited that small and remote islands should have species-poor communities compared to the mainland (and large islands nearby), owing to limits on dispersal. Mimicry rings in the habitat island that is the Western Ghats beautifully demonstrate this pattern. It is conceivable that as the Western Ghats mimicry rings get older, they will become more species-rich, potentially showing widespread convergent and parallel evolution of butterfly wing patterns. Dr. Kunte wonders, “Would we see many of the same species and wing colour patterns in mimicry rings of the Western Ghats if we time-traveled tens of millions of years in the future?”
Most biological diversity on earth is concentrated in the tropics. If we want to truly understand and conserve this diversity, biological sciences need to flourish in tropical and developing countries. “The historical, ecological and evolutionary processes that give rise to the precise composition of biological communities is still largely a mystery. The best people to solve this problem are scientists who are sympatric with the rich biodiversity of the tropics, but they are seldom up to the task. This study is a notable exception and should help motivate more tropical biologists to take pride in contributing to solving such major biological puzzles, especially when they happen to be located in their backyard.” said Prof. Raghavendra Gadagkar of the Indian Institute of Science, a well-known evolutionary biologist who has himself made fundamental contributions with his research on tropical wasps and ants.
Dr. Kunte’s lab is planning to expand this work to mimicry rings not only in the Asian tropics but also elsewhere. “There is great value in comparative research on the grander global scale on which natural selection—that singular evolutionary force—has performed breath-taking experiments in bio-diversification over a great many million years”, says Dr. Kunte.
About the ASN and its Presidential Award:
The ASN is the oldest scientific society dedicated to the study of evolution, ecology, and animal behavior, having been formed in 1883. The society journal, The American Naturalist, had been started in 1867, and is thus the oldest journal devoted to evolutionary biology. The Presidential Award of the ASN is a prestigious annual award, first given in 1984, that honours an outstanding paper published in Am. Nat. in the previous year. Previous recipients of the award include such prominent scientists as Richard E. Lenski (1985, 1991), Nancy A. Moran (1988), Dolph Schluter (1996), Robert E. Ricklefs (1998), and Robert D. Holt (2012).
American Society of Naturalists (ASN): http://www.amnat.org/home.html
ASN Awards: http://www.amnat.org/awards.html
Original research paper: https://www.journals.uchicago.edu/doi/full/10.1086/690907
Dr. Kunte’s lab: http://biodiversitylab.org/