Butterflies and Evolution
How a 2018 Award Illuminates Nature's Masterpiece
The delicate patterns on a butterfly's wings reveal evolutionary secrets that have shaped life on Earth for millions of years.
The American Society of Naturalists, established in 1883, has long championed research that uncovers the fundamental principles governing the natural world. Each year, the society recognizes exceptional contributions to evolutionary biology, ecology, and animal behavior through its prestigious awards program. In 2018, one investigation into the beautiful complexity of butterfly mimicry demonstrated how meticulous fieldwork combined with innovative genetic analysis can transform our understanding of evolution's intricate processes.
The American Society of Naturalists: Honoring Scientific Excellence
The American Society of Naturalists (ASN) represents the oldest scientific society dedicated to the study of evolution, ecology, and animal behavior. Founded in 1883, the society aims to "advance and diffuse knowledge of organic evolution and other broad biological principles so as to enhance the conceptual unification of the biological sciences"1 .
Honors scientists whose careers epitomize the society's mission, with membership limited to just twelve living individuals1 .
Recognizes senior investigators making fundamental contributions to conceptual unification of biological sciences (renamed in 2022 from the Sewall Wright Award)1 .
Celebrates mid-career investigators who have made significant contributions to knowledge of particular ecosystems or organism groups (renamed in 2022 from the E. O. Wilson Naturalist Award)1 .
Honors the best paper published in The American Naturalist during the preceding calendar year1 .
The 2018 ASN Presidential Award recognized a groundbreaking study that reshaped our understanding of how evolutionary processes shape ecological communities in tropical ecosystems. This research combined decades of evolutionary theory with cutting-edge genetic tools to solve a mystery that had fascinated naturalists for generations.
The Puzzle of Butterfly Mimicry Rings
In tropical forests around the world, diverse butterfly species cluster into distinct "mimicry rings"—groups where multiple species share similar wing patterns, colors, and markings. These patterns aren't random aesthetic arrangements but sophisticated survival systems honed by evolution.
The mechanism behind these mimicry rings involves complex ecological relationships:
- Toxic Models: Some butterfly species are unpalatable to predators due to toxins accumulated from their host plants during caterpillar stage.
- Palatable Mimics: Numerous edible, unrelated butterfly species evolve to resemble these toxic models, gaining protection from predators through deception.
- Predator Learning: Birds and other predators learn to avoid the warning coloration after unpleasant experiences with toxic butterflies, subsequently avoiding the lookalikes.
This evolutionary strategy, known as Batesian mimicry, creates clearly defined ecological communities where appearance determines membership rather than genetic relationship. For over a century, biologists assumed these rings formed primarily through convergent evolution—the process where distantly related species independently develop similar traits in response to comparable environmental pressures.
The Western Ghats of India, a UNESCO World Heritage site and biodiversity hotspot, provided the ideal natural laboratory to test these assumptions. This mountain range functions as a "habitat island"—an isolated ecological patch separated from similar habitats—allowing scientists to study how geography influences evolutionary processes.
Scientific Detective Work: Unraveling Evolutionary Mysteries
The research team from the National Centre for Biological Sciences (NCBS) in Bangalore, India, embarked on an ambitious project to decipher the evolutionary origins of mimicry rings in the Western Ghats. Led by Dr. Krushnamegh Kunte, the team included Dr. Jahnavi Joshi, an expert in phylogenetic methods, and Anupama Prakash, who specialized in analyzing mimicry ring diversity.
Fieldwork & Data Collection
The team conducted extensive fieldwork in the Western Ghats, carefully documenting and collecting butterfly specimens from various mimicry rings.
Genetic Analysis & Phylogenetics
The researchers constructed a molecular phylogeny—a family tree based on genetic similarities—for the Western Ghats butterfly species.
Comparative Biogeography
The team compared their findings from the Western Ghats with mimicry rings in mainland regions like the Southeast Asian tropics and eastern Himalayas.
Research Tools and Applications
| Research Tool/Method | Specific Application in the Study | Scientific Function |
|---|---|---|
| Field specimen collection | Documenting mimicry rings in Western Ghats | Establishing ecological patterns and relationships |
| Molecular phylogenetics | Building species trees of butterfly communities | Revealing evolutionary relationships and history |
| Phylogenetic community analysis | Studying assembly of mimicry rings | Understanding how ecological communities form evolutionarily |
| Biogeographic comparison | Contrasting Western Ghats with mainland Asia | Isolating effects of geographical isolation on evolution |
Surprising Revelations: Challenging Evolutionary Assumptions
The NCBS team's findings, published in the April 2017 issue of The American Naturalist, overturned long-standing assumptions about how mimicry rings develop. Contrary to expectations, the research revealed:
Ancestral Inheritance
The toxic model butterflies in each mimicry ring were closely related genetically, sharing warning color patterns through common ancestry rather than convergent evolution.
Mimics as Evolutionary Joiners
The palatable mimics joined mimicry rings through remarkable convergent evolution, sometimes diverging from their ancestral forms by tens of millions of years.
The Island Effect
The isolated nature of the Western Ghats resulted in species-poor mimicry rings compared to the rich, diverse rings found in mainland Southeast Asia.
Comparison of Mimicry Ring Characteristics Between Regions
| Characteristic | Western Ghats (Habitat Island) | Mainland SE Asia & Eastern Himalayas |
|---|---|---|
| Species diversity | Low | High |
| Primary formation mechanism | Ancestral inheritance (models) | Not specified in study |
| Convergent evolution | Primarily in mimics | Not specified in study |
| Geographical influence | Strong isolation effect | Continental connectivity |
These findings demonstrated that the formation of mimicry rings involved more complex evolutionary pathways than previously thought. The combination of ancestral trait retention in models and dramatic convergence in mimics created the beautiful ecological communities observed in nature.
Significance and Future Directions
The recognition of this research with the ASN Presidential Award highlighted its importance in advancing evolutionary biology. The study provided a novel framework for understanding how evolutionary processes shape biological communities over time.
"The historical, ecological and evolutionary processes that give rise to the precise composition of biological communities is still largely a mystery. This study is a notable exception and should help motivate more tropical biologists to take pride in contributing to solving such major biological puzzles".
The research also underscored the importance of studying tropical ecosystems, which harbor most of Earth's biological diversity. Scientists based in these regions have unique opportunities to observe and analyze evolutionary processes in their backyards.
Dr. Kunte's lab plans to expand this research to mimicry rings beyond the Western Ghats. As Dr. Kunte explained, "There is great value in comparative research on the grander global scale on which natural selection—that singular evolutionary force—has performed breathtaking experiments in bio-diversification over many million years".
Steps in the Experimental Process and Key Findings
| Research Phase | Methodology | Key Outcome |
|---|---|---|
| Field sampling | Documenting mimicry rings in Western Ghats | First proper characterization of these ecological communities |
| Phylogenetic analysis | Building molecular species trees | Revealed evolutionary relationships among species in mimicry rings |
| Community assembly analysis | Applying novel phylogenetic methods | Discovered different evolutionary pathways for models vs. mimics |
| Biogeographic analysis | Comparing Western Ghats with mainland | Confirmed "island effect" on species diversity in mimicry rings |
Conclusion: Evolution's Enduring Mysteries
The 2018 ASN Presidential Award-winning research transformed our understanding of how evolutionary processes create and maintain biological diversity. By revealing the complex interplay between ancestral inheritance and convergent evolution in butterfly mimicry rings, the NCBS team demonstrated that nature's patterns often conceal surprising evolutionary histories.
This study exemplifies the mission of the American Society of Naturalists—to advance conceptual unification across biological sciences. It connects evolutionary theory, ecology, genetics, and biogeography, showing how multiple disciplinary perspectives can converge to solve longstanding biological puzzles.
Perhaps most importantly, this research reminds us that countless evolutionary mysteries remain waiting to be solved, many in the tropical ecosystems that are rapidly disappearing. As Dr. Kunte mused about future possibilities in the Western Ghats, "Would we see many of the same species and wing color patterns in mimicry rings if we time-traveled tens of millions of years in the future?". Only continued scientific exploration will reveal the answer.
References
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