From: National Centre for Biological Sciences
Published October 3, 2017 10:28 AM

To Breed or Not to Breed? Migratory Female Butterflies Face a Monsoonal Dilemma

What do CPUs, stockbrokers, and butterflies have in common? They are good at investing their resources in the right place at the right time so as to maximize their returns! Trade-offs are a way of life for butterflies and other small insects that must budget their energy between numerous morphological features and activities during their short lifespans. Time, food, and space are always at a premium, and optimizing resource use is particularly important for migratory butterflies that must prepare for arduous journeys in uncertain environments. A new study by researchers at the National Centre for Biological Sciences (NCBS-TIFR, Bengaluru) reports on butterfly migrations in peninsular India and explores the effect of migration on resource investment strategies of migratory butterflies. It reveals that migration affects the morphology and physiological states of female butterflies much more prominently compared to that of males.

Milkweed butterflies (so called because they feed on plants with a milky sap) are commonly found in gardens and wooded areas in southern India. Every year, four species – the Double-branded Crow (Euploea sylvester), Common Crow (Euploea core), Dark Blue Tiger (Tirumala septentrionis), and Blue Tiger (Tirumala limniace) – undertake a bidirectional migration between the Western Ghats and the southern Eastern Ghats and surrounding eastern plains. Swarms composed of millions of these butterflies grace the environs of Bengaluru on their way. This spectacular phenomenon first occurs between April and June, before the southwestern summer monsoons hit the Western Ghats, when butterflies are driven by pre-monsoon showers to the eastern plains and hills. The return migration to the Western Ghats, undertaken by newly emerged butterflies of the next generation, takes place between October and December, after the south-west monsoons are over.

During the migration, these butterflies fly for long hours through unfamiliar landscapes and unpredictable environments, and still manage to remain in stable conditions that allow them to breed at the end of the migration. Migration allows these butterflies to escape the torrential monsoonal rains in the Western Ghats, but the physically exhausting and energetically demanding 350-500 kilometer journey also forces these insects to make some peculiar changes to their lifestyle. This must take some carefully balanced investments in flight morphology and reproductive tissue that allow them to switch their physiological states and deploy fat reserves when needed. How do they do this?

Read more at National Centre for Biological Sciences

Image: This is an image of a Euploea sylvester. (Credit: Dr. Krushnamegh Kunte, NCBS-TIFR)

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