Thursday 13 February 2020

How some butterflies developed the ability to change their eyespot size


FEBRUARY 11, 2020

by eLife

New insight on how a butterfly species developed the ability to adjust its wing eyespot size in response to temperature has been published today in eLife.

The study reveals that the African satyrid butterfly Bicyclus anynana (B. anynana), a member of the sub-family of the nymphalidae (or 'brush-footed') butterflies, changes its eyespot size using a complex physiological and molecular response that evolved gradually over millions of years. The findings also highlight that while temperature modulates hormone levels in various species of satyrid butterfly, B. anynana is just one of a few that take advantage of this response to regulate eyespot size.

Many butterflies in the nymphalidae family have circular eyespot patterns on their wings that are typically used to deflect attacks from predators. However, in certain seasons, such as the dry season in Africa, the butterflies' best survival strategy is to avoid drawing attention to themselves, and they will shrink the size of their eyespots to make them look like a dead leaf.

How butterflies accomplish this feat has only been studied in one species of African satyrid, B. anynana. In this species, low temperatures that signal the arrival of the dry season lower the quantity of a hormone called 20E during the late larval stage. This alters the function of hormone-sensitive cells in the centre of the eyespots and subsequently shrinks their size.

"For our study, we investigated how this hormone-mediated system came to regulate the size of eyespots by examining the process in several other species of butterflies with and without eyespots," explains lead author Shivam Bhardwaj, who conducted this work as part of his doctoral research in the Department of Biological Sciences at the National University of Singapore (NUS), and who is now a postdoctoral fellow at Mississippi State University. "We wanted to find out which other species change their eyespot size in response to temperature and whether they achieve this through the same mechanism as B. anynana. This comparative work would allow us to explore for the first time how a temperature-regulated system evolves at the genetic and physiological level."


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