A butterfly can change its spots
Assoc Prof Monteiro with one of the butterflies in her laboratory, the Squinting Bush Brown (Bicyclus anynana)
A team from NUS Biological Sciences has conducted a study which revealed that the size and brightness of eyespots on the hindwings of certain butterflies were regulated by temperature during their development. The study was published in PLOS Genetics on 25 September.
There are many butterfly species whose eyespots change in size but not all of them do so in the same way. Led by Associate Professor Anto'nia Monteiro, the researchers set out to find out why the eyespots of certain butterflies varied during the wet and dry seasons. The team reared groups of caterpillars of an African species of butterfly in a number of different environments. One group of caterpillars was reared at 17 degrees Celsius and another group at 27 degrees Celsius. Some others were reared primarily at one temperature but shifted to another rearing temperature for 48 hours.
The team discovered that the butterflies' eyespot size, centre size and brightness became larger and brighter when the caterpillars were reared at high temperatures starting at the wandering stage of their development. The wandering stage referred to the period when caterpillars had stopped feeding and were wandering around looking for a place to pupate. "That stage in development seems to be very sensitive to temperature, said Assoc Prof Monteiro. Higher temperatures led to increased concentrations of a steroid hormone in the blood of the insects at that particular time in development. In addition, cells in the centre of the hindwing eyespots produced the necessary hormone receptors that allowed these cells to respond to the hormone and produce larger and brighter eyespots. However, cells at the centre of the forewing eyespots shut down the necessary hormone receptors at that particular time in development, thus becoming insensitive to the hormone and to temperature, and maintained a fixed appearance.
"These animals have evolved these incredible adaptations to the dry season and the wet season because they have been experiencing recurrent fluctuating environments in their evolutionary history, Assoc Prof Monteiro explained. The phenomenon of butterfly eyespots' appearance changing in relation to temperature is similar to animals changing their coats in different seasons.
Assoc Prof Monteiro said that climate change comes with unpredictable fluctuations. The butterflies could start producing different seasonal forms with inappropriate environmental cues, leading to a mismatch between their form and the environment they will later find themselves in. "It's unclear whether we're going to have enough time for them to gather the mutations that they require to tweak their patterns in a way that is adaptive to the new environment, she said, adding that the butterflies might require a few hundred years to adapt.
The researchers are now rearing 13 species of butterflies from Singapore and Malaysia, including the Blue Pansy (Junonia orithya) and the Grey Pansy (Junonia atlites). Interestingly, they exhibit the exact opposite response to temperature, that is, their eyespots become smaller at higher temperatures and larger at lower temperatures. Assoc Prof Monteiro said the research team is currently studying which state is the ancestral, original state and which state has evolved over time.
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