Learned odour preferences can be inherited in butterflies

NUS researchers found that caterpillars and butterflies can learn to prefer new food odours and sex pheromone blends, and that these new preferences are inherited by their offspring.

It was long believed that physical characteristics acquired by organisms during their lifetime could not be passed on to their offspring. The theory of inheritance of acquired traits, however, has received increased support in the last few years with the publication of studies showing how offspring inherit behaviours that were acquired by their parents in response to particular environmental stimuli, even when the stimulus is no longer present in the offspring generation.

This inheritance of acquired traits was previously shown in rats and tiny worms, but NUS researchers have recently discovered that the inheritance of acquired traits also happens in butterflies, especially in the bush brown butterfly Bicyclus anynana. Two research teams under the supervision of Prof Antónia MONTEIRO, from the Department of Biological Sciences, NUS showed that both caterpillars and adult butterflies can learn to prefer new odours if they are exposed to them during their development or early in life. The researchers also found that the offspring of the exposed caterpillars and butterflies show the same new preferences as their parents, even though they were not exposed to the odours. The parent butterflies had transmitted their new acquired preferences to their offspring.

The research team which includes research fellow, Dr Emilie DION and Ph.D. student, Ms V. GOWRI, together with their collaborators, exposed caterpillars and butterflies to new odours they typically do not experience in their natural environment. In the first experiment, caterpillars were fed with corn leaves, which is their usual food plant, but coated with banana or mango essence throughout their development. Most caterpillars preferred to eat the leaf with the essence after a few days of exposure. In the second experiment, young female butterflies were exposed to new sex pheromone blends, a perfume produced by males to entice females to mate with them. The exposed females later preferred to mate with the male having the new pheromone blend.

Dr Dion said, “These results are interesting because they show that insects are not only driven by their instincts, but that they actually can learn from their previous experience and adjust their future behaviour accordingly. The implications of their learning abilities on their survival and reproduction can be very important!”

Both teams then examined the behaviour of the offspring of the exposed caterpillars and butterflies. They found that this new generation also exhibited the preference for the new food odours, or the new sex pheromone blends, except that they were never exposed to these odours themselves. The teams concluded that the offspring inherited the preferences acquired by their parents. While these learning and inheritance processes are hypothesised to facilitate the evolution of diet diversity across insects, and mate selection over the course of insect diversification, the impact of this inheritance mechanism on evolution is still unknown.

“We are now investigating whether this behavioural transmission is maintained for more than one generation, and also probing the underlying molecular mechanisms in our model species, as these remain some of the most exciting unanswered questions in the field of evolutionary biology,” added Prof Monteiro.

(Left) Bicyclus anynana butterfly caterpillars munching on a maize leaf. (Right) Male and Female Bicyclus anynana butterflies. [Credit: William H. PIEL and Antónia Monteiro]

References

E Dion*; LX Pui; K Weber; A. Monteiro*, “Early-exposure to new sex pheromone blends alters mate preference in female butterflies and in their offspring” NATURE COMMUNICATIONS Volume: 11, Article number: 53 Published: 2020.

Gowri V; Dion E; Viswanath A; Piel FM; Monteiro A*, “Transgenerational inheritance of learned preferences for novel host plant odors in Bicyclus anynana butterflies” EVOLUTION DOI: 10.1111/evo.13861 Published: 2019.