Watch out what you say around eggs – they might be listening. A team of researchers, led by Mylene Mariette of Deakin University, has found that a plethora of unhatched embryos rely on sound signals to control how they grow – a phenomenon called “acoustic developmental programming”.
“Acoustic developmental programming occurs when a sound informs embryos about the environment they’ll encounter postnatally and changes their development to better suit this environment,” says Mariette.
Previous research has found evidence of this in birds, where parents warn youngsters about heatwaves or predators, and also in cricket nymphs, which use male songs to predict the level of competition for a mate.
But this new analysis shows that this is a strikingly widespread feat, with sound information helping many different embryos adapt to environmental changes they have been told about by a parent.
“For example, across all animal groups that lay eggs, such as insects, frogs, reptiles and birds, embryos use sound or vibration to know when the best time is to hatch,” Mariette says. “This suggests that acoustic developmental programming is likely to happen in many animal species and for a whole range of conditions. But, until recently, we did not know it was happening.”
This research was sparked when Mariette noticed that zebra finches let out a strange high-pitched noise when alone with eggs, so she began to search through the scientific literature to understand why. While it is still unclear exactly how it works, she did uncover some interesting potential mechanisms.
“In crickets, when developing nymphs hear many sexy songs, female develop quickly to make the most of the opportunity, whereas males delay metamorphosis to grow bigger and invest more in reproduction,” says Mariette.
“In zebra finches, embryos exposed to parental heat calls grow less to reduce the physiological damage of heat exposure, which then allows them to produce more babies at adulthood.
“But embryos cannot decide to change their development, it just happens.”
She explains that this is because sound directly changes behaviour and bodies, without the need for conscious processing.
“This is why, for example, music triggers spontaneous emotions of sadness or happiness, without us having to remember which movie that soundtrack came from, or in fact without us even noticing our reaction to the music,” Mariette says.
“It seems to occur on its own, because there are direct connections in the brain between the auditory pathway and the areas that control emotion, reflex learning, and hormone production, so the higher cortical areas do not need to decode the information.
“Sound experienced early in life could trigger the same spontaneous reactions and, in fact, have long-lasting effects, because this is when the brain is developing, and consolidating connections.”
This type of technique to help embryos grow in the right way points to the importance of the soundscape in animal adaption, particularly in fast-changing environments.
“It is quite amazing that sound alone can prepare babies for heat, particularly given the alarming rate of climate change,” Mariette concludes.
The analysis is published in Trends in Ecology and Evolution.
“Sing to me, mother, so I may know how to live beyond this egg.” – A baby crocodile, probably.
Dr Deborah Devis is a science journalist at The Royal Institution of Australia.
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