Most butterflies live only a few weeks after reaching maturity. So when scientists at the University of Bristol, UK, started studying a group of tropical insects belonging to the genus Heliconius, what they found came as a surprise.
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Some species in this group, found across the rainforests of Central and South America, don’t just live longer than other butterflies – they also appear to age slower. One species, Heliconius hewitsoni, can live up to 348 days.
Its close relative, Dione juno, survives only 14. That’s almost a 25-fold difference in lifespan between two insects that, in evolutionary terms, aren’t far apart at all.
But longevity is only half of the story. Working in collaboration with scientists at the Smithsonian Tropical Research Institute in Panama, the team tested the physical performance of another species, Heliconius hecale, using a grip strength test.
Older butterflies performed at virtually the same rates as younger ones, with no obvious signs of deterioration. In a closely related shorter-lived species, Dryas iulia, the deterioration with age was what you’d expect.
So why are these species aging slower? A leading theory for years has been the butterflies’ diet – unlike most butterflies, which rely on nectar, Heliconius species feed on pollen. It’s a richer food source, packed with proteins and amino acids – with better nutrition potentially leading to a longer life.
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Except, when researchers removed pollen from the diet of Heliconius hecale, the butterfly still outlived its relatives by a significant margin – suggesting the secret isn’t diet alone, but something written into the biology of the animal itself.
“As the most species-rich animal class, insects are renowned for their extraordinary morphological and ecological diversity,” explains Jessica Foley, the study’s lead author from the University of Bristol.
“They also exhibit extreme variation in longevity, with maximum lifespans ranging from just a few days in adult mayflies to several decades in the reproductive castes of some ants and termites. This represents a roughly 5,000-fold difference within the class, compared with around a 100-fold difference in lifespan observed in mammals.”
Scientists have frequently studied long-lived animals to uncover the mysteries of longevity, but this instance offers a rare natural experiment: two closely related species, one that ages as expected and one that barely seems to age at all. Understanding the difference between them could be key to understanding the secrets of aging itself.
Read the full findings here.
Top image: Tiger longwing (Heliconius hecale). Credit: 49pauly/Getty Images
