Why do some live longer than others? Researchers from Leiden University, the Netherlands, turned to tropical African butterflies to find the answer. "The definitive answer is still not known, but our results give an interesting new insight into the evolution of lifespan," says Jeroen Pijpe, first author of a new article.
He and his colleagues used what is called artificial selection to create genetically long-lived butterflies of the species Bicyclus anynana. "Basically, we use what the species does naturally, and magnify the bit we're interested in here in the lab in Leiden."
In the field, the temperature experienced by the caterpillar sets up the butterfly to become the form that matches the season. This is called phenotypic plasticity, and in this species it has evolved as a response to the alternating seasons.
The dry season form is long-lived and more starvation resistant. In the wet season, reproduction takes place. In this case, the authors selected on starvation resistance under wet-seasonal conditions.
They discovered that female butterflies had shifted their reproduction from quantity to quality of offspring. Next, they found that males and females had responded differently to the artificial selection: males seemed to have lowered their energy consumption, whilst females had increased the amount of energy to spend.
"Both results offer interesting details not found previously in comparable experiments using fruit flies," Pijpe states. However, the most important finding was that the artificial selection in a wet seasonal environment had produced butterflies that resembles the long-lived dry season form.
Pijpe says: "In other words, we targeted genes that are needed to live longer, and the result is very much like how temperature induces butterflies to live longer in the dry season."
It suggests that, in this species, the evolution of lifespan is closely associated with phenotypic plasticity. Is it a general mechanism? "We think it is likely that the regulation of lifespan involves mechanisms of phenotypic plasticity during development, also in humans."
This research was published in the January issue of the American Naturalist.
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