A few revelations about moths and butterflies

A comprehensive evolutionary tree of Lepidoptera, the order that includes butterflies and moths, reveals that this assorted group of insects has been around for up to 300 million years – much longer than previously thought.

It also finds that moths had ultrasonic “ears” well before bats came into existence, challenging theories that they developed them to outsmart their flying mammal predators.

Butterflies and moths play key roles in virtually every terrestrial ecosystem and “are inextricably connected to the natural histories of many plants, predators and parasitoids”, write Akito Kawahara, from the University of Florida, US, and a substantial team of co-authors in the journal Proceedings of the National Academy of Sciences.

As such, these tiny flying wonders give clues to environmental change and are central to notions of co-evolution. However, many theories about the evolution of Lepidoptera, which include nearly 160,000 described species, remain untested.

“Having a fossil-dated family tree gives us our most detailed look yet at the evolutionary history of moths and butterflies,” says Kawahara. 

“We’ve thought for a long time that flowering plants must have contributed to the extraordinary number of moth and butterfly species we see today, but we haven’t been able to test that.”

Kawahara and colleagues scoured the planet for insect specimens and sequenced the genomes of more than 2000 samples from 186 surviving species – representing 34 superfamilies.

Comparing these with painstakingly appraised fossil records, they found that the most recent common ancestor of Lepidoptera emerged in the Late Carboniferous, about 100 million years earlier than previous fossil records from the Triassic-Jurassic boundary around 200 million years ago. 

Their efforts did, however, support the insects’ tight co-evolution with plants.

“Our results are pretty consistent with previous studies that estimate the origin of the oldest flowering plant lineages, now extinct, at around 300 million years ago,” says Kawahara.

The first apparent ancestor likely fed on nonvascular land plants before evolving their “tube-like proboscis” in the Middle Triassic, around 240 million years ago, which enabled them to suck nectar from flowering plants (angiosperms).

The research also implies that ancestral butterflies were nocturnal and became diurnal in the Late Cretaceous nearly 100 million years ago – before bats took flight around 50-60 million years ago.

This contradicts the theory that butterflies started daytime flights to escape bats, according to the authors, which suggests they “likely became diurnal to capitalise on day-blooming flowers”.

Their most unexpected discovery was that moth hearing organs appeared several times before flying bats came onto the scene, although that doesn’t discount their protective role for avoiding the hungry hunters.

Kawahara and co-author Jesse Barber from Boise State University, US, theorise that moths “probably used these hearing organs to detect the sounds made by other predators, like footfall, flight or rustling, and later co-opted them to pick up on bat sonar”.

Kawahara says this study helps confirm that butterflies and moths are part of a larger, impressive order of insects

“We tend to appreciate butterflies because they’re often flashy and charismatic,” he says, “but we shouldn’t forget about moths, which can be just as striking.”

“Moths and plants were interacting some 50 million years before the first dinosaur roamed the Earth, and those interactions helped lead to the diversity we see on our planet today.”

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