Amphibious caterpillars discovered in Hawaii


— Moths of the Hawaiian genus Hyposmocoma are an oddball crowd: One of
the species’ caterpillars attacks and eats tree snails. Now researchers
have described at least a dozen different species that live underwater
for several weeks at a time.

“I couldn’t believe it,” said study co-author Daniel Rubinoff, an evolutionary biologist at the University of Hawaii at Honolulu,
of the first time he spotted a submerged caterpillar. “I assumed
initially they were terrestrial caterpillars … how were they holding
their breath?”

Each of the 12 species lives in and along streams running down the mountains on several different islands of Hawaii, said Rubinoff, who has studied Hyposmocoma, a group of more than 350 moth species, for more than seven years.

They usually eat algae or lichen, and build silk
cases — which one species even adorns with bird feathers — for shelter
and camouflage. They spin silk drag lines to withstand the high
pressure of fast flood waters.

Unlike other amphibious creatures that can survive
underwater on stored oxygen but must come back up for air, these
caterpillars can spend several weeks without ever breaking the surface,
according to the paper, which was published online Monday in
Proceedings of the National Academy of Sciences.

It isn’t yet clear how the insects do it. Rubinoff and co-worker Patrick Schmitz of the University of Hawaii
did not find any water-blocking stopper over the caterpillars’ tracheae
or evidence of gills. The animals drowned quickly when kept in standing
water, so they seem to need the higher levels of oxygen present in
running water, and probably absorb it directly through pores in their
body, the scientists said.

The trait appears to have evolved more than once,
Rubinoff said. After analyzing the DNA of the 12 amphibious species,
the scientists found that three separate lineages of moth had developed
the ability to breathe underwater at different points in the past.

Why they evolved this trick isn’t clear, but animals
and plants are known to often evolve in surprising directions after
arriving at new, sparsely populated habitats such as islands, said Felix A.H. Sperling, an entomologist with the University of Alberta in Edmonton.

In a new environment, released of the pressure of
having to fight for food sources or evade predators, they are freer to
expand into new niches.

“When the pressures on an environment are released, what crazy things are animals capable of doing?” said John W. Brown, a research entomologist with the U.S. Department of Agriculture.

“You just wonder … do all animals have that potential?”


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