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
coauthor 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 floodwaters.
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 on 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?"
— Amina Khan
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Scientists have discovered 12 species of caterpillars that can survive
for weeks underwater without ever breaking the surface. They don’t have
gills and they don’t hold their breath. Credit: University of Hawaii