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Insulin may fuel overgrown organs
By Susan Milius
Some of the animal kingdom’s
showiest extremes, from deers’
antlers to the outsized horns of
male rhinoceros beetles, may be
natural insulin meters.
As an animal grows, the nubbins of tissue that will form its big
weapons or displays may be more
sensitive to insulin than other
developing body parts, Douglas
Emlen of the University of Montana said July 10.
The proposal “potentially narrows the range of explanations for the
evolution of ornaments and weapons,”
said Bob Montgomerie of Queen’s University in Kingston, Ontario, who studies
courtship-related features in birds.
Insulin orchestrates growth in tune
with how much food a young animal
gets, Emlen said. A well-fed youngster
The tissue forming the horn on the rhinoceros
beetle Trypoxylus dichotomus is more sensitive to insulin than tissue elsewhere, offering
a possible explanation for how some animals’
outsized body parts evolved.
flush with insulin will presumably grow
the most spectacular horns or other
paraphernalia, while underfed rivals
remain stunted. If the growing antlers
or other extreme structures are supersensitive to insulin, they will supersize
out of proportion to less sensitive tissue.
That’s the case for the horns of the
rhinoceros beetle Trypoxylus dichoto-
mus. Males grow horns about two-thirds
as long as the rest of their bodies. They
use these weapons to knock rivals away
from sap-oozing wounds on trees where
females feed. The horns are eight times
more responsive to insulin or insulin-like
growth factors than other body parts.
Young fruit flies
go cannibalistic
Surprising actions may aid
future studies of predation
By Susan Milius
Larval fruit flies, supposedly relentless
devourers of rotting fruit, at times leave
their regular laboratory food to stalk,
kill and group-cannibalize some of their
older, fatter fellows, scientists report.
This predatory cannibalism shows
up in Drosophila melanogaster, the fly
species that generations of biologists
have grown in untold numbers, Roshan
Vijendravarma of the University of Lausanne in Switzerland reported July 7. He
and Lausanne colleagues documented
the behavior in both Canton S fruit flies,
a strain raised in labs for more than six
decades, and the Valais strain, brought
into labs only in the last two years.
“I have never read or heard about
this, and I was absolutely stunned that
nobody has ever noticed this before,”
said Thomas Flatt of the University of
Veterinary Medicine in Vienna. “This
story is to my mind of great biological
interest, and it shows very clearly that
there are many surprises left, even in a
well-studied model organism.”
Because fruit fly genetics is known in
such detail, Vijendravarma said his dis-
covery may allow researchers to study
the evolution of predatory cannibalism
at the molecular level.
The closest reports Vijendravarma has
found to what he’s witnessed describe
larvae of fruit fly D. hydei dining on
already dead larvae of other insects.
What Vijendravarma reported is not just
feeding on a happenstance free lunch, but
hunting as well. He showed close-up vid-
eos of the dark, pronged mouthparts of
a smaller larva scraping again and again
against the wide, cream-colored body of
a larger one. Finally the big larva’s body
rips open, exposing softer flesh. He also
showed photographs of clusters of small
larvae side-by-side with their mouths
against the flesh of a much larger one.
