LIFE & EVOLUTION
How birds avoided
Terrestrial lifestyle linked to
surviving the dino apocalypse
LIFE & EVOLUTION
Caterpillar thwarts corn’s smelly SOS
Pest may co-opt plant’s distress signal to avoid wasp attacks
BY SUSAN MILIUS
Nothing against trees. But maybe it’s better not to get too dependent on them if
you want to survive a big flaming space
object crashing into Earth.
The asteroid impact that caused a
mass extinction 66 million years ago
probably also triggered the collapse of
forests worldwide, a new investigation of
the plant fossil record concludes. Needing trees and extensive plant cover for
nesting or food could have been a fatal
drawback for winged dinosaurs, including some ancient birds. Reconstructing
the ecology of ancient birds suggests that
modern fowl descended from species
BY SUSAN MILIUS
Here’s the story of a caterpillar that foils
gruesome violence orchestrated by corn.
No, that’s not backward. Plants often
look helpless to a human, but they fight
that survived because they could live on
the ground, researchers propose in the
June 4 Current Biology.
“You probably would have died any-
way, regardless of habitat,” says study
coauthor Daniel Field, an evolutionary
paleobiologist at the University of Bath
in England. “But if you could get along on
the ground, you at least had a shot at sur-
viving across this devastated landscape.”
with smells and other invisible chem-
istry. A growing body of evidence, for
example, shows that plants under attack
can waft out scents that attract help,
such as tiny wasps that deal a lingering
before the asteroid hit and again start-
ing about a thousand years afterward. In
between those times of diversity, how-
ever, ferns dominated, the team notes.
A kind of “disaster flora,” ferns (making
spores instead of flowers and seeds) do
well at recolonizing land. Seed plants,
however, weren’t thriving.
Analyzing evolutionary histories
of modern birds supports the idea of
tree dependence as a vulnerability for
the earliest fowl, the researchers say.
Specialists in bird evolution generally
agree on the lowest, oldest branches
of the bird family tree, Field says. The
bottommost one includes such modern
species as ground-dwelling ostriches
and smaller, flight-capable birds called
tinamous, which might be more like the
ancient birds that dodged extinction
than ostriches are.
Working backward along these low
branches of the family tree, researchers used fossils and known bird traits
death to leaf-chewing caterpillars.
A dream for future farming is to boost
such crop powers. Yet a tale, published
May 16 in Science Advances, of how
attacking Spodoptera littoralis
caterpillars can escape a trap set for them by
maize plants shows how complex a task
that could be.
These attackers are “greenish, brownish, ugly caterpillars,” says Ted Turlings
of the University of Neuchâtel in
Switzerland, who makes no secret of
where his allegiance lies. The caterpil-
lars damage maize, cotton and a variety
of other crops in the Middle East, Africa
and elsewhere. But maize fights back, of
course. As the caterpillars crunch into
a leaf, substances in their spit trigger a
burst of furious plant chemistry, which
causes the release of certain scents.
The first wave of odors from dam-
aged plants, the cut-grass smell, comes
just from ripped tissues spilling their
innards. Then within hours, maize
sends out new scents that can advertise
the kind of pests attacking it. “You can
actually smell it yourself,” Turlings says.
Or at least his trained nose can.
Release of volatiles
Fresh caterpillar damage
Several hours after caterpillar damage
Smell the leaves Maize leaves don’t normally give off much in the way of smells (top graph,
each peak represents an airborne compound). When caterpillars bite into a leaf, though, a wave of
leafy green volatile compounds rises (middle). In a few hours, the leaf synthesizes other volatiles
(bottom), including indole and terpenes, that lure such caterpillar enemies as a female parasitoid
wasp. New work suggests that caterpillars that bulk up on indole-rich foliage can repel wasps.