[Leps-l] Spiders, Not Birds, May Drive Evolution of Some Butterflies

[Mike Quinn]

*ScienceDaily*Spiders, Not Birds, May Drive Evolution of Some Butterflies
Mar. 12, 2013 — <snip>

In the first behavioral study to directly test the defense mechanism of
hairstreak butterflies, UF lepidopterist Andrei Sourakov found that the
appearance of a false head -- a wing pattern found on hundreds of
hairstreak butterflies worldwide -- was 100 percent effective against
attacks from a jumping spider. The research published online March 8 in the
Journal of Natural History shows small arthropods, rather than large
vertebrate predators, may influence butterfly evolution.

"Everything we observe out there has been blamed on birds: aposematic
coloration, mimicry and various defensive patterns like eyespots," said
study author Andrei Sourakov, a collection coordinator at the Florida
Museum of Natural History's McGuire Center for Lepidoptera and Biodiversity
on the UF campus. "It's a big step in general and a big leap of faith to
realize that a creature as tiny as a jumping spider, whose brain and life
span are really small compared to birds, can actually be partially
responsible for the great diversity of patterns that evolved out there
among Lepidoptera and other insects."

Sourakov's behavioral experiments at the McGuire Center showed the
Red-banded Hairstreak butterfly, *Calycopis cecrops*, whose spots and tail
imitate a false head, successfully escaped all 16 attacks from the jumping
spider,*Phidippus pulcherrimus*. When 11 other butterfly and moth species
from seven different families were exposed to the jumping spider, they were
unable to escape attack in every case. Sourakov videotaped the experiments
and analyzed the results in slow motion.

"From the video, you can see the spider is always very precise," Sourakov
said. "In one video, the spider sees a moth that looks like a leaf and it
walks very carefully around to the head and then jumps at the head region.
The spider has an innate or acquired ability to distinguish the head region
very well and it always attacks there to deliver its venom to the vital
center to instantly paralyze the prey. Most importantly, the spider is very
small, so sometimes its prey is 10 times larger."

The species of hairstreak butterfly and jumping spider used in the
experiment are both common in the southeastern U.S., with similar relatives
spread worldwide. In nature, the spider and hairstreak come into contact
when the butterfly lands on leaves or flowers to rest and feed. Female
red-banded hairstreak butterflies lay their eggs in leaf litters, which are
often crawling with spiders.

David Wagner, a professor of ecology and evolutionary biology at the
University of Connecticut who was not involved with the study, said the
research shows scientists need to rethink what drives adaptive coloration
patterns because the results suggest that "birds are only part of the
story."

"I'm just so impressed with Andrei's experimental protocol and the fact
that the jumping spider could not catch the hairstreak butterflies," Wagner
said. "His empirical study will do much to cause us to rethink the vision
and the visual acuity that certain invertebrate predators have when hunting
their prey and how this has really molded how some organisms not only look
like, but perhaps how they act, as well."

Unlike other butterflies, hairstreaks constantly move the hind wings that
carry the false head pattern, a behavior that seems to increase in the
presence of the spider, as if the butterfly is attracting attention to
itself, Sourakov said. In museum collections, hairstreak specimens are
frequently found with the false-head portion of the wings missing. During
the experiments, the spider always attacked the butterfly's false head,
thereby avoiding its vital organs.

"The false head hypothesis in hairstreaks has been in circulation for a
long time because people always speculated that their tails move around in
order to fake out the predators, but there was little experimental
evidence," Sourakov said.

Sourakov said he hopes the study encourages behavioral ecologists to
further test the idea that evolution in butterflies and moths may be driven
by small invertebrate predators.

"This clearly shows it's possible that many spectacular patterns that we
find in smaller insects may be due to spider pressure rather than bird
pressure," Sourakov said. "The butterfly escapes from the spider -- it's a
fairytale story."

full text: http://www.sciencedaily.com/releases/2013/03/130312102547.htm

*Journal Reference*:

   1. Andrei Sourakov. *2013. Two heads are better than one: false head
   allows Calycopis cecrops (Lycaenidae) to escape predation by a Jumping
   Spider, Phidippus pulcherrimus (Salticidae)*. *Journal of Natural History
   *, 1 DOI: 10.1080/00222933.2012.759288<http://dx.doi.org/10.1080/00222933.2012.759288>


Mike Quinn, Austin
________________
Texas Entomology
http://texasento.net
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