EMBARGOED FOR RELEASE UNTIL OCTOBER 11, 2006
Contact:
Christine Guilfoy
Office: (301) 634-7253
cguilfoy@the-aps.org
Have Traits, Will Travel
Some butterflies travel farther, reproduce
faster than their neighbors
virginia Beach,
Va (October 11, 2006) – Researchers have uncovered physiological
differences among female Glanville fritillary butterflies that allows some
to move away from their birth place and establish new colonies. These
venturesome butterflies are stronger fliers and reproduce more quickly
compared to their less mobile female relatives.
The study is a window to how genetic differences
influence behavior and how the environment influences genetic change by
favoring individuals with certain traits, said lead author Howard W.
Fescemyer. The new study found significant physiological differences that
may account for the more adventuresome behavior of certain of the females.
The work is important because human activity is
disrupting many animal habitats, forcing more and more species to do what
the fritillary has long done in its naturally fragmented environment.
Scientists want to know how this fragmentation influences a species’
evolution.
“We may be selecting for genes that enhance the
dispersal or migratory capability of animals when we fragment the
landscape,” Fescemyer said. The animals best able to migrate are more likely
to survive and reproduce. “What we learn could apply to any organism that
has to move to find food,” he added
Åland Islands are natural
laboratory
The study, “Population history-dependent reproductive
physiology in a butterfly metapopulation,” will be presented on Oct. 10 at
Comparative Physiology 2006: Integrating Diversity, Oct. 8-11,
Virginia Beach, Virginia. Howard W. Fescemyer and James H. Marden of
Pennsylvania State University, Ilkka Hanski of the University of Helsinki
and A. Daniel Jones of Michigan State University carried out the study.
Marden was the senior researcher.
The researchers studied the Glanville fritillary
butterfly (Melitaea cinxia) on the Åland Islands of Finland, located
between Finland and Sweden in the Baltic Sea. The research team was composed
of a population biologist, molecular biologist, physiologist and chemist.
The study built on the work of Hanski who has recorded changes in the
butterfly population on the islands for years.
It’s in the genes
The fritillary live in distinct patches -- rocky
outcroppings containing plants that serve as food and provide a hospitable
home for the butterfly larvae to spend the winter. There are about 4,000
such patches on the Ålands, with about 500 patches occupied in a given
season, Hanski has found. Some of the patches are farther apart than most
individual butterflies can migrate, Fescemyer said.
Each year, new populations begin in some patches while
others go extinct because of parasites, disease and the disappearance of
plants that serve as food and shelter. Populations established on an
isolated patch may require a good flier to reach a new patch to start a new
population.
Flight capability varies quite a lot among females, who
carry the eggs and establish new populations. For those reasons, natural
selection on flight and reproductive capability acts primarily on the
females.
Travelers reproduce more
quickly
This study examined whether there is a difference in
physiology between the females in the newly established populations and
females in the older populations. The researchers found out there are.
The study looked at seven patches which had not been
colonized the year before and six old populations, Fescemyer said. Hanski’s
group collected larvae from the seven new patches and reared them on host
plants in the laboratory, where they moved to the pupae stage.
Fescemyer recorded when the pupa emerged to become
butterflies and periodically collected individual butterflies to determine
the number of mature eggs they carried.
“The females from the new patches develop very
quickly,” Fescemyer said. They developed mature eggs sooner (three days
after emerging from the pupa) which could enable them to mate and lay eggs
sooner. Females from older populations took an additional day to mature
their eggs.
What’s in a day? A lot. The butterflies live between
two and three weeks after emerging from the pupa, so they have to produce
eggs quickly. In the fragile world of a butterfly, a day can make all the
difference between reproducing and not.
The physiological
difference
The researchers delved into what was behind these
differences in egg production and development. They obtained blood samples
from butterflies from old populations and new populations. Compared to
females in the established patches, the females in these newly colonized
patches had more
-
total protein
-
vitellogenin
-
juvenile hormone
Juvenile hormone appears to be a key. It plays an
important role in regulating egg and larval development and also regulates
reproduction, particularly egg maturation, in adults, Fescemyer said.
Vitellogenin is the protein precursor to egg yolk, which the embryo uses for
food. Total protein is the most important nutrient for egg maturation, he
said.
Adds to previous study
Previous studies had found other physiological
differences between these more robust butterflies and their status quo
sisters and brothers. They found that individuals that established new
populations mate sooner, lay more eggs and have a different form of an
enzyme important to flying, phosphoglucose isomerase. They also found they
have a higher metabolic rate.
Future research will try to further uncover more
physiological and molecular differences that account for the differences in
reproduction and in flight, Fescemyer said. The researchers also hope to see
what part host plant nutrition plays in these differences.
* * *
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