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Science Daily
ScienceDaily (July 10, 2012) —
This is one smart egg. Talk about adjusting your internal clock. New
research at North Dakota State University, Fargo, shows that some chicks
can sense day length, even while they are still in the egg, which in
turn, affects how they develop.
North Dakota
State University biological science researchers Dr. Mark Clark and Dr.
Wendy Reed, along with NDSU students, conducted field research on
Franklin's gulls at J. Clark Salyer National Wildlife Refuge and Lake
Alice National Wildlife Refuge in north-central North Dakota along the
Souris River. Their research, published in Functional Ecology, shows
that the birds sense day length before hatching and change how they
develop. (Credit: M.E. Clark, NDSU)
Dr. Mark E. Clark, associate professor, and Dr. Wendy Reed, head of
biological sciences at NDSU, found in their study that embryos in eggs
appear to sense external environments and adjust how they develop. The
research is being published in
Functional Ecology, a British Ecological journal.
Franklin's gull is a bird that migrates long distances and requires
precise timing. It winters along the west coast of South America until
returning to the prairie wetlands of North America, where it nests in
large colonies come springtime. The dark hood, gray wings and
pink-tinted breast are a harbinger of spring to the people of the
Northern Great Plains, who affectionately call it the prairie rose gull.
Soon after large wetlands thaw, Franklin's gulls arrive to build
floating nests from wetland vegetation to hold three green-and-black
speckled eggs.
Inside these dark eggs, the developing chicks also sense spring days.
"The growing embryos integrate signals from the nutrients provided to
eggs by mothers with the amount of daylight," said Dr. Clark. "The
signals let the chick know whether the egg was laid at the beginning, or
at the end of the nesting period."
Clark and Reed note that chicks from eggs produced at the beginning
of nesting take longer to hatch, but are larger than chicks from eggs
laid at the end of nesting. Contrast that with eggs laid at the end of
the nesting period, which hatch in less time, but at a smaller size.
"Chicks hatching later in the season have less time to grow, less
time to become independent, and less time for flying lessons before they
must migrate to South America in the fall," said Dr. Reed.
According to Dr. Clark, data indicate embryos in late season eggs
appear to be sensing external environments and adjusting their
development. These changes in development time and size may be important
for chicks to successfully migrate.
Many birds, including Franklin's gulls, are arriving earlier on their
breeding grounds. "This research suggests that the impacts of changing
seasonal signals have far reaching effects on bird biology, including
chick development," said Dr. Clark.
Researchers evaluated the ability of avian embryos to integrate cues
of season from photoperiod and maternal environments present in eggs to
produce season variation among phenotypes among Franklin's gull
(Leucophaeus pipixcan) hatchlings.
Field research was conducted at the J. Clark Salyer National Wildlife
Refuge and Lake Alice National Wildlife Refuge in north-central North
Dakota along the Souris River. Researchers collected early and late
season eggs, separating some into component parts and incubating others
for short or long photoperiods. Upon hatching, chicks were evaluated for
size and yolk sac reserves.
Results of the study show that hatchling size is sensitive both to
egg contents provided by mothers and to photoperiod, and development
time increases across the season. When cues of season from eggs are
mismatched with cues from photoperiod, alternate phenotypes are created.
Clark and Reed also found that seasonal variation in egg size, yolk,
albumen or shell content of the eggs does not account for the seasonal
maternal egg effect on hatchling size. "We expect our results to
initiate new studies on how vertebrate embryos integrate environmental
cues with maternal effects and offspring responses to optimize the
expression of offspring phenotype," said Clark.
Previous NDSU graduate students who participated in the research
include Shawn Weissenfluh and Emily Davenport-Berg. Other NDSU students
who assisted in the research include Nathaniel Cross, Peter Martin, Dan
Larsen, Michelle Harviell and Andrew Nygaard, along with Petar Miljkovic
from Grinnell College.
Research funding was provided by the National Science Foundation
(IOS-0445848), the North Dakota Game and Fish Department and the U.S.
Fish and Wildlife Service.
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It
is generally recognized that pointed wings allow a faster flight than
rounded wings and hence, this shape has been favoured in migrating
species or subpopulations. On the other side, rounded wings allow more
manoeuvrability, being favoured in closed habitats.
