X-Message-Number: 31820
Date: Mon, 20 Jul 2009 20:01:25 -0700 (PDT)
From: 
Subject: Ecologist Brings Century-old Eggs To Life To Study Evolution

Ecologist Brings Century-old Eggs To Life To Study Evolution


ScienceDaily (July 19, 2009) - Suspending a life in time is a theme that 
normally finds itself in the pages of science fiction, but now such ideas have 
become a reality in the annals of science.


Cornell ecologist Nelson Hairston Jr. is a pioneer in a field known loosely as 
"resurrection ecology," in which researchers study the eggs of such creatures as
zooplankton -- tiny, free-floating water animals -- that get buried in lake 
sediments and can remain viable for decades or even centuries. By hatching these
eggs, Hairston and others can compare time-suspended hatchlings with their more
contemporary counterparts to better understand how a species may have evolved 
in the meantime.


The researchers take sediment cores from lake floors to extract the eggs; the 
deeper the egg lies in the core, the older it is. They then place the eggs in 
optimal hatching conditions, such as those found in spring in a temperate lake, 
and let nature take its course.


"We can resurrect them and discover what life was like in the past," said 
Hairston, who came to Cornell in 1985 and is a professor and chair of Cornell's 
Department of Ecology and Evolutionary Biology. "Paleo-ecologists study 
microfossils, but you can't understand much physiologically or behaviorally" 
with that approach, he said.


Hairston first became interested in the possibilities of studying dormant eggs 
in the late 1970s, when he was an assistant professor of zoology at the 
University of Rhode Island. There, he noticed that the little red crustaceans --
known as copepods -- in the pristine lake behind his Rhode Island home 
disappeared in the summer, only to return as larvae in the fall.


The observation prompted him to study why they disappear, research that revealed
the copepods stay active under the ice in the winter, but they die out as their
eggs lie dormant on the lake floor through the summer when the lake's fish are 
most active. When the fish become less active in the fall, larvae hatch from the
eggs, and the copepods continue their life cycle.


This time suspension, where zooplankton pause their life cycles to avoid heavy 
predation or harsh seasonal and environmental conditions, also increases a 
species' local gene pool, with up to a century's worth of genetic material 
stored in a lake bed, Hairston said. When insects, nesting fish and boat anchors
stir the mud, they can release old eggs that hatch and offer a wider variety of
genetic material to the contemporary population.


In 1999 Hairston and colleagues published a paper in Nature that described how 
40-year-old resurrected eggs could answer whether tiny crustaceans called 
Daphnia in central Europe's Lake Constance had evolved to survive rising levels 
of toxic cyanobacteria, known as blue-green algae. In the 1970s, phosphorus 
levels from pollution rose in the lake, increasing the numbers of cyanobacteria.
The researchers hatched eggs from the 1960s and found they could not survive 
the toxic lake conditions, but Daphnia from the 1970s had adapted and survived.


Hairston and colleagues have organized a resurrection ecology symposium in 
September 2009, in Herzberg, Switzerland, to bring together researchers in this 
growing new field.


Adapted from materials provided by Cornell University. Original article written 
by Krishna Ramanujan.

____________________________________________________
Brief Communications
Nature 401, 446 (30 September 1999) | doi:10.1038/46731

Lake ecosystems: Rapid evolution revealed by dormant eggs

Nelson G. Hairston, Jr1, Winfried Lampert2, Carla E. Caceres3, Cami L. 
Holtmeier1, Lawrence J. Weider2, Ursula Gaedke4, Janet M. Fischer1, Jennifer A. 
Fox1 & David M. Post1


Natural selection can lead to rapid changes in organisms, which can in turn 
influence ecosystem processes1. A key factor in the functioning of lake 
ecosystems is the rate at which primary producers are eaten, and major 
consumers, such as the zooplankton Daphnia2, can be subject to strong selection 
pressures when phytoplankton assemblages change. Lake Constance in central 
Europe experienced a period of eutrophication (the biological effects of an 
input of plant nutrients) during the 1960s-70s3, which caused an increase4 in 
the abundance of nutritionally poor or even toxic5 cyanobacteria. By hatching 
long-dormant eggs6 of Daphnia galeata found in lake sediments, we show that the 
mean resistance of Daphnia genotypes to dietary cyanobacteria increased 
significantly during this eutrophication. This rapid evolution of resistance has
implications for the ways that ecosystems respond to nutrient enrichment 
through the impact of grazers on primary production.

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