A Living Time Capsule Shows the Human Mark on Evolution

Gabriella Ricciardone
January 13, 2014

Author: Carl Zimmer
Published: January 8, 2014
http://www.nytimes.com/2014/01/09/science/a-living-time-capsule-shows-the-human-mark-on-evolution.html?_r=1

Summary:

        In South Center Lake in the small town of Lindstrom, Minnesota, scientists have made a remarkable discovery by reviving Daphnia, shrimp-like animals more often known as water fleas.  Each fall, the Daphnia reproduce by laying eggs with tough cases, which then float to the bottom of the lake.  In the spring, many produce new water fleas, but some remain under the sediment, and do not hatch.  In 2009, Dr. Lawrence J. Weider, an evolutionary ecologist, and his team set out to dig up Daphnia eggs in lakes in Minnesota, expecting to find eggs a few decades old, reproducing research he had done in the mid-1990s in Germany.  They had figured out how to coax the eggs into hatching as well, and planned to do this again.  Once they successfully hatched the eggs they dug up in South Center Lake, they ran a DNA extraction, which determined that the eggs were approximately 700 years old.  Dr. Weider and his team also estimated the ages of the sediment to support their findings, and they did this by measuring levels of the radioactive isotope lead-210 and then confirming the results by measuring another isotope, carbon-14.   The paper documenting their discovery was published on January 8, 2014.

        The creatures the team found had been at the bottom of South Center Lake for an estimated 700 years, buried under sediment, which luckily had preserved these centuries-old specimens.  The resurrected water fleas provide insight to the changes that this lake has been through over the past several hundred years.  The scientists found that, about a century ago, a major evolutionary jump occurred, around the time when Europeans started to change the land they were settling on.  Previously for centuries, phosphorus was a scarcely found element in the lake, and the Daphnia had adapted and learned to feed on the phosphorus and hold onto it for days.  But around the late 1800s, the Europeans began using fertilizer on their farms, which dramatically increased the amounts of phosphorus in the area around them.  This affected the Daphnia population in the South Center Lake, as these organisms began to stop relying on their ability to hold on to phosphorus because there were now high levels of it in the environment.  This discovery shows that humans are indeed influencing the evolution of wild species.

Connection:

        During our studies of Chapter 14 and Chapter 15, we discussed evolution and adaptations.  We have also repeatedly talked about how humans influence the environment, including how humans affect evolutionary patterns of other species.  This article discusses how early European settlers in the late 1800s affected the evolutionary path of the Daphnia, due to their farming methods and use of fertilizers containing phosphorus.  We have also learned about radioactive isotopes in Chapter 4 and the dating of specimens using isotopes in Chapter 15.  DNA extraction was discussed earlier in the term in Chapter 13.  The scientists mentioned in the article used DNA extraction to calculate the ages of the Daphnia specimens they found at the bottom of South Center Lake.