“Maladaptation to acute metal exposure in resurrected Daphnia ambigua clones after decades of increasing contamination”

Posted on

Mary Alta Rogalski

Daphnia resurrected from egg banks have evolved increased sensitivity to metals following decades of contamination

Outer shell (ephippia) of long-lived Daphnia resting eggs. These particular resting eggs were hatched as part of this research.
(Credit: Eric Lazo-Wasem, Peabody Museum of Natural History, Yale University)

Human activities can drive rapid evolutionary responses in wild animal populations. These evolutionary responses often leave the population better able to cope with human activities, but sometimes populations appear to be maladapted to local conditions. While maladaptation has been observed in multiple systems, it has received much less attention than adaptation. One reason we don’t have a better understanding of maladaptation is that if we uncover a population that appears to be maladapted to local conditions, it is often impossible to determine the trajectory of that population and the environment over time. How have key traits in the population evolved over time? And how does that correspond with changes in the environment?

In a new article in The American Naturalist, Dr. Rogalski uses dated lake sediment archives to quantify metal pollution and evolutionary responses to this contamination in three lakes in Connecticut, USA, over the past 50-75 years. She hatched microscopic animals known as Daphnia from long-lived resting eggs from multiple time periods to track their sensitivity to metals through time. In contrast to the predicted trend of adaptation to metal exposure, she found that Daphnia from contaminated time periods were more sensitive to copper and cadmium exposure. In one lake where copper contamination has dramatically declined, the Daphnia remain sensitive to copper 30 years after peak exposure. It is difficult to know what mechanisms are driving this evolutionary pattern or even whether the animals are truly maladapted to their natural environment (that is, to be sure that their fitness has declined over time). However, the release of toxicants (including heavy metals) is widespread and other researchers have also observed local maladaptation to contaminants. Thus, this research suggests that we need to do more to uncover both the drivers and implications of maladaptation in nature. Read the Article