Daphnia, go-to freshwater plankton
Data bite When Daphnia from a Minnesota lake were screened against exposure to the pesticide chlorpyrifos, which was introduced commercially in 1965, researchers found that samples of the crustaceans originating from preindustrial times (1301–1646) were 2.7 times as sensitive (judged by their mobility level) to chlorpyrifos as samples originating just after the chemical began to be used (1967–1977). These results indicate that the creatures evolved some tolerance to chlorpyrifos exposure. Daphnia originating more recently (2007–2011), when chlorpyrifos was no longer detected in the lake, seem to be losing that tolerance (Ecotoxicology 2014, DOI: 10.1007/ s10646-014-1397-1).
“
for centuries in sediments. Scientists have learned how to hatch the dormant eggs and use the resurrected Daphnia to study the effects of synthetic chemicals that didn’t exist when the eggs were produced. With the aid of the latest genomic technologies, researchers are now using DNA and RNA sequencing to track how gene expression in Daphnia changes over time. This ability allows scientists to compare how different generations of Daphnia adapt to natural and human-induced shifts in nitrogen and phosphorus nutrient levels, the influx of synthetic chemicals in the environment, and climate change. The results are helping researchers extrapolate the toxicity of existing chemicals and new chemical substances to other animal and plant species, all the way up to humans. Sources: Lawrence J. Weider, University of Oklahoma; Joseph R. Shaw, Indiana University.
Immobility concentration, µg/L
Did you know?
0.5 0.4 0.3 0.2 0.1 0 1301–1646
1967–77
2007–11
Sample origination date S Cl
N
Cl
O Cl Chlorpyrifos
O P O
Daphnia have more genes (~31,000) than humans do (~20,000).
The role of Daphnia as critical sentinel organisms—an aquatic version of the ‘canary in the coal mine’—will only increase as technological developments continue in emerging fields such as environmental genomics.”
28
C&EN | CEN.ACS.ORG | NOVEMBER 20, 2017
—Lawrence J. Weider, University of Oklahoma
C R E D I T: S H UT T E RSTO CK
Daphnia are tiny crustaceans about the size of the equal sign on a computer keyboard. They live in ponds and lakes, where their color, size, and abundance serve as a sentinel of good water quality and environmental health. Naturalists began studying the creatures, commonly known as water fleas, in the 1600s. They found early on that Daphnia are a keystone species, providing a link between the algae, bacteria, and protozoans that they eat and the fish that prey on them for food. In the early 1900s, during a period of rapid growth in human use of pharmaceuticals, pesticides, petroleum products, and munitions, Daphnia became important tools for toxicological screening—studies of the chemical limits tolerated by Daphnia helped policy-makers develop food and drug safety laws. Among Daphnia’s more fascinating features is that they generate two types of eggs, one of which can remain dormant
