The water flea, genus Daphnia, is a small (1–5 mm) crustacean known to inhabit bodies of water all over the world. Its genome (DNA in the nucleus) was recently sequenced and found to contain a remarkable 31,000 genes. Humans are only estimated to have 20,000–25,000 genes. Why are so many genes needed for such a small and relatively simple (in comparison to humans) organism? Unlike humans, water fleas have to deal with their environment. I usually put it this way—they can’t come in from the rain (or snow, etc.) so they have to adapt or die. God designed the water flea with an amazing spectrum of genes and mechanisms to change its phenotype (characteristics) to allow it to adapt to a wide range of environments. Dieter Ebert, in an article about the research, stated the following:
Water fleas react to chemicals (kairomones) released by different predators by expressing highly speciﬁc characteristics, such as protective tail spines, helmets, and neck teeth. They are also able to adapt physiologically to wide ranges of pH, toxins, oxygen concentrations, food, and temperature regimes. Moreover, maternal effects allow them to prepare their offspring for environmental challenges, including infectious disease, and the offspring’s sex depends on the mother’s environmental conditions. Amazing—even the mother water fleas can “prepare” their offspring before they are born for what they will face in the environment. I hope to write an article for the web discussing more of the genetics behind the research.
You may have noticed that my blogs this week have been on the “light” side. I’m trying to focus my time and energy on a research project that needs to be completed in the next month or so. I really enjoy blogging and will continue to do so, but the topics may be a bit lighter. Hope you’ll enjoy.
 Ebert, Dieter. 2011. A genome for the environment. Science 331:539-540.