Nature, Nurture, Feast, Famine and Nematodes
August 10, 2015
We’ve all heard the cliches of harsh conditions breeding hardy underdogs. The “nature vs. nurture” trope plays this out in every good underdog story; where the underdog’s adversity gives him or her something the person with everything going for him can’t possibly match.
Whether it’s a tolerance of pain, a strategic insight or just plain pluck, the underdog is fundamentally different from the favorite, and he or she has his or her background to thank.
A simply ludicrous number of stories follow this same model — that many people can’t “beat the odds” otherwise they wouldn’t be “the odds” — but biology bears out the idea that adversity can build a tougher, pluckier competitor...at least in the world of nematodes, according to a new study from Duke University. Biologist Ryan Baugh showed that nematodes that had undergone conditions of starvation at a young age would produce young that are better able to withstand hunger.
The nematodes Baugh used in his study were C. elegans roundworms, which are about a millimeter long and eat bacteria. Baugh split thousands of genetically identical nematodes into two groups. He starved one group for one day and the other for eight days during the first stages of their larval development.
After providing both groups with food again, the nematodes looked very different. The short-starvation worms were big, fat and fertile while the long-starvation worms were much smaller and did not grow or reproduce as quickly as the short-starvation group.
Also, nematodes are predominantly hermaphroditic, meaning they are simultaneously male and female and have the capability to self-fertilize. In the long-starvation group, a larger percentage of the population was strictly male.
And these were not one-off changes. Baugh let the nematodes breed and both the children and grandchildren of the long-starvation group were smaller, slower growing and less fertile than the children and grandchildren of the short-starvation group. Further, when Baugh starved these new nematodes, the descendants of the long-starvation group survived much better than those of the short-starving group.
Baugh says the smaller size, slower growth rate and decreased reproduction of the long-starving nematodes allows them to expend less energy and therefore survive better when food runs out. This experiment shows that they are able to pass this resilience down at least two generations.
If you’re familiar with Darwin’s theory of natural selection, this may seem like a simple case of survival of the fittest. When the worms began to starve, the big fat nematodes died off because they needed too much energy, and the runty ones lived on and passed all their runty genes to their kids.
The change in these nematodes, however, is a little more complicated. Remember that all the nematodes in each group were newborn and genetically identical. If genetics were left to run free, all of the nematodes would have grown up to be exactly the same.
Instead, Baugh saw fat, fertile nematodes and runty survivalist nematodes. This shows that from birth, every nematode had the capacity to grow up fat or runty, and the environment they grew up in determined how they would turn out.
Scientists call this epigenetics, which is a fancy way of saying the difference is not in the genes themselves, but how the organism reads the genes. Baugh says these epigenetic controls can be changes to the chemical switches on the DNA, how the DNA is packaged or the molecules that do the reading. He says he isn’t sure exactly which ones might control nematode runtiness, but these epigenetic controls can be passed down along with the DNA itself when the nematodes reproduce.
Baugh says that in their natural environments, nematodes hit patches of feast and famine. During feast times, the runty nematodes are clear underdogs. The fat ones grow and reproduce much more prolifically, and therefore pass on the DNA controls to make big robust nematodes. During famine, the script flips and the runty survivalists that can make the most of their food are the heavy favorites and pass on their DNA controls.
The nematodes will live large while they can, but when famine strikes the newborns will grow up tough and runty. They will pass their runty toughness down for a few generations until they find a feast again and the population can flourish once again thanks to the tough underdogs.
Baugh says this effect is most likely not limited to nematodes, and may even apply to humans, but more research will be needed to determine to what degree adversity may or may not affect our physiology.
The paper describing this research was published in the journal Genetics.
— Daniel Lane
Daniel Lane covers science, engineering, medicine and the environment in North Carolina.