Otherways- Fiction Fanatics

I guess I’ve been feeling cheerful lately, what with the blog posts on the plague, intestinal flora, and now famine. Perhaps I should do a nice friendly post about fluffy bunnies instead, but as I have a deep fascination with genetics, you’ll need to bear with me. Trust me, it’s pretty cool.

Most of us have a basic grasp of genetics. Mom plus dad equals baby. The fittest organisms survive. DNA is what carries the code that tells us what we are, and whether a trait shows up or not is determined by whether or not it is dominant. That’s the shortest of short forms, anyway.

It isn’t that simple, of course, and as a very young science indeed one might well expect to find that we’ve been wrong about a good many things. This would be one of those times, and of all things, it’s the lowly flatworm giving us fits.

You see, starvation is a thing for flatworms. Like a lot of other species, they live in boom-bust cycles, replicating like mad until the food runs out and famine kicks in. Of course, not everybody dies, and the cycle repeats itself, as you might expect.

The thing is, it doesn’t really. You see, the survivors of the famine grow up to be smaller and less fertile than the generation before them. Not surprising, I know, as they didn’t have much food to work with. Standard genetic theory, though, says that the offspring of these survivors, given plenty of food, should be normal. They aren’t.

In fact, offspring of these famine survivors are just like the survivors themselves: smaller, and less fertile. The only exception is that they are far more often male. I did forget to mention that flatworms are most often hermaphrodites, but apparently being starved increases their need for sex with an outside partner to the point that males actually begin to spontaneously appear in the population. It also makes the second generation tougher, and more resistant to starvation than the one before it.

Researchers haven’t figured out exactly what the mechanism is here, but it doesn’t seem to involve the DNA, so it isn’t the genetics we’re familiar with. It may well be one of the duties of mRNA, but if so, it’s a new one on us.

Evolutionarily, this makes perfect sense. If your population has plenty, then expanding to meet the resources available is a great survival tactic. Then, when those resources can no longer support your numbers, the offspring born in famine will necessarily be smaller and less able to reproduce in great numbers. Lack of nutrients could certainly account for these changes, but even they are beneficial in a famine. Smaller creatures need less to survive, and wasting your energy churning out hundreds of offspring that will simply starve is less efficient than creating ten that live.

It’s the ten that live that are so cool. Their genes are the same as the pre-famine worms, given that most of the parents are hermaphrodite, they aren’t even as genetically different from their parents as our kids are from us, because they often only have one parent’s DNA to pick from. Yet, the percentage of male offspring is substantially increased, allowing the remaining population to scramble their genes more effectively, increase genetic diversity, and increase the odds of beneficial changes showing up in following, normal generations.

For us, such an adaptation would be senseless, as our lives are typically far longer than a drought or famine. For flatworms, their entire lifecycle, and that of their offspring, may easily fall within a single cycle of famine. Think of it like genetically enforced resource rationing on the second generation.

Cheers,

Michelle