View Full Version : question on drought conditions

10-10-2007, 02:31 PM
should the trout that survive this drought to be considered genetically superior to those that did not make it--if so--will the babies of these trout be hardier and less delicate than those living in the streams prior to the drought.

Rog 1
10-10-2007, 03:05 PM
So says Darwin.....

10-10-2007, 03:09 PM
You can only assume that the actual selective pressure itself will be transferred to the next generation. In this case, one could say that what has killed the trout this summer has been the high temps, maybe extra predation since the fish are herded tightly, and maybe some starvation from the low water. A real biologist may think of more pressures than me.

And you usually need many generations of these selective pressures to change the genome in a significant way. Right now, lets guess that half the fish survived this summer. Some of the survivors are just lucky, some of them genetically can withstand starvation a little better, some of them genetically are more skittish, and some of them genetically can tough out higher temps. The offspring of this year should be very slightly better able to withstand these pressures, although it would take many generations of consistent pressure to actually change them noticeably. That is how humans made St. Bernards and Chihuahuas from the same dog ancestor.

Your question about their genetic superiority is a more complicated one that it may seem on the surface. You have to define superiority first. Yes, you could say that next year's fish should be slightly better able to handle the bad conditions of this year. But what if those genetic changes make it harder for next year's conditions (let's assume for example that next year is very wet)? What if the gene that makes a fish better able to handle starvation also lowers that fish's metabolism, making it smaller than the others even when a lot of food is available? Or maybe that lower metabolism makes it more sluggish, and it gets eaten.

Incidentally, this is why biodiversity is such a good thing. It is a good thing to have a large gene pool to draw from when you have selective pressures killing off a segment of a population. The genes can respond pretty rapidly if they were already present in some of the individuals to begin with.

For the sake of argument, if this year's drought were tied to global warming, and that proved to be a long-standing situation, then yes, I'm sure you'd see a different kind of fish living in the Smokies. But I doubt one year will change them much. Luckily, as has been discussed in older threads, assuming that the spawns are successful, the fish biomass should recover extremely rapidly once these pressures are gone, since what usually limits fish biomass in the Smokies has historically been the low food availability.