Added 1 new A* page:Speaking of clones, yesterday the BBC published an article declaring that "a mutant species of all-female crayfish taking over the world is not the latest science fiction film but a real-life environmental thriller": the first ten-legged marbled crayfish, born in a German pet shop in the 1990s from Floridian slough crayfish parents, had an additional set of chromosomes, allowing her to reproduce all by herself—and so could her children, and their children... This made their pet population growth unstoppable, and soon extra, unwanted marbled crayfish were being dumped into the wild, where they have spread to threaten native species across Europe.|
Now, after reading that, I thought, okay, before I welcome our marbled crayfish overladies, maybe there's no need to panic—after all, with a genetic diversity of pretty much zero, they're bound to hit some sort of road-block they can't overcome in their quest to take over the world, and eventually natural selection will find against them. Right?
Well, the BBC kind of shut down that hope today in an article about the Amazon molly fish, another (nearly) all-female species: the molly mates with a male from one of four other fish species, but "genetic material from the male is not incorporated into the already diploid egg cells the mother is carrying (except in extraordinary circumstances), resulting in clones of the mother being produced en masse." This again results in near zero genetic diversity, and a popular theory in evolutionary biology, "Muller's ratchet," had postulated that a gradual accumulation of disadvantageous mutations would lead to the demise of such a species within 20,000 generations.
Thing is, genome sequencing shows that the molly has been doing its gynogenetic thing for 100,000 years—about 500,000 generations—and it is still going strong. Now, counter-theory is saying that even a case of such low genetic diversity, evolution would still tend to wipe out the negative mutations.
So! Nothing says that the Earth won't be entirely peopled by marbled crayfish in that far-flung future just before it is boiled by the dying, expanding Sun.
Speaking of animal tricks that aren't actually as silly as they may appear, in looking up something like "landing in deep snow" on YouTube today as research for this A* page, a Discovery channel YouTube video called Fox Dives Headfirst Into Snow taught me that red foxes make incredibly silly-looking, head-first leaps and dives into snow—and not just for fun, like foolish humans do, but rather to catch delicious little animals burrowing along beneath the snow.
And the observers found that the foxes were much more successful at this acrobatic, hearing-dependent hunting technique when they were jumping north-east; their leading hypothesis on why this would be the case is that the foxes—like some other species—are sensitive to the Earth's magnetic field, and are using it, along with hearing, to confirm that their hidden prey is at a certain fixed range: "the Earthís magnetic field tilts downward in the northern hemisphere, at an angle of 60-70 degrees below the horizontal. As the fox creeps forward, it listens for the sound of a mouse. Itís searching for that sweet spot where the angle of the sound hitting its ears matches the slope of the Earthís magnetic field. At that spot, the fox knows that itís a fixed distance away from its prey, and it knows exactly how far to jump to land upon it."
So that was interesting. But they *do* look silly doing it. ^_^
(That article also discusses several biological mechanisms giving magnetic field sensitivity: embedded magnetite crystals that align with magnetic fields, releasing a protein to trigger a nerve cell when being moved into certain configurations, or light-sensitive chryptochrome molecules in the retina (so far found only in birds) that trigger a reaction resulting in unpaired electrons, which can be induced to switch states in a magnetic field, resulting in a magnetically induced nervous signal.)