March 24, 2011
Once again, I have taken a sabbatical from this blog. While I have been away, the earth has been shaken by both agitated tectonic plates and agitated world leaders. Also, one of science’s stalwarts, Darwin’s theory of evolution, may be agitated by the ungrateful, invasive and ugly cane toad.
After humans foolishly introduced the toads to Australia, the cane toad invasion took off. The toads spread across the continent at unbelievable speeds. And they were reproducing like mad, as well. Survival of the fittest and screw any native species in the way, right? But scientists noticed that the adaptations for speedy dispersal did not necessarily create fitter individuals. In fact, the toads that dispersed the fastest had the highest mortality rates. But those same toads only had other toads with the adaptations for speedy dispersal to choose for mates. So they reproduced.
The scientists who noticed this phenomenon call it “spatial sorting.” They claim that natural selection is still the supreme overlord of the situation since if the speedy dispersal genes stopped the toads from reproducing all together, the genes would die out. However, the spatial distribution of the genes is an important evil minion deciding which genes are passed on. If toads can only mate with other toads with the fast genes, they will be passed to the next generation even if those genes create individuals that are more likely to break their spines.
I don’t quite understand how this is different from natural selection. Cane toads are currently invading much of Australia and speedy dispersal genes are advantageous for those on the front lines. Longevity does not necessarily mean fitness as long as the toads reproduce anyway. Maybe in a hundred years when cane toads are dispersed throughout the continent, the speedy dispersal genes will no longer be advantageous and the high percentage of the genes might be detrimental to the population. Maybe then the genes from the cane toads who stayed behind and moved slower will become more dominant in the overall population. Right now, it seems like speedy dispersal genes aren’t really that bad as cane toads are thriving.
This is very theoretical and the scientists behind the study acknowledge that it is difficult to separate natural selection and spatial sorting. I like the idea because I enjoy thinking spatially. I think I need to read more on the theory to truly understand why spatial sorting might be separate from rather than a component of natural selection.