Monday, March 11, 2013

Dollo's Law, Is it a law at all?

Sci Daily & Int Business Studies .  Evolutionary principle states that once an organism diverges from its original model, there is no going back. This is called Dollo's law, claiming unidirectionality and irreversibility. Clearly, this law is up for debate with the new study on dust mites at the University of Michigan. This marcogenetic study shows that house dust mites, which evolved from parasites, had free-living origins, but could revert to old ways. Genetic homology between them and their parasitic counterparts shows specialization in a variety of habitats  which happen to be alongside human beings.

Mites are related to spiders, part of the arachnid class, and are pests to the human population in terms of allergic reactions. Scientists at the U of Michigan used DNA sequencing and tree phylogenies to test the hypotheses along with statistical analyses. The immediate ancestors of dust mites are skin mites of livestock and companion animal ear mites.  Parasites evolve at a quick rate to exploit host functions. They will lose specific genes that code for specific functional ability no longer required for survival, thus depending on the host.

In 2006 the National Science Foundation gave them a grant to conduct research. First they obtained free-living and parasitic mites, some of which were only found upon rare species. For two years a team of 64 biologists went to 19 different countries to obtain the samples. With the 700 mite species collected, 5 nuclear genes were resequenced in each species. Depending on the environmental factors, each mite phylogeny underwent its own unique change. Whether it was closer to a parasitic way of life or free-living.

Originally, free-living mites were without keratin digestive enzymes, could not tolerate low humidity, but were highly unspecialized when it came to hosts. When mites moved indoor, the enzymes and other factors were a large source of human allergic reactions.

1 comment:

  1. Well if there's anything certain about the world, it's about how uncertain it is probably. I wished the articles mentioned what benefit these mites have by reverting back to their past parasitic ways. While the article mentioned that parasites could evolve quicker to better adapt to their environment, I'd still like to hear some real-world examples on how these mites did evolve to better adapt.

    In either case, this reminds me of what we discussed in class which is how science doesn't really prove if anything is true, but rather, tends to prove on how things are wrong. Dollo's Law might have seem right to the scientists at the time, but, it's very hard to prove if something is true for everything as seen here.