Hybridization and Extinction
Source: Donald A. Levin, American Scientist, May/June, 2002, 90(3):254-261.
Under normal conditions species don’t usually interbreed. There are things that make interbreeding either unlikely or impossible. Some of these include where they live, their behavior, or seasons in which they reproduce, just to name a few. Even with separating factors there is still some species that end up interbreeding. Their offspring are called hybrids. It is proposed that this happens in 6-16% of plants and 9% of bird species. Generally most hybrids do not survive, some will die before birth, some will die when they are young, and some will survive but will be unable to pass their genes on because of infertility. There are hybrids that are fertile though, and these can cross with either their parents or each other. Fertile hybrids like this can contaminate either of the parent species so that it is rare that a pure offsprings of the parent would be born. This over time can lead to the extinction of the parent species. The drive to extinction, though rare, can make a rare species extinct and replaced with the hybrid species. One of the reasons some hybrids are created in the first place is humans placing animals in habitats that they were not originally from. Now scientists are being very careful with the relocation and interaction of two species that might have the chance to interbreed.
As mentioned earlier it is true that there are factors that either do not allow a certain crossing to occur or allow a certain hybrid survive to pass on it’s genes. Other than the ones mentioned above there are some other factors that were not mentioned. One of these is the fact of “having the right fit”. You will not have a cat and a horse breeding to have a hybrid for this reason. Another one factor has to do with the gametes or sex cells of the parents. Animals have different numbers of chromosomes in their gametes and just like an odd number of gametes can cause deformities and death in humans the same happens to these animals. In some cases the egg cannot even be fertilized due to the difference in the gametes. Another factor has to do with separation. If one species lives on one side of a mountain and another lives on the other side it is not likely that these two will even meet, let alone have offspring. Also factors that deal with a specific farimone or a mating dance can keep two species from mating. For instance many species of birds have a certain dance or ritual in which they go through to attract a mate. Some have a nest of shiny things that will attract a mate. The bird that does this makes a large nest or house out of anything pretty it can find, including flowers, stones, and various shiny objects. This “house” acts as a sort of “wedding bower” and the bird with nicest nest attracts the most females. This behavior also happens with humans, believe it or not! Haven’t you ever heard of a girl liking a guy for his cool car? “Oh, it is so shiny with all it’s chrome and painted sides! The inside is great two with blacklight and glow buttons...” Hmmmm...It is not just the birds that like shiny objects I guess! Another attracting habit that is unique to some species and would separate them is the use of bright plumage (As you can see birds are the most ingenuative in their attracting habits). Bright plumage can be seen in many of the bird species in the world and one birds particular plumage will not necessarily attract a bird of a different species (they might find him repulsive in fact!). One example of this is the peacock, talk about plumage! The peacock spends a lot of it’s time and energy growing it’s massive tail of feathers and the only purpose for them is to attract a mate. A bird like a cardinal, who’s males are red in color, might find the peacock not attractive at all.
Out of looking at bird separating factors, bugs have a few that are quite useful at keeping species in species. For an example of attracting a mate, we have the lightning bug. This unique bug uses a chemical reaction in it’s abdomen that creates light to attract it’s mate. The female will wait on a leaf or the ground will flash a signal in code with their lights that says “Come and get me!”. This also keeps different species of lightning bugs from cross mating with each other. How you ask? Each lightning bug species has a different flashing pattern. So if a certain female uses a long, long, short flashing pattern and the male is looking for a short, short, long pattern he is not going to go to the female with the long, long, short pattern. This keeps the species separate.
| Mad Cow Disease | Habitual Loss and Extinction In Hotspots | Crossbreeding |
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