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RE: Should there be aGenus reclassificat

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Posted by: CKing at Fri Apr 18 13:39:06 2008  [ Report Abuse ] [ Email Message ] [ Show All Posts by CKing ]  

>>Emdoidea blandingi (underlined) the Blanding's turtle and Glyptemys ( Clemmys) insculpta (underlined), the North American wood turtle. These two species have repeatly breed and produced hybrids - with interesting combined features. Harding and Davis (1999) wrote a paper on these hybrids and Harding has taken photes (2003) of many hybrid individuals with interesting traits form both Genus species. The standard criteria for a viable species is the inability to breed and produce a viable offspring capable of reproduction. If two different species produce living young, the best to expect is a sterile 'mule'. Thus, if E. blandingii and G. insculpta are producing hardy hybrids ( As far as known no reproduction of the hybrids is known - and if so, would totally throw scientific turtle classifcation on it's ear!) Then, at best, according to the Linnanean scientific classification standard, the two above species of turtle should be then reclassified as separate species within the same genus (probably Glyptemys - thus, the blanding's turtle may become Glyptemys blandingii {underlined}).

Things are a bit more complicated than that. First of all, any human classification is merely an attempt to describe nature. Nature needs not and often does not obey any human definitions. A well known example is the wave-particle dichotomy. Humans define waves and particles as separate entities. Yet nature shows us that all particles exhibit wave characteristics, including big particles the size of humans and even the earth itself, and waves exhibit particle characteristics.

The classic definition of the biological species concept is an attempt to describe nature. In nature, organisms do not interbreed freely. Each "kind" of organism attempts to interbreed only with its own kind. The question one may ask is why? A horse, for example, is not forbidden to try to mate with, say, a cow by anyone. So, why would a horse and a cow avoid mating on a purely voluntary basis? The answer to what we see in nature is that each species appears to have evolved with its own unique set of features that will permit it to cope with its environment (finding food, avoiding predators etc.). If this set of features is permitted to be "polluted" or diluted by a different set of features (from another species which is adapted to a different way of life), then the organism with this mixed set of features from two different species may have lower fitness (i.e. lower rates of survival) and be unable to survive and reproduce. We see an example of this in nature. Hyla chrysoscelis and Hyla versicolor, the two gray treefrog species, produce infertile offspring because one species has twice as many chromosomes as the other. One is a so-called diploid, and the other is a tetraploid. Since the outcome of interspecific species is often disastrous, many species have evolved mating rituals to ensure that it is only going to be mating with its own species. Different species of turtles, for example, will only mate with individuals that are showing mating behavior that is unique to its own species.

Of course, accidents do happen in nature, and occasionally interspecific hybrids are produced. In general, these hybrids often are much less fit because their phenotypes are less adaptive to their environment. In some rare cases, however, hybrids may be more fit to a new environment than either parental species. The hybrids may then be able to survive and reproduce and become established as a new population or even a new species. As I said, nature does not obey any human definitions, so interspecific hybridization can and do occur. It does not mean that if two species hybridize, then they are the same species. It will depend on whether the hybrids are able to survive and reproduce, and on whether the two species will continue to mix freely. If they do, then they are the same species. If not the occasional hybrid will die out, and the two species will remain distinct and be recognized as distinct species.


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