Rassenkreis and speciation, Biology

According to the current concept of speciation, a widely distributed species should break up into partially isolated rule species. The different subspecies become differentiated further due to the action of selection and other factors. This would result in a circle or group of races or Rassenkreis. And the terminal members of such a circle will be sufficiently different from others, so that a sterility barrier sets in. We shall try to explain the concept with an example of an amphibian species. In the west coast of USA there are two high mountain ranges, the Coastal Range and the Sierra Nevada. At their northern ends, near the Canadian border they are united. Proceeding south, they are separatcd by a hot and arid desert, Further south, close to the Mexican border, these high mountains meet again. There is an amphibian species Ensatina eschscholtzii at the place marked as A in Fig, It is supposed that this original species split into two populations, B and G, which then moved down the two respective mountain ranges. On one range the populations can be seen to change gradually from B to C to D to E and on to F.

On the other mountain range the population G, like B derived from A, gradualljl moved south changing into H, I, J and K. While these changes were taking place the two series were isolated from each other by the desert, and isolating mechanisms were gradually developing. Since this amphibian Ensatina has poor locomotor powers, it must have taken hundreds of thousands of years for them to proceed from the Canadian border to the Mexican border. It stands to reason that populations B and G will have the least amount of isolating mechanisms. The isolating mechanisms will be more between D and I. They will be greater between E and J. Remember, both the series, BCDE and GHIJ, are derived from a single species, Ensatina eschscholtzii, designated in Fig. as A. But when they reach the Mexican border, the two populations F and K are able to overlap, as seen in the cross-hatched area, without mating. They have passed the test of sympatry. F and K are now two distinct species.

Similar ring species have been shown to occur in sea-gulls forming a circumpolar ring around the world.

Posted Date: 4/5/2013 5:34:56 AM | Location : United States







Related Discussions:- Rassenkreis and speciation, Assignment Help, Ask Question on Rassenkreis and speciation, Get Answer, Expert's Help, Rassenkreis and speciation Discussions

Write discussion on Rassenkreis and speciation
Your posts are moderated
Related Questions
Q. What is the structure through which the neural impulse is transmitted from one cell to another? What are its parts? The structure through which the neural impulse passes fro

What is cellular regeneration? How is mitosis related to this process? Some tissues are able to regenerate when injured. The liver, for instance, regenerates when small pieces

How to make and why one needs to make cDNA library??

Name two possible why the number of live bacteria cell have reached the stationary growth by 60hrs and start to die off after 12hrs?

Explain Other lipids in biological compound? Other Lipids :  Another important type of lipids are the steroids, with a basic structure consisting of four interconnecting carb

Illustrate the Respiratory System In general, respiration and breathing are understood to be same. But it is not so. Breathing simply means taking in oxygen from air and giving

Explain the term - Neurochemical Manipulations Neurochemical and immunological methods have been used to identify groups of neurons in the central nervous system that use speci

what is detergent pollution and it''s effects and causes

Describe a. the factors responsible for promoting lactation, and b. the mechanism responsible for the cessation of lactation when a mother weans her baby.

why should breathe faster after a hard work