Rassenkreis and speciation, Biology

Assignment Help:

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.


Related Discussions:- Rassenkreis and speciation

Explain the indole production test, Explain the Indole Production Test? ...

Explain the Indole Production Test? Many microorganisms produce an enzyme tryptophanase which oxidizes amino acid tryptophan to produce pyruvic acid, indole and ammonia. We can

Define type of root canal perforations according to location, Define Types ...

Define Types of Root Canal Perforations According to location According to location (level) in relation to crestal bone): Coronal perforation: (supragingival) coronal to

Determine the factors that influence manganese absorption, Determine the Fa...

Determine the Factors that Influence manganese absorption? Let us now see which factors influence Mn absorption. Major factors which may influence the absorption of this min

Explain the law of segregation, Explain how the events of meiosis account f...

Explain how the events of meiosis account for the law of segregation and the law of independent assortment. In meiosis, the two alleles of every gene are segregated when the tw

Guanine, Guanine is one of the nitrogenous bases in the nucleic acids, gua...

Guanine is one of the nitrogenous bases in the nucleic acids, guanine is one of the two purine bases.

LIVING THINGS, CHARACTERICTICS OF PLATYHELMENTUS

CHARACTERICTICS OF PLATYHELMENTUS

Agro-industrial by-products (aibp), Agro-industrial by-products (AIBP) ref...

Agro-industrial by-products (AIBP) refer to the by-products derived due to processing of the main crop products and allied industries. They are in comparison to crop residues, are

Rule of distal transformation of blastema, Rule of Distal Transformation of...

Rule of Distal Transformation of Blastema An intriguing phenomenon characteristic of limb regeneration is, that just only the part of the limb removed distal to the level of a

Peculiarities of mitosis - cleavage, Peculiarities of Mitosis - Cleavage ...

Peculiarities of Mitosis - Cleavage From the following you will learn that the mitosis in the phase of cleavage has some striking peculiarities: a) Synchronization of cell

How dietary constituents affecting the calcium absorption, How dietary cons...

How dietary constituents affecting the calcium absorption? Several dietary constituents have an effect on calcium absorption. The differences in fractional absorption from diff

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd