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

What is meant by substrates of enzymatic reactions, Substrates are reagent ...

Substrates are reagent molecules upon which enzymes act. The enzyme has spatial binding sites for the attachment of its substrate. These sites are known as activation centers of

Define the miscellaneous applications of sugar, Define the Miscellaneous Ap...

Define the Miscellaneous Applications of Sugar? Sugars are used in 1. Custards, 2. puddings, 3. pie fillings and meringues Depending on the sugar to perform vital c

Explain about genetic diversity, Q. Explain about Genetic Diversity? Ge...

Q. Explain about Genetic Diversity? Genetic diversity is the "fundamental currency of diversity" that is responsible for variation. This is the diversity of basic units of here

Hypothesis - nursing research, Hypothesis: The  spelling of hypothesis...

Hypothesis: The  spelling of hypothesis when written  as  "hypotheses"  indicate plural. The hypothesis is a statement or declaration of  the expected outcome of a research st

Why do preserved foods not spoil, Why do preserved foods not spoil? Pla...

Why do preserved foods not spoil? Plant and animal cells must stay in an isotonic, or neutral, solution to survive. When salt or sugar is added, more of the cells wither and di

Protein prediction., I am trying to get help on the creation of a dataset f...

I am trying to get help on the creation of a dataset for protein prediction in matlab

Symptoms of serum sickness, Symptoms contain fever, weakness, rashes, with ...

Symptoms contain fever, weakness, rashes, with erythema and edema. Serum sickness depends on the immune difficult formed and the size of the complexes.

Temperature regulation in homeotherms, Temperature Regulation in Homeotherm...

Temperature Regulation in Homeotherms Homeothermy is regulation of body temperature by physiological means. The stabilisation of body temperature permits a steady high level

Define essential parts of photocolorimeter - monochromators, Define Essenti...

Define Essential Parts of Photocolorimeter - Monochromators? This is a means of selecting a sufficiently narrow waveband. Early colorimeters used glass filters that transmitted

Human factor theory - accident causation, Human Factor Theory - Accident Ca...

Human Factor Theory - Accident Causation This theory of accident causation suggests that a chain of events caused by human error is the cause of accident. The chain of events

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