Question

Select one form of SPECIATION and share your rendition of this process of speciation. You can upload a drawing you have made or you can list the steps that occur. Once again mutation which provides variation is at the heart of the process. Mutation is the engine that runs evolutionary change. IF VARIATION IS NOT PRESENT IN THE ORIGINAL POPULATION THERE IS NO VARIETY AVAILABLE TO ADAPT TO THE NEW ENVIRONMENT AFTER THE CHANGE IN THE HABITAT OCCURS . IF YOU SAY THAT THE CHANGE IN THE ENVIRONMENT MAKES A MUTATION HAPPEN YOU WILL NOT RECEIVE CREDIT - BECAUSE THIS IS NOT CORRECT. MUTATIONS OCCUR RANDOMLY - NOT ON DEMAND

Make sure you account for this in your rendition.

By this I mean, you must show that a mutation has randomly occurred in the species prior to any other steps occurring. Once again showing the steps in the process is what is important here.

Draw or list each step in an example of speciation.

Allopatric speciation is just a fancy name for speciation by geographic isolation,

Peripatric speciation is a special version of the allopatric speciation model and happens when one of the isolated populations has very few individuals.

Sympatric speciation does not require large-scale geographic distance to reduce gene flow between parts of a population. Merely exploiting a new niche may automatically reduce gene flow with individuals exploiting the other niche.

In parapatric speciation, Individuals are more likely to mate with their geographic neighbors than with individuals in a different part of the population’s range.

Answer 1

In this answer Sympatric speciation will be discussed. But let us fist understand all the speciation in simple words. Allopatric speciation is the evolution of species where geographic isolation of two or more populations of a species comes into play. In this case, divergence occurs by the absence of gene flow. Parapatric speciation is the evolution of geographically adjacent populations into distinct species. In this case, divergence occurs despite limited interbreeding where the two diverging groups come into contact. In sympatric speciation, there is no geographic constraint to interbreeding. Hence Sympatric speciation is always a special case.

Sympatric Speciation :

Although Two models of speciation are proposed, one is “ecological speciation “ and the other “mutation order model” , Mutation induced becomes difficult to demonstrate. When gene flow occurs it can be ignored because the same, most advantageous allele will fix in all populations. However, quantitative examination of the factors causing mutation-order speciation is lacking.

Cichlid fish probably represent the largest catalogue of examples of speciation and reproductive isolation without geographical or ecological separation. More than 3000 species of cichlid fish are known to exist worldwide, making this group the largest family of species in vertebrates. Almost 2000 cichlid species of fish have evolved in lakes of East Africa (Victoria, Malawi, and Tanganyika) during “the very recent evolutionary past” (Kocher, 2004).

The likelihood of occurance of Sympatric Speciation is most controversial aspect of speciation, and certainly one of the most contested questions in evolutionary biology.

Sympatric speciation in Greek means “from the same place” . It involves the splitting of an ancestral species into two or more reproductively isolated groups without geographical isolation of those groups. The unique feature of sympatric speciation is it occurs between incipient species when they are in physical contact with each other, able to interbreed and exchange genes.

The Process :

1. Sympatric speciation begins with complete genetic mixing between the diverging groups.

2. Then disruption selection starts which is natural selection driving a population in two different directions at once.

3. If this selection is strong enough, it can cause the population to divide into two subpopulations, each specializing on a different resource, with hybrids between the subpopulations. The subpopulation may suffer reduced fitness because they are not well adapted to either resource.

Note : Such hybrids are hard to achieve because of the genetic recombination that occurs when incipient species interbreed. This recombination breaks up the correlation between co-adapted groups of genes that is necessary for species to form. Because recombination is so powerful at preventing sympatric speciation, the conditions under which such speciation can occur can be quite rare. Selection should be very strong for such occurance. And there are also restrictions on the number of genes that can contribute to differences in species-specific traits, and on their linkage relationships to each other.

Example : A special case of species of cichlid fish in two very small Nicaraguan volcanic lakes. With all the cichlids in each lake being closely related descendants of a single common ancestor. It's very unlikely that fish in these lakes could ever have been geographically isolated. These fishes have different species formed from same ancestor through sympatric speciation.