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The mechanisms of reproductive isolation have been classified in a number of ways. Zoologist Ernst Mayr classified the mechanisms of reproductive isolation in two broad categories: pre-zygotic for those that act before fertilization (or before mating in the case of animals) and post-zygotic for those that act after it. [5]
[5] [3]: 369 That is, if gene flow is not zero (if hybrids aren't completely unfit), selection cannot drive the fixation of alleles for prezygotic isolation. [28] For example: If population has the prezygotic isolating allele and the high fitness, post-zygotic alleles and ; and population has the prezygotic allele a and the high fitness, post ...
An example of ethological isolation in Ophrys apifera where the orchids structure mimics that of a female bee to attract the male counterparts. Floral Isolation is a form of reproductive isolation found in angiosperms. Reproductive isolation is the process of species evolving mechanisms to prevent reproduction with other species.
For example, an ancestral species has the alleles a and b fixed in its population, resulting in all individuals having the aabb genotype. When two descendant populations are separated from each other and each undergo several mutations the allele A can occur in one population while the allele B occurs in the second population.
The coastal snail species Littorina saxatilis has been a focus of research [4] as two ecotypes residing at different shore levels exhibit reproductive isolation as a result of mate choice regarding the body size differences of the ecotype. [34] Both marine and freshwater stickleback fish have shown strong evidence of having speciated this way.
Testing the role of natural selection in parallel speciation have focusing on the reinforcement of premating isolation. [2] But for the reinforcement, the requirement is preexisting reproductive isolation in the form of decreased hybrid fitness and is normally considered a final stride towards the process of speciation.
The reversal in chirality to sinistrality must have evolved as an isolating mechanism, [49] with patterns of reproductive character displacement suggesting speciation by reinforcement. [48] Satsuma largillierti lives on the western half of Okinawa Island while Satsuma eucosmia lives on the eastern half.
Genetic divergence will always accompany reproductive isolation, either due to novel adaptations via selection and/or due to genetic drift, and is the principal mechanism underlying speciation. On a molecular genetics level, genetic divergence is due to changes in a small number of genes in a species, resulting in speciation. [2]