Q: What is a species?
A: A species is a group of populations whose members have the potential to interbreed in nature and produce viable offspring.
Q: What is the reproductive isolation?
A: The existence of biological factors that impede members of two species from producing viable, fertile offspring.
Q: What is a hybrid zone?
A: A region in which members of different species meet and mate, producing at least some offspring of mixed ancestry.
1. The biological species concept emphasizes reproductive isolation.
2. Speciation can take place with or without geographic separation.
3. Hybrid zone provide opportunities to study factors that cause reproductive isolation.
4. Speciation can occur rapidly or slowly and can result from changes in few or many genes.
5. The punctuated pattern suggests that once the process beings, speciation can be completed relatively rapidly
Figure 24.19 Single-gene speciation
A mutation in one gene causes the shell of the Japanese land snail to spiral in the opposite direction from others. (the one on top of the picture). Snails with opposite spirals cannot mate, resulting in reproductive isolation.
Speciation—the origin of new species—is at the focal point of evolutionary theory because the appearance of new species is the source of biological diversity. Speciation addresses the question of how new species originate and develop through the subdivision and subsequent divergence of gene pools. Species are based on interfertility, not physical similarity. Because the distinction between biological species depends on reproductive incompatibility, the concept hinges on reproductive isolation, the existence of biological barriers that prevent members of two species from producing viable, fertile hybrids.
Reduced hybrid viability. Genetic incompatibility between the two species may abort the development of the hybrid at some embryonic stage or produce frail offspring.Evolutionary biologists have proposed several alternative concepts of species. Two general modes of speciation are distinguished by the way gene flow among populations is initially interrupted. How significant a barrier must be to limit gene exchange depends on the ability of organisms to move about. Individuals of two closely related sympatric cichlid species will not mate under normal light because females have specific color preferences and males differ in color.
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