Article Summary–Speciation and Hybridization

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Article Summary–Speciation and Hybridization

Grant, P.R., and B.R. Grant. 1996. Speciation and hybridization in island birds. Philosophical Transactions of the Royal Society of London B Biological Sciences 351: 765-772.

It may be confusing to the scholar of natural selection and evolution to learn about all the details of micro-evolutionary change in Darwin's finches and relate them to each other. Therefore, it is nice to step back from these details for a while and attempt a synopsis of the processes that allow the speciation in island birds, and try to generalize beyond Darwin's finches. This is what Peter and Rosemary Grant did in this publication. The most difficult problem in speciation, in a nutshell, is the problem of how two species are generated from one. There are two alternative models to explain speciation in island birds: allopatry or peripatry (or founder speciation).

The present publication highlights every step during the presumed speciation of Darwin's finches in allopatry and provides background mechanistic data, in order to really evaluate each step of the model. The punch line is: "Differences that evolve in allopatry are reinforced by a regime of divergent selection on the taxa in sympatry arising from ecological pressures and not from reproductive (genetic) incompatibility.... Hybridization potential may last for many million of years after two taxa diverge, implying that post-zygotic isolation evolves slowly."

1. For two species to be separate, there must be a mechanism by which individuals can distinguish whether to breed with a conspecific or a heterospecific. Why do females often discriminate more strongly than males in their choice of mating partners (i.e., females will not mate with a heterospecific male that displays toward them)? Discuss this point with regard to the costs and benefits of mating for males and females.
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

2. If the hybridization potential lasts for many million of years after two taxa diverge, what kind of implications does it have for the biological species concept?
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.

3. During some years, hybrids are not less fit than members of the original species. Thus, why should Darwin's finches court and mate only with members of their own species, if interbreeding has no obvious fitness disadvantages? Discuss this question with regard to mate choice and what you know about the fitness of hybrids.
To create paragraphs in your essay response, type at the beginning of the paragraph, and at the end.




1.	For two species to be separate, there must be a mechanism by which individuals can distinguish whether to breed with a conspecific or a heterospecific. Why do females often discriminate more strongly than males in their choice of mating partners (i.e., females will not mate with a heterospecific male that displays toward them)? Discuss this point with regard to the costs and benefits of mating for males and females. To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



2.	If the hybridization potential lasts for many million of years after two taxa diverge, what kind of implications does it have for the biological species concept? To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.



3.	During some years, hybrids are not less fit than members of the original species. Thus, why should Darwin's finches court and mate only with members of their own species, if interbreeding has no obvious fitness disadvantages? Discuss this question with regard to mate choice and what you know about the fitness of hybrids. To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.

Chapter 15: Literature: Speciation, Hybridization, and Ecotones

Article Summary–Speciation and Hybridization