Bird guides once listed the myrtle warbler and Audubon's warbler as distinct species. Recently, these birds have been classified as eastern and western forms of a single species, the yellow-rumped warbler. Which of the following pieces of evidence, if true, would be cause for this reclassification?
a. The two forms interbreed often in nature, and their offspring survive and reproduce well.
b. The two forms live in similar habitats and have similar food requirements.
c. The two forms have many genes in common.
d. The two forms are very similar in appearance.

Verified step by step guidance

1. Identify the criteria used to classify organisms as the same species. One key criterion is the ability to interbreed and produce viable, fertile offspring.
2. Evaluate option (a): If the two forms interbreed often in nature and their offspring survive and reproduce well, this suggests they are not reproductively isolated, which is a strong indicator they are the same species.
3. Consider option (b): Living in similar habitats and having similar food requirements does not necessarily indicate they are the same species, as different species can share ecological niches.
4. Analyze option (c): Having many genes in common can occur between different species, especially if they are closely related, so this alone is not sufficient for reclassification.
5. Review option (d): Similar appearance can be misleading, as convergent evolution can lead to similar traits in different species. Therefore, this is not a strong basis for reclassification.

Key Concepts

Species Definition

A species is typically defined as a group of organisms that can interbreed and produce fertile offspring. This biological species concept emphasizes reproductive isolation as a key factor. If two forms can interbreed successfully and their offspring are viable and fertile, they are often considered the same species, which is relevant to the reclassification of the warblers.

Hybridization

Hybridization refers to the process where two different species or forms interbreed to produce hybrid offspring. In the context of the warblers, frequent interbreeding with successful reproduction suggests that the myrtle and Audubon's warblers are not reproductively isolated, supporting their classification as a single species.

Genetic Similarity

Genetic similarity involves comparing the DNA sequences of different organisms to assess their relatedness. High genetic similarity between two forms can indicate they are closely related or even the same species. In the case of the warblers, sharing many genes could be a factor in their reclassification as a single species, although interbreeding evidence is more definitive.