Which statement correctly distinguishes benthic and limnetic ecotypes in freshwater sticklebacks?

Which statement correctly distinguishes benthic and limnetic ecotypes in freshwater sticklebacks?

• A. Benthic ecotypes feed near the bottom and have morphology suited for bottom feeding.
• B. Limnetic ecotypes feed in open water and have different jaw shapes and body proportions.
• C. Benthic ecotypes are found only in saltwater.
• D. Limnetic ecotypes have armor plates identical to marine forms.

Answer: (A)

The key idea is that sticklebacks in freshwater lakes split into two ecotypes that exploit different parts of the environment: the bottom and the open water. This division drives distinct morphologies that fit each niche. Benthic forms specialize in feeding near the lakebed, so their features are shaped for bottom feeding. Their jaw design and body shape support manipulating prey on or from the substrate and maneuvering close to the bottom. In contrast, limnetic forms feed in open water and typically show jaw shapes and body proportions that optimize catching zooplankton away from the bottom. Some statements about other scenarios aren’t accurate. Benthic and limnetic ecotypes are freshwater, not confined to saltwater. Armor plates in freshwater forms are often reduced compared with marine populations, and they aren’t identical to marine forms. So, the bottom-feeding morphology paired with near-bottom feeding behavior is the clearest distinguishing feature between the two ecotypes.

The key idea is that sticklebacks in freshwater lakes split into two ecotypes that exploit different parts of the environment: the bottom and the open water. This division drives distinct morphologies that fit each niche.

Benthic forms specialize in feeding near the lakebed, so their features are shaped for bottom feeding. Their jaw design and body shape support manipulating prey on or from the substrate and maneuvering close to the bottom. In contrast, limnetic forms feed in open water and typically show jaw shapes and body proportions that optimize catching zooplankton away from the bottom.

Some statements about other scenarios aren’t accurate. Benthic and limnetic ecotypes are freshwater, not confined to saltwater. Armor plates in freshwater forms are often reduced compared with marine populations, and they aren’t identical to marine forms.

So, the bottom-feeding morphology paired with near-bottom feeding behavior is the clearest distinguishing feature between the two ecotypes.