Which trait is commonly used as a proxy for diet adaptation in sticklebacks?

• A. Gill raker length only
• B. Jaw strength
• C. Fin shape
• D. Gill raker number and length

Answer: (D)

The feeding apparatus morphology is a key indicator of diet adaptation in sticklebacks. Gill rakers act like a sieve in the throat, and having more of them and longer rakers increases the fish’s ability to retain small prey such as zooplankton, which is typical of limnetic (open-water) feeding strategies. Because both the number and the length of gill rakers directly influence what size prey is captured, the combination of gill raker number and length provides the most complete and reliable proxy for diet adaptation across populations. Traits like jaw strength or fin shape can be influenced by other pressures such as bite force or swimming performance and don’t map as directly to diet type, while focusing on length alone misses variation in raker count.