Question

an industrial accident five years ago spilled thousands of gallons of toxic chemicals into a freshwater lake inhabited by several species of fish. after the spill, a biologist began studying three of these species of fish over a five-year period.

species a	lost 80% of its population; the remaining population migrated upriver to another lake.
species b	lost 95% of its population; the remaining population survived and eventually became larger than the pre-spill population.
species c	showed no change in population size over the five-year period.

which fish species most likely underwent a genetic adaptation as a result of the chemical spill?
○ a. species b only
○ b. species a, b, and c
○ c. species c only
○ d. species b and c only

Explanation:

To determine which species underwent genetic adaptation, we analyze each:

• Species A: Migrated, so no genetic adaptation in this lake.
• Species B: Lost 95% but remaining population grew larger than pre - spill. This suggests genetic traits (adaptation) helped survival and growth in the toxic environment.
• Species C: No population change, so no genetic adaptation (no pressure or change to drive it).

Only Species B shows evidence of genetic adaptation.

Answer:

A. Species B only