Question

Bell and collaborators painstakingly documented a population of fossil sticklebacks from an ancient freshwater lake over a 20,000-year period. The prevalence of sticklebacks with full and reduced pelvises changed over time. Which is true?1. Initially (time A), fish with full pelvises dominated the lake population.2. By the end of the studied period (time D) there was an approximately equal number of sticklebacks with and without spines.3. In this population, having pelvic spines seemed to provide a selective advantage to stickleback fish.4. The evolution of pelvic reduction seen in the fossil record is different from the phenomenon occurring in the lakes in Alaska today.5. The population of fish with pelvic spines that arrived in the lake at time B evolved a reduced pelvis over time (beginning at time C).

Answer 1

Answer:

The population of fish with pelvic spines that arrived in the lake at time B evolved a reduced pelvis over time (beginning at time C).

Explanation:

Having a reduced pelvis must have been advantageous for this ancient stickleback population, just as it is for many current freshwater stickleback populations. Sticklebacks developed traits that made them better adapted to fresh water and, as a result, they moved to a freshwater environment. Stickleback populations swam to freshwater lakes to spawn and stayed because there were no predators. Ocean stickleback have bony side plates and pelvic spines as protection from predators. In Bear Paw lake, pelvic spines reduce fitness and chances for reproduction because predators grab the spines; most fish have no pelvic spines.