Question

Salt is dangerous to land snails. It will rapidly kill them. However, some populations of aquatic, freshwater snail have adapatations that allow them to live in a mix of salt and fresh water. This allows them to live in different parts of a river system. A group of scientists monitored salt concentrations in the habitats of two freshwater snail populations. They recorded the salt level as follows (in ppt, parts per thousand):

Location 1 (Day 1): 0.1 ppt (morning), 0.0 ppt (afternoon), 0.1 ppt (evening)

Location 2 (Day 1): 0.3 ppt (morning), 0.5 ppt (afternoon), 0.2 ppt (evening)

In 3–5 sentences, describe in which population you'd expect to see more adaptations for salt water. Make sure to also explain how such adaptations would become more common in this population.

(4 points)

Answer 1

I would expect to see more adaptations for salt water in the population at Location 2, which experienced higher salt concentrations (0.3 ppt to 0.5 ppt) compared to Location 1 (0.0 ppt to 0.1 ppt). The presence of saltier conditions would exert greater selective pressure on the snails, favoring individuals with traits that allow them to tolerate or thrive in saltier environments. Over time, these adaptations, such as more efficient osmoregulation or specialized shell structures, would become more common in the population due to increased survival and reproductive success of those individuals best suited to handle the saltier conditions. Consequently, as these traits are passed on to subsequent generations, the population at Location 2 would become increasingly adapted to its environment.