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.

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 to 0.5 ppt) compared to Location 1 (0.0 to 0.1 ppt). The increased exposure to salt in Location 2 would create selective pressure on the snails, favoring individuals with traits that allow them to tolerate or thrive in saline conditions. Over time, those individuals are more likely to survive and reproduce, passing on their advantageous adaptations to future generations, leading to a higher prevalence of salt tolerance in that population.