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 freshwater snail population at Location 2, which experiences higher average salt concentrations (0.3–0.5 ppt) compared to Location 1 (0.0–0.1 ppt). The higher levels of salinity at Location 2 create a challenging environment for snails that are sensitive to salt, leading to increased selection pressure. Over time, individuals in this population that possess beneficial adaptations for tolerating salt, such as enhanced osmoregulation mechanisms, would have a survival advantage, allowing them to reproduce and pass these traits on to future generations. As a result, these adaptations would become more common in the population at Location 2 through the process of natural selection.