Salt is notoriously
dangerous to land snails;
however, some populations
of aquatic, freshwater snail
have brackish (or a mix of
salt and fresh water) water
adaptations and live in
different parts of a river
system. A group of
scientists monitored salt
concentrations in the
habitats of two freshwater
snail populations located
nearby and recorded the
salt level as follows (in ppt,
parts per thousand):
Population 1 (Day 1): 0.1
ppt (morning), 0.0 ppt
(afternoon), 0.1 ppt
(evening)
Population 2 (Day 1): 0.3
ppt (morning), 0.5 ppt
(afternoon), 0.2 ppt
(evening)
In 1–2 sentences, 1)
describe in which
population you'd expect to
see more adaptations for
salt water and 2) explain
how such adaptations
would become more
common in this population.
1) You would expect to see more adaptations for salt water in Population 2, as the salt concentrations in their habitats are consistently higher throughout the day compared to Population 1.
2) Such adaptations would become more common in Population 2 because individuals with traits that allow them to survive and reproduce in high salt concentrations would have a higher fitness and be more likely to pass on their genes to the next generation. Over time, this would lead to an increase in the frequency of these adaptations in the population.