What do you think prompted the changes?
Changes in the formation of shells have evolved over time as a defence mechanism against the shell-breaking claws of predators. These predators are like crabs and lobsters, fish jaws even other snails with shell-drilling radulas. The shell is a disguise of their real function, which is assumed to be for beauty purposes. From the graph, we see that the number of shell breaking predators have been on the increase over time. The number of families has increased from around 3 to over 30 within a short period. Following this increase, comparisons of most of the traits of snail’s shells as well as other attributes have been changing with the increase in the number of predators. For example, as the number of predators increase, the number of weak shell designs has decreased as the number of high sphires and narrow apertures have increased.
How does Vermeij’s data exhibit this phenomenon (hint: think “arms race”)?
Vermeij’s data exhibits how predator prey relationship has led to the evolution of snails shell structures (Vergara 121). Some traits that have been developing to frustrate the predators include thick walls and as from the graph, the number of shells with a weak shell design has rapidly decreased from over 60 to less than 30. A narrow aperture is another change that has occurred since the opening of the shells makes them vulnerable to attacks. The increase has been positive although not rapid, similar to the protrusions and high sphires that were developed to keep away claws from the area where the animal is found. Since the siphonal canal is a channel for attack/ entry by the predators, snails have developed a long and slender canal that makes it hard for predators to enter and at the same time allows the snails to burrow.
Vergara, Daniela, et al. "Evaluating shell variation across different populations of a freshwater snail." Molluscan Research 3...
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