Introduction

Darwinian Snails Introduction

All animals require a food source to survive, where and when they get their food is determined on availability and natural selection. Flat periwinkle snails are small marine snail that is part of the “Littorinidae” family. They are typically found on seaweed that grows off the shores of New England (Britannica). Predators bring out the best traits in a species which helps future generations. Periwinkle snails have several predators, but one of the main ones it the green crab. The green crab is not native to North America, instead it was introduced during the 1800’s via ships arriving at Cape Cod from Europe (Washington Dep.). These crabs have caused many problems, they rapidly spread and they are theorized to have caused the major decline in “soft shell fishery”. This experiment was used to study and understand the impact green crabs have on the periwinkle snail population as well as observe any evolutionary traits that are carried onto the next generation. These snails have only one line of defense against the crabs—their shells. Biologist Robin Seeley discovered this rapid morphological transition by comparing a museum shell collection from 1871 to shells she collected from the same area. Her study shows how rapidly the periwinkle snails evolved. Seeley’s work demonstrated that prior to the green crabs arriving in North America, periwinkle snails’ shell thickness averaged out as “thin” with the majority of the population having the same shell thickness. Her work later showed that after green crabs were introduced shell thickness rapidly changed. In about 80 years, shell thickness double with the population having a wide range of thickness (Seeley).
Evolution is defined as; “change in the gene pool of a population from generation to generation by such processes as mutation, natural selection, and genetic drift”, while Natural Selection is defines as; “the process by which forms of life having traits that better enable them to adapt to specific environmental pressures, as predators, changes in climate, or competition for food or mates, will tend to survive and reproduce in greater numbers than others of their kind, thus ensuring the perpetuation of those favorable traits in succeeding generations..” (Dictionary.com). Both Evolution and Natural Selection work together to bring out the genes required by a species to survive and reproduce. For natural selection to occur, four things are required. 1) Reproduction, 2) Heredity, 3) Variation, 4) Variation (Ridley). If all four of these are met properly for a species, natural selection will occur. Knowing all of this, I predict that with a large population, and through several generations, the periwinkle snails will develop thicker shells to better survive against the green crabs.