A study first begun in 1915 has recently been completed by a team of undergraduate and postgraduate students from the University of Pennsylvania. They found that samples of Nucella lapillus, a predatory sea snail more commonly know as "Dog Whelk", collected in 2007 had a shell length, on average, 22.6% greater than those collected in the period 1915-1922.
The 12,000 shells collected by Harold Sellers Colton and his team nearly a century ago have since been stored at the Academy of Natural Sciences of Philadelphia, while descriptions and maps left by Colton of the 19 sites in the vicinity of Mount Desert Island, Maine, enabled the collection of a corresponding re-sample.
Many reasons for the evolutionary change have been suggested. Mortality rates could have lowered due to reductions in the snail's predators, perhaps due to over-fishing; or the rise in ocean temperature. It has also been suggested that with the prevalence of larger-sized predators, snails with a smaller shell could have come off second best when faced with natural selection.
The significance of this finding was illustrated by University of Pennsylvania professor Peter S. Petraitis in making note that if this same change had occurred in humans, the average person could be over 7 feet tall.
This post was based on an article found in the "Research at Penn" section of the University of Pennsylvania website; Penn Biologists Demonstrate that Size Matters…in Snail Shells, 27/03/09. For more information, visit http://www.upenn.edu/researchatpenn/article.php?1588&sci
