Monday, January 28, 2008

Hendersonia occulta

Last year, Aydin over at Snail's Tales posted a note about an interesting land snail, Hendersonia occulta. This particular snail is one of the few operculate land snails in North America and represents an important evolutionary link between terrestrial and marine snails. It also is an important snail when one thinks about climate.

In the late Pleistocene (a mere 20,000 years ago), this snail roamed over a large portion of the interior of North America. Once the climate started warming, this snail started restricting its range, eventually becoming isolated in a few key regions today. One is in my field area - the Driftless Area of Wisconsin, Minnesota, Iowa, and Illinois. Another place was in eastern Wisconsin, where the dolomite bedrock is close to the surface. And finally, in the western Appalachian region including Pennsylvania.

Distribution map of H. occulta showing live (solid dots) and fossil (yellow dots) sites where it has been found.

What this tells us about climate is important when we think in terms of how organisms responded to past climate change, and how they might deal with future changes. In the late Pleistocene (i.e. Ice Age), much of North America had suitable habitat for this snail. They like relatively cool summers, but not intense winters. They often live near standing water, or places with plenty of moisture. A source of calcium is important (that makes sense, since they have pretty robust shells - with opercula - for land snails), and they need food. These snails generally live in dense leaf litter, probably feeding on Birch, Maple and other deciduous leaf material. So we can infer that many places in the Midwest had these conditions. As the climate warmed, however, the available moisture, temperature, and food/shelter sources disappeared throughout much of its previous habitat. Now, it is left in places that still have these conditions - refugia.

Suitable refugia exist in several locations - but what about future change? What would happen if these refugia disappeared? This snail has adjusted its range to stay in suitable areas, but now that we have drastically altered the landscape, there might not be a path for these snails to find refuge. A sad thought indeed.

So when people poo-poo climate change as just a "natural cycle" and that we shouldn't worry about it, they are ignoring an important point. We have created an artificial obstacle course that will interfere with organisms trying to adjust their ranges to match changes in climate. We may not be the sole cause of global warming, but we are actively placing many organisms at peril because of our existence. Food for thought...

Some H. occulta information:
MNFI (Michigan) zoological abstract

L. Watrous images of H. occulta and other land snails in Missouri

Wednesday, January 23, 2008

African Land Snails

A recent post by Aydin at Snail's Tales recently got some shells of an African land snail, which were the leftovers of a meal rich in snaily goodness. These are among the largest of terrestrial gastropods; very impressive critters. In some regions these are kept as pets.

This brings up an interesting point: in the U.S., it is illegal to keep live GALS. The reasons being economical and ecological. They are voracious eaters, are highly fecund, and can carry parasites harmful to people. The last reason is touted by the CDC and other government agencies, although no cases of snail-transmitted meningitis has been reported.

Recently in Wisconsin, there was a sweep of pet stores, private exotic pet owners, and schools in the Milwaukee area and more than 100 snails were confiscated. So if your classroom has an African land snail as a pet, the recommended thing to do is to contact APHIS at the USDA to have it removed. DO NOT release these critters into the wild! There may be a case-by-case way to get a permit to raise live GALS, so if you want to raise them, be sure to do your homework.

That being said, they are amazing animals - their size alone makes them pretty unique among gastropods. I can't imagine empty shells are a problem, and I would love to have a few as an example to show next to some of the smallest gastropods such as Carichium exile. Oh, and there must be some fascinating ecological implications of body size, egg volume, and habitat that are just waiting to be done.

GALS from an exhibit by the USDA

Discus whitneyi from Iowa - a smallish land snail.

Tuesday, January 22, 2008

A new semester begins!

Okay, so it's been a while. What am I up to? I'm getting ready to teach my Dinosaur course again, that's what. For those of us in the paleo world, we are sometimes guilty of avoiding dinosaurs, because of their immense popular appeal. However, Dinosaurs are a perfect gateway science. They tell us about the history of life, the relationship between earth history and living organisms. They are an excellent example to use for introducing cladistics to non-scientists, and so on...

I love to use demonstrations in class. It's much more exciting when the professor brings an object into the classroom: something other than a picture on the blackboard. I'm building a few 3D prehistoric animals to show anatomy, give the impression of relative size of various dinosaurs, and so on...

Here's an outline of the skull of Allosaurus fragilis that I'm building at about 1:6 scale.

Sunday, January 20, 2008

It's the calcium, stupid!

I've been doing a little thinking about calcium. Snail's have one absolute requirement that has a rather striking impact on their distribution and diversity. Calcium-rich environments have enough free building material for snails to manufacture and maintain an external shell. It should come as no surprise that the dolomite (a type of calcium-magnesium carbonate rock) outcrops in eastern Wisconsin have a rich snail fauna: dozens of species can share the same square meter space quite happily.

So what about areas that do not have calcium carbonate bedrock? For instance, here on the North Shore of Lake Superior, there aren't any carbonate outcrops. What do snails do to get their calcium? Well, plants contain calcium. But there are also igneous rocks that have calcium as a major constituent. Magnesium, and calcium are important cations in mafic igneous rocks, and many of the outcrops up here are these types of rocks. Along rock ledges near streams, there is a pretty impressive snail fauna crawling around, relatively unnoticed.

More about snails in northeast Minnesota will come in the following months...