OBJECT OF THE MONTH - November, 2010

Talus Snails

[Photo 1 by Heather Hamilton: Sonorella sp., UCM 46503, collected in 2005 from the Pinaleno Mountains, Graham County, Arizona.]

The University of Colorado Museum of Natural History's Mollusca collection, housed within the Invertebrate Zoology section, contains an amazing diversity of approximately 800,000 specimens from all over the world, including freshwater, marine and terrestrial species. Mollusca itself is a highly complex and diverse group of animals that includes snails, slugs, clams, mussels, chitons, abalone, squids, octopus, cuttle fish, nautilus, among others. The CU Museum's mollusc collection dates back to the start of CU Museum's own history due to the early director's interests in Malacology, the study of molluscs. Extensive and critical treatments of Rocky Mountains and Great Plains molluscs were based on specimens in CU Museum's collection, which has continued to grow substantially for over 100 years.

One group of molluscs that have been studied in depth by CU Museum curatorial staff and students are snails of the genus Sonorella, commonly known as talus snails due to the habitat in which they occur. These snails are primarily restricted to the Madrean Archipelago of the southwestern United States and south into Mexico. These mountainous regions are referred to as 'Sky Islands' due to the isolation of the mountain ranges to each other. Sonorella are found in most of the Madrean Sky Islands from the bases of the islands to their peaks, but not in the surrounding desert and grassland areas. As well, most Madrean Sky Islands are inhabited by unique species of Sonorella, suggesting that these 'sky islands' have remained isolated enough from each other for speciation processes to occur. Curator Robert Guralnick and former PhD student Kathleen Weaver studied the conservation status and origin of species of Sonorella in the Pinaleno Mountains utilizing molecular genetic approaches. They were able to document a broader extent for across the Pinalenos for some species and much narrower than expected ranges for others. They also showed that species in the mountain range likely radiated in-situ. Such work brings together conservation and biogeography.

There are approximately 80 known species of talus snails, and like most other organisms are at times difficult to study in their natural habitat due to their specific life histories and habits. While this group of snails does not occur in Colorado and is restricted in distribution to Sonoran and Chihuahuan deserts of Arizona, New Mexico and Mexico, this has not hindered their presence in the Museum's collection and our desire to learn more about this fascinating group of snails. In fact, our holdings of Sonorella are impressive for a collection with an emphasis on the Rocky Mountains and Great Plains regions. Our field collections of Sonorella date as far back as 1905 to as recently as 2010, representing 75 lots of more than 500 specimens. The majority of these specimens were collected in the southeastern mountains of Arizona.

The talus snails of the Madrean Sky Islands are just one example of the ongoing and diverse research programs in Malacology being conducted by CU Museum's Invertebrate Zoology section.

[Photo 1 by Heather Hamilton: Sonorella baboquivariensis, UCM 7025, collected in September 1910 from the Baboquivari Mountains, Pima County, Arizona. ]