The freshwater gastropod family Physidae
(Pulmonata: Basommatophora) has largely a Holarctic distribution, which extends
southward into Central and South America (Burch,
1982, Taylor, 2003). Physids, particularly Physa acuta have been introduced around the world. Physidae diversity is concentrated in the
United States and Canada, which has 47 species (Johnson et al.
2013). Wethington and Lydeard (2007) were
the first to examine the evolutionary relationships of the family using modern
phylogenetic analyses of two mitochondrial genes of 66 specimens representing
28 taxa. Wethington and Lydeard (2007)
confirmed the recognition of a number of formal and informal taxonomic groups
that had been identified by penial morphology (Te,
1978). Although a complete
systematic treatment is still needed for the family, the study at least
provided an evolutionary framework that other studies could use as a starting
point and/or an hypothesis of relationships that could be tested with
additional data.
Recently, an interesting paper entitled “Recognition
of a highly restricted freshwater snail lineage (Physidae: Physella) in
southeastern Oregon: convergent evolution, historical context, and conservation
considerations” was published this year in Conservation Genetics by
Alexandria Moore, John Burch and Thomas Duda, Jr. The authors examined the phylogenetic status
of the Owyhee wet-rock physa, which is restricted to a series of geothermal
springs within the Owyhee River drainage in southeastern Oregon. The Owyhee wet-rock physa has a shell-shape
reminiscent of P. zionis rather than the typical physid
shape exhibited by members of the gyrina
species group, so P. zionis was included in the analysis as
well (see photo above showing a) Owyhee wet-rock physa, b) P. zionis and c) P. cf gyrina). Phylogenetic
analyses of sequences of mitochondrial cytochrome oxidase I and two nuclear
genes (internal transcribed spacer genes I and II), revealed the Owyhee
wet-rock physa is genetically distinct and closely related to P. cf gyrina from California. It
is distantly related to P. zionis, so the similar shell shape
evolved independently. The authors plan
to formally describe this unique species and recommend that it be considered critically
endangered based on its limited distribution.
Clearly, physids offer a wealth of opportunity for those interested in
sorting out evolutionary relationships, delimiting species boundaries and discovering
taxa.
Literature
Cited
Burch, J.
B. 1982.
North American freshwater snails: identification keys, generic synonymy,
supplemental notes, glossary, references, index. Walkerana, 1:1-365.
Johnson, P.
D., A. E. Bogan, K. M. brown, N. M. Burkhead, J. R. Cordeiro, J. T. Garner, P.
D. Hartfield, D. W. Lepitzki, G. L. Mackie, E. Pip, T. A. Tarpley, J. S.
Tiemann, N. V. Whelan, and E. E. Strong.
2013. Conservation status of
freshwater gastropods of Canada and the United States. Fisheries 38(6):247-282.
Moore, A.
C., J. B. Burch, and T. F. Duda, Jr. 2014. Recognition of a highly restricted freshwater
snail lineage (Physidae: Physella) in southeastern Oregon: convergent evolution,
historical context, and conservation considerations. Conservation Genetics http://link.springer.com/article/10.1007/s10592-014-0645-5
Taylor, D.
W. 2003.
Introduction to Physidae (Gastropoda: Hygrophila) biogeography,
classification, morphology. Revista de
Biologia Tropical, Supplement 51:1-287.
Te, G.
A. 1978. The systematics of the family Physidae
(Basommatophora: Pulmonata). Ph.D.
thesis, University of Michigan.
Wethington,
A., C. Lydeard. 2007. A molecular phylogeny of Physidae
(Gastropoda: Basommatophora) based on mitochondrial DNA sequences. J. Molluscan Studies 73:241-257.
