Saturday, 9 May 2015

Tryonia infernalis: A new species of Cochliopid Snail from a hot spring in the southern Nevada Desert.


The deserts of southeast California and southwest Nevada have been shown to host a distinctive fauna of endemic (found nowhere else) Caenogastropod Snails, with many species with very limited distributions belonging to the families Assimineidae, Cochliopidae and Hydrobiidae found along tributaries to the Great Basin and lower Colorado Rivers and in the many hot springs found across the area.

In a paper published in the journal ZooKeys on 30 March 2015, RobertHershler of the Department of Invertebrate Zoology at the Smithsonian Institution and Hsiu-Ping Liu and Jeffrey Simpson of the Department of Biology at the Metropolitan State University of Denver describe a new species of Cochliopid Snail from Blue Point Spring, a hot spring close to Lake Mead in Clark County, southern Nevada.

The new Snail is placed in the genus Tryonia and given the specific name infernalis, meaning ‘hellish’, in reference to the proximity of Blue Point Spring to Nevada’s Valley of Fire. Tryonia infernalisis described from over 200 specimens ranging in length from 2.41 mm to 3.09 mm in shell height, with between 5 and 5¾ whorls. The males are on average slightly smaller than the females. The shells of the Snails are light brown, the bodies darker.

Tryonia infernalis, (A) female shell, (B) male shell, (C, D) opercula (outer, inner sides). Scale bars (A, B): 1.0 mm; (C, D): 200 μm. Hershler et al. (2015).

The species is known only from close to the source of Blue Point Springs, in waters within about 10 m of the spring from which the waters issue, which have a temperature of about 30˚C. The Snails were first observed in 1988, but appeared to have gone extinct in 2002. However they reappeared in 2007 and are now locally abundant.

Photographs of Blue Point Spring. (A) Outflow channel; spring originates below one of the mesquite trees in the upper right (photograph taken on 24 March 2009). (B) Ponded area where Tryonia infernalis occurs abundantly; the USGS gage house is in the lower left (15 May 2014). Hershler et al. (2015).

A genetic study of Tryonia infernalis suggests that it is most closely related to Tryonia clathrata, a species known from the White River Valley, which drains into Lake Mead, via the Muddy River, a few kilometres up-flow from Blue Point Spring. Two other Snail species present at the spring, Pyrgulopsis coloradensis and Assiminea sp., as well as a species of Amphipod Crustacean, Hyalella sp., appear to be more closely related to species from Death Valley in California, roughly 200 km to the west, and on the other side of the Spring Mountains.

Map showing the location of Blue Point Spring relative to other geographic areas. The collecting localities for specimens of Pyrgulopsis sanchezi and Tryonia clathrata (sister taxa of Blue Point Spring endemics) used in the molecular phylogenetic analyses are also shown. Hershler et al. (2015).

A molecular clock analysis of the three Snail species suggests that Assiminea sp. diverged from its closest known relative 1.42-1.60 million years ago, Tryonia infernalis from its nearest known relative 2.14-2.41 million years ago and Pyrgulopsis coloradensis from its closest relative 2.46-2.78 million years ago, suggesting that in all cases divergence occurred during the Pleistocene.The age of Blue Point Spring is not known, but the oldest spring deposits showing evidence of groundwater discharge associated with it are thought to be at least 2.6 million years old (Early to Middle Pleistocene). At no point during this time has Blue Point Spring or the surrounding area shared a common watershed with Death Valley, so Hershler et al. suggest that they may have been transferred to the site by Birds (which is thought to be common in for small invertebrates).

Hershler et al. suggest that Blue Point Spring represents a unique, if tiny, biodiversity hotspot with at least two (and possibly three) endemic Snail species. The site is currently administered by the National Park Service as part of the Lake Mead National Recreation Area, but Hershler et al. believe that it is in need of extra protective measures to ensure the survival of its unique fauna. The site is currently located close to a paved highway and small parking area, which makes it liable to disturbance by foot traffic and other activities. The Snail population might benefit from fencing off the spring, but the site is also home to one of the few known populations of the Relict Leopard Frog, Rana onca, which is known to be adversely affected by fencing, ruling this option out. Blue Point Spring was also used as an exotic-fish rearing site for the aquarium trade until the mid-1950s, and is known to host a population of the Convict Cichlid, Amatitlania nigrofasciata, which is omnivorous and may present a threat to the Snails, as well as the Red-rimmed Melania, Melanoides tuberculata, a highly invasive Gastropod species which has been shown to have an adverse effect on endemic Snail populations at other southwest American spring sites.

See also…

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