Monday, August 26, 2013

Species Profile: East Tennessee Cave Beetle (Pseudanophthalmus tennesseensis)

Pseudanophthalmus tennesseensis, Roane County, TN. (Photo by Michael E. Slay)
East Tennessee Cave Beetle
Pseudanophthalmus tennesseensis

Conservation status: IUCN Red List - Not Assessed; NatureServe - G3 (Tennessee: S2). This species is tracked by the state of Tennessee.

Description: Pseudanophthalmus tennesseensis is a small, eyeless and depigmented ground beetle red to reddish-brown in coloration. Adults are only 4 mm in length and lack wings. They have prominent, long legs and thread-like antennae. Like most Pseudanophthalmus, this species is pubescent, possessing three well-defined pairs of discal setae (chitinous hairs) on the elytra, a character used to separate the genus from other co-occurring genera of cave carabid beetles. Species identification is difficult in this genus and requires the dissection and microscopic examination of male genitalia. This species is the type species of the P. tennesseensis species group found in east Tennessee.

Distribution: Pseudanophthalmus tennesseensis is known from only four cave systems in the Ridge and Valley of east Tennessee: three caves in Knox County and one cave in Roane County. All of these cave systems lie south of the Copper Creek Fault in Knox and Roane counties. A potential new population was discovered in Knox County in the Keller Bend area of the Tennessee River to the southeast of all known localities, but taxonomic identification has not yet been confirmed.

Habitat: Most specimens of P. tennesseensis have been collected primarily under rocks or rotting wood found on damp silt away from streams. However, the lone specimen found in the potential new locality in Knox County, Tennessee, was found near a rimstone pool. 

Natural History: Little information is available regarding the life history and ecology of P. tennesseensis. Larvae have not been reported. Based on information from studies of other Pseudanophthlamus species, eggs of this species are probably laid in autumn with larvae appearing in winter. Larvae then pupate in late winter into early spring with tenerals (soft-bodied adults shortly after emerging from pupae or from molting) appearing the following summer in June and July. By the following autumn, beetles are almost fully sclerotized. Pseudanophthalmus beetles are predatory and are often actively observed walking along cave mud and sediments along streams and other sources of water. The diet of P. tennesseensis has not been studied but likely includes enchytraid and tubificid worms found in association with cave mud and sediments. Predators are unknown. This species is not known to co-occur with any other cave carabid beetles. Data on population size is unavailable. Valentine (1937) collected a male and female on separate trips from the type locality, Cherokee Caverns (TKN22) in Knox County, while Barr (1965) collected five topotypes from the same cave in 1958. Barr (1965) also reported that the species was "comparatively abundant" from a cave in Roane County, Tennessee. A recent bioinventory of this cave found only two P. tennesseensis in May 2013.

Conservation: Pseudanophthalmus tennesseensis is known from just four localities in a relatively small geographic area. Most populations are reportedly small in size based on collection information. Accordingly, the species is assigned a global NatureServe conservation rank of 'Vulnerable' (G2) but has not yet been assessed under IUCN Red List criteria. Cave beetle populations may be threatened by habitat degradation, pollution, flooding associated with impoundments, and human visitation. At least two localities currently or have received considerable human visitation. With increased human presence in caves comes increased risk to beetle populations because of vandalism, littering, disruption of cave microhabitats, and potential trampling. However, no data exist linking any of these threats with possible population declines. No species-specific management or conservation plans are being conducted for P. tennesseensis at this time. Entrances to all known cave localities are owned by private landowners. The type locality was formerly a small, commercial cave but operations have since ceased. A potential new locality was discovered during a biological inventory of caves in Knox County in May 2013.

Select References

Barr TC. 1965. The Pseudanophthalmus of the Appalachian Valley (Coleoptera: Carabidae). American Midland Naturalist 73: 41-72.

Barr TC. 1981. Pseudanophthalmus from Appalachian caves (Coleoptera: Carabidae): the engelardti complex. Brimleyana 5: 37-94.

Barr TC. 2004. A classification and checklist of the genus Pseudanophthalmus Jeannel (Coleoptera: Carbidae: Trechinae). Virginia Museum of Natural History Special Publication 11. 52 pp.

Valentine JM. 1937. Anophthalmid beetles (fam. Carabidae) from Tennessee caves. Journal of the Elisha Mitchell Science Society 53: 93-100.