Tuesday, November 19, 2013

Species Profile: Appalachian Cave Harvestman (Tolus appalachius)

Adult from Grundy Co., TN (Photo by Dante Fenolio)
Appalachian Cave Harvestman
Tolus appalachius
Goodnight and Goodnight, 1942

Conservation status: IUCN Red List - Not Assessed; NatureServe - G3G4 (Alabama: SNR; Tennessee: S3). This species is tracked by the state of Tennessee.

Description: Tolus appalachius is one of three described species of troglobiotic harvestmen in the Interior Plateau. Harvestmen are arachnid cousins of spiders but they lack silk organs and venom glands in their chelicerae (mouthparts). In addition, the cephalothorax and abdomen are fused in harvestmen but are distinct in spiders. Tolus appalachius is a small cave-dwelling relative of the "daddy longlegs" you might find in your basement or shed. It lacks eyes, is depigmented and has exceptionally long legs relative to the size of the body. The body is oval in shape and 2-4 mm long in adults, with legs up to 20 mm in length. The legs and chelicerae appear white in color, while the body is often a light creamy orange-white. The body of younger instars appears completely white.

Distribution: This harvestman occurs in caves primarily along the Western Escarpment of the Cumberland Plateau from southern Fentress and Overton counties, Tennessee, south-southwestward into Jackson County, Alabama. Tolus has been reported from about 20 caves but likely occurs in many other cave systems.

Habitat: Tolus is primarily reported from the dark zone of caves where it often found in moist microhabitats, such as on or underneath decaying wood, rocks along the stream margins or within crevices in cave walls, particularly near the junction of mud banks and solid rock. It is seldom found in drier cave passages.

Adult from Grundy Co., TN (Photo by Matthew L. Niemiller)
Natural History: Very little is known about the natural history of cave-dwelling harvestmen, including T. appalachius. Presumably, this species has an omnivorous diet like other harvestmen, feeding on smaller invertebrates and scavenging on fungi, decaying vegetation and animal matter. Nothing is known regarding reproduction in this species. Small instars have been found throughout the year, suggesting that reproduction may be not be seasonal. Like other harvestmen, Tolus clean their legs after feeding by running each leg through their chelicerae. When disturbed, Tolus will often play dead tucking their long legs into their body. Unlike several species of surface-dwelling harvestmen, cave-dwelling T. appalachius are not known to aggregate in large numbers of individuals.

Conservation: Most populations are reportedly small based on collection data. I have seen as many as 18 individuals during a cave bioinventory. This species is assigned a global NatureServe conservation rank of 'Vulnerable' to 'Apparently Secure' (G3G4), but it has not yet been assessed under IUCN Red List criteria. Like other cave terrestrial invertebrates, Tolus populations may be threatened by habitat degradation, pollution, flooding associated with impoundments and significant human visitation. No species-specific management or conservation plans are being conducted at this time. Entrances to almost all known cave localities are owned by private landowners.

Notes: A population in Overton County, Tennessee, may be distinct and warrant recognition as a new species. Hedin and Thomas (2010) recently investigated convergent morphological evolution in cave harvestmen, including Tolus appalachius.

Select References

Goodnight CJ, Goodnight ML. 1942. New Phalangodidae (Phalangida) from the United States. American Museum Novitates 1188: 1-18.

Goodnight CJ, Goodnight ML. 1960. Speciation among cave opilionids of the United States. American Midland Naturalist 64: 34-38.

Hedin M, Thomas SM. 2010. Molecular systematics of eastern North American Phalangodidae (Arachnida: Opiliones: Laniatores), demonstrating convergent morphological evolution in caves. Molecular Phylogenetics and Evolution 54: 107-121.

Lewis JJ. 2005. Bioinventory of caves of the Cumberland Escarpment Area of Tennessee. Final Report to Tennessee Wildlife Resources Agency & The Nature Conservancy of Tennessee. Lewis & Associates LLC, 158 pp.

Niemiller ML, Zigler KS, Fenolio DB. 2013. Cave life of TAG: A guide to commonly encountered species in Tennessee, Alabama and Georgia. Biology Section of the National Speleological Society, Huntsville, Alabama. 46 pp.

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