Cottus specus: Missouri's new species of cavefish

The Grotto Sculpin, Cottus specus (from Adams et al. 2013).

Ginny Adams and colleagues describe a new troglomorphic species of sculpin (family Cottidae) endemic to just five cave systems of the Central Perryville and Mystery-Rimstone karst in Perry County, Missouri in a recent article in Zootaxa (Adams et al. 2013). This new species, the Grotto Sculpin (Cottus specus Adams and Burr), was previously recognized as several unique troglomorphic populations of the widespread Banded Sculpin (C. carolinae) (Burr et al. 2001). Currently, C. specus is only known from cave systems and their spring resurgences in tributaries of the Bois Brule River drainage, including Cinque Hommes Creek and Blue Spring. The type-locality is Mystery Cave in Perry County, Missouri.

The Grotto Sculpin can be distinguished from other members of the genus Cottus, including the closely-related C. carolinae, by reduced eyes (typically 1-5% of standard length versus 5-9% standard length) and an increase in cephalic lateralis pore size. The overall eye volume, lens and dermal cornea of the eye are also reduced in C. specus compared to C. carolinae. Pigmentation is highly variable with some individuals of C. specus lacking all apparent pigmentation in the fins and on the body, while others possess the general banding pattern of dorsal saddles typically found in C. carolinae. Cottus specus is also distinct genetically from C. carolinae based on analyses of the mitochondrial control region.

Cottus specus is a species of high conservation concern. The known distribution of this cavefish is comprised of just five populations that are threatened by groundwater pollution in the form of bioaccumulative organic contaminants. Two of the five populations have experienced mass mortalities of unknown origin in the past 15 years. In addition, C. specus is generally found at much lower densities than C. carolinae, which may limit the ability of populations to recover from acute anthropogenic disturbances. Consequently, Adams et al. advocate the formal protection of C. specus at both the state state and federal level.

Although not directly discussed in the paper, C. specus likely represents a cave form that has only recently colonized subterranean waters based on less elaborate troglomorphic features compared to other cavefish species in North America and levels of molecular sequence divergence between C. specus and other nearby C. carolinae populations. My interpretation is that C. specus likely colonized caves only recently sometime within the last million years, perhaps caused by or associated with climatic fluctuations during the Pleistocene.

The cave and karst regions of Missouri are now home to three species of cavefishes, including Cottus specus. The other two species are the federally threatened Ozark Cavefish (Troglichthys rosae) and  the Salem Plateau Cavefish (Typhlichthys eigenmanni). Typhlichthys eigenmanni was recently resurrected from T. subterraneus by Niemiller et al. (2012). Troglomorphic populations of sculpins (Cottus sp.) have been reported from Pennsylvania and West Virginia as well (Williams & Howell 1979; Espinasa & Jeffery 2003).

References

Adams GL, Burr BM, Day JL, Starkey DE (2013) Cottus specus, a new troglomorphic species of sculpin (Cottidae) from southeastern Missouri. Zootaxa 3609: 484-494.
 
Burr BM, Adams GL, Krejca JK, Paul RJ, Warren Jr ML (2001) Troglomorphic sculpins of the Cottus carolinae species group in Perry County, Missouri: distribution, external morphology, and conservation status. Environmental Biology of Fishes 62: 279-296.

Espinasa L, Jeffery WR (2003) A troglomorphic sculpin (Pisces: Cottidae) population: geography, morphology and conservation status. Journal of Cave and Karst Studies 65: 93-100.

Niemiller ML, Near TJ, Fitzpatrick BM (2012) Delimiting species using multilocus data: diagnosing cryptic diversity in the southern cavefish Typhlichthys subterraneus (Teleostei: Amblyopsidae). Evolution 66: 846-866.

Williams JD, Howell WM (1979) An albino sculpin from a cave in the New River drainage of West Virginia (Pisces: Cottidae). Brimleyana 1: 141-146.