Research Article |
Corresponding author: Matthew L. Niemiller ( cavemander17@gmail.com ) Academic editor: Eike Neubert
© 2019 Nicholas S. Gladstone, Kathryn E. Perez, Evelyn B. Pieper, Evin T. Carter, Katherine E. Dooley, Nathaniel F. Shoobs, Annette S. Engel, Matthew L. Niemiller.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Gladstone NS, Perez KE, Pieper EB, Carter ET, Dooley KE, Shoobs NF, Engel AS, Niemiller ML (2019) A new species of stygobitic snail in the genus Antrorbis Hershler & Thompson, 1990 (Gastropoda, Cochliopidae) from the Appalachian Valley and Ridge of eastern Tennessee, USA. ZooKeys 898: 103-120. https://doi.org/10.3897/zookeys.898.46917
|
A new species of cave snail (Littorinimorpha: Cochliopidae) in the genus Antrorbis is described from the dark zone of two caves in the Appalachian Valley and Ridge province in eastern Tennessee, United States. The Tennessee Cavesnail, Antrorbis tennesseensis Perez, Shoobs, Gladstone, & Niemiller, sp. nov. is distinguished from its only known congener, Antrorbis breweri, by the absence of raised tubercles on its finely spirally striate protoconch, and its unique radular formula. Moreover, A. tennesseensis is genetically distinct from A. breweri based on substantial divergence at the mitochondrial CO1 locus. This is the first cavesnail to be described from the Appalachian Valley and Ridge (AVR) physiographic province in the state of Tennessee, which previously represented a substantial gap in the distribution of stygobitic (i.e., aquatic, subterranean-obligate) gastropods.
Antrorbis, cavesnail, Cochliopidae, stygofauna, systematics
Among the hydrobioid snails (i.e., Hydrobiidae s.l.;
Of the North American stygobitic snails, the Lithoglyphidae initially contained the highest species diversity and has been traditionally divided into several groups on the basis of morphology and geographic distribution: 1) Phreatodrobia, Phreatoceras, Balconorbis, Stygopyrgus, and Texapyrgus, endemic to the Edwards-Trinity Aquifer System in south and central Texas; 2) Antrorbis and Holsingeria, found in the Appalachians karst region of the eastern United States; and 3) Pterides from northeastern Mexico (
The Appalachians karst region occurs within the Appalachian Valley and Ridge (AVR) physiographic province that extends from southeastern New York to eastern Tennessee, northwestern Georgia, and northeastern Alabama in the eastern United States. The province is situated between the Blue Ridge Mountains to the east and the Appalachian Plateau (specifically the Cumberland Plateau) to the west. Karst terrain in the AVR has developed in valleys of folded and faulted shale and carbonate rocks between parallel ridges of sandstone strata. The Appalachians karst region harbors the highest stygobitic diversity in North America (
During ongoing cave biological inventory efforts to address the previously identified sampling gaps in the AVR of eastern Tennessee, we discovered three distinct populations of an undescribed stygobitic snail within the Tennessee River watershed of Roane and Knox counties, Tennessee. These snails resembled the Manitou Cavesnail, Antrorbis breweri
Since 2012, the authors have conducted more than 200 biological inventories in caves throughout the AVR in Tennessee and neighboring states (
Distribution of Antrorbis spp. in relation to USGS hydrologic units: regions (HU2, shaded areas), basins (HU6, solid black lines), and subbasins (HU8, solid grey lines; unlabeled in map). Antrorbis breweri occurs within the Upper Coosa subbasin of the South Atlantic-Gulf region, whereas A. tennesseensis and Antrorbis cf. tennesseensis occurs in the Watts Bar Lake and Lower Clinch subbasins within the Upper Tennessee basin (Tennessee region), respectively.
Cave name | TCS no. | County | Visitation dates | Personnel | Lithology | Cave description | Water depth | Benthic habitat | Watershed |
---|---|---|---|---|---|---|---|---|---|
Cave Creek Cave | TRN5 | Roane | 28 June 2014; 3 May 2018, 3 June 2018, 3 July 2018, 15 December 2018 | 1st trip: MLN, ASE, ETC, CDR Stephen, S Engel, A Paterson, and J Carter; Later trips: NSG and EBP | Ordovician Mascot Dolomite | Ca. 135 m traversable passage with stream, discharging as a spring entrance | 5 cm to 3 m at normal flow | Primarily silt and sand with interspersed gravel and cobbles | The cave stream flows into Cave Creek, which empties directly into Watts Bar Lake on the Tennessee River. |
Pedigo Cave | TKN103 | Knox | 14 July 2018; 27 July 2018; 15 December 2018 | 1st & 3rd trip: NSG and EBP; 2nd trip: MLN and NSG | Cambrian Maynardville Limestone | Ca. 35 m of traversable passage, with stream flow in small room near cave terminus | 2-meter deep pool | Fine silt, sand, and gravel mixed with larger cobble and smooth-faced rocks | The cave is within the Melton Hill Lake watershed of the Clinch River, which flows into Watts Bar Lake and the Tennessee River. |
Eblen Cave | TRN6 | Roane | 24 March 2019 | ETC, NSG, and EBP | Copper Ridge Dolomite | 1,020 m of traversable passage, with 200 m of cave stream | <0.3 m deep | Larger rocks at first ~25 m, with cobble/fine silt/ sand throughout passage | The cave stream flows into Mill Creek on the surface, which is in the Clinch River watershed of the Tennessee River. |
Snails to be dissected for examination of the internal anatomy were collected, relaxed using dissolved menthol in the field, then preserved in 70% ethanol. Shells were partially dissolved in 1:1 water to hydrochloric acid, with remaining shell removed by hand. Following shell removal, tissues were immersed in Bouin’s solution as a staining fluid to enhance contrast of the tissues.
Shells and other hard parts were prepared, examined, and imaged at ANSP by NFS. Measurements in Table
Shell measurements of A. tennesseensis sp. nov. and Antrorbis cf. tennesseensis.
Specimen | Diameter | Height | Minimum Diameter | Whorls |
---|---|---|---|---|
ANSP 476793 (holotype) | 1.75 | 0.77 | 1.40 | 3.15 |
ANSP A477042 (paratopotype) | 1.35 | 0.58 | 1.12 | 3.2 |
ANSP A477042 (paratopotype) | 1.17 | 0.63 | 0.93 | 2.75 |
ANSP A476794 (Pedigo Cave) | 1.00 | x | 0.80 | 2.85 |
ANSP A476794 (Pedigo Cave) | 1.18 | x | 0.97 | 3.2 |
ANSP A476794 (Pedigo Cave) | 1.27 | x | 1.01 | 3.25 |
Specimen photographs for Figs
Shell, opercula, and radula of Antrorbis tennesseensis sp. nov. A, B Holotype, ANSP 476793 C protoconch of Antrorbis cf. tennesseensis, ANSP 476793 D operculum, outer side, ANSP A477042 E operculum, inner side, ANSP 476793 F radula of ANSP 476793 G central teeth, ANSP 476793 H lateral teeth, ANSP 476793 I inner marginal teeth, ANSP 476793 J outer marginal teeth, ANSP 476793 Scale bars: 0.5 mm (A, B); 200 μm (C); 200 μm (D, E); 20 μm (F); 5 μm (G); 5 μm (H); 10 μm (I, J). Photograph credits: NFS.
Genomic DNA was isolated from three specimens from two populations (Cave Creek and Pedigo) each using the Qiagen DNeasy Blood and Tissue Kit following the manufacturer’s protocol. We amplified a 658-bp fragment of the mitochondrial cytochrome oxidase subunit 1 (CO1) locus using primers LC01490 and HC02198 (
We generated a CO1 phylogeny using a maximum likelihood (ML) method in W-IQ-TREE (
We conducted IUCN Red List and NatureServe conservation assessments for Antrorbis tennesseensis (IUCN 2001;
ANSP 476793 (one dry shell in vial, radula, and operculum on SEM stub), stream in Cave Creek Cave (TCS no. TRN5), Roane County, Tennessee, U.S.A.
ANSP A477042 (same lot as holotype, two whole wet specimens, two dissected wet specimens, one operculum on SEM stub). Three specimens (one dry shell on SEM stub, two whole wet specimens) from Eblen Cave (TCS no. TRN6), Roane County, Tennessee, U.S.A. Specimens are currently housed at the University of Alabama in Huntsville.
ANSP A476794 (three whole wet specimens), stream in Pedigo Cave (TCS no. TKN103), Knox County, Tennessee, U.S.A. Tentatively classified as Antrorbis cf. tennesseensis.
A minute, planispiral Antrorbis, which can be readily distinguished from its sole known congener by the absence of raised tubercles on its finely spirally striate protoconch and its unique radular formula.
Average uncorrected pairwise genetic distance at the mitochondrial CO1 locus between A. tennesseensis and A. breweri is 11.7%, with 74.5 ± 2.14 mutations separating the two species. Additionally, average uncorrected pairwise genetic distance at CO1 between the holotype A. tennesseensis and the Pedigo Cave population (Antrorbis cf. tennesseensis) is 9.8%.
Shell (Figs
Operculum (Fig.
Radula (Fig.
Animal soft body is absent of pigment except for scattered clumps of black granules on stomach and digestive gland; intestine with orange, oval fecal pellets extends from terminal end of animal through body whorl. Digestive system anatomy similar to that described for A. breweri, including intestinal coil in anterior pallial roof exhibiting “reversed-S-shape.” Digestive gland extends for ~1 whorl. Penis simple, strap-like, tapers to a blunt distal end, not as sharply tapered as in A. breweri. Neither terminal papillae nor specialized penial glands observed. Testis one mass with no lobes. Seminal vesicle short and uncoiled, attaching at end of testis. Ovary an orangish mass, filling ~less than 25% of one whorl, capsule gland and albumen gland approximately equal in size, both underly and posterior to the intestine, bursa copulatrix pear shaped. Shells of individuals from Cave Creek Cave are somewhat thicker than those from Pedigo Cave and the fecal pellets are larger and more ovate in shape.
The specific epithet tennesseensis is in reference to this species being from the state of Tennessee. It is also a reference to the University of Tennessee in Knoxville, where several of the authors received degrees (MLN, NSG, and ETC) or are faculty (ASE). Suggested common name is Tennessee Cavesnail.
Antrorbis tennesseensis is known only from two caves developed within karst valleys near the confluence of the Clinch and Tennessee rivers and in upper Cambrian to lower Ordovician carbonate rocks of the Knox Group of the AVR of eastern Tennessee (Fig.
Snails are largely found amongst cobble in shallow cave streams in the dark zone. At Cave Creek Cave, several snails could be observed on a single cobble, and Caecidotea spp. and Crangonyx spp. amphipods were found on the same rocks as snails. From Pedigo Cave (Antrorbis cf. tennesseensis), a single small crayfish (Cambarus bartonii) was observed, but no other aquatic species were seen in the cave stream. Several snails were also found in close proximity on the same rock, with up to seven individuals on a single rock. No other fauna was found in Eblen Cave, and no egg masses or other aspects of the reproductive biology of A. tennesseensis have been observed from any of the caves. Although annual physicochemical measurements were not acquired in this study, the parameters measured once from each system (Table
Antrorbis tennesseensis has been observed on the sides and undersurface of larger cobble and flat rocks in shallow water (< 12 cm water depth) of the stream in Cave Creek Cave and more than one meter of water depth in Pedigo Cave (Antrorbis cf. tennesseensis). At Cave Creek Cave, A. tennesseensis has been found only from a small (55 m2) area ca. 40 m from the entrance (Fig.
The resulting CO1 gene topology of the ML phylogeny is shown in Fig.
This species is currently only known from two caves that are within geologically and hydrologically restricted strata. However, the third cave population for Antrorbis cf. tennesseensis was incorporated in these analyses. The NatureServe rank calculated for Antrorbis tennesseensis is Critically Imperiled (G1). For the IUCN Red List assessment, A. tennesseensis was assessed as Endangered (EN) B1a, as the species is known from fewer than five sites and has an EOO <5,000 km2. The AOO was calculated as 12.0 km2 and EOO was 73.3 km2. A maximum of 23 (on 3 June 2018), 54 (on 15 December 2018), and 3 individuals (on 24 March 2019) were observed at Cave Creek, Pedigo, and Eblen Caves, respectively. Mean number of snails observed at Cave Creek Cave and Pedigo Cave (for which multiple surveys were conducted) was 18.4 ± 4.3 and 36 ± 7.8, respectively. Overall, threat impact for this species was calculated as Very High, with the two most outstanding categories of the threat assessment being Human Intrusion and Disturbance and Pollution.
We describe a new species of stygobitic snail, Antrorbis tennesseensis, which is distinguished from its only congener A. breweri by the absence of raised tubercles on the spiral striae on the external protoconch and substantial divergence at the mitochondrial CO1 locus (holotype, Cave Creek Cave). Given the geographic proximity, geological similarity, and identical morphology, we additionally diagnose the Eblen Cave population as a second population of A. tennesseensis. Antrorbis tennesseensis and A. breweri form a modestly supported clade in the ML phylogeny. Individuals from the third population discovered in this region (Pedigo Cave), despite being morphologically similar to A. tennesseensis, form a paraphyletic group with A. tennesseensis in the ML phylogeny. In the ML phylogeny, the Pedigo Cave population shows closer genetic similarity to Holsingeria unthanksensis, another stygobitic snail in the northern AVR that was initially thought to form a clade with Antrorbis due to morphological similarity (
Within the superfamily Truncatelloidea, observing paraphyly and high intraspecific divergence among species within other gastropod families (especially subterranean groups) is common when analyzing mitochondrial genes (
These two Antrorbis species are separated by ca. 250 km and occur in caves developed in different strata and in different major hydrological river basins, as A. tennesseensis is distributed within the Tennessee River watershed, which flows into the Ohio River, and A. breweri is from Manitou Cave in the Coosa River watershed that flows directly into the Gulf of Mexico. However, from the Eocene (55 million years ago) through the mid-Miocene, the ancestral Appalachian River occupied the drainage basins of the Tennessee and Coosa river and flowed through the southern AVR, across Alabama, and emptied into Mobile Bay at the Gulf of Mexico (
Based on the modern distribution of Antrorbis, the common ancestor for the two currently known species must pre-date the late Pliocene emergence of the Tennessee-Coosa drainage divide. Similar timing for the isolation of distinct genetic lineages of the Southern Cavefish, Typhlichthys subterraneus, in the Tennessee and Coosa river drainages has also been proposed (
Original designation of the stygobitic genera Antrorbis, Holsingeria, and Phreatodrobia to Lithoglyphidae was based on soft tissue anatomy (
Freshwater snails have experienced significant declines globally, with nearly 93% of all recorded extinctions being narrow endemic species (
This study was supported by a grant from the Cave Conservancy Foundation (to ASE and MLN) and the U.S. Fish & Wildlife Service (grant no. F17AC00939 to MLN). We thank S Engel, CDR Stephen, A Paterson, J Carter, ML McKinney, and V Frazier for assisting with cave surveys. We thank D Delicado for providing sequence data for Antrorbis breweri, L Bailey for assisting with molecular aspects of this study, FE Anderson for helpful advice related to the phylogenetic analyses, and T Wilke for a thorough review of the manuscript. Collection of specimens was permitted by scientific collection permits no. 1605 and 1385 issued to MLN, ASE, ETC, and NSG.
Table S1. GenBank accession numbers for all taxa utilized for the phylogenetic analysis
Data type: species data