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Popenaias popeii

(I. Lea, 1857)

Texas Hornshell

G1Critically Imperiled Found in 4 roadless areas NatureServe Explorer →
G1Critically ImperiledGlobal Rank
Critically endangeredIUCN
Very high - highThreat Impact
Texas Hornshell (Popenaias popeii). Photo by U.S. Fish & Wildlife Service, Public Domain (U.S. Government Work), via ECOS.
U.S. Fish & Wildlife Service, https://www.usa.gov/government-works
Identity
Unique IDELEMENT_GLOBAL.2.121272
Element CodeIMBIV36010
Record TypeSPECIES
ClassificationSpecies
Classification StatusStandard
Name CategoryInvertebrate Animal
IUCNCritically endangered
Endemicoccurs (regularly, as a native taxon) in multiple nations
KingdomAnimalia
PhylumMollusca
ClassBivalvia
OrderUnionoida
FamilyUnionidae
GenusPopenaias
Synonyms
Popenaias popei(I. Lea, 1857)
Concept Reference
Turgeon, D. D., J. F. Quinn, Jr., A. E. Bogan, E. V. Coan, F. G. Hochberg, W. G. Lyons, P. M. Mikkelsen, R. J. Neves, C. F. E. Roper, G. Rosenberg, B. Roth, A. Scheltema, F. G. Thompson, M. Vecchione, and J. D. Williams. 1998. Common and scientific names of aquatic invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society Special Publication 26, Bethesda, Maryland. 526 pp.
Taxonomic Comments
Heard and Guckert (1970) used Popenaias to represent a group of Elliptio-like species with a reproductive cycle which was aberrant to what was considered typical for the short-termed brooding species (summer-spawners or so-called tachytictic). Heard (1979) has abandoned this use for Popenaias and returned buckleyi to Elliptio. Based on the generic description of Haas (1969) [Frierson (1927), established Popenaias, with popei the type by virtual taxonomy, without description - Haas (1969), wrote the first description for several of Frierson's superspecific taxa], buckleyi would not be identifiable with Popenaias. As Haas (1969) noted by his use of Popenaias as a subgenus, it may be closer to Nephronaias. This needs to be resolved. The species spelling "popeii" follows the spelling in the orginal description and "popei" is a misspelling (Turgeon et al., 1998). Also, Turgeon et al. (1998) mistakenly spelled the genus "Popenais" in the species list but used the correct "Popenaias" in the appendix. Smith et al. (2003) found the species to be an asynchronous short-term brooder with extended oviposition period, thereby causing confusion in placement of subfamily. The protracted breeding season in New Mexico near the northern limit of distribution might indicate a geographic affinity to Mexico or Central America rather than a strictly phylogenetic relationship. Chapman et al. (2008), in a study of evolutionary relationships of lampsilines, concluded that the Lampsilini is monophyletic and Popenaias is a sister taxon; and they include Amblema and Plectomerus in a clade with the traditional lampsiline taxa but reject the hypothesis of Campbell et al. (2005) that Plectomerus and Toxolasma are sister genera. Further, Chapman et al. (2008) suggest the tribe Amblemini for the lampsiline/Popenaias/Plectomerus/Amblema clade because usage of Amblemini Rafinesque, 1820, in a tribal context has priority over Lampsilini Ihering, 1901.
Conservation Status
Review Date2010-02-22
Change Date1998-05-30
Edition Date2007-02-26
Edition AuthorsCordeiro, J. (2007); Howells, R. G. (1998)
Threat ImpactVery high - high
Range Extent250-1000 square km (about 100-400 square miles)
Number of Occurrences1 - 5
Rank Reasons
The only confirmed living specimens known at this time occur in the Black River drainage of New Mexico and a Webb County portion of the Rio Grande in Texas. Both are very much reduced from historical range but appear stable. Several additional recently dead shells in the Rio Grande of Texas downstream of Big Bend suggest some stragglers probably still persist there as well. None have been reported from Mexico in recent decades, and although historic sites were recently documented for several drainages in Mexico and southern Texas, only historical dead shells are known from them indicating historical extirpation. The high conservation priority ranking is suggested; however, although Texas Parks and Wildlife Department has made over 100 collections in the Rio Grande drainage since January 1992 and is actively in the field at this time, many areas remain to be examined.
Range Extent Comments
Historically this species occurred in the lower Pecos River of New Mexico, downstream throughout the Lower Rio Grande River system of (Brownsville) Texas and major tributaries in Texas, southward to the Río Pánuco drainage of San Luis Potosí, México (USFWS, 2003). Upstream records are documented as far as the North Spring River near Roswell, Chaves County, New Mexico (Cockerell 1902), in the Pecos River in Ward County, Texas (Singley, 1893), the Rio Grande River to sites just downstream of Big Bend, Brewster Co., Texas, and in several Mexican tributaries of the lower Rio Grande (Johnson, 1999); and as far downstream as Brownsville, Cameron County, Texas (Howells et al., 1996; Johnson, 1999). Johnson (1999) also reports historic museum collection data from the Rio Sota de Marina drainage, Tamaulipas, Mexico; Rio Sabinas, Rio Guayalego, and Rio Panuco drainages (all Rio Tamesi system), Tamaulipas and San Luis Potosi, Mexico; and Rio Cazones drainage, Vera Cruz, Mexico. Historical collections in Mexico are from the Rio Salado (type locality), and was reported from two disjunct drainages, ríos Pánuco and Valles, San Luis Potosí, some 500 miles south of the Rio Grande Basin (these also require confirmation) (USFWS, 2003). Strenth et al. (2004) document additional range extensions (based on dead shells only with no live specimens found) from west-central Texas and northern Coahuila, Mexico (Rio Sabinas drainage). Weathered shells from the Llano River in Texas (1972) and South Concho River in Texas (1991) (both Colorado River drainage) could suggest a disjunct population may have occurred in the Colorado River drainage of Central Texas, but several recent visits to the site either found no specimens or only old weathered shells (Strenth et al., 2004). A population at Fort Clark Springs in Kinney Co., Texas is also likely extirpated (Howells et al., 1996).
Occurrences Comments
In over 20 years, this species has been known only from a single recently dead specimen found in the Rio Grande, Brewester County, Texas, collected in January 1992 (Howells et al. 1997). Recently, 5 shells (three recently dead) were found in the Big Bend reach of the Rio Grande in Brewster and Terrell counties, Texas, in March 1998 (Texas Parks and Wildlife Department; Unpublished Data; Howells and Ansley, 1999); and 35 living specimens in the Black River, New Mexico, 1997-1998 (Lang et al., 1998). Since 1996, a live population of Texas hornshell has been confirmed in the Black River, New Mexico, from Black River Village downstream to the U.S. Highway 285 bridge crossing (Lang, 2001). Although recently dead shells were found in the Rio Grande between Big Bend and the mouth of the Pecos River in 1997-2000 (Strenth et al., 2004), no living specimens were found in Texas and Mexico (Howells, 2000). Subsequent surveys in 2003 revealed nearly 30 living specimens in the Rio Grande in the Webb County area of Texas (Howells, 2004). None have been found in Mexican tributaries of the Rio Grande in recent years and none are known to survive in any Texas tributaries. One shell was collected in 1972 from the Llano River (Colorado River drainage), Llano County, Texas (OSUM collections), but subsequent surveys there in 1992, 1997, 1999, 2000, and 2001 revealed no evidence of the species there (Strenth et al., 2004; Howells et al., 1997). Another single valve was collected in 1991 from the South Concho River (Colorado River drainage), Tom Green County, Texas, and these two collections could suggest a disjunct population may have occurred in the Colorado River drainage of Central Texas, as well (Strenth et al., 2004). Dead shell material was recently (2001 and 2002) found from the dry river bed of the Rio Sabinas drainage in Coahuila, Mexico (Strenth et al., 2004). Strenth et al. (2004) also revisited the Devil's River drainage at Amistad Reservoir in Val Verde Co., Texas; as well as the Rio Salado in Tamaulipas, Mexico; and Anahuac River drainage (Rio Salado) in Nuevo Leon, Mexico; but only old, weathered shell material was found. Overall, there are currently only two isolated populations in the U.S.: the Black River, Eddy Co., New Mexico (Lang, 2001) and Rio Grande near Laredo, Webb Co., Texas (Strenth et al., 2004) (see Carman, 2007).
Threat Impact Comments
The decline in freshwater mussel populations in New Mexico and Texas can be directly attributable to human actions that modify physical conditions in streams. Direct changes in stream environments occur from impoundments and diversions for water storage, agricultural irrigation and flood control. The release of pollutants into streams from point and non-point sources have immediate impacts on water quality conditions and may make environments unsuitable for habitation by mussels. The channel morphology and flow regimes of the Rio Grande and Pecos River have been severely modified over the past century for flood control, water supply, and border maintenance, through channelization, levee construction, destruction of native riparian vegetation, dredging, and water diversion. Excessive human consumption of river water for agricultural irrigation and municipal use have also contributed to the degraded state of the aquatic ecosystems that no longer support populations. Oil and gas industry operations (exploration, transfer, storage, and refining) are ongoing in the Black River sub-basin and lower Pecos River valley of New Mexico and Texas. Cumulative impacts of insensitive land-use practices (e.g., removal of native vegetation, prolonged over-grazing, non-point source runoff pollution [sediments, toxic chemicals, hydrocarbons], etc.) within the watershed of the Black River have increased erosion and sedimentation in the river (USFWS, 2003; Carman, 2007).

Other (much less serious and immediate) threats include: overcollecting (very minor); disease and predation (either unknown or minor); inadequacy of existing regulatory mechanisms (New Mexico lists as endangered since 1983, Texas does not recognize any mussels as threatened or endangered and only requires a fishing license for collection and a special permit for commercial collections; 28 no-harvest mussel sanctuaries in Texas but none occur within the Rio Grande or Pecos river basins) (USFWS, 2003; Carman, 2007).

The only known surviving specimens in the Rio Grande are in areas experiencing major development and modification, separated by saline waters of the Pecos River that prevent interbreeding, and subject to siltation and drought-related dewatering (Howells, 2004).
Ecology & Habitat

Description

Shell elongate and subtrapazoidal; compressed; beaks low but sharp; hinge tooth compressed; beak cavity shallow; externally olive-green to dark brown; nacre white, occasionally somewhat iridescent purple posteriorly (Howells et al. 1996).

Habitat

Typically this species occurs at the head and terminus of shallow, narrow run habitat over travertine bedrock where small-grained substrata (clays, silts, sands, and gravel) collect in undercut riverbanks, crevices, shelves, and at the base of large boulders (USFWS, 2003). It occurs in sand and sand-cobble accumulated in travertine bedrock cracks and at the base of large boulders at depths of 0.25-1.38 m and at flow rates of 0.02-0.75 m/sec; often in colonies; often at the head or lower end of travertine runs (Lang et al. 1998).

Reproduction

The Texas hornshell breeds over an extended period of time from late spring (April) through August, which implies that females and males are not tied to a restricted period of synchronous reproduction; rather an opportunistic reproductive strategy seems to prevail. Females either sequentially or alternately release ova into the gills while males are releasing sperm continuously over several months; such reproductive asynchronicity is not common in unionids. Smith et al. (2003) found this species to be an asynchronous breeder with short-term brooding and an extended period of potential oviposition. Although spawning can extend over 8 months or more, field observations suggest that only 4 to 6 weeks actually might be required for an individual brood to be produced from oviposition to release of glochidia. The ectobranchous marsupia exhibit minimal specialization but differ from non-marsupial demibranchs by significantly more and modified septa. Inner demibranchs probably funciton in facultative capacity as an overflow reservoir for larvae unable to fit into full marsupia of the specialized outer demibranchs due to occasional elevated fecundity of a particular female. Glochidia of Texas hornshell metamorphosed into juvenile mussels within 6-10 days post-inoculation on 25 of 28 species of fish representing 10 families and 6 orders, including several non-native fish species (Gordon et al., In Review, cited in Carman, 2007). Thes include longnose gar (Lepistosteus osseus), Mexican tetra (Astyanaz mexicanus), red shiner (Cyprinella lutrensis), common carp (Cyprinus carpio), roundnose minnow (Dionda episcopa), plains minnow (Hybognathus placitus), speckled chub (Macrhybopsis aestivalis), Rio Grande shiner (Notropis jemezanus), fathead minnow (Pimephales promelas), central stoneroller (Campostoma anomalum), river carpsucker (Carpiodes carpio), grey redhorse (Moxostoma congestum), yellow bullhead (Ameiurus natalis), channel catfish (Ictalurus punctatus), plains killifish (Fundulus zebrinus), rainwater killifish (Lucania parva), western mosquitofish (Gambusia affinis), Rio Grande cichlid (Herichthys cyanoguttatum), green sunfish (Lepomis cyanellus), bluegill (Lepomis macrochirus), longear sunfish (Lepomis megalotis), largemouth bass (Micropterus salmoides), and greenthroat darter (Etheostoma lepidum). These may not translate, however, into conclusive hosts in the wild. The New Mexico Department of Game and Fish is investigating ecological hosts and preliminary results indicate encysted glochidia have been confirmed in the Black River on gizzard shad (Dorosoma cepedianum), red shiner (Cyprinella lutrensis), river carpsucker (Carpiodes carpio), blue sucker (Cycleptus elongates), grey redhorse (Moxostoma congestum), channel catfish (Ictalurus punctatus), and longear sunfish (Lepomis megalotis) (in Carman, 2007). The presence of principally ectobranchous brooding location in the genus suggest Popenaias has greater propinquity to the "traditional" lampsiline genera than to Amblema or Plectomerus (Chapman et al., 2008). Gametogenesis (production of eggs and sperm) occurs from January through September in the Black River (Lang, 2001). Females are gravid from late April to early August.
Other Nations (1)
United StatesN1
ProvinceRankNative
New MexicoS1Yes
TexasS2Yes
Threat Assessments
ThreatScopeSeverityTiming
1 - Residential & commercial developmentLarge - restrictedSerious - moderateHigh (continuing)
1.1 - Housing & urban areasLarge - restrictedSerious - moderateHigh (continuing)
2 - Agriculture & aquacultureLarge - restrictedSerious - moderateHigh (continuing)
2.1 - Annual & perennial non-timber cropsLarge - smallSerious - slightHigh (continuing)
2.2 - Wood & pulp plantationsRestricted - smallSerious - moderateHigh (continuing)
2.3 - Livestock farming & ranchingLarge - restrictedSerious - moderateHigh (continuing)
3 - Energy production & miningLarge - restrictedExtreme - moderateHigh (continuing)
3.1 - Oil & gas drillingLarge - restrictedExtreme - moderateHigh (continuing)
3.2 - Mining & quarryingLarge - restrictedExtreme - moderateHigh (continuing)
4 - Transportation & service corridorsSmall (1-10%)Moderate - slightHigh - moderate
4.1 - Roads & railroadsRestricted (11-30%)Moderate - slightHigh - moderate
5 - Biological resource useSmall (1-10%)Slight or 1-10% pop. declineInsignificant/negligible or past
5.4 - Fishing & harvesting aquatic resourcesSmall (1-10%)Slight or 1-10% pop. declineInsignificant/negligible or past
7 - Natural system modificationsPervasive - largeExtreme - moderateHigh (continuing)
7.2 - Dams & water management/usePervasive - largeExtreme - moderateHigh (continuing)
8 - Invasive & other problematic species, genes & diseasesSmall (1-10%)Slight or 1-10% pop. declineLow (long-term)
8.2 - Problematic native species/diseasesSmall (1-10%)Slight or 1-10% pop. declineLow (long-term)
9 - PollutionLarge - restricted—High (continuing)
9.2 - Industrial & military effluentsRestricted - smallExtreme - moderateHigh (continuing)
9.3 - Agricultural & forestry effluentsLarge - restrictedSerious - slightHigh (continuing)
11 - Climate change & severe weatherPervasive - largeUnknownModerate - low
11.2 - DroughtsPervasive - largeUnknownModerate - low

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Roadless Areas (4)
New Mexico (4)
AreaForestAcres
Last Chance CanyonLincoln National Forest8,934
Little Dog And Pup CanyonsLincoln National Forest25,412
North Rocky CanyonLincoln National Forest8,068
South Guadalupe MountainsLincoln National Forest20,930
References (38)
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