Quadrula houstonensis - (I. Lea, 1859)
Smooth Pimpleback
Taxonomic Status: Accepted
Related ITIS Name(s): Quadrula houstonensis (I. Lea, 1859) (TSN 80078)
Unique Identifier: ELEMENT_GLOBAL.2.117311
Element Code: IMBIV39060
Informal Taxonomy: Animals, Invertebrates - Mollusks - Freshwater Mussels
 
Kingdom Phylum Class Order Family Genus
Animalia Mollusca Bivalvia Unionoida Unionidae Quadrula
Genus Size: D - Medium to large genus (21+ species)
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Concept Reference
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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.
Concept Reference Code: B98TUR01EHUS
Name Used in Concept Reference: Quadrula houstonensis
Taxonomic Comments: This species has been confused with Quadrula pustulosa, Quadrula mortoni, and Quadrula aurea, with some weathered or subfossil shells difficult to differentiate from Quadrula petrina (Howells et al., 1996). The term "houstonensis" may have sometimes been used as a "catch-all" for generally unusual pimplebacks in Texas. Preliminary electrophoretic analysis by Texas Parks and Wildlife Department (Unpublished Data) found that while all of the pimpleback quadrulids in Texas are genetically very polymorphic,Quadrula houstonensis specimens from the Brazos River drainage were distinct from Q. aurea from the Nueces River, and Q. mortoni from several eastern Texas locations. Pimplebacks from the upper Trinity River drainage remain problematic and have been variously assigned to houstonensis, pustulosa, and mortoni. One reservoir population from the upper Trinity drainage examined electrophoretically by Texas Parks and Wildlife Department was found to unique alleles at several genetic loci which differed from other pimpleback species comparatively examined, thus leaving their exact taxonomic status unresolved. Pimplebacks taken in the lower Trinity River and lower San Jacinto River in recent years appear to be Q. mortoni (Howells et al., 1996; 1997). In a study of molecular phylogeny of the genus Quadrula, sequence data from the ND1 gene portion did not resolve relationships among populations of Quadrula aurea and Quadrula pustulosa and additional data will be necessary to test the validity of these taxonomic entities (Serb et al., 2003).
Conservation Status
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NatureServe Status

Global Status: G2
Global Status Last Reviewed: 20Jul2006
Global Status Last Changed: 30May1998
Rounded Global Status: G2 - Imperiled
Reasons: Although found over the past decade at several sites in at least two, perhaps three, drainage basins, no large or stable populations are known and the effects of declines from recent habitat loss continues to affect the species. Following a rapid loss of habitat and decline in numbers in 1978, surviving populations have continued to experience environmental stresses which have further reduced their numbers.
Nation: United States
National Status: N2 (30May1998)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Texas (S1S2)

Other Statuses

U.S. Endangered Species Act (USESA): C: Candidate (06Oct2011)
Comments on USESA: In a 12-month petition finding, USFWS (October 6, 2011) found listing this species to be warranted but precluded by higher priority actions. It has been added to the candidate species list. As of November 22, 2013, there is no change in status and listing is still warranted-but-precluded by higher priority actions (USFWS 2013).
U.S. Fish & Wildlife Service Lead Region: R2 - Southwest
IUCN Red List Category: NT - Near threatened
American Fisheries Society Status: Threatened (01Jan1993)

NatureServe Global Conservation Status Factors

Range Extent: 1000-5000 square km (about 400-2000 square miles)
Range Extent Comments: Limited abundance, patchy distribution, and recent losses associated with pollution, flooding, or droughts confound defining exact distribution. This species is currently known to survive in the central Colorado and Brazos River drainages in Texas (Howells et al., 1996). Small populations in the upper Trinity River system may or may not be this species, but pimplebacks now found in the lower Trinity and San Jacinto rivers are almost certainly another species. Recently a live individual was discovered in the Navasota River, Texas (Reimer and Linam, 2005).

Area of Occupancy: 501-12,500 4-km2 grid cells
Area of Occupancy Comments:  

Number of Occurrences: 6 - 20
Number of Occurrences Comments: Following scouring floods in 1978 throughout its range in Central Texas, surviving populations appear limited in number (Howells et al., 1997). Since that time living or very recently dead specimens have been documented at several sites on the central Brazos River drainage, several sites on the Little Brazos River, one site on the San Saba River, several locations on the Leon River, and in one reservoir in the central Colorado River drainage (Howells et al., 1997). However, a chemical dump on the Little Brazos River in 1993 eliminated much of the unionid population there (although living specimens were reported as recently as 2006), drought conditions in the Leon River in the 1980s caused extensive mussel losses there as well, and no living or recently dead specimens have been found in the San Saba River in about 10 years (Howells, 1994; 1995; 1996a; 1996b; 1997). A single live individual was recently found in the Navasota River in Texas (Reimer and Linam, 2005).

Population Size: 2500 - 10,000 individuals
Population Size Comments: This species cannot be considered abundant at any of the sites where living specimens have been documented within the past 25 years.

Number of Occurrences with Good Viability/Integrity: None (zero)
Viability/Integrity Comments: This species cannot be considered abundant at any of the sites where living specimens have been documented within the past 25 years.

Overall Threat Impact Comments: Environmental decline associated with increased human development and associated poor land- and water-management practices continue to suggest concern for the future security of this species.

Short-term Trend: Decline of 10-30%
Short-term Trend Comments: Following a rapid loss of habitat and decline in numbers in 1978, surviving populations have continued to experience environmental stresses which have further reduced their numbers.

Long-term Trend: Decline of <30% to increase of 25%

Intrinsic Vulnerability: Moderately vulnerable
Intrinsic Vulnerability Comments: Although there is no specific recognition of particular traits related to fragility of this species, it has declined even in areas where other related species like Quadrula apiculata and Quadrula petrina have endured, thus suggesting as-yet undefined issues.

Environmental Specificity: Moderate to broad.
Environmental Specificity Comments: This species occurs in small- to moderate-size streams and rivers as well as moderate-size reservoirs; found on mud, sand, and gravel in water as shallow as 3-4 cm; tolerates very slow to moderate flow rates (Howells et al., 1996). It appears not to tolerate dramatic water level fluctuations, scoured bedrock substrates, or shifting sand bottoms (Texas Parks and Wildlife Department, unpublished data).

Other NatureServe Conservation Status Information

Inventory Needs: Many sites within the historic range of this species remain to be surveyed or should be resurveyed in greater detail. Status of some populations like those in the Little Brazos River which were reduced by pollution or one in the central Colorado River which experienced drawdown dewatering need to be reexamined.

Distribution
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Global Range: (1000-5000 square km (about 400-2000 square miles)) Limited abundance, patchy distribution, and recent losses associated with pollution, flooding, or droughts confound defining exact distribution. This species is currently known to survive in the central Colorado and Brazos River drainages in Texas (Howells et al., 1996). Small populations in the upper Trinity River system may or may not be this species, but pimplebacks now found in the lower Trinity and San Jacinto rivers are almost certainly another species. Recently a live individual was discovered in the Navasota River, Texas (Reimer and Linam, 2005).

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
Endemism: endemic to a single state or province

U.S. & Canada State/Province Distribution
United States TX

Range Map
No map available.


U.S. Distribution by County Help
State County Name (FIPS Code)
TX Austin (48015), Bastrop (48021), Bell (48027), Brazos (48041), Burleson (48051), Burnet (48053), Colorado (48089), Comanche (48093), Coryell (48099), Falls (48145), Fort Bend (48157), Grimes (48185), Hamilton (48193), Lampasas (48281), Leon (48289), Llano (48299), McLennan (48309), Milam (48331), Mills (48333), Robertson (48395), San Saba (48411), Waller (48473), Washington (48477), Wharton (48481)
* Extirpated/possibly extirpated
U.S. Distribution by Watershed Help
Watershed Region Help Watershed Name (Watershed Code)
12 Middle Brazos-Millers (12060101), Lower Clear Fork Brazos (12060104), Middle Brazos-Palo Pinto (12060201), Middle Brazos-Lake Whitney (12060202)+, Bosque (12060203)+, North Bosque (12060204)+, Lower Brazos-Little Brazos (12070101)+, Yegua (12070102)+, Navasota (12070103)+, Lower Brazos (12070104)+, Leon (12070201)+, Cowhouse (12070202), Lampasas (12070203)+, Little (12070204)+, San Gabriel (12070205)+, Middle Colorado-Elm (12090101), Middle Colorado (12090106)+, Pecan Bayou (12090107), San Saba (12090109)+, Buchanan-Lyndon B (12090201)+, Llano (12090204)*, Austin-Travis Lakes (12090205)+, Pedernales (12090206)*, Lower Colorado-Cummins (12090301)+, Lower Colorado (12090302)+
+ Natural heritage record(s) exist for this watershed
* Extirpated/possibly extirpated
U.S. Distribution by Watershed (based on multiple information sources) Help
Ecology & Life History
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Basic Description: A freshwater mussel with a dark brown to black colored shell.
General Description: Shells are subquadrate to nearly round; to about 65 mm shell length; slightly to moderately inflated; solid; beaks elevated well above hinge line; disk typically unsculptured and smooth, but occasionally with few to many pustules; tan to dark brown or black externally; white internally (Howells et al. 1996).
Reproduction Comments: Glochidial hosts are unknown.
Habitat Type: Freshwater
Non-Migrant: N
Locally Migrant: N
Long Distance Migrant: N
Riverine Habitat(s): MEDIUM RIVER, Pool
Lacustrine Habitat(s): Shallow water
Special Habitat Factors: Benthic
Habitat Comments: This species occurs in small- to moderate-size streams and rivers as well as moderate-size reservoirs; found on mud, sand, and gravel in water as shallow as 3-4 cm; tolerates very slow to moderate flow rates (Howells et al., 1996). It appears not to tolerate dramatic water level fluctuations, scoured bedrock substrates, or shifting sand bottoms (Texas Parks and Wildlife Department, unpublished data).
Economic Attributes Not yet assessed
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Management Summary
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Biological Research Needs: Many aspects of species' biology remain to be defined. Spawning and brooding seasons, glochidial descriptions, fish hosts, length of the parasitic period, environmental tolerances, and many other factors are unknown. Taxonomic status of populations like those in the upper Trinity River drainage need to be compared to other populations in the Brazos and Colorado River drainages.
Population/Occurrence Delineation
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Group Name: Freshwater Mussels

Use Class: Not applicable
Minimum Criteria for an Occurrence: Occurrences are based on some evidence of historical or current presence of single or multiple specimens, including live specimens or recently dead shells (i.e., soft tissue still attached and/or nacre still glossy and iridescent without signs of external weathering or staining), at a given location with potentially recurring existence. Weathered shells constitute a historic occurrence. Evidence is derived from reliable published observation or collection data; unpublished, though documented (i.e. government or agency reports, web sites, etc.) observation or collection data; or museum specimen information.
Mapping Guidance: Based on the separation distances outlined herein, for freshwater mussels in STANDING WATER (or backwater areas of flowing water such as oxbows and sloughs), all standing water bodies with either (1) greater than 2 km linear distance of unsuitable habitat between (i.e. lotic connections), or (2) more than 10 km of apparently unoccupied though suitable habitat (including lentic shoreline, linear distance across water bodies, and lentic water bodies with proper lotic connections), are considered separate element occurrences. Only the largest standing water bodies (with 20 km linear shoreline or greater) may have greater than one element occurrence within each. Multiple collection or observation locations in one lake, for example, would only constitute multiple occurrences in the largest lakes, and only then if there was some likelihood that unsurveyed areas between collections did not contain the element.

For freshwater mussels in FLOWING WATER conditions, occurrences are separated by a distance of more than 2 stream km of unsuitable habitat, or a distance of more than 10 stream km of apparently unoccupied though suitable habitat. Standing water between occurrences is considered suitable habitat when calculating separation distance for flowing water mussel species unless dispersal barriers (see Separation Barriers) are in place.

Several mussel species in North America occur in both standing and flowing water (see Specs Notes). Calculation of separation distance and determination of separation barriers for these taxa should take into account the environment in which the element was collected. Juvenile mussels do not follow this pattern and juveniles are typically missed by most standard sampling methods (Hastie and Cosgrove, 2002; Neves and Widlak, 1987), therefore juvenile movement is not considered when calculating separation distance.

Separation Barriers: Separation barriers within standing water bodies are based solely on separation distance (see Separation Distance-suitable, below). Separation barriers between standing water bodies and within flowing water systems include lack of lotic connections, natural barriers such as upland habitat, absence of appropriate species specific fish hosts, water depth greater than 10 meters (Cvancara, 1972; Moyle and Bacon, 1969) or anthropogenic barriers to water flow such as dams or other impoundments and high waterfalls.
Separation Distance for Unsuitable Habitat: 2 km
Separation Distance for Suitable Habitat: 10 km
Alternate Separation Procedure: None
Separation Justification: Adult freshwater mussels are largely sedentary spending their entire lives very near to the place where they first successfully settled (Coker et al., 1921; Watters, 1992). Strayer (1999) demonstrated in field trials that mussels in streams occur chiefly in flow refuges, or relatively stable areas that displayed little movement of particles during flood events. Flow refuges conceivably allow relatively immobile mussels to remain in the same general location throughout their entire lives. Movement occurs with the impetus of some stimulus (nearby water disturbance, physical removal from the water such as during collection, exposure conditions during low water, seasonal temperature change or associated diurnal cycles) and during spawning. Movement is confined to either vertical movement burrowing deeper into sediments though rarely completely beneath the surface, or horizontal movement in a distinct path often away from the area of stimulus. Vertical movement is generally seasonal with rapid descent into the sediment in autumn and gradual reappearance at the surface during spring (Amyot and Downing, 1991; 1997). Horizontal movement is generally on the order of a few meters at most and is associated with day length and during times of spawning (Amyot and Downing, 1997). Such locomotion plays little, if any, part in the distribution of freshwater mussels as these limited movements are not dispersal mechanisms. Dispersal patterns are largely speculative but have been attributed to stream size and surface geology (Strayer, 1983; Strayer and Ralley, 1993; van der Schalie, 1938), utilization of flow refuges during flood stages (Strayer, 1999), and patterns of host fish distribution during spawning periods (Haag and Warren, 1998; Watters, 1992). Lee and DeAngelis (1997) modeled the dispersal of freshwater into unoccupied habitats as a traveling wave front with a velocity ranging from 0.87 to 2.47 km/year (depending on mussel life span) with increase in glochidial attachment rate to fish having no effect on wave velocity.

Nearly all mussels require a host or hosts during the parasitic larval portion of their life cycle. Hosts are usually fish, but a few exceptional species utilize amphibians as hosts (Van Snik Gray et al., 2002; Howard, 1915) or may metamorphose without a host (Allen, 1924; Barfield et al., 1998; Lefevre and Curtis, 1911; 1912). Haag and Warren (1998) found that densities of host generalist mussels (using a variety of hosts from many different families) and displaying host specialists (using a small number of hosts usually in the same family but mussel females have behavioral modifications to attract hosts to the gravid female) were independent of the densities of their hosts. Densities of non-displaying host specialist mussels (using a small number of hosts usually in the same family but without host-attracting behavior) were correlated positively with densities of their hosts. Upstream dispersal of host fish for non-displaying host specialist mussels could, theoretically, transport mussel larvae (glochidia) over long distances through unsuitable habitat, but it is unlikely that this occurs very often. D. Strayer (personal communication) suggested a distance of at least 10 km, but a greater distance between occurrences may be necessary to constitute genetic separation of populations. As such, separation distance is based on a set, though arbitrary, distance between two known points of occurrence.

Date: 18Oct2004
Author: Cordeiro, J.
Notes: Contact Jay Cordeiro (jay_cordeiro@natureserve.org) for a complete list of freshwater mussel taxa sorted by flow regime.
Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank) Not yet assessed
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Authors/Contributors
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NatureServe Conservation Status Factors Edition Date: 20Jul2006
NatureServe Conservation Status Factors Author: Cordeiro, J. (2006); Howells, R. G. (1998)
Element Ecology & Life History Edition Date: 20Jul2006
Element Ecology & Life History Author(s): Cordeiro, J.

Zoological data developed by NatureServe and its network of natural heritage programs (see Local Programs) and other contributors and cooperators (see Sources).

References
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  • Howard, A.D. 1915. Some exceptional cases of breeding among the Unionidae. The Nautilus 29:4-11.

  • Howells, R.G. 1994. Distributional surveys of freshwater mussels bivalves in Texas: progress report for 1992. Texas Parks and Wildlife Department, Management Data Series 105, Austin, Texas.

  • Howells, R.G. 1995. Distributional surveys of freshwater mussels bivalves in Texas: progress report for 1993. Texas Parks and Wildlife Department, Management Data Series 119, Austin, Texas.

  • Howells, R.G. 1996a. Distributional surveys of freshwater mussels bivalves in Texas: progress report for 1994. Texas Parks and Wildlife Department, Management Data Series 120, Austin, Texas.

  • Howells, R.G. 1996b. Distributional surveys of freshwater mussels bivalves in Texas: progress report for 1995. Texas Parks and Wildlife Department, Management Data Series 125: Austin, Texas.

  • Howells, R.G. 1997c. Distributional surveys of freshwater mussels bivalves in Texas: progress report for 1996. Texas Parks and Wildlife Department, Management Data Series 144: Austin, Texas.

  • Howells, R.G., R.W. Neck, and H.D. Murray. 1996. Freshwater Mussels of Texas. Texas Parks and Wildlife Press: Austin, Texas. 218 pp.

  • Lefevre, G. and W.T. Curtis. 1912. Studies on the reproduction and artificial propogation of fresh-water mussels. Bulletin of the Bureau of Fisheries 30:102-201.

  • Moyle, P. and J. Bacon. 1969. Distribution and abundance of molluscs in a fresh water environment. Journal of the Minnesota Academy of Science 35(2/3):82-85.

  • Serb, J.M., J.E. Buhan, and C. Lydeard. 2003. Molecular systematics of the North American freshwater bivalve genus Quadrula (Unionidae: Ambleminae) based on mitochondrial ND1 sequences. Molecular Phylogenetics and Evolution, 28: 1-11.

  • Strayer, D. 1983. The effects of surface geology and stream size on freshwater mussel (Bivalvia, Unionidae) distribution in southeastern Michigan, U.S.A. Freshwater Biology 13:253-264.

  • Strayer, D.L. 1999a. Use of flow refuges by unionid mussels in rivers. Journal of the North American Benthological Society 18(4):468-476.

  • Strayer, D.L. and J. Ralley. 1993. Microhabitat use by an assemblage of stream-dwelling unionaceans (Bivalvia) including two rare species of Alasmidonta. Journal of the North American Benthological Society 12(3):247-258.

  • 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.

  • U.S. Fish and Wildlife Service (USFWS). 2011. Endangered and threatened wildlife and plants; 12-month finding on a petition to list Texas Fatmucket, Golden Orb, Smooth Pimpleback, Texas Fawnsfoot as Threatened or Endangered. Federal Register 76(194):62166-62212.

  • U.S. Fish and Wildlife Service (USFWS). 2013. Review of Native Species That are Candidates for Listing as Endangered or Threatened; Annual Notice of Findings on Resubmitted Petitions; Annual Description of Progress on Listing Actions. Federal Register 78(226):70104-70162.

  • Van der Schalie, H. 1938a. The naiad fauna of the Huron River in southeastern Michigan. Miscellaneous Publication of the Museum of Zoology, University of Michigan 40:7-78.

  • Watters, G.T. 1992a. Unionids, fishes, and the species-area curve. Journal of Biogeography 19:481-490.

  • Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993b. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9): 6-22.

References for Watershed Distribution Map
  • Howells, R.G., C.M. Mather, and J.A.M. Bergmann. 1997. Conservation status of selected freshwater mussels in Texas. Pages 117-126 in K.S. Cummings, A.C. Buchanan, C.A. Mayer, and T.J. Naimo (eds.). Conservation and Management of Freshwater Mussels II: Initiatives for the Future, Proceedings of a UMRCC Symposium, 16-18 October, 1995, St. Louis, Missouri. Upper Mississippi River Conservation Committee, Rock Island, Illinois.

  • Reimer, M.M. and L.A. Linam. 2005. Texas mussel watch, a citizen based volunteer monitoring program. Ellipsaria, 7(3): 5-6.

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