MALACOLOGIA, 2019, 62(2): 345–363

STATUS OF RARE ENDEMIC : MOLECULAR PHYLOGENY, DISTRIBUTION AND CONSERVATION OF FRESHWATER MOLLUSCS MACRODON AND TRUNCILLA COGNATA IN TEXAS

Lyubov E. Burlakova1*, David Campbell2 & Alexander Y. Karatayev1

ABSTRACT

Freshwater bivalves in the family are one of the most endangered groups of in North America. In Texas, where over 60% of unionids are rare or very rare, 15 species have been added to the state’s list of threatened species, and 10 are under con- sideration for federal listing. Due to insufficient survey efforts in the past decades, however, primary data on current distribution and requirement for most of these rare species are lacking, thus challenging their protection and management. Although the species are listed as valid, there was no genetic confirmation to test for the possibility of ecophenotypes, which complicates conservation efforts. In this paper, we present genetic and distributional data for two rare Texas species, Truncilla macrodon and Truncilla cognata, and we suggest appropriate conservation measures. Tests of genetic affinities of these species using three gene regions, cox1, nad1 and ITS1, supported recognition of T. cognata and T. macrodon as full species. Analysis of historic and current showed that both these regional endemics are particularly vulnerable, and their distribution range has been reduced in the last 80 years. Key words: freshwater molluscs, Truncilla macrodon, Truncilla cognata, molecular identifica- tion, , distribution, habitat requirements, conservation priorities.

Introduction are very rare (Burlakova et al., 2011a). Due to its size, geological features and diverse Molluscs are among the most threatened landscapes, Texas is listed among the top animals on the planet: the number of mollusc U.S. states in species diversity and endemism extinctions worldwide is higher than the number (Stein, 2002), but the conservation status of of extinctions in all other taxa combined (Ré- most of Texas’ ecoregions is vulnerable or gnier et al., 2009). Among freshwater bivalves critical (Abell et al., 2000). The major threats world-wide, have the highest percent- to Texas freshwaters include damming, pollu- age of near-threatened, threatened and extinct tion, water extraction and urban development species (Lopes-Lima et al., 2018), similarly to (Dahm et al., 2005). As a result, the state of North America (Bogan, 1993; Lydeard et al., Texas ranks fourth in the country in terms of 2004) where over 76% of the Unionidae and the number of species extinctions (Stein, 2002). Margaritiferidae presumed extinct, threatened, Of the 15 unionid species listed as Texas state endangered or deemed of special concern threatened species (Texas Register 35, 2010), (Williams et al., 1993). Sensitivity to water ten are currently under consideration for fed- and habitat quality, long life span, sedentary eral listing by the U. S. Fish & Wildlife Service lifestyle, complex life cycle with parasitic larvae (Federal Register, 74, 66261, 2009; Federal requiring specific fish hosts, slow growth and Register, 74, 66866, 2009), and one species low reproductive rates are among the main (Popenaias popeii) has recently been added to reasons for their decline (reviewed in Bogan, the federal List of Endangered and Threatened 1993; Grabarkiewicz & Davis, 2008; McMahon Wildlife (Federal Register, 83, 5720, 2018). & Bogan, 2001; Strayer et al., 2004). Accurate identification is a necessary com- In the U. S. state of Texas, 65% of all unionid ponent for taxa monitoring and protection, but species are rare, and most endemic species few morphological characters are evident,

1Great Lakes Center, SUNY Buffalo State, 1300 Elmwood Ave., Buffalo, New York, 14222, U.S.A. 2Department of Natural Sciences, Box 7270, Gardner-Webb University, Boiling Springs, North Carolina, 28017, U.S.A. *Corresponding author: [email protected] 345 346 BURLAKOVA ET AL. making quantitative morphologically based In addition to limited distributional data, taxo- unionid taxonomy difficult (Roe & Hoeh, 2003) nomic status of both species is unclear as well. and resulting in many synonyms of morpho- Johnson (1999) combined T. cognata and T. logically variable taxa in the literature (e.g., macrodon with T. donaciformis, likely based on Burch, 1973; Ortmann, 1923; Simpson, 1914). a limited number of museum specimens and in Although our understanding of relationships absence of genetic analysis (Howells, 2010), within Unionidae has greatly increased over whereas other scientists recognize them as recent decades due to application of molecular separate species (Howells et al., 1996, 2010; tools, a limited number of phylogenetic studies Turgeon et al., 1998; Williams et al., 1993). In have been conducted on freshwater unionid this paper, we analyze genetic and distribu- in Texas, and it is quite possible that tional data of T. macrodon, and T. cognata to some of the nominal species and genera do define their proper taxonomic status and bioge- not represent natural units. Conservational ography, and suggest conservation measures laws and methods cannot be implemented until to protect these rare endemic species. the endangered organism is properly clarified and its geographical range is known (Lydeard & Roe, 1998). The knowledge of genetic diver- MATERIAL AND METHODS sity is also important for captive breeding and reintroduction of endangered species, as it will Molecular Techniques be successful only if the genotypes used can tolerate particular conditions. Molecular investigation used three gene re- In this paper, we analyze genetic and distri- gions, cox1, nad1, and ITS1. DNA extraction butional data of two very rare Texas species: used Zymo DNA Tissue Miniprep kits. Primers Truncilla macrodon and T. cognata. Truncilla for cox1 were 5′-GTTCCACAAATCATAAGGA- macrodon was described by Lea (1859) from TATTGG-3′ and 5′-TACACCTCAGGGTGAC- Fayette County, Texas. The species is a very CAAAAAACCA-3′, adapted from Folmer rare central Texas endemic (Howells et al., et al. (1994). Primers for nad1 were 5′-TG- 1996, 1997) and is currently under consid- GCAGAAAAGTGCATCAGATTTAAGC-3′ and eration for federal listing by the U. S. Fish & 5′-GCTATTAGTAGGTCGTATCG-3′ (Buhay et Wildlife Service (Federal Register, 74, 66261, al., 2002; Serb & Lydeard, 2003), and primers 2009). Although reported by Strecker (1931) for ITS1 were 5′-AAAAAGCTTCCGTAGGT- as “an abundant shell in the Colorado and GAACCTGCG-3′ and 5′-AGCTTGCTGCGT- Brazos rivers”, less than 200 specimens of T. TCTTCATCG-3′ (King et al., 1999). The primer macrodon had been reported until recently, and LoGlyR (5’-CCTGCTTGGAAGGCAAGTG- even fewer were alive at the time of collection TACT-3’) (Serb et al., 2003) was used as an (Howells, 2010, 2011). Due to their rarity, T. additional external primer option for nad1 macrodon biology and ecology, including repro- and primers UNIOCOII.2 (5’-CAGTGGTAT- ductive cycle, potential fish hosts and habitat TGGAGGTATGAGTA-3’) from Walker et al. have never been studied (Howells, 2010). (2007) and/or HCOout (CCAGGTAAAAT- Truncilla cognata is endemic to the Rio Grande TAAAATATAAACTTC; Carpenter & Wheeler, drainage (Neck, 1984) and was described 1997) were used as external primers for some from Rio Salado, Mexico (Lea, 1857). Taylor cox1 amplifications. PCR used 10 min denatur- (1966) believed that T. cognata is “one of the ing at 95°C, followed by 40 cycles of 95°C for few mussels … that is actually endangered”. 30 sec, 5°C under the annealing temperature This species is considered endangered by the of the lower-annealing primer for 30 sec, and American Fisheries Society (Williams et al., 60 sec at 72°C, and then a final 10 min hold at 1993), listed as threatened in Texas (Texas 72°C. PCR products were cleaned with Zymo Register 35, 2010), and is under consideration DNA Clean & Concentrator kits and sequenced for federal listing by the U. S. Fish & Wildlife by Macrogen. For all phylogenetic analyses, Service (Federal Register, 74, 66261, 2009). identical sequences were combined into a During the last 100 years, T. cognata was re- single sequence. Sequences were aligned in ported only from a few sites in the Rio Grande BioEdit (Hall, 1999) and, for the ITS region, drainage in Texas (Karatayev et al., 2012). This with MAFFT (Katoh & Standley, 2013), followed species is likely to be present in Mexico, but by manual editing to check for consistency in no data exist from the Mexican portions of the the alignment. The data were analyzed using Rio Grande, limiting the estimation of species’ PAUP* 4.0 a159 (Swofford, 2002), TNT 1.5 geographic range and conservation status. (Goloboff & Catalano, 2016), MrBayes 3.2 ENDEMIC TRUNCILLA SPP. IN TEXAS 347

(Ronquist et al., 2012), and bppX (Xu, 2012, was used to reveal the presence of mussels a user interface for the BP&P 3.1 program of and species diversity (Strayer et al., 1997; Yang, 2015). Gaps were coded as missing Vaughn et al., 1997) at all sites (Karatayev et data. The sequences were concatenated, and al., 2012, 2018a). Due to poor water visibility, identical sequences were grouped together tactile searches (running fingers over the sedi- for parsimony and Bayesian analyses. Maxi- ment, usually up to 15 cm deep, depending on mum parsimony analyses used 500 random substrate type) were used at all sites. Collected replicates. Jackknife analyses used 500 repli- live mussels and shells were counted and cates, each using a random parsimony search measured with calipers to the nearest mm, and of 10 replicates. We used the GC jackknife then live mussels were carefully bedded back value, which subtracts support for competing into the sediment from which they were taken. clades as a more conservative evaluation of Shell condition of dead mussels was recorded the support level (Goloboff et al., 2003). Both for each shell. When surveys were conducted used all of the “new technology” tree search from private land, landowner permission was options in TNT. Automated model selection in acquired from each property owner before PAUP* favored a TVM+I+G model, which was entering the property. The work was carried implemented as the closest more complex out with an appropriate Scientific Research option available, GTR+I+G, in MrBayes, with Permit issued by the Texas Parks and Wildlife 2,000,000 generations and eight chains: rev- Department (TPWD), National Park Service mat, shape, pinvar and statfreq were unlinked. Scientific Permit for Big Bend National Park Table 1 lists the sequences analyzed and their and Amistad National Recreational Area Re- sources. search Permit. All sequences for Truncilla (no outgroups) For T. macrodon, we surveyed 206 sites at 73 were analyzed with BP&P. This implements locations in 20 rivers, creeks and reservoirs in the methods of Rannala & Yang (2003) and central Texas in the Colorado and Brazos riv- Yang & Rannala (2010) for Bayesian species ers systems. To estimate population densities delimitation and phylogenetic tree estimation. of T. macrodon in San Saba River, we used We tested the six models used by Pfeiffer et quadrats and strip transect sampling with ran- al. (2016): population size parameters (θs) are dom starts (Seber, 1982; Smith, 2006; Smith assigned the gamma priors of either G(1,10), et al., 2003). The river was surveyed at five G(1.5,150), or G(2,2000), each paired with locations: at CR 208, northeast of San Saba; divergence times (τ0) with gamma priors of at San Saba River Golf Course; at San Saba G(1,10) or G(2,2000). This provides a range Rd. and China Creek Rd. (CR 200); at CR 126, of possible population sizes and divergence and at CR 340. Each location was surveyed times. Truncilla cognata, T. macrodon, T. trun- using consecutive 50-m long non-overlapping cata, the Texas specimens of T. donaciformis, strata, and from 8 to 17 strata were sampled and the upper specimens of T. in each location. In each stratum we sampled donaciformis were defined as populations for from 2 to 3 transects that run from one shore to the program to analyze for distinctiveness. another (perpendicular to the shores) to ensure unbiased sampling and considering that mus- Current Distribution and Density sels beds often are located in riffles across the whole breadth of the river. The location of the To assess the current (2001–2014) distribu- first transect in each stratum was chosen ran- tion of T. macrodon and T. cognata, we used domly, and the other transect(s) run 2 m apart data from our statewide surveys reported in from the first one (systematic strip transect previous publications (Burlakova & Karatayev, sampling with random start, Seber, 1982). 2010a, b, 2012; Burlakova et al., 2011a, b; To ensure full recovery, we searched Karatayev & Burlakova, 2008; Karatayev et substrate (up to 10–15 cm deep whenever al., 2012), the authors’ unpublished data, and possible) in 0.25 m2 quadrats along sampling data reported by other authors (reviewed in transects. Depending on the width of the river, Brewster, 2015; Howells, 2010; Randklev et al., anywhere from 5 to 20 quadrats were used 2009, 2010, 2013, 2018; Tsakiris & Randklev, along each of the sampled transects. A total of 2016; USFWS, 2015). 86 transects were searched at 42 strata. We During our surveys, both live and dead mus- recorded the number of each species in each sels were collected by snorkeling (at most quadrat. That data was used to calculate the of the sites), wading in low water or diving. mean population at each sampled location size Reconnaissance sampling (timed search) using formulae from Seber (1982). To estimate 348 BURLAKOVA ET AL.

TABLE 1. Sources for molecular data. UAUC = University of Unionoid Collection; * = new sequence; coll. = collected by.

Taxon Gene Accession Source

Amblema plicata cox1 AF156512 Graf & Ó Foighil, 2000 Amblema plicata ITS1 AY294561 Manendo et al., 2008 Amblema plicata nad1 AY158796 Serb et al., 2003 Cambarunio simus cox1 *MH161352 UAUC260: 35.5350°N, 85.7900°W Collins Ri., Hwy. 56 bridge, near Beersheba Springs, Grundy Co., Tennes- see, coll. L. Levine Cambarunio simus ITS1 *MH167925 UAUC3213: Witty Creek, Bridge off Herman Lange Rd., Warren Co., Tennessee, coll. S. Ahlstedt, B. Butler, Rob Towes, J. Widlak Cyrtonaias tampicoensis cox1 AF231749 Bogan & Hoeh, 2000 Cyrtonaias tampicoensis ITS1 *MH167927 UAUC316: Lake Corpus Christi, Live Oak Co., Texas, coll. R. G. Howells Cyrtonaias tampicoensis nad1 AY655090 Campbell et al., 2005 Dromus dromas cox1 AY654993 Campbell et al., 2005 Dromus dromas nad1 JF326439 Campbell & Lydeard, 2012b Ellipsaria lineolata cox1 AY654994 Campbell et al., 2005 Ellipsaria lineolata nad1 GU085344 Boyer et al., 2011 Elliptio crassidens cox1 AY613820 Campbell et al., 2005 Elliptio crassidens ITS1 *MH167928 UAUC 3527: Tennessee Ri. at Diamond Id., Decatur/ Hardin Cos., Tennessee, coll. S. Ahlstedt Elliptio crassidens nad1 AY613788 Campbell et al., 2005 Epioblasma rangiana cox1 JF326432 Campbell & Lydeard, 2012b Epioblasma rangiana ITS1 *KY207336 Allegheny Ri., Hunter Station Bridge, Venango Co., Pennsylvania Epioblasma rangiana nad1 DQ220720 Zanatta & Murphy, 2006 Glebula rotundata cox1 AF231729 Bogan & Hoeh, 2000 Glebula rotundata ITS1 KT285686 Pfeiffer et al., 2016 Glebula rotundata nad1 AY613795 Campbell et al., 2005 Lampsilis hydiana cox1 *MH161354 UAUC3508: 30.3565°N, 94.0943°W, Neches Ri. at Rte. 96 bridge, Hardin Co., Texas, coll. H. McCullagh Lampsilis hydiana ITS1 *MH167929 UAUC3508: 30.3565°N, 94.0943°W, Neches Ri. at Rte. 96 bridge, Hardin Co., Texas, coll. H. McCullagh Lampsilis ovata cox1 EF033262 Chapman et al., 2008 Lampsilis ovata nad1 AY613797 Campbell et al., 2005 Lampsilis siliquoidea cox1 AF156521 Graf & Ó Foighil, 2000 Lampsilis siliquoidea ITS1 AY319384 Manendo et al., 2008 Lampsilis siliquoidea nad1 AY158747 Serb et al., 2003 Lampsilis straminea cox1 *MH161355 UAUC3543: Sipsey Ri. at Benevola Id., Greene Co., Alabama, coll. Jamie Hendrickson Lampsilis straminea ITS1 *KY207337 UAUC3543: Sipsey Ri. at Benevola Id., Greene Co., Alabama, coll. J. Hendrickson Lampsilis straminea nad1 DQ445163 Buhay, 2006 (unpublished data on GenBank) Lampsilis teres cox1 AF406803 Hoeh et al., 2002 Lampsilis teres ITS1 KT285688 Pfeiffer et al., 2016 Lampsilis teres nad1 AY655102 Campbell et al., 2005

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Taxon Gene Accession Source

Leaunio lienosus cox1 *MH161356 Red Creek at CR34 bridge, Washington Co., Alabama, coll. S. Clark & D. Campbell Leaunio lienosus ITS1 KT285704 Pfeiffer et al., 2016 Leaunio lienosus nad1 *MH161359 Red Creek at CR34 bridge, Washington Co., Alabama, coll. S. Clark & D. Campbell Lemiox rimosus cox1 HM230406 Campbell & Lydeard, 2012a Lemiox rimosus ITS1 *KY207338 muskrat midden, largest island at Lillard’s Mill, side near dam, Marshall Co., Tennessee, coll. L. J. Levine Lemiox rimosus nad1 HM230417 Campbell & Lydeard, 2012a Leptodea fragilis cox1 AF049519 Roe & Lydeard, 1998 Leptodea fragilis ITS1 KT285687 Pfeiffer et al., 2016 Leptodea fragilis nad1 *MH161360 UAUC1660: 34.9247°N, 84.8403°W, Coosawattee Ri. 100 m above mouth of Sugar Creek, 2.7 km down from U. S. 411 bridge, Murray Co., Georgia, coll. J. Williams acutissimus cox1 AY655005 Campbell et al., 2005 Medionidus acutissimus ITS1 *KY207339 UAUC3382: Brushy Creek at FS Rd. 254 near church, Winston Co., Alabama, coll. P. Hartfield Medionidus acutissimus nad1 *MH161361 UAUC3382: Brushy Creek at FS Rd 254 near church, Winston Co., Alabama, coll. P. Hartfield Obliquaria reflexa cox1 EF033254 Chapman et al., 2008 Obliquaria reflexa nad1 AY655108 Campbell et al., 2005 unicolor cox1 HM230407 Campbell & Lydeard, 2012 {Fusc} Obovaria unicolor ITS1 *MH167930 UAUC1261: Bogue Chitto Ri. below sill, St. Tammany Parish, Lousiana, coll. P. Hartfield Obovaria unicolor nad1 KF035411 Inoue et al., 2013 Plectomerus dombeyanus cox1 AY655011 Campbell et al., 2005 Plectomerus dombeyanus ITS1 DQ383444 Campbell et al., 2008 Plectomerus dombeyanus nad1 AY655110 Campbell et al., 2005 Pleurobema rubellum cox1 AY613840 Campbell et al., 2005 Pleurobema rubellum ITS1 DQ383462 Campbell et al., 2008 Pleurobema rubellum nad1 AY613813 Campbell et al., 2005 Popenaias popeii cox1 AY655020 Campbell et al., 2005 Popenaias popeii ITS1 *KY207340 UAUC3161, Rio Grande, Laredo, Webb Co., Texas, coll. T. Miller Popenaias popeii nad1 AY655118 Campbell et al., 2005 metnecktayi cox1 *MH161357 Rio Grande near Dryden, Terrell Co., Texas, coll. T. Miller Potamilus metnecktayi ITS1 *KY207341 Rio Grande near Dryden, Terrell Co., Texas, coll. T. Miller Potamilus metnecktayi nad1 *MH161362 Rio Grande near Dryden, Terrell Co., Texas, coll. T. Miller rumphiana cox1 HM230409 Campbell & Lydeard, 2012a Quadrula rumphiana ITS1 *MH167932 Sucarnoochee Ri. above Hwy.11 bridge, Sumter Co., Alabama, coll. S. Clark & D. Campbell Quadrula rumphiana nad1 HM230421 Campbell & Lydeard, 2012a Reginaia ebenus cox1 AY654999 Campbell et al., 2005 Reginaia ebenus ITS1 HM230352 Campbell & Lydeard, 2012a Reginaia ebenus nad1 AY655098 Campbell et al., 2005 Sagittunio nasutus cox1 AF156515 Graf & Ó Foighil, 2000

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Taxon Gene Accession Source

Sagittunio nasutus ITS1 AY319383 Manendo et al., 2008 Sagittunio nasutus nad1 EF213059 Zanatta & Murphy, 2006 (unpublished data on GenBank) Toxolasma lividum cox1 *MH161358 Tennessee Ri. Mile 249, Colbert/Lauderdale Co., Ala- bama, coll. J. Garner & A. C. Suddith Toxolasma lividum ITS1 *MH167933 Tennessee Ri. mile 249, Colbert/Lauderdale Co., Ala- bama, coll. J. Garner & A. C. Suddith Toxolasma lividum nad1 *MH161363 Tennessee Ri. mile 249, Colbert/Lauderdale Co., Ala- bama, coll. J. Garner & A. C. Suddith Truncilla cognata 403 cox1 *KY205902 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 403 ITS1 *KY207343 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 403 nad1 *KY205915 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 403b ITS1 *KY207344 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 419 cox1 *KY205903 Rio Grande above Laredo, Webb Co., Texas Truncilla cognata 419 ITS1 *KY207345 Rio Grande above Laredo, Webb Co., Texas Truncilla cognata 419 nad1 *KY205916 Rio Grande above Laredo, Webb Co., Texas Truncilla cognata 420 cox1 *KY205901 Rio Grande above Laredo, Webb Co., Texas Truncilla cognata 420 ITS1 *KY207346 Rio Grande above Laredo, Webb Co., Texas Truncilla cognata 420 nad1 *KY205917 Rio Grande above Laredo, Webb Co., Texas Truncilla cognata 420b ITS1 *KY207347 Rio Grande above Laredo, Webb Co., Texas Truncilla cognata 69 cox1 *KY205904 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 69 ITS1 *KY207348 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 69 nad1 *KY205918 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 70 cox1 *KY205905 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 70 ITS1 *KY207349 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 70 nad1 *KY205919 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 70b ITS1 *KY207350 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 71 ITS1 *KY207351 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata 71 nad1 *KY205920 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata Laredo cox1 *KY205907 Rio Grande at Laredo, Webb Co., Texas Truncilla cognata Laredo nad1 *KY205921 Rio Grande at Laredo, Webb Co., Texas Truncilla donaciformis 197 ITS1 *KY207352 Village Creek at US96, Hardin Co., Texas Truncilla donaciformis 197 nad1 *KY205922 Village Creek at US96, Hardin Co., Texas Truncilla donaciformis 224 cox1 *KY205909 Neches Ri. at US69, Angelina Co., Texas Truncilla donaciformis 224 ITS1 *KY207353 Neches Ri. at US69, Angelina Co., Texas Truncilla donaciformis 224 nad1 *KY205923 Neches Ri. at US69, Angelina Co., Texas Truncilla donaciformis 385 cox1 *KY205910 Neches Ri. at CR354, Anderson/Cherokee Cos., Texas Truncilla donaciformis 385 ITS1 *KY207354 Neches Ri. at CR354, Anderson/Cherokee Cos., Texas Truncilla donaciformis 385 nad1 *KY205924 Neches Ri. at CR354, Anderson/Cherokee Cos., Texas Truncilla donaciformis 162 cox1 GU085323 Boyer et al., 2011 Truncilla donaciformis 162 nad1 GU085378 Boyer et al., 2011 Truncilla macrodon 351 cox1 *KY205911 San Saba Ri. at CR 208, San Saba Co., Texas Truncilla macrodon 351 ITS1 *KY207355 San Saba Ri. at CR 208, San Saba Co., Texas Truncilla macrodon 351 nad1 *KY205925 San Saba Ri. at CR 208, San Saba Co., Texas Truncilla macrodon 351b ITS1 *KY207356 San Saba Ri. at CR 208, San Saba Co., Texas

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Taxon Gene Accession Source

Truncilla macrodon 363 cox1 *KY205912 San Saba Ri. at CR 200, San Saba Co., Texas Truncilla macrodon 363 ITS1 *KY207357 San Saba Ri. at CR 200, San Saba Co., Texas Truncilla macrodon 363 nad1 *KY205926 San Saba Ri. at CR 200, San Saba Co., Texas Truncilla macrodon 83 cox1 *KY205913 Colorado Ri. at FM 1950, Colorado Co., Texas Truncilla macrodon 83 ITS1 *KY207358 Colorado Ri. at FM 1950, Colorado Co., Texas Truncilla macrodon 90 cox1 HM849165 Breton et al., 2011 (GenBank listing, not cited in text) Truncilla macrodon 95 cox1 *KY205914 Colorado Ri. at FM 1950, Colorado Co., Texas Truncilla macrodon 95 ITS1 *KY207359 Colorado Ri. at FM 1950, Colorado Co., Texas Truncilla macrodon 95b ITS1 *KY207360 Colorado Ri. at FM 1950, Colorado Co., Texas Truncilla macrodon FL cox1 KT285658 Pfeiffer et al., 2016 Truncilla macrodon FL ITS1 KT285702 Pfeiffer et al., 2016 2 cox1 AF156513 Graf & Ó Foighil, 2000 Truncilla truncata 2 nad1 AY655125 Campbell et al., 2005 Truncilla truncata 84 cox1 HM852948 Boyer et al., 2011 Truncilla truncata 49 nad1 HM852943 Boyer et al., 2011 Truncilla truncata MMTC22 cox1 HM852947 Boyer et al., 2011 Truncilla truncata MMTC22 nad1 GU085380 Boyer et al., 2011 Uniomerus declivus cox1 AY613846 Campbell et al., 2005 Uniomerus declivus ITS1 DQ383435 Campbell et al., 2008 Uniomerus declivus nad1 JF326450 Campbell & Lydeard, 2012b Venustaconcha pleasii cox1 JF326438 Campbell & Lydeard, 2012b Venustaconcha pleasii nad1 JF326452 Campbell & Lydeard, 2012b Villosa villosa cox1 AF385109 Roe et al., 2001 Villosa villosa nad1 AY094387 Buhay et al., 2002

the total population size (± 95% confidence For T. cognata, 250 sample locations (“sub- interval) of T. macrodon, we used the total area sites”) pooled into 42 larger sites (“pooled of the lower San Saba River where there was sites”) were surveyed within the Rio Grande enough water to support mussel populations system (for details please see Karatayev et (from the confluence of Brady Creek to the al., 2012, 2018a). Fourteen of these sites mouth of the river, total length 50 km, and the were sampled once, while 28 sites were average width of the river calculated using data sampled from 2 to 25 times. At two sites from our sampling sites, 18 m), the calculated in Laredo (in Justo Penn Park) where live T. macrodon population size in surveyed area, mussels were present in timed searches, we and the proportion of the surveyed area from sampled river bottom using 0.25 m2 quad- the total area of the lower San Saba River that rats (total 39 quadrats with excavation of supported the populations. sediments to 20–30 cm deep). Fifty-five more In the lower Colorado River (Colorado quadrats were sampled near Islitas (Webb County) in 2009, we conducted a quantitative County, above Laredo). estimation of T. macrodon population on a sand Voucher specimens were deposited in the bar with unusually high density of mussels. Great Lakes Center Invertebrate Collection Two hundred twenty five 0.252 m quadrats (BSGLC) (SUNY Buffalo State, Buffalo, New (with excavation down to 15 cm depth) along York), in the North Carolina State Museum of 17 transects were sampled in this bar to es- Natural Sciences (Raleigh, North Carolina), timate T. macrodon density, population size, and in the Invertebrate Zoology Collection standard error, and 95% confidence interval of the National Museum of Natural History (Seber, 1982). (Smithsonian Institution, Washington, D.C.). 352 BURLAKOVA ET AL.

Historical Distribution fered by a single base indel in a string of mul- tiple identical bases. The nad1 gene showed To reconstruct the historical (prior to 2000) greater variation within T. cognata but not in distribution range of T. macrodon and T. cog- the other species. The Texas populations of T. nata in Texas, we used data from museum donaciformis consistently placed as a subclade collections and published accounts (Brewster, sister to the published sequences from the up- 2015; Howells, 1994, 1995, 1996, 1997, 1999, per Mississippi River system in the parsimony 2000, 2001, 2003, 2006, 2010; Howells et and Bayesian analyses. Relationships between al., 1996, 1997; Johnson, 1999; Karatayev et the species within Truncilla were not well re- al., 2012; Metcalf, 1974, 1982; Murray, 1975; solved. The parsimony analyses produced 35 Neck & Metcalf, 1988; Randklev et al., 2009, trees of length 3704. Bayesian analyses had 2010, 2013, 2018; Singley, 1893; Strecker, a final average standard deviation of split fre- 1931; Tsakiris & Randklev, 2016; USFWS, quencies of 0.008580, with a burnin of 19000, 2015) along with our records of shells found an average ln likelihood of -17931.37, and a during field surveys. Similar to our previous maximum ln likelihood of -17898.30. Figure 1 study (Karatayev et al., 2018a), we made the shows the maximum parsimony consensus following assumptions: (1) the historical range tree, with jackknife percentages and Bayesian of T. macrodon, and T. cognata in Texas cor- posterior probabilities. responds with waterbodies where live or dead The analyses in BP&P did not strongly sup- shells were ever recorded; (2) historically T. port any one phylogenetic tree. The 5th model macrodon and T. cognata were present in had one tree with a posterior probability of the whole river stretch between the two most 81%, but no other analysis had a tree that distant points where live or dead shells have received over 50% posterior probability. The been recorded; (3) T. macrodon and T. cognata average posterior probability for recognizing records were considered living unless other- all five populations as distinct species was wise stated; (4) year of record was one year 98.4% across all six models, with a minimum of prior to publication, unless otherwise stated 95.3% posterior probability (model 1). Treating (excluding papers where museum collections T. donaciformis as a single species received were analyzed and mussels had collection most of the remaining probability (average dates on their labels); (5) current range is 1.3% posterior probability). given by waterbodies and counties where live or recently dead shells of T. macrodon and T. Species Distribution and Densities cognata were recorded after 2000. Shells were considered very recently dead if soft tissue re- Truncilla macrodon mained attached to the shell and recently dead if internal and external colors were not faded Based on literature records (Howells, 1994, (nacre still lustrous), or somewhat faded. Shells 1995, 1996, 1997, 1999, 2000, 2001, 2010; with most or all of the internal coloration and Howells et al., 1996, 1997; Johnson, 1999; gloss faded, shell periostracum absent, or aged Metcalf, 1982; Neck & Metcalf, 1988; Randklev and flaking, were considered long dead. Shells et al., 2013; Singley, 1893; Strecker, 1931; with little or no epidermis, with nacre and entire Tsakiris & Randklev, 2016), museum collec- shell faded white, often with extensive signs of tions and our shell findings,T. macrodon in the erosion, staining, and calcium deposition were past (before 2000) likely occurred in 47 central considered subfossil. Texas counties in the Brazos and Colorado drainages (Fig. 2). Reports of T. macrodon from the Trinity River and other east Texas RESULTS locations (e.g., Parks & Batchel, 1936, 1940) are likely of misidentified T. donaciformis Molecular Analysis (Howells, 2010). Based on historic records, T. macrodon was always rare. Since the initial All gene analyses strongly supported the description by Lea (1859), only a few findings distinctiveness of T. cognata and T. macrodon have been reported until the end of the 20th relative to T. truncata and T. donaciformis. For century. Singley reported this species from cox1 and ITS1, there was little variation within four counties in the Brazos River (Brazos and the species. For ITS1, some individuals had Robertson counties) and in the Colorado River two alleles. In all such cases, the alleles dif- (Travis and Wharton counties). Strecker (1931) ENDEMIC TRUNCILLA SPP. IN TEXAS 353

FIG. 1. Maximum parsimony strict consensus tree, all genes. Numbers on branches are parsimony jackknife GC percentage, followed by Bayesian posterior probability, if jackknife percentage was over 50 or posterior probability was over 80; * = 100, - = no support. Numbers after taxon names indicate specimen designations; multiple numbers indicate multiple specimens with the same sequence; b indicates a second ITS allele from one individual. 354 BURLAKOVA ET AL.

FIG. 2. Past (before 2000) and present (2001–2014) distribution of Truncilla macrodon and T. cognata in Texas. Data are provided by counties in agreement with historic records. gave additional records in four rivers in the River (Mason County) systems. The two next Brazos River system (the Leon River in Coryell available reports were both from the Brazos County; Aquilla Creek, the Bosque, and the River in 1961 in Palo Pinto County (Pratt & North Bosque rivers in McLennan County), as Goode, 2017) and in 1976 in Hood County well as in two counties (Barnet and Colorado) (Johnson et al., 2017), and only a few live on the Colorado River and one on the Llano and recently dead specimens were collected ENDEMIC TRUNCILLA SPP. IN TEXAS 355 in 1990s (Howells et al., 1997). Therefore, for mussels (± 1,379, 95% confidence interval). almost 150 years since the initial discovery All mussels were found in a sandy shore, at up to the 1990s, T. macrodon was reported low depths (0.1–1.0 m). Unfortunately, there is only from 12 counties in Brazos and Colorado some evidence that this population may have drainages, and was present historically in at not survived the 2011 Texas drought (Charrish least 15 rivers and creeks. Stevens, U.S. Fish & Wildlife Service, personal The current distribution range estimated communication). based on the records of live and recently dead The average density of T. macrodon in T. macrodon includes at least 16 counties in transects in the lower San Saba River (San the Brazos drainage and four counties in the Saba County) was 0.027 + 0.01 mussel m-2 Colorado drainage (Fig. 2). The species current (maximum 0.5 m-2), and it was found only at range in the Brazos drainage include the Bra- 12% of the total 42 strata we surveyed using zos, Clear Fork Brazos, Navasota, and Little strip-transect method. The population size of rivers and Yegua Creek. In Colorado drainage T. macrodon in the sampled area was 782 ± the species range includes the Colorado and 779 mussels (mean ± 95% confidence interval). the San Saba rivers. In addition, the current Using our calculations, we estimated that the distribution includes recent discoveries of T. total population size of Texas fawnsfoot in the macrodon in rivers and streams from which San Saba River may be approximately 18,995 the species has not been known historically. mussels (± 18,900 mussels, 95% confidence In March of 2011, T. macrodon was found for interval). In the San Saba River, T. macrodon the first time in the lower San Saba River (San were found more frequently in riffles, in a Saba County, Burlakova & Karatayev, 2012). mixture of gravel and sand. While some of the In 2011, the species was first discovered in the mussels in the Colorado River were found on Navasota River (USFWS, 2015). the surface, the majority of mussels at both lo- After 2000, live or recently dead T. macrodon cations were found buried in the substrate, and have not been found in the Bosque River, North excavation within the quadrats was necessary Bosque, Llano, Concho and Leon rivers, and to find them. Truncilla macrodon, especially in Aquilla and Onion creeks. Only long dead the young specimens, were often found in shells of T. macrodon have been found in the sand and a mixture of sand and gravel. Adult Deer Creek in 2006, and in 2011 in the Llano mussels were found sometimes up to 15–20 River (our data). Although being reported to cm deep in sand, or in a mixture of sand with be extirpated from the Little River and Yegua gravel at the shore or in riffles. Creek (USFWS, 2015), live T. macrodon have been recently found in these waterbodies Truncilla cognata (Randklev et al., 2013; Tsakiris & Randklev, 2016). Truncilla cognata originally was described During our study, T. macrodon was extremely from the Rio Salado, Nuevo Leon, Mexico (Lea, rare at most of the sites sampled, and often 1857). Unfortunately, data are unavailable on represented by dead shells. From a total of 73 the current status of the species in its whole locations sampled in the Brazos and Colorado range in Mexico. In the U.S., T. cognata was drainages in 2005–2011 the species was found reported later only from a few sites in west only at eight locations: in the Brazos (2 loca- Texas including the Rio Grande River near tions), Colorado (one location) and San Saba Del Rio in 1972 and in the Pecos River mouth River (five locations). In total, we found 67 live at the former U.S. Hwy. 90 crossing in 1968 and 4 recently dead T. macrodon. The aver- (Metcalf, 1982). No living or dead specimens age size of live mussels was 28.09 ± 0.75 mm were collected since 1972 (Howells, 2001; (mean ± standard error here and elsewhere Howells et al., 1997). However, in 2002–2013 unless noted) (n = 53), range: 16.0–45.8 mm. in the Rio Grande we found a total of 41 live Shell length of dead mussels was 36.12 ± 4.94 mussels, and 152 recently dead specimens. mm and varied from 25.0 to 54.6 mm (n = 5). Based on literature records (Karatayev et One of the largest populations of T. macrodon al., 2012; Metcalf, 1974, 1982; Murray, 1975, to date was found in 2009 in the lower Colorado Neck, 1987; Neck & Metcalf, 1988) and our River (Colorado County) at an average density shell findings, T. cognata historically has oc- of 0.62 ± 0.13 m-2 (± standard error). By our curred in the Rio Grande River in Val Verde, conservative estimates, the total T. macrodon Maverick, Webb, and Zapata counties (Fig. 2). population size near Garwood was 2,794 Our recent records of live mussels and recently 356 BURLAKOVA ET AL. dead shells indicate that T. cognata still occurs in the middle of the 19th century, relatively in at least three counties (Maverick, Webb and few specimens were recorded (Howells, Zapata). This was confirmed by recent studies 2010, 2011; Howells et al., 1997). Moreover, on the Rio Grande (Brewster, 2015; Randklev several surveys conducted at the end of the et al., 2018). No live or recently dead T. cog- 20th century failed to recover both T. macro- nata were found in the Devils and Pecos rivers don and T. cognata. Thus, the Texas Parks & and in the Rio Grande River near Del Rio, Val Wildlife Department sampled over 190 sites Verde County. within the range of T. macrodon and found no Usually T. cognata were found in unconsoli- evidence of it at nearly all locations (Howells dated sediments (sand with some silt, often on et al., 1997). Similarly, collections by TPWD top of gravel), captured in shallow protected at over 40 sites in the Rio Grande have failed areas adjacent to gravel riffles. Some were to find even subfossil fragments ofT. cognata found up to 15-20 cm deep in a mixture of (Howells, 2003; Howells et al., 1997). These gravel and sand, between large boulders. data, coupled with the increase in habitat de- Because of its small size, it was difficult to struction, pollution, and water over-withdrawal distinguish T. cognata from gravel, adding to created an impression that both species were the difficulty of detecting this cryptic species. either extinct or on the edge of extinction. Con- The average density of T. cognata in quadrats trarily, numerous records of live T. macrodon was 0.4 ± 0.2 m-2 (79 quadrats total). The shell and T. cognata, including discovery of new length of live mussels varied from 19.2 mm to populations over the last two decades suggest 38 mm (average 29.98 ± 0.84 mm, n = 36) and that both species still maintain sizable popula- was significantly lower than the average shell tions in Texas. We believe that there are two length of dead mussels (35.54 ± 0.83 mm, reasons for this controversy. First, there are range 17–56, n = 79, P << 0.001, t-test). reasonable evidences that, due to the habitat alteration and environmental degradation, the overall range of both species have been DISCUSSION substantially reduced over the last century. The second reason, however, is related to Our study recognized both Truncilla cog- methodological challenges in sampling of nata and T. macrodon as valid species and these two species. documented species’ historical and current distribution, local densities and , thus Habitat Alteration providing information necessary for species assessment. Since 1800, 200 major reservoirs and over Tests of genetic affinities supported recogni- 1,000,000 small ponds have been created tion of both T. cognata and T. macrodon as in Texas, dramatically altering the hydrology full species, along with T. donaciformis and of the state which historically had no natural T. truncata, in agreement with most previous lentic waters (Estaville & Earl, 2008; Masser classifications. Although BP&P recognized the & Schonrock, 2006). Seventy-four major res- Texas populations of T. donaciformis as distinct ervoirs and numerous smaller impoundments from the upper Mississippi populations, the were constructed within the historical and cur- lack of data for geographically intermediate rent range of T. macrodon, altering their envi- populations and the tendency of BP&P to split ronment and fragmenting the range (USFWS, populations with low dispersal (Pfeiffer et al., 2015). Dams and impoundments reduce water 2016) lead us to believe that this is probably flows and habitat diversity, increase accumula- intraspecific variation. Relationships among tion of silt, interrupt fish and mussel life cycles the four species were not resolved. Unlike in and dispersal, and facilitate homogenization of the results of molecular studies on many other fish and mussel fauna (Burlakova et al., 2011a; amblemine genera (e.g., Campbell et al., 2005; Clavero & Hermoso, 2011; Karatayev et al., Inoue et al., 2013; Roe & Lydeard, 1998; Roe 2018b; Petts, 1984; Poff et al., 2007; Vaughn et al., 2001; Watters, 2018; Zanatta & Murphy, & Taylor, 1999). Similar to the majority of Texas 2006), Truncilla is strongly supported as mono- endemic mussels, both Truncilla species had phyletic in our analyses. In turn, it is closely never been found in lentic environments (Bur- related to Ellipsaria within Lampsilini. lakova et al., 2011a; Karatayev et al., 2012; During the first 150 years after the initial USFWS, 2015). Other threats to T. macrodon discovery of both Truncilla species in Texas include dewatering, droughts, siltation, pollu- ENDEMIC TRUNCILLA SPP. IN TEXAS 357 tion, overgrazing, overpopulation and urban- cobble) are among the main potential sources ization (Burlakova et al., 2011a; Burlakova of collector bias in qualitative sampling, & Karatayev, 2012; Howells, 2010; USFWS, abundances of small, smooth, and deeply- 2015). Most importantly, Central Texas suffers burrowed species are most underestimated from acute droughts, and the recent droughts compared to other species (Miller & Payne, of 2007–2009 and 2011 were the most severe 1993). The degree of size bias also depends since the all-time record drought of the 1950s on substrate and is higher on larger (coarser) (Nielsen-Gammon, 2011), resulting in losses versus fine substrates (Hornbach & Deneka, of previously rich mussel beds (Burlakova & 1996). Therefore, quantitative sampling with Karatayev, 2012). Habitat loss, dewatering and excavation is essential for the detection pollution has already resulted in the reduction of small individuals and accurate density of the distribution range of this central Texas estimations (Reid & Morris, 2017; Smith et endemic (Fig. 2) and have likely affected the al., 2000). Qualitative visual searches of river host fish populations as well. banks are likewise biased toward detecting Similarly, impoundments, habitat degrada- live mussels or dead shells laying near the tion, salinization, pollution, and over-extraction sediment surface, while mussels buried in of water affectT. cognata, whose range in the sediments will be overlooked. For example, United States was always limited to the Rio during a decade of qualitative visual searches Grande drainage (reviewed in Karatayev et of mussels on the Rio Grande River drainage al., 2012). The Rio Grande is at present one (2001–2010) only 2 live T. cognata were found of the most impaired rivers in the world, with (together with 270 recently dead to fossilized both water quantity and water quality issues shells, Karatayev et al., 2012), less than we being the major concerns (Dahm et al., 2005). found during one sampling with excavation (20 Although the Rio Grande still supports popu- quadrats, 3 live mussels). The recent discovery lations of T. cognata in Maverick, Webb and of numerous T. macrodon in central Texas is a Zapata counties, the distribution range of the direct result of not only more funding available species has been substantially reduced over for surveys, but also due to employment of the last 50 years (Karatayev et al., 2012). Wa- quantitative surveys, often with excavation. ter diversion from the Rio Grande during the Thus, quadrat sampling with excavation in 20th century resulted in more than a five-fold San Saba River not only resulted in the first loss of lower Rio Grande stream flow between discovery of T. macrodon, but also allowed 1905–1934 and 1951–1980 (reviewed in quantitative population estimation. Likewise, Douglas, 2009), the river bed between El Paso a detailed study revealed live T. macrodon in and Presidio/Ojinaga often lies dry (Dahm et Yegua Creek (Tsakiris & Randklev, 2016) and al., 2005; Douglas, 2009; Wong et al., 2007), in the Little River (Randklev et al., 2013), where and in 2002 and 2003 the river failed to reach T. macrodon was believed to be extirpated the Gulf of Mexico (Dahm et al., 2005). In ad- (USFWS, 2015). Therefore, effective sampling dition, impoundments alter hydrological regime of small unionid species like T. macrodon and T. and lead to extirpation of lotic unionids and cognata require quantitative sampling methods fragmentation of their range. It is likely that T. with sediment excavation and could be more cognata is now extinct in the Pecos system time- and resource-consuming than surveys because of impoundment of its lowermost of larger species. However, more thorough part by Amistad Reservoir (Metcalf & Stern, surveys will allow a better estimate of species 1976; Karatayev et al., 2012). Creation of recruitment and population size, necessary for Falcon Reservoir most likely decimated the assessment and monitoring, and may result in lotic habitat of the bivalves in the lower Rio discovery of species in waterbodies where they Grande (Neck & Metcalf, 1988). Waste water were considered to be extirpated. discharge from Laredo Sewage Plant also restricts T. cognata range in the Rio Grande Application for Conservation (Karatayev et al., 2012). In North America, three quarters of all Sampling Challenges freshwater mollusc species are considered imperiled or extinct, exceeding the imperil- Considering that small physical size, the ment levels of fish (39%) and crayfish (48%) extent of burrowing, and shell sculpture (which (Johnson et al., 2013; Williams et al., 1993). enables to distinguish mussels from gravel and Nevertheless, at a global scale, only 10% of 358 BURLAKOVA ET AL. all molluscs have been evaluated for extinc- ACKNOWLEDGMENTS tion risks, compared to 100% of mammals and birds, 86% of amphibians and 49% of This study was funded by the U.S. Fish & fish (IUCN, 2017). Lack of information on es- Wildlife Service, and Texas Parks & Wildlife De- sential parameters for these species, such as partment (TPWD) as a Joint Traditional Section distribution range and population size, greatly 6 Project to LEB, AYK, B. Lang (New Mexico hampers the assessment of their conserva- Department of Game and Fish) and M. May tion status. As a result, mussel species may (TPWD) (2011-2013), as State Wildlife Grant become rare, endangered, and even extinct Program projects to AYK, LEB (2004-2012), before the first population assessment is and a part of this study was funded by Texas conducted (Burlakova et al., 2011a; Strayer et Water Development Board (2006-2007). LEB al., 2004). This is especially true for endemic was also supported by the Research Founda- species which have a limited range restricted tion of SUNY. We appreciate the aid of Steve to remote regions with difficult access (Kara- and Don Barclays in airboat surveys of the tayev et al., 2018a). For Truncilla spp. mus- Rio Grande, T. Miller and his students (Laredo sels, rarity, small size, burrowing behavior, Community College, Texas), T. Vaughan and and location in remote areas (especially true his students (Texas International A&M Uni- for T. cognata) explained the lack of reliable versity in Laredo, Texas) in field work, and K. historic information on their population density Mehler (Great Lakes Center, SUNY Buffalo and distribution range. Therefore, thorough State) for help with maps. The TNT program surveys with appropriate techniques specifi- is available through support by the Willi Hen- cally targeting these species are necessary nig Society. Tyler Hemmingway assisted with to conduct through their historic and potential generating sequence data. range to reveal information necessary for spe- cies assessment and conservation. Both endemic Truncilla species in Texas are LITERATURE CITED in the state’s list of threatened species (Texas Register 35, 2010) and are under consider- ABELL, R., D. OLSON, E. DINERSTEIN, P. HUR- ation for federal listing by the U. S. Fish & LEY, J. DIGGS, W. EICHBAUM, S. ALTERS, W. WETTENGEL, T. ALLNUTT, C. LOUCKS & P. Wildlife Service (Federal Register, 74, 66261, HEDAO, 2000, Freshwater ecoregions of North 2009). Our surveys classified these species America: a conservation assessment. Island as rare based on their occurrence and density Press, Washington, D.C., 368 pp. (Burlakova et al., 2011a). Due to their rarity, BOGAN, A. E., 1993, ex- their biology and ecology, including reproduc- tinctions (: Unionidae): a search for tive cycle, and potential fish hosts have never causes. American Zoologist, 33: 599–609. BOGAN, A. E. & W. R. HOEH, 2000, On be- been studied (Howells, 2010). Until the present coming cemented: evolutionary relationships study, even the species’ taxonomic status was among the genera in the freshwater bivalve unclear. Our study supported recognition of family Etheriidae (: Unionidae). Pp. T. cognata and T. macrodon as full species 145–158, in: E. M. Harper, J. D. Taylor & J. and therefore warranted for protection and A. Crame, eds., The evolutionary biology of the conservation. The reasons for decline of both Bivalvia. Geological Society of London, Special Publications 177. Geological Society, London, endemic Truncilla are similar and include water vii + 494 pp. flow alteration and impoundments, water pollu- BOYER, S. L., A. A. HOWE, N. W. JUERGENS & tion and over-withdrawal. Therefore, the most M. C. HOVE, 2011, DNA-barcoding approach important priority for species conservation is to to identifying juvenile freshwater mussels guarantee the unimpeded water flow, including (Bivalvia: Unionidae) recovered from naturally- infested fishes. Journal of the North American implementation of environmental flows as an Benthological Society, 30: 182–194. integral part of the water management, further BRETON, S., D. T. STEWART, S. SHEPARDSON, limitation of water withdrawal, and restriction R. J. TRDAN, A. E. BOGAN, E. G. CHAPMAN, of new dam and reservoir construction. The A. J. RUMINAS, H. PIONTKIVSKA & W. R. second most important factor in Truncilla HOEH, 2011, Novel protein genes in habitat protection is more stringent control of mtDNA: a new sex determination system in freshwater mussels (Bivalvia: Unionoida)? Mo- water pollution. Protection of these species lecular Biology and Evolution, 28: 1645–1659. will contribute to conservation of other Texas BREWSTER, B. E., 2015, Conservation sta- imperiled and endemic species in the area. tus and habitat assessment of the Mexican ENDEMIC TRUNCILLA SPP. IN TEXAS 359

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Revised ms. accepted July 7, 2018