Cyprogenia aberti

Cyprogenia aberti is not a monophyletic group and may comprise 2 and possibly 5 distinct taxa that are cryptic and difficult to distinguish. Kim and Roe (2021) suggest breaking C. aberti into the following units: 1 C. "aberti" in Black/Spring rivers, Arkansas, 2. C. "aberti" . Saline River, Arkansas (Ouachita Highlands) 3. C. "aberti" in the Ouachita/Caddo rivers, Arkansas, 4. C. "aberti" in the St. Francis River, Missouri, . 5. C. "aberti" in Spring and Fall rivers (Ozark Highlands) in Kansas. However, because of the small number of samples from the in the Fall River and total lack of samples from the Verdigris River, formal taxonomic changes will require more thorough sampling. Confusion regarding the type locality of Unio lamarckianus Lea, 1852, requires resolution to determine whether that name is available for the Ouachita River drainage population. Williams et al. (2017) recognize the distinctiveness of this species but defer including it in their list until a specific epithet can be designated.

In analyses by Serb (2003, 2006), there are 2 major clades of fanshells, A and B. Cyprogenia from the Black River (White River system) are closely related to C. stegaria from the Clinch River in Tennessee, and form one clade within clade A. Cyprogenia from the upper Arkansas system also form one well-supported clade within clade A. A portion of the Cyprogenia from the Ouachita and St. Francis River systems form the final clade in clade A. Cyprogenia from the St. Francis, White and Ouachita River systems form the two clades within Clade B. Serb (2006) surmises that the best fit scenario to the phylogenetic results obtained is that C. aberti contains cryptic biological diversity including distinct lineages (species) of unionids on separate evolutionary paths including two distinct non-interbreeding entities occurring sympatrically in the Ouachita System with reproductive barriers. She does not go so far as to separate the entities into distinct species yet but suggests other independent data (such as life history traits) are needed to support designation of multiple species. Based on morphology, the above work by Serb, and differences in host specificity and conglutinate morphology, Eckert (2003) and Barnhart and Eckert (2004) believe the type population in the Verdigris River system should retain the name Cyprogenia aberti. Further study of genetics and host requirements of populations in the Black River and populations east of the Mississippi are needed. In a study of mitochondrial DNA sequences, conglutinate morphology, and host fish compatibility, two different mtDNA clades were found to exist sympatrically within most populations (also diagnosed by at least one morphological character- egg color), but the hypothesis of heritage infidelity of the two different mitochondrial genomes was tested and falsified. However, populations from the major river systems utilized different host fish suggesting populations are not ecologically exchangeable with one another and may represent different taxa (cryptic species) (see Serb and Barnhart 2008).

The taxon is a regional endemic that has experienced significant declines in the last 40 years and is predicted to continue to do so. It has been extirpated from a 17 of the 32 historically occupied watersheds and is at low numbers throughout most of its remaining range. Most populations are under some threat of habitat degradation. A 2020 analysis by the USFWS concludes that declines are almost certain to continue over the next 40 years.

Endemic to the USA. Mostly likely this "species" represents a complex of cryptic species found in Kansas, Oklahoma, Missouri, and Arkansas. It is extirpated from Louisiana. Cyprogenia shells are known from archeological samples in Mississippi but species identification of those samples is uncertain (USFWS 2020). The species complex is considered endemic to the Ozark and Ouachita mountain ranges of the interior highlands west of the Mississippi River. It is known historically from the Little Missouri, Saline, Caddo and Ouachita Rivers (Red River drainage); Spring, Elk, Fall, Caney, Neosho, Verdigris and Shoal Rivers (Arkansas River drainage) Little Black, Black, Buffalo, Current, Spring, Strawberry, and White Rivers, and Cane and Castor Creeks (White River drainage) and the St. Francis River. The species is now extirpated from the Caney, Elk and Neosho rivers (Obermeyer et al., 1997; Vaughn, 1998; Couch, 1997), the Oklahoma portion of the Verdigris and Spring rivers (Vaughn, 1998), and from Castor and Cane Creeks, Missouri (Oesch, 1995). Occurrences in Arkansas are more viable with populations in at least 8 rivers and locally abundant in 2 or 3 of them (Harris et al., 1997). It was collected in the Saline River, Arkansas, after several years of supposed absence (Davidson and Gosse, 2003). Archeological remains exist on Big Sunflower and Yazoo Rivers in Mississippi, but there are no extant populations (Jones et al 2005). The most recent genetic investigation (Kim and Roe 2021) of suggests that C. aberti could be regarded as 6 taxonomic groups.

The species complex is currently known from nine streams in Arkansas, five in Missouri, and three in Kansas. Based on the definition of an occurrence, there are 20 total known occurrences (nine in Arkansas, seven in Missouri, and four in Kansas).

USFWS (2020, 2023) summarized the factors that were the largest risk to future viability of the species: water quality degradation, altered flow, landscape changes, and habitat fragmentation, all of which are exacerbated by climate change. The "species" currently occupies 15 of 31 historical watersheds. That assessment looked at two likely scenarios, 1. with a moderate deterioration in conditions, 2. with a severe deterioration in conditions. Under scenario 1. extirpation was likely within 40 years for 7 of 15 currently occupied watersheds with 5 in moderate condition and the remainder in low condition (i.e. no recruitment). Under scenario 2 extirpation was likely in 7 of the 15 currently occupied watersheds in the same time period but all in low condition where there was no recruitment of young mussels in the population and long-term extinction. No watershed was predicted to have a population in a high condition in either scenario.

The species is threatened by impoundments and channelization, gravel mining, agricultural practices that result in siltation and organic inputs, and the ultimate spread of the zebra mussel which now occurs in the Arkansas River drainage. Obermeyer (2000) found a reduction in the overall range associated with habitat loss due to large impoundments. St. Francois, Reynolds, and Iron Counties in Missouri are located within the Southeast Missouri Lead Mining District, an area that was mined extensively for lead and zinc for more than a century. As a result of this, large amounts of toxic metals including cadmium, lead, zinc, and nickel were released and are continuing to be released into Missouri's environment (Mosby and Weber, 2009). These metals are known to have an impact on freshwater mussels (Naimo 1995). Non-native species, such as Asian Clam (Corbicula fluminea) and Zebra Mussel (Dreissena polymorpha) occur in portions of the Fanshell mussels range and negatively affect mussel survival and reproduction. The Asian Clam competes with native mussels, particularly juveniles, for food, nutrients, and space (Neves and Widlak 1987, Leff et al. 1990). Both of these non-native mollusks may ingest sperm, glochidia, and newly metamorphosed juveniles of native mussels (Strayer 1999, Yeager et al. 2000). The introduced Black Carp (Mylopharyngodon piceus), which feeds on mollusks as an adult, is a potential threat to mussels (Strayer 1999). Climate change is expected to exacerbate several of the threats because of increased flood events. Flooding increases sedimentation, runoff of chemical contaminants, and facilitates the movement of alien species into new watersheds. Direct impacts of climate change include droughts which reduce waterflows and causes rising water temperatures that are predicted to increase mortalities (USFWS 2020, 2023).