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Federal Register / Vol. 86, No. 119 / Thursday, June 24, 2021 / Rules and Regulations
the authors findings Sorensen 2014, pers. comm. As a result, we have a high level of confidence in the results of the Culver et al. 2013 genetic study.
For the Kanab ambersnail to be considered a distinct subspecies, nuclear and mitochondrial DNA tests should show that the three populations cluster together when compared to other populations of ambersnails Culver et al.
2013, p. 55. However, the Vaseys Paradise population does not cluster with the other two Kanab ambersnail populations and the degree of variation shown in Vaseys Paradise from the other populations is not unique enough to constitute a subspecies on its own, as it shares markers with several nearby populations of non-listed Oxyloma snails Stevens et al. 2000, p. 41; Culver et al. 2013, pp. 5557.
The genetic uniqueness in Vaseys Paradise may be attributable to flooding, which can erode away ideal vegetation or habitat, leaving only a few individuals able to survive and reestablish the population at that site, creating genetic bottlenecks. Genetic diversity at these types of sites will often be lower than at sites that have experienced shortor long-distance dispersals Culver et al. 2013, p. 55.
Furthermore, ambersnails have the ability to self-reproduce, allowing for colonization of new areas by only one individual. This ability may explain how many genetically distinct populations of Oxyloma developed in a relatively short time period Culver et al. 2013, p. 56. At least one or more bottleneck events in the past, likely due to flooding, caused unusual population genetic events Culver et al. 2013, p. 55.
Overall, these studies show that shell morphology and anatomical characteristics that were once considered diagnostic do not alone reliably correspond with the results from genetic analyses of Succineidae snails Hoagland and Davis 1987, p. 519;
Pigati et al. 2010, p. 523. Samples originally identified as different species or subspecies based on physical differences are consistently found to be related closely enough to qualify as members of the same species based on genetic studies Culver et al. 2013, entire; Miller et al. 2000, entire; Stevens et al. 2000, entire. Traditionally, shell morphology, such as their slender and drawn-out spire and short shell aperture, was used to distinguish the Kanab ambersnail from other members of Oxyloma Pilsbry 1948, pp. 797798.
However, shell shape can vary as much within a population as within a species Hoagland and Davis 1987, p. 519.
Therefore, it is important to consider other factors such as genetics, anatomy,
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and habitat to determine a species within Oxyloma Hoagland and Davis 1987, p. 519; Sorensen and Nelson 2002, p. 5.
In addition to shell morphology, reproductive anatomy phallus shape was previously a main determining factor of the Oxyloma genus Miller et al. 2000, p. 1853. However, anatomical descriptions used to classify the Kanab ambersnail had no quantifying factors, such as prostate gland length, and soft tissues were difficult to measure objectively Pilsbry 1948, p. 798; Culver et al. 2013, pp. 5253. It is difficult to achieve standard anatomical measurements with repeatability because of the flexibility and elasticity of soft tissues Culver et al. 2013, p. 18.
Overall, anatomical characteristics have been found to vary greatly within Oxyloma Culver et al. 2013, p. 52.
There have been at least two instances when a species of snail was placed in the wrong genus due to relying solely on the reproductive anatomy Johnson et al. 1986, p. 105; Miller et al. 2000, p.
1853. In another case, variation in anatomical structure was found in the blunt ambersnail, leading the authors to conclude that the species was not restricted geographically as initially believed Franzen 1963, p. 94. Previous Oxyloma studies have used only one or two specimens to determine the species taxonomic status, which makes it difficult to properly assess the true status Hoagland and Davis 1987, p.
515.
Standards for quantifying anatomy are minimal and not descriptive enough, with the use of such words as small, medium, and large, which are vague terms and not measurable Hoagland and Davis 1987, p. 478. Anatomical characteristics should not be the only factor to determine a species within Oxyloma, even with an understanding of the individual and geographical variation Franzen 1963, p. 83.
Variation between populations, anatomical differences among individuals, overlapping habitat, and minimal repeatability with measurements of anatomical features make it difficult to rely on anatomical descriptions to determine species classification Franzen 1964, p. 80;
Sorensen and Nelson 2002, pp. 45.
Overall, reproductive anatomy is likely not a good species indicator in snails;
instead, genetic relationships provide the most reliable method of classifying taxa.
In summary, these analyses present multiple interpretations of the taxonomy of the Kanab ambersnail, none of which correlates to that of our original listing. Although the exact
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taxonomy of the genus Oxyloma and its constituent species remains uncertain, it is clear that the populations designated as the Kanab ambersnail do not make up, together or separately, a valid subspecies. The 1992 final listing rule for the Kanab ambersnail 57 FR 13657;
April 17, 1992 relied on the best available information at the time, and included only snails found in Vaseys Paradise in Arizona and Three Lakes and Kanab Creek in Utah. This situation has changed with the addition of the 2013 genetic study of the Oxyloma genus in Utah and Arizona Culver et al.
2013, entire.
The various published and unpublished genetics reports described above offer different conclusions about how Succineid snails should be classified, particularly within the genus Oxyloma. However, none of the genetic studies provides support for Oxyloma haydeni kanabensis as a valid subspecies. Additionally, available genetic evidence suggests that at least one population identified as Kanab ambersnail is more closely related to other nearby Oxyloma populations than it is to the other two Kanab ambersnail populations.
Therefore, we are delisting the Kanab ambersnail due to new taxonomic information that indicates that it is not a valid taxon, based on the best available science. The currently listed entity for the Kanab ambersnail, restricted to Vaseys Paradise and Upper Elves Canyon, Arizona, and Three Lakes, Utah, is not a valid taxonomic subspecies. We are unable to evaluate the populations identified as the Kanab ambersnail relative to the larger entity because the larger entity has not yet been defined from a taxonomic perspective. If we had additional updated information available about the taxonomy of the Oxyloma genus, we would conduct a status assessment of the larger entity, but in this case we do not have enough information to conduct that analysis. We do not consider the absence of information on the larger taxonomy of a group to be sufficient reason to keep an invalid subspecies listed as endangered.
Summary of Comments and Recommendations In the proposed rule published in the Federal Register on January 6, 2020 85
FR 487, we requested that all interested parties submit written comments on our proposal to delist the Kanab ambersnail by March 6, 2020. We also contacted appropriate Federal and State agencies, scientific experts and organizations, and other interested parties and invited them to comment on the proposal.

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