Diversity and Conservation of the Southern Cavefish, Typhlichthys subterraneus

Abstract

The Southern Cavefish, Typhlichthys subterraneus, is one of the most fascinating stygobionts of the Amblyopsidae due to undescribed diversity within it. I investigated aspects of morphological and molecular diversity for their potential to describe diversity and how those aspects influenced the conservation status of the species. I first quantified differences in shape within the Southern Cavefish utilizing Geometric Morphometrics. Firstly, the presence of ontogenetic allometry within the species was investigated. Relative Warps analysis was utilized to identify the axes of major shape variation. Specimens were then grouped into life history stages. Support for ontogenetic allometry was discovered by the significant prediction of shape (Relative Warps) by life history stage (standard length). Secondly, I performed an allometric correction to develop a size-independent morphospace. Principal Components Analysis indicated the size-independent major axes of shape variation occurred within the head length to predorsal length ratio and head size and shape in both lateral and dorsal views. Specimens were grouped by four categories: 1) aquifer association, 2) genetic lineage, 3) hydrological basin, and 4) ecoregion. Utilizing ANOVA and Tukey’s Post-Hoc tests, I found shape differences among categories for some groups, but shape could not distinguish all groups from one another in any category. Poor agreement between morphology and multiple categories can be explained by convergent evolution of forms in caves, low genetic resolution, and possibly cryptic morphology (i.e., no morphological characters to define diversity). Cryptic morphology coupled with collection difficulties and recent divergence of genetic lineages can inhibit the designation of species in stygobiont taxa. By designating Evolutionarily Significant Units (ESUs), the conservation community can create management plans to conserve the genetic diversity within a group. The lineages of Typhlichthys subterraneus were designated as ESUs and given conservation ranks; however, newly sampled populations had not been previously investigated as to their association with existing lineages. Genomic DNA was extracted from fin clips and three genes were amplified (ND2, S7, Rhod). Sequences were aligned and edited manually in Geneious, and Maximum Likelihood phylogenies were generated for each gene as well as a concatenated dataset. Newly sampled populations were recovered within existing lineages but unique positions of two previously designated caves were found. Conservation ranks utilizing both the NatureServe and IUCN Red List criteria were recalculated for each lineage. One lineage was downgraded to Vulnerable due to population sizes and another newly designated lineage was given a rank of Critically Imperiled (NatureServe) and Critically Endangered (IUCN Red List). Nonmonophyletic relationships within the phylogenies may be a result of gene flow between aquifers or low genetic resolution due to incomplete lineage sorting.