The Carpiodes Conundrum: Molecular Hypothesis Testing Informs Conservation Applications for Carpsuckers...

Sufficient taxonomic understanding is critical for biodiversity conservation. This is particularly relevant among freshwater fishes, where cryptic undescribed species cause difficulties for promoting conservation efforts. Catostomidae (i.e., suckers) is a family of freshwater fishes with cryptic diversity and biological traits that make them difficult to classify taxonomically. Among suckers, the Carpsuckers (Carpiodes carpio, Carpiodes cyprinus, Carpiodes velifer) possess uncertain taxonomic classifications and cryptic diversity despite a rich history of research. Within Carpiodes, uniquely slender-bodied populations occurring in Western Gulf of Mexico drainages suggest potential for an undescribed species. Originally collected in the Llano River, tributary to the Texas Colorado River, Llano River Carpsucker are morphologically similar to C. cyprinus. Our study explores how historical biogeographic scenarios may have led to lineage diversification of Llano River Carpsucker. We test competing molecular hypotheses (i.e., Native Endemic Species Hypothesis, Native Lineage Hypothesis) to explain the native origin of Llano River Carpsucker and further assess whether the taxon is nonnative C. cyprinus (i.e., Species Introduction Hypothesis), each carrying vastly different conservation and management implications. Additionally, we assessed phylogenetic relationships across the entire genus Carpiodes. Phylogenetic analyses recovered divergent lineages of C. cyprinus in Eastern Gulf of Mexico drainages, suggesting the presence of cryptic undescribed species. Llano River Carpsucker specimens were resolved in unique lineages relative to C. cyprinus, with mitochondrial haplotypes closely related to Mississippi C. cyprinus (p-distance < 0.005). Our study suggests Llano River Carpsucker represent native C. cyprinus, supporting our Native Lineage Hypothesis. We further provide evidence that C. cyprinus readily hybridizes with C. carpio, resulting in mitochondrial introgression across much of their distribution. Lastly, we provide recommendations to promote conservation efforts and discuss further research directions to understand deeper evolutionary and environmental mechanisms behind morphologically and genetically unique C. cyprinus inhabiting Western Gulf of Mexico drainages of Texas.