Genetic diversity in the American elephantfish (Chimaeriformes: Callorhinchus callorynchus ) and among its congeners

Abstract

Understanding genetic population structure and connectivity is essential for effectivespecies-specific management and conservation strategies. The American elephantfishCallorhinchus callorynchus is targeted and retained as incidental catch in commercialand recreational fisheries in Chile and Argentina. Its wide-ranging distribution acrosssouthern South America may require transnational co-operation to ensure sustainable use, but its current population structure is not known. In this work, we analysedthe levels of genetic diversity and differentiation within C. callorynchus in SouthAmerica using two mitochondrial markers, the control region (CR) and the cytochrome oxidase subunit I gene (CO1). Moreover, we assessed levels of genetic diversity within, and divergence among, the three extant callorhinchids (genusCallorhinchus), a group that exhibits allopatric geographical distributions in the southern hemisphere. Overall, sequence analyses of the mitochondrial CR and the CO1revealed extremely low levels of sequence variation both within and among Callorhinchus species. Genetic homogeneity was found throughout the range ofC. callorynchus coupled to low-frequency haplotype sharing across spatially distantlocations in Chile and Argentina, suggesting gene flow along the South Americancoast. Moreover, our analyses supported a scenario of recent population expansionof the species in South America. Given the absence of dispersive eggs or juvenilestages in chondrichthyans, gene flow is mainly mediated by actively swimming adults.Based on the available data, gene flow in callorhinchids appears to occur along continuous coastal regions, with deep oceanic waters serving as strong barriers. Findingshere provide an important baseline for future research on dispersal and gene flow inholocephalans.