Population structure of Squatina guggenheim (Squatiniformes, Squatinidae) from the south‐western Atlantic Ocean

Abstract

Population genetic analyses based on both mitochondrial cytochrome b and the internal transcribed spacer 2 of recombinant (r)DNA genes were implemented to examine hypotheses of population differentiation in the angular angel shark Squatina guggenheim, one of the four most-widespread endemic species inhabiting coastal ecosystems in the south-western Atlantic Ocean. A total of 82 individuals of S. guggenheim from 10 sampling sites throughout the Río de la Plata mouth, its maritime front, the outer shelf at the subtropical confluence and the coastal areas of the south-west Atlantic Ocean, were included. The analysis of molecular variance (AMOVA) based on the second internal transcribed spacer (its-2) region supports that the samples from the outer shelf represent an isolated group from other sites. Historical gene flow in a coalescent-based approach revealed significant immigration and emigration asymmetry between sampling sites. Based on the low level of genetic diversity, the existence of a long-term population decline or a past recent population expansion following a population bottleneck could be proposed in S. guggenheim. This demographic differentiation suggests a degree of vulnerability to overexploitation in this endemic and endangered south-west Atlantic Ocean shark, given its longevity and low reproductive potential.

Angel sharks (Squatinidae): A review of biological knowledge and exploitation

“…Available information from tagging studies (Capapé et al, 1990;Quigley, 2006;Standora & Nelson, 1977) indicates that spatial movements of angel sharks may be limited, with genetic studies (Gaida, 1997;Garcia et al, 2015;Ramírez-Amaro et al, 2017) and associated life history parameters (Natanson & Cailliet, 1986;Romero-Caicedo et al, 2016) indicating that fine-scale population structuring may occur. Cailliet et al (1993) even listed the "lethargic and residential behaviour" of S. californica as one of the factors that would make it susceptible to overfishing, and the expansion of the fishery targeting a localized stock of S. californica had also been highlighted as a cause for concern by Holts (1988) between 1976-1977 (32.6 kg h −1 ) and 1996-1997 (1.3 kg h −1 ) at locations off New South Wales, although there was also pronounced variability in the catch rates between survey locations and depth strata, as well as between surveys.…”

Multilocus phylogeography of the endemic and endangered angular angelshark (Squatina guggenheim) in the Southwest Atlantic Ocean

“…Low genetic diversity is considered a common pattern in the elasmobranch group due to its slow rates of molecular evolution and life history characteristics (O'Brien et al 2013;Domingues et al 2018). In contrast, this genetic diversity pattern (high haplotype diversity and low nucleotide diversity) is not consistent with the previous regional study by García et al (2014), which can be justified by its narrow geographic sampling scale. Substantial intraspecific differences were observed among populations, where southern Southwest Atlantic regions (SOBR and UYAG) showed higher levels of genetic diversity and a larger number of unique haplotypes compared to southeastern Brazil regions (BSSP and SCSP), as well as reported for the Brazilian sharpnose shark, Rhizoprionodon lalandii, in the same region (Mendonça et al 2013).…”

“…Regionally, the species is reported as Critically Endangered in the Brazilian regional conservation status classification (ICMBio/MMA, 2018) and Endangered for the Patagonian Sea (Cuevas et al 2020) Regardless of the high vulnerability and endemism of S. guggenheim, only one population genetics study was performed in the Southwest Atlantic and was around the Rio de La Plata front, remaining its regional connectivity in an early stage of understanding (García et al 2014). Against this background, the aim of the present study was to evaluate the phylogeography, connectivity, and evolutionary process that may shaped the current pattern of S. guggenheim over its distribution range in the Southwest Atlantic through a multilocus approach, based on three mitochondrial DNA (mtDNA) molecular markers.…”

Population genetics of zig-zag eel (Mastacembelus armatus) uncover gene flow between an isolated island and the mainland China

“…Additionally, mitochondrial markers were mostly used in M. armatus population studies, only few nuclear markers like SSR and EPICs, while no reports were based on nuclear ribosomal DNA (nrDNA) markers to reveal their genetic diversity (Wang et al, 2012;Zou, 2013;Chen, 2014;Yang et al, 2016;Lin, 2017;Jiang, 2018;Gao et al, 2022). It is well known that nrDNA markers have been successfully employed in various fish population research (Mladineo et al, 2013;Garcia et al, 2015;Agdamar and Tarkan, 2019), such as 18S, ITS1, ITS2 and 28S, due to their high evolutionary rates (Presa et al, 2002). Therefore, in this study, we employed the concatenated 18S and ITS2 sequences to assess levels of genetic diversity and differentiation of M. armatus populations from China and Vietnam at different spatial scale.…”