M.S. Marine Biology
Once so abundant as to be called the ‘common’ angelshark, Squatina squatina has been extirpated from nearly the entirety of its historical range, from the eastern North Atlantic, to the Mediterranean Sea [International Union for the Conservation of Nature (IUCN) Red List: Critically Endangered]. The angelshark now only occurs in any abundance in the waters surrounding the Canary Islands. I present the first genetic assessment of the angelshark’s population dynamics and diversity from three locations within the Canary Islands archipelago: Gran Canaria, Tenerife, and Lanzarote. Using a suite of individual mitochondrial genome regions [Control region (CR), NADH dehydrogenase subunit 2 (ND2), NADH dehydrogenase subunit 4 (ND4), and Cytochrome c oxidase subunit 1 (COI)], the complete mitogenome, and nuclear markers [microsatellites and Internal Transcribed Spacer 2 (ITS2)] this work aimed to i) assess the genetic diversity of the angelshark in comparison to other endangered or historically overfished elasmobranchs, ii) examine the relative nucleotide variability across different marker sets, and iii) assess fine-scale multi-locus population structure within the Canary Islands, as well as broad-scale population genetic structure of angelsharks throughout its historic Eastern Atlantic and Mediterranean range. Results revealed exceptionally low genetic diversity across all individual mitochondrial regions sequenced (CR, π % = 0.0046 ± 0.016; ND2, π % = 0; ND4, π % = 0; COI, π % = 0), yielding some of the lowest values reported to date in any elasmobranch. Mitogenome analysis followed this low diversity trend with only 11 single nucleotide polymorphisms seen across all Canary Island individuals in a genome of 16,689 bp (π % = 0.0257 ± 0.0166). Furthermore, screening of 35 microsatellite markers across 34 individuals revealed all but two loci to be monomorphic and nuclear ITS2 showed negligible diversity. Lanzarote showed significant population differentiation from both Gran Canaria (ΦST = 0.073, p = 0.004, FST = 0.113, p = 0.00) and Tenerife (ΦST = 0.029, p = 0.001, FST = 0.065, p = 0.001) at the CR. Haplotype analysis of whole mitogenomes also demonstrated Lanzarote individuals forming a separate lineage from angelsharks at the other two islands. Broad- scale structure across the angelshark’s historical range was detected between the Canary Islands and Mediterranean (ΦST = 0.792, p = 0.000, FST = 0.785, p = 0.000), indicating a regional break between populations. The exceptionally low levels of genetic diversity in angelsharks in the Canary Islands, as well as indications of population isolation from the rest of the angelshark’s historical range, suggest an immediate need for strong conservation measures to ensure the protection and continued persistence of this highly vulnerable and ecologically unique species.
Cristin Keelin Fitzpatrick. 2018. Genetic Population and Evolutionary Dynamics of the Angel Sharks, Squatina spp.. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, . (478)
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