Not every skate is a Biscuit: a multimarker genetic characterisation of Raja straeleni and related taxa in the Central-Western Africa

Understanding species boundaries and population connectivity in elasmobranchs is essential for biodiversity assessment and conservation management. This study investigates the genetic diversity and population structure of skates of the genus Raja along the Central-Western African coast, with particular focus on Raja straeleni. Samples from Angola previously identified as Raja sp. were also analysed to assess whether mitochondrial differentiation is supported by nuclear markers. A multilocus molecular approach was applied, combining mitochondrial markers (Cytochrome c Oxidase I – COI, and NADH dehydrogenase subunit 2 – NADH2) with nuclear microsatellites (SSRs), to evaluate divergence among closely related taxa and intraspecific genetic diversity within R. straeleni. Analyses included 310 individuals for COI, 130 for NADH2, and 90 for SSRs, integrating newly collected data with public sequences from related species. Mitochondrial analyses confirmed a clear genetic separation between R. straeleni and closely related taxa, identifying Raja sp. as a distinct evolutionary lineage. Moderate haplotype and nucleotide diversity within R. straeleni suggest demographic stability across its distribution. Microsatellite analyses of R. straeleni and Raja sp. samples from Cape Town, South Coast, and Angola revealed weak geographic structuring. FST values, Bayesian clustering, and multivariate analyses supported the presence of a single genetically cohesive population, with no clear nuclear differentiation between R. straeleni and Raja sp. Overall, integrating mitochondrial and nuclear data highlights strong interspecific divergence but limited intraspecific variability. These results improve taxonomic resolution within Rajidae and provide a basis for conservation strategies in a poorly studied marine biodiversity hotspot.