Diversification of beaked redfish, Sebastes mentella, along a depth gradient in the central North Atlantic
Despite the striking physical and environmental gradients associated with depth variationin the oceans, relatively little is known about their impact on population diversification,adaptation and speciation. The pelagic beaked redfish, Sebastes mentella, exhibits depthassociatedpatterns of population genetic substructure in the central North Atlantic, with awidely distributed population inhabiting waters between 200 and 550m depth and localisedputative populations dwelling at greater depths, between 550 and 900m. This PhD projectimplements a multidisciplinary approach to explore and understand aspects of thisbiological complexity, in the context of depth.To investigate depth as a factor driving population divergence and adaptation,sampling was carried out to target S. mentella at different depth layers and across most ofits distribution range. Through the use of mitochondrial and nuclear markers on samplesspanning a period between 2006 and 2013, the existence of two strongly divergentevolutionary lineages is revealed, with significantly different geographic distributionpatterns and dwelling at different depths. The first empirical evidence to explicitly testgenotype and phenotype of Sebastes vision associated with shifts in habitat depth ispresented, by conducting spectral analysis of rod visual pigments. Additionally, de novoRNA-seq analysis of redfish retina transcriptome is presented for a subset of “shallow” and“deep” individuals, in order to characterise differential expression of candidate genesinvolved in visual perception in organisms adapted to different depths. Furthermore, amarket accuracy survey of redfish sampled across Europe from various retailers was crossreferencedagainst data currently held in public databases. Results revealed the existence ofinaccurate reference sequences in data bases, likely stemming from speciesmisidentification from previous studies, which currently hinders the efficacy of DNAmethods for the identification of Sebastes products. Overall, we cast new light on the roleof depth in maintaining biodiversity in the oceans, and consider the practical implicationsof such findings.
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