Divergence by depth in an oceanic fish

Abstract

Despite the striking physical and environmental gradients associated with depth variation in the oceans, relatively little is known about their impact on population diversification, adaptation and speciation. Changes in light associated with increasing depth are likely to alter the visual environment of organisms, and adaptive changes in visual systems may be expected. The pelagic beaked redfish, Sebastes mentella, exhibits depth-associated patterns of substructure in the central North Atlantic, with a widely distributed shallow-pelagic population inhabiting waters between 250 and 550 m depth and a deep-pelagic population dwelling between 550 and 800 m. Here we performed a molecular genetic investigation of samples from fish collected from ‘shallow’ and ‘deep’ populations, using the mitochondrial control region and the gene coding for the visual-pigment rhodopsin. We identify patterns suggestive of potential adaptation to different depths, by detecting a specific amino acid replacement at the rhodopsin gene. Mitochondrial DNA results reflect a scenario of long-term demographic independence between the two S. mentella groups, and raise the possibility that these ‘stocks’ may in fact be two incipient species.

Three‐dimensional post‐glacial expansion and diversification of an exploited oceanic fish

“…The data set was also complemented by the 50 mtDNA control region and 22 rhodopsin sequences that first revealed the existence of two depth‐associated S. mentella clades in the Irminger Sea (Shum et al . ; GenBank Accession nos: mtDNA, ‐; rhodopsin, ‐) and by 68 randomly selected archived tissue samples (previously genotyped at 12 microsatellite loci by Stefánsson et al . ), to better cover the current biogeographical spread of the species: west Faroe ( n = 20) and east Faroe ( n = 18) collected off the Faroese shelf in 2007, Norwegian shelf ( n = 10), and pelagic collections from Norwegian international waters ( n = 20), also from 2006 to 2007 surveys (Fig.…”

“…; Shum et al . ). While a demersal unit is recognized along the Icelandic continental shelf and slopes (Cadrin et al .…”

“…; Shum et al . ), with a lack of adequate standardized sampling and replication across depth layers where different beaked redfish assemblages occur (Bergstad ; Planque et al . ).…”

“…Specifically, we aim to (i) examine the phylogeographic history of oceanic S. mentella across the northeast Atlantic, with special attention to the main two clades identified in Shum et al . (), (ii) assess the degree to which mitochondrial lineage distribution fits with the currently perceived S. mentella stock structure and (iii) reconstruct the most realistic scenario for the evolution of this species in the North Atlantic.…”

The life aquatic: advances in marine vertebrate genomics

“…The range of species that inhabit different marine zones are very different and face distinct challenges, including -but not limited to -varying salinity, light and pressure due to depth. For example, rockfishes of the genus Sebastes have radiated to inhabit a range of depths 113 , and within some species (for example, the beaked redfish, S. mentella, in the North Atlantic) these populations have diverged into shallow (250-500 m) and deep (550-800 m) ecotypes 114 . The shifts in light levels that occur with increasing depth are also associated with repeated independent parallel occurrence of the same putatively functional amino acid replacements in the rhodopsin (RHO) gene, at the interspecific level among different Sebastes species 113 and at the intraspecific level within S. mentella 115 .…”