Comparative assessment of population genetics and demographic history of two congeneric deep sea fish species living at different depths

Abstract

The mechanisms that determine population genetic structure in the marine environment are poorly understood, as are the processes that drive population dynamics. One potential factor is depth, with especially those species living in the abyss inhabiting a distinct environment with respect to habitat complexity, pressure, the distribution of resources and environmental change over time. Here we consider a deep sea fish genus, Coryphaenoides, which has many named species, including 8 abyssal species. We provide data in support of the existence of 2 distinct evolutionary lineages within the genus, associated with depth, and also provide detailed population genetic data for the abyssal species (C. brevibarbis) for comparison with available data on a congeneric species inhabiting shallower waters (C. rupestris). The abyssal species showed no sign of population genetic structure across a thermal oceanographic boundary (the Sub-Polar Front), for which C. rupestris showed differentiation. An assessment of historical demographics suggested a decline in population size for both species, but a faster and more severe decline for the abyssal species. We consider these data in the context of environmental gradients and potential evolutionary mechanisms. Relatively low effective population size estimates for both species emphasize the importance of understanding these processes for the effective conservation and management of deep sea fish stocks. KEY WORDS: Population genetics · Demographic decline · Marine fish · Deep sea Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 434: [155][156][157][158][159][160][161][162][163][164] 2011 habitat in the deep sea, and focus on 2 species inhabiting different depths with respect to their population size, structure and dynamics over time.Deep water at the Mid-Atlantic Ridge of the North Atantic is inhabited by at least 16 macrourid species in 9 genera (Bergstad et al. 2008a). The most numerically dominant genus is Coryphaenoides. In particular, the species C. rupestris, C. brevibarbis and C. armatus rank amongst the most abundant demersal fishes on the ridge or in the deep axial valleys and fracture zones.The round-nosed grenadier Coryphaenoides rupestris is a deep-sea demersal fish distributed across the North Atlantic and found primarily at a depth range of 800 to 2600 m (Coad & Reist 2004). A commercial fishery for C. rupestris began in the NW Atlantic in 1967 (Atkinson 1995, with declining catches since the 1970s (Koslow et al. 2000), resulting in an estimated 99.6% decline in abundance over a period of 26 yr (Devine et al. 2006). In the NE Atlantic, fisheries began in the 1970s, quickly peaking before undergoing a severe decline (Koslow et al. 2000) with an estimated loss in spawning biomass to approximately 30% of pre-fishery levels (ICES 2002).Previous work on this species has identified geographically well-separated spawning areas in Norwegian fjords and in the Skagerrak (Bergstad 1990, Bergstad & Gordon 1994, as well ...

Population Differentiation and Species Formation in the Deep Sea: The Potential Role of Environmental Gradients and Depth

“…Finally, we often find closely related congeners separated bathymetrically (e.g. [52,54,109,130,131,133,134]), precisely the pattern that would emerge if species formation was frequently mediated by depth-related environmental gradients. Depth is the most frequently observed habitat difference between sibling species [23].…”

“…Speciation, ongoing or recent, is often invoked in explaining discordance between nuclear and mitochondrial loci (e.g. [24,70,98-100]), and such evidence has been found recently in several marine taxa [52,54,58-60,101]. …”

“…For example, population divergence based on mitochondrial markers was much greater for protobranch bivalves separated by 3km of depth than 10,000 km of geographic distance [48,51]. Another interesting pattern is that population divergence appears to decrease with depth, suggesting that continental margins might be the primary site of adaptive radiation for deep-sea organisms [47,52-54]. Probably the most surprising result to emerge is that population divergence can occur on extremely small scales despite the lack of obvious oceanographic or topographic features that might impede gene flow [55,56].…”

Spatio‐temporal genetic structure and the effects of long‐term fishing in two partially sympatric offshore demersal fishes

“…Merluccius paradoxus exhibited both low historical and contemporary genetic diversity levels ( h = 0.562; AR = 16.325, H E = 0.602), while M. capensis had higher historical but lower contemporary genetic diversity ( h = 0.867; AR = 13.25; H E = 0.581), when compared with other marine fish (White et al . ; Knutsen et al . ; Henriques et al .…”

Seascape genetics of the stalked kelp Pterygophora californica and comparative population genetics in the Santa Barbara Channel

“…CPG has been used to examine the role of larval strategies (Lambert et al 2003, Watts and Thorpe 2006, Barbosa et al 2013, life history characteristics (Criscione and Blouin 2004), and environmental gradients (White et al 2011, DeFaveri et al 2012 in understanding patterns of gene flow in a variety of marine and aquatic systems. We define CPG as the study of genetic differentiation of two or more taxa that share many life history traits and demographic history in a restricted geographic area.…”