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

摘要

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.