Genetic Structure of Bluefin Tuna in the Mediterranean Sea Correlates with Environmental Variables

Abstract

BackgroundAtlantic Bluefin Tuna (ABFT) shows complex demography and ecological variation in the Mediterranean Sea. Genetic surveys have detected significant, although weak, signals of population structuring; catch series analyses and tagging programs identified complex ABFT spatial dynamics and migration patterns. Here, we tested the hypothesis that the genetic structure of the ABFT in the Mediterranean is correlated with mean surface temperature and salinity.MethodologyWe used six samples collected from Western and Central Mediterranean integrated with a new sample collected from the recently identified easternmost reproductive area of Levantine Sea. To assess population structure in the Mediterranean we used a multidisciplinary framework combining classical population genetics, spatial and Bayesian clustering methods and a multivariate approach based on factor analysis.ConclusionsFST analysis and Bayesian clustering methods detected several subpopulations in the Mediterranean, a result also supported by multivariate analyses. In addition, we identified significant correlations of genetic diversity with mean salinity and surface temperature values revealing that ABFT is genetically structured along two environmental gradients. These results suggest that a preference for some spawning habitat conditions could contribute to shape ABFT genetic structuring in the Mediterranean. However, further studies should be performed to assess to what extent ABFT spawning behaviour in the Mediterranean Sea can be affected by environmental variation.

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“…Better understanding of the patterns of local adaptation would lead to better identification of marine population units, and could be useful for management decisions (Funk et al ., ). Local patterns can be highly structured in time and space (Dannewitz et al ., ; Riccioni et al ., ). A consequence of this observation is that the population delineation of marine organisms as inferred by genetic data may be more complex than assumed previously (Hauser & Carvalho, ).…”

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“…These selective forces also affect the distribution of adults in several marine species with high potential for dispersion and vagility (Riccioni et al . ; Milano et al . ) and are found to be associated with molecular markers usually deemed as neutral ( i.e .…”

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