Global Population Genomic Structure and Life History Trait Analysis of Yellowfin Tuna (Thunnus Albacares)

Yellowfin tuna (Thunnus albacares; YFT) represents one of the most important seafood commodities in the world. The rationale of this Ph.D. project was identified by prioritizing key issues as objectives for contributing to the conservation of YFT and helping to develop a more realistic stock assessment and sustainable management of this species. Specifically, in this work the current mismatch between the biology and/or ecology and the realized management strategies was highlighted, putting particular emphasis on YFT population structure, which is currently characterized by a high degree of uncertainty at both local and global scale. This general pattern was confirmed by the results obtained using a panel of microsatellite loci, which cannot reject the null hypothesis of the existence of only one panmictic population at the global scale. On the contrary, the access to more powerful and cost effective genetic tools would represent the first step for resolving YFT population structure at both global and local scale. After having evaluated the efficiency and usefulness of 2b-RAD genotyping technique for investigating population genetic structure in highly migratory fish species, a panel of 972 SNPs (Single Nucleotide Polymorphisms) was generated. Using this panel, three distinct populations were identified in the Atlantic, Indian and Pacific Oceans. Additionally, it was possible to define a subset of 33 outlier loci putatively under selection to delineate and separate sub-populations within both the Atlantic and the Pacific Oceans (following an east-west division). Finally, it was emphasized for the first time that in the Atlantic Ocean larger YFT females allocate a greater fraction of surplus energy to egg production than smaller ones, improving noticeably the spawning quality. This result sheds light on the important contribution that larger and most experienced spawners have for the YFT productivity.