Spatio-temporal population structuring and genetic diversity retention in depleted Atlantic Bluefin tuna of the Mediterranean Sea

Abstract

Fishery genetics have greatly changed our understanding of population dynamics and structuring in marine fish. In this study, we show that the Atlantic Bluefin tuna (ABFT, Thunnus thynnus), an oceanic predatory species exhibiting highly migratory behavior, large population size, and high potential for dispersal during early life stages, displays significant genetic differences over space and time, both at the fine and large scales of variation. We compared microsatellite variation of contemporary (n = 256) and historical (n = 99) biological samples of ABFTs of the central-western Mediterranean Sea, the latter dating back to the early 20th century. Measures of genetic differentiation and a general heterozygote deficit suggest that differences exist among population samples, both now and 96-80 years ago. Thus, ABFTs do not represent a single panmictic population in the Mediterranean Sea. Statistics designed to infer changes in population size, both from current and past genetic variation, suggest that some Mediterranean ABFT populations, although still not severely reduced in their genetic potential, might have suffered from demographic declines. The short-term estimates of effective population size are straddled on the minimum threshold (effective population size = 500) indicated to maintain genetic diversity and evolutionary potential across several generations in natural populations.ancient DNA | effective population size | genetic structure | large pelagic fishes | Thunnus thynnus

Otolith shape variation provides a marker of stock origin for north Atlantic bluefin tuna (Thunnus thynnus)

“…Further speculation regarding the origin of the subtle differences in otolith shape that were observed within the Mediterranean and East Atlantic would be beyond the limitations of currently available data. However, the results indicate that variation in otolith shape could potentially be used to distinguish between Atlantic bluefin spawning in different areas of the Mediterranean and to resolve the structuring that has been observed here (Carlsson et al 2004;Riccioni et al 2010). This would require the collection of baseline samples from putative spawning areas during the spawning season, which were not available for the present study.…”

“…Analyses of DNA microsatellites (Carlsson et al 2007), mitochondrial DNA (Boustany et al 2008) and single nucleotide polymorphisms (Albaina et al 2013) all show significant genetic divergence of the two populations. In addition, there is evidence of genetic heterogeneity within the Mediterranean, and the existence of separate spawning populations in the western and eastern Mediterranean has been proposed (Carlsson et al 2004;Riccioni et al 2010). The occurrence of mature adult Atlantic bluefin tuna in areas other than the main spawning grounds during the spawning season may also be indicative of a more complex structure than the currently accepted two-stock model (Galuardi et al 2010).…”

Genetic architecture of the marbled goby Pomatoschistus marmoratus (Perciformes, Gobiidae) in the Mediterranean Sea

“…Many other examples derive from the population structure of Mediterranean pelagic species, which do not mirror palaeo-oceanographic events to such an extent. This has been demonstrated by: the European anchovy Engraulis encrasicolus (Grant, 2005;Grant et al, 2005;Magoulas et al, 2006), the Atlantic Bluefin tuna Thunnus thynnus (Riccioni et al, 2010), and the goby Aphia minuta (Giovannotti et al, 2009). And data from demersal species, such as the European hake Merluccius merluccius (Cimmaruta et al, 2005), or benthic species, e.g.…”

“…These are characterized by different hydrographic and ecological features, and are variously interconnected (Quignard, 1978;Bianchi and Morri, 2000;Agostini and Bakun, 2002). Such features render several marine species inhabiting the Mediterranean Sea of particular interest, since their genetic structure has been demonstrated to have been shaped by the combined effects of historical events and the complex interactions of ecological factors (Grant, 2005;Domingues et al, 2005;Lemaire et al, 2005;Zitari-Chatti et al, 2009;Riccioni et al, 2010).…”

Misidentification of bluefin tuna larvae: a call for caution and taxonomic reform

“…Advances in NGS and historical DNA analysis are allowing researchers new access to archived samples (larvae, scales, otoliths, spines and vertebrae), revealing important ecological and evolutionary changes in fish stocks and populations over time (Riccioni et al 2010;Cuveliers et al 2011;Poulsen et al 2011;Seeb et al 2011). Although molecular sampling techniques have been making great advances in reducing impact on voucher specimens in the recent past (Nielsen and Hansen 2008;Gibbon et al 2009), the same cannot be said for the majority of morphological taxonomists that still preserve their samples in formalin; an outdated practice that renders genetic analysis very difficult if not impossible (Ward et al 2009).…”