Mitochondrial DNA reveals Pleistocenic colonisation of the Mediterranean by loggerhead turtles (Caretta caretta)

Abstract

As the loggerhead turtle (Caretta caretta) is a philopatric species with a strong genetic structure, the analysis of mtDNA can be used to track evolutionary and colonisation events. In this study we use a genetic approach to understand the population structure of C. caretta in the Mediterranean Sea and to test whether loggerheads could have colonised the Mediterranean during the Pleistocene and survived the cold phases in warm refugia. We amplified a long mtDNA D-loop fragment (815 bp) from 168 dead hatchlings sampled from a selection of rookeries in the Eastern Mediterranean: Libya, Israel, Lebanon, Cyprus and Greece. Previously published data from Turkey and Calabria (Southern Italy) were also included in the analyses. The population nesting in Libya emerged as the oldest population in the Mediterranean, dating from the Pleistocene ca. 65,000 years ago (20,000). This reveals that the Libyan population might have settled in the Mediterranean basin before the end of the last glacial period. The remaining nesting sites, except Calabria, were subsequently colonised as the population expanded. The populations nesting in Eastern Turkey and Western Greece settled ca. 30,000 years ago (10,000-100,000), whereas the remaining populations originated as a result of a more recent Holocenic expansion. As Calabria presented a unique Atlantic haplotype, found nowhere else in the Mediterranean, we consider this nesting site as the result of an independent colonisation event from the Atlantic and not the recent spread of Mediterranean populations. This reveals that the current genetic structure of C. caretta rookeries in the Mediterranean would be the result of at least two colonisation events from the Atlantic, the oldest one in Libya and a most recent in Calabria, combined with local extinctions during Pleistocenic glaciations and re-colonisations from glacial refugia in Libya, Eastern Turkey and Western Greece.

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…However, this approach is made difficult by the relatively poor genetic characterisation of Mediterranean rookeries (i.e. the presence of shared genetic markers), partly due to the recent colonisation of the Mediterranean Sea by loggerheads (Clusa et al 2013), the gaps in the sampled rookeries and other intrinsic methodological limits, which prevent a complete assessment of the dispersal and migratory patterns of individual rookeries. Satellite tracking, although intrinsically limited in sample size, can be helpful on this aspect and can also identify migratory connectivity, including the routes followed by single individuals.…”

“…The Mediterranean loggerhead population shows a genetic divergence from the Atlantic populations (Bowen & Karl 2007), and a population substructure (Laurent et al 1998;Carreras et al 2007;Clusa et al 2013), indicating the presence of independent management units for conservation. Loggerhead turtles are carnivorous: for the first period of life they mainly feed upon pelagic prey at the sea surface, then they increasingly shift towards benthic prey (Bjorndal 1997), although they also feed through the whole water column (e.g.…”

Mitochondrial DNA reveals the natal origin of Caretta caretta (Testudines: Cheloniidae) stranded or bycaught along the Southwestern Adriatic coasts

“…mitochondrial DNAmtDNA henceforth; Encalada et al 1998;Hatase et al 2002;Carreras et al 2007;Shamblin et al 2012;Clusa et al 2013). Specifically, the use of mtDNA has allowed the identification of genetically separate rookeries, characterised by unique haplotypes or specific haplotype frequencies.…”

Genetic composition of loggerhead turtle feeding aggregations: migration patterns in the North Pacific

“…However, by using the 817 bp fragment, additional polymorphic sites have been detected in Atlantic (Monzón-Argüello et al 2010, Shamblin et al 2012 and Mediterranean loggerhead turtles (Yilmaz et al 2011, Saied et al 2012, Clusa et al 2013. Although the haplotypes CcP-2.1 and CcP-3.1 were observed in most samples in Sanriku (69.2 and 14.0%, respectively), there were some variations in the traditional haplotypes B and C (e.g.…”