The Effects of Paleoclimatic Events on Mediterranean Trout: Preliminary Evidences from Ancient DNA

Abstract

In this pilot study for the first time, ancient DNA has been extracted from bone remains of Salmo trutta. These samples were from a stratigraphic succession located in a coastal cave of Calabria (southern Italy) inhabited by humans from upper Palaeolithic to historical times. Seven pairs of primers were used to PCR-amplify and sequence from 128 to 410 bp of the mtDNA control region of eleven samples. Three haplotypes were observed: two (ADcs-1 and MEcs-1) already described in rivers from the Italian peninsula; one (ATcs-33) belonging to the southern Atlantic clade of the AT Salmo trutta mtDNA lineage (sensu Bernatchez). The prehistoric occurrence of this latter haplotype in the water courses of the Italian peninsula has been detected for the first time in this study. Finally, we observed a correspondence between frequency of trout remains and variation in haplotype diversity that we related with ecological and demographic changes resulting from a period of rapid cooling known as the Younger Dryas.

Fig 1. Geographic position of Grotta del Santuario della Madonna.

Fig 2. Salmo trutta sub-fossil samples analysed in this study.

Fig 3. Primer pairs designed and used in this study.

Primer pairs were designed on the basis of the brown trout complete mitochondrial genome present in GenBank (Accession no. AM910409.1) to amplify a 633 bp fragment of the mtDNA, including 85 bp of tRNA Pro-gene and 548 bp of mtDNA D-loop. *StCR-2c primer pair was designed to substitute for StCR-2a in the cases in which the amplification with the latter pair of primers was not successful.

Fig 4. Statistical parsimony haplotypes network.

Haplotype network showing the relationships between modern haplotypes and haplotypes observed in the archaeological samples analysed in the present study (indicated by asterisks).

Fig 5. Relationship between abundance of remains, mitochondrial haplotypes observed in this study and Pleistocene-Holocene climatic fluctuations.

The continuous line in the graph indicates the frequency of Salmo trutta remains and the dotted line indicates the frequency of Patella and Monodonta remains in all sections of the stratigraphic succession of GSM (approximate reconstruction from [40]). Mitochondrial haplotypes observed in this study are indicated by coloured squares: ATcs-33 in yellow, ADcs-1 in green and MEcs-1 in red. This information is related with the δ¹⁸O (‰) climate proxies of the GRIP ice core record represented by a blue line (dataset from NOAA website: http://www1.ncdc.noaa.gov/pub/data/paleo/icecore/greenland/summit/grip/isotopes/gripd18o.txt).