In Search of the Lost Brown Trout ( <scp> <i>Salmo trutta</i> </scp> Complex) Using <scp>DNA</scp> of Ancient and Modern Samples From the Southern Italian Peninsula

ABSTRACT The current diversity and distribution of species and populations have been shaped by the major climatic oscillations during the Quaternary. The brown trout ( Salmo trutta ) is a striking example of the strong effect of past climate changes on the evolutionary history of species, in fact, the alternation of glacial/interglacial cycles has led to continuous phenomena of expansion and contraction of its distribution and, consequently, to the evolution of different genetic lineages. This phenomenon was also directly observed by the genetic analysis of S. trutta bones recovered from the archaeological assemblage of a coastal cave named ‘Grotta del Santuario Della Madonna’ (Southern Italy). In this study, additional S. trutta remains were morphologically and genetically analysed, and the genetic results were compared with those of modern samples caught from streams close to the cave locality. The analysis of S. trutta bones confirms that changes in abundance, body size and genetic diversity observed in different stratigraphic sections were determined by environmental changes caused by the Younger Dryas‐Holocene transition and by the ability of the species to perform anadromous migration, a behaviour that had disappeared at the end of the Pleistocene in the Mediterranean region. The comparison between ancient and modern samples highlights that extinctions and recolonizations due to past environmental changes affected also the current diversity and distribution of S. trutta in Southern Italian streams. Unfortunately, incorrect management policies related to sport fishing (i.e., stocking with alien brown trout strains) have been eroding millions of years of the trout evolution in just a few centuries.