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The influence of Pleistocene glacial refugia on tawny owl genetic diversity and phylogeography in western Europe
PATRÍCIA H. BRITO American Museum of Natural History, Ornithology Department, Central Park West at 79th Street, New York, NY 10024, USA
The glacial refugiahypothesis indicates that during the height of the Pleistocene glaciations the temperate species that are today widespread in western Europe must have survived in small and climatically favourable areas located in the southern peninsulas of Iberia, Italy and Balkans. One such species is the tawny owl, a relatively sedentary, nonmigratory bird presently distributed throughout Europe. It is atree-nesting species closely associated with deciduous and mixed coniferous woodlands. In this study I used control region mtDNA sequences from 187 individuals distributed among 14 populations to determine whether current genetic patterns in tawny owl populations were consistent with postglacial expansion from peninsular refugia. European, North African and Asian tawny owls were found to represent threedistinct lineages, where North Africa is the sister clade to all European owls. Within Europe, I found three well-supported clades that correspond to each of the three allopatric refugia. Expansion patterns indicate that owls from the Balkan refugium repopulated most of northern Europe, while expansion out of Iberia and Italy had only regional effects leading to admixture in France. Estimates ofpopulation divergence times between refugia populations are roughly similar, but one order of magnitude smaller between Greece and northern Europe. Based on a wide range of mutation rates and generation times, divergence between refugia appears to date to the Pleistocene.
Keywords: divergence time, gene flow, glacial refugia, phylogeography, Pleistocene, Strix Received 14 February 2005; revisionreceived 6 May 2005; accepted 20 May 2005
Quaternary climatic fluctuations have been widely recognized as the main historical process influencing the genetic diversity of natural populations of the temperate Northern Hemisphere (e.g. Frenzel 1973; Hewitt 1996, 2004). During the late Pleistocene the climate fluctuated from full-glacial conditions to full-interglacial. The lastglacial maximum (LGM) occurred in Europe around 18 000 before present (bp) and was characterized by an extensive decrease of the average temperatures that led to the formation of the Scandinavian ice sheet (coverings parts of Britain and northern Europe), and ice caps on the top of such major mountain ranges as the Pyrenees, the Alps and the Caucasus (Frenzel 1973; Nilsson 1983). Between the main icesheet in the north and the southern mountains, Europe was covered by tundra and cold steppe (Prentice
Correspondence: Patrícia H. Brito, Fax: 212 7695759; E-mail: firstname.lastname@example.org © 2005 Blackwell Publishing Ltd
et al. 2000; Tzedakis et al. 2002). The term ‘glacial refugia’ was used to describe the only suitable localities where temperate fauna and flora could have existed during fullglacialconditions (Hewitt 1996, 1999). The reconstruction of palaeo-vegetation maps has indicated three main glacial refugia of deciduous temperate forest located in the southern peninsulas of Iberia, Italy, and Balkans (Frenzel 1973; Hewitt 1996; Tzedakis et al. 2002). Due to the severe climatic oscillations, temperate flora and fauna are expected to have gone through many contractions and rangeexpansions, which are expected to have left signatures in the geographical distribution and genetic diversity of extant populations (Bennett et al. 1991; Slatkin 1993; Avise 2000; Furlong & Brookfield 2001). Refugial populations that evolved in allopatry are expected to have accumulated independent genetic differences that may be used as genetic markers to trace expansion routes. It is also expected...