Genetic variation in Irish pygmy shrews Sorex minutus (Soricomorpha: Soricidae): implications for colonization history ALLAN D. MCDEVITT 1 *, RAMUGONDO V. RAMBAU 2,3,4 , JOHN O’BRIEN 1 , C. DAMIEN MCDEVITT 5 , THOMAS J. HAYDEN 1 and JEREMY B. SEARLE 2 1 School of Biology and Environmental Science, University College Dublin, Belfield, Dublin 4, Ireland 2 Department of Biology, University of York, PO Box 373, York YO10 5YW, UK 3 Evolutionary Genomics Group, Department of Botany and Zoology, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa 4 DST-NRF Centre of Excellence for Invasion Biology, Stellenbosch University, Private Bag X1, Matieland 7602, Stellenbosch, South Africa 5 Deele College, Raphoe, Lifford, Co. Donegal, Ireland Received 10 November 2008; accepted for publication 16 January 2009 The status of the pygmy shrew (Sorex minutus L.) as a native or an introduced species in Ireland has been subject to much debate. To examine this and other aspects of the colonization history of the Irish pygmy shrew, genetic variation was determined in 247 pygmy shrews collected throughout Ireland, using mitochondrial control region sequences and five polymorphic microsatellite loci. Genetic diversity was low for both types of marker. The median-joining network for control region sequences was star-like, suggesting that the colonization of Ireland involved a small number of founders and rapid population expansion thereafter; this was supported by other statistics. Molecular dating with both mitochondrial DNA and microsatellite data is consistent with a human introduction. This would have been several thousand years ago; a recent colonization within historical times can be ruled out. This is the first detailed population genetic study of the pygmy shrew anywhere in its range. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 918–927. ADDITIONAL KEYWORDS: control region – human introduction – Ireland – microsatellites – mitochondrial DNA – phylogeography – small mammal. INTRODUCTION In recent years, there has been an upsurge in interest in how and when Ireland acquired its current impov- erished mammalian fauna (Searle, 2008). It is certain that some of the species that are found in Ireland (e.g. the stoat Mustela erminea) colonized naturally (i.e. native to Ireland; Martínková, McDonald & Searle, 2007) and others (e.g. the house mouse Mus muscu- lus) were brought by humans (i.e. introduced to Ireland; Searle et al., 2009). One species for which there has been considerable debate about its coloni- zation history is the pygmy shrew Sorex minutus (Yalden, 1981; Hayden, 2002; Mascheretti et al., 2003). So much so, that it has been highlighted as a species whose mode of colonization needs to be under- stood to appreciate properly the origin of Ireland’s biota (the ‘pygmy shrew syndrome’; Devoy, Sleeman & Woodman, 1986). The widespread distribution of the pygmy shrew on Ireland gives the impression that it is a native, although this may be illusory, given that introduced species may spread rapidly (e.g. the American mink Mustela vison was introduced onto Ireland in the 1950s and is now nearly ubiquitous; Dunstone & MacDonald, 2008). Among those who *Corresponding author. Current address: Allan D. McDevitt, Faculty of Environmental Design, University of Calgary, 2500 University Drive NW, Calgary, Alberta, Canada T2N 1N4. E-mail: amcdev@gmail.com Biological Journal of the Linnean Society, 2009, 97, 918–927. With 3 figures © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 918–927 918