Skull shape and Bergmann’s rule in mammals: hints from Old World porcupines E. Mori 1,† , L. Ancillotto 2,† , S. Lovari 1,3 , D. Russo 2 , L. Nerva 4,5 , W. F. Mohamed 6 , Y. Motro 7 , P. Di Bari 8 & M. Plebani 9 1 Unit a di Ricerca in Ecologia Comportamentale, Etologia e Gestione della Fauna, Dipartimento di Scienze della Vita, Universit a di Siena, Siena, Italy 2 Wildlife Research Unit, Dipartimento di Agraria, Universit a degli Studi di Napoli Federico II, Portici, Italy 3 Museo di Storia Naturale della Maremma, Grosseto, Italy 4 Research Centre for Viticulture and Enology, CREA, Conegliano Veneto (Treviso), Italy 5 Institute for Sustainable Plant Protection, Torino, Italy 6 Department of Biological and Geological Sciences, Faculty of Education, Ain Shams University, Roxy, Cairo, Egypt 7 Vertebrate and Snail Division, Ministry of Agriculture and Rural Development, Rishon Leziyyon, Israel 8 Dipartimento di Scienze Biologiche, Geologiche e Ambientali – Universit a di Catania, Catania, Italy 9 School of Life Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa Keywords body size; skull size; skull shape; evolution; morphometrics; porcupines; Bergmann’s rule; Hystrix. Correspondence Emiliano Mori, Unit a di Ricerca in Ecologia Comportamentale, Etologia e Gestione della Fauna, Dipartimento di Scienze della Vita, Universit a di Siena, Via P.A. Mattioli 4, 53100, Siena, Italy. Email: moriemiliano@tiscali.it †These authors contributed equally to this work Editor: Andrew Kitchener Received 7 April 2018; revised 14 November 2018; accepted 18 December 2018 doi:10.1111/jzo.12651 Abstract The genus Hystrix includes eight species of porcupines distributed in Eurasia and Africa, across a broad latitudinal gradient. Our aim was to assess whether porcu- pine skulls: (1) allow for a reliable interspecific distinction; (2) change in size pro- portionally with body size; (3) follow the Bergmann’s rule. We measured 235 Hystrix skulls from museums and private collections. We tested for differences in skull size and we assessed whether variability in skull shape allows species recog- nition through a multivariate approach. All Hystrix species considered could be reliably identified by skull shape. Skull size was correlated with body size and spe- cies differed in skull shape and size, with skulls of Hystrix javanica and Hystrix africaeaustralis being respectively the smallest and the largest ones. Within Hystrix cristata, the Mediterranean and the sub-Saharan clades differed for both skull size and shape. Using skull size, we could distinguish among African, mainland Italian and Sicilian populations. Skull size of this species decreased in size for increasing latitude values, contrary to prediction by the Bergmann’s rule. Such latitudinal pat- tern may depend on the adaption of H. cristata to Equatorial African conditions, where the species evolved. In Italy (where H. cristata was introduced in the VI Century AD) and in North Africa, a smaller body size may be due to the local cli- mate, or to a ‘founder effect’. Introduction One of the major challenges faced by biogeographers is the assessment of global trends in the geographic distribution and morphological variation of animal species (Lomolino et al., 2006a). Abiotic factors, for example, latitude, altitude, climatic conditions, as well as biotic factors, for example, interspecific interactions and resource availability, may affect geographic variation of body shape and size (e.g. Monteiro-Filho, Mon- teiro & Reis, 2002; Caumul & Polly, 2005; Cardini, Jansson & Elton, 2007; C aceres et al., 2014; Tomassini et al., 2014). Past climatic and geographic changes, such as, continental drift, climate oscillations and changes in the sea level, have influenced the present geographic distribution of organisms, together with their morphology, for example, shape and body size (Owen-Smith, 1987; Taberlet et al., 1998; Jablonski et al., 2000; Anthony et al., 2007; Schmitt, 2007; Mouline et al., 2008). Several ‘rules’ have been proposed to describe the patterns of size variation in animal species (Lomolino et al., 2006b; McNab, 2010). Among those, the Bergmann’s rule is one of the most debated (Blackburn, Gaston & Loder, 1999; Raia & Meiri, 2011; Lokatis & Jeschke, 2018). The Bergmann’s rule states that, within closely related endotherm taxa, body size tends to decrease from colder to warmer climates The (Berg- mann, 1847; Salewski & Watt, 2016; Stanchak & Santana, 2018). Bergmann’s rule has been revised several times (e.g. Blackburn et al., 1999; Pincheira-Donoso, 2010; Watt, Mitchell & Salewski, 2010). We here follow its definition by Blackburn et al. (1999), expressed in a biogeographical context as ‘the Journal of Zoology  (2019) – ª 2019 The Zoological Society of London 1 Journal of Zoology. Print ISSN 0952-8369