Sexual size dimorphism in greater mouse-eared bat Myotis myotis (Chiroptera: Vespertilionidae) from a Mediterranean region Fulgencio Liso ´n, 1 A ´ ngeles Haz, 2 Carlos Gonza ´lez-Revelles 1 and Jose ´ F. Calvo 1 1 Departamento de Ecologı ´a e Hidrologı ´a, Universidad de Murcia, Campus de Espi- nardo, 30100, Murcia, Spain; 2 Paseo Rosales, 10, 4º D, 30500, Molina de Segura, Spain Keywords: biometry, fitness, sexual selection, reversed size dimorphism, wing measurements Accepted for publication: 16 October 2012 Abstract Liso ´n, F., Haz, A ´ ., Gonza ´lez-Revelles, C. and Calvo, J.F. 2012. Sexual size dimorphism in greater mouse-eared bat Myotis myotis (Chiroptera: Vespertilionidae) from a Mediterranean region. — Acta Zoologica (Stockholm) 00: 000–000. Although sexual size dimorphism (SSD) is common among mammals, there is no clear explanation for its maintenance in nature. Bats are one of the few groups of mammals where reverse SSD appears. In this group, the size of individuals may have very important ecological consequences related with flight. In this study, we examine sexual dimorphism in the wing measurements of 195 adult individuals (141 males and 54 females) of the greater mouse-eared bat Myotis myotis in the south-east of the Iberian Peninsula. We also investigated size differ- ences between paired and single males in a swarming roost. The results indicate that there are significant differences in the wing measurements between sexes, females being bigger than males in this respect. While no significant differences in the wing measurements of paired and single males were observed, significant differences were found in their relative weight and fitness, single males being sig- nificantly heavier and having a better physical condition. We discuss the implica- tions of SSD for the female of M. myotis in terms of reproductive advantages, trophic niche segregation and a greater ability to move, which may favour gene flow between populations. Fulgencio Liso ´ n, Departamento de Ecologı ´a e Hidrologı ´a, Universidad de Mur- cia, Campus de Espinardo, 30100 Murcia, Spain. E-mail: lison@um.es Introduction In vertebrates, many species display strong sexual size dimor- phism (SSD), which affects species of every group, from fish to mammals (Fairbairn et al. 2007). The presence of SSD has important ecological implications in populations, and it is assumed that there are different mechanisms involved to ensure its persistence. In mammals, different causes have been suggested to explain the SSD (Hedrick and Temeles 1989; Isaac 2005; Lindenfors et al. 2007): (i) sexual selection, (ii) pairing success, (iii) reproduction success, (iv) latitudinal influence, (v) influence of nursery time, (vi) variation in the population density and (vii) the Rensch’s rule. The Rensch’s rule is the tendency for size dimorphism to scale with body size (Rensch 1959), so when increases in the male mass are correlated with smaller increases in the female mass, a correla- tion between size and size dimorphism is produced (Fairbairn 1997; Lindenfors et al. 2007). However, in the mammals groups with a smaller weight (Rodentia, Chiroptera and In- sectivora), there is not found a correlation between weight and the dimorphism (Lindenfors et al. 2007); the studies made are not conclusive, and no unique cause for SDD can be established. Moreover, in most of mammalian species, it has been observed that SSD biases to males, and it is highly atypical to find reverse SSD, where females are larger than males (Lindenfors et al. 2007). Bats are one of the mammals groups with the presence of reverse SSD (Lindenfors et al. 2007), and it is especially prominent in the Vespertilionidae family (Ralls 1976; Myers 1978; Willig and Hollander 1995; Storz et al. 2001; Senior et al. 2005; Bornholdt et al. 2008). Most of these studies are based on dental or cranial characteristics, which cannot be obtained in the field and which are taken from carcasses in museums or private collections (Benda 1994; Paz 1995; © 2012 The Authors Acta Zoologica © 2012 The Royal Swedish Academy of Sciences 1 Acta Zoologica (Stockholm) doi: 10.1111/azo.12012