Geographic and gender shape differences in the carapace of Liocarcinus depurator (Brachyura: Portunidae) using geometric morphometrics and the influence of a digitizing method M. M. Rufino 1,2 , P. Abell ´ o 1 & A. B. Yule 2 1 Institut de Cie ` ncies del Mar (CSIC), Pg. Mar´ ıtim de la Barceloneta, Barcelona, Spain 2 School of Ocean Sciences, University of Wales, Bangor, UK Keywords geometric morphometrics; crabs; Mediterranean; Albor ´ an; warp analysis. Correspondence Marta Rufino. Current address: CripSul, Ipimar/Iniap, Av. 5 Outubro, s/n 8700-305 Olha ˜ o, Portugal. Email: mrufino@cripsul.ipimar.pt Received 9 March 2005; accepted 5 October 2005 doi:10.1111/j.1469-7998.2006.00086.x Abstract The current work describes the use of geometric morphometrics in the study of the portunid crab Liocarcinus depurator carapace shape variation along the Mediter- ranean coast of Spain. As a first step, the differences in shape induced by digitizing the carapace with either a digital camera or a flat bed scanner were investigated. Carapace shape information inferred from the camera images proved different from that obtained from the scanner images. This difference was greater than any shape variation because of crab gender or sample location. Carapace shape was analysed using multiple analysis of covariance (with centroid size as a covariate) of the partial warps and uniform components indicating differences between genders and between sample location; however, significant three-way interaction implied that such differences were gender and location specific. Landmarks identifying carapace width, carapace length and posterior carapace width showed greatest variation; hence gender and location differences were further analysed through the interrelationships between these linear measures. Regression analysis of the relationship between posterior carapace width and the ratio of carapace width to carapace length indicated clear differences between locations but not between genders. Crabs from the Albor´an Sea had proportionally wider posterior cara- paces than those from Alicante or North Catalonia. This finding may represent the difference between a southern influx of an Atlantic population distinguishable from a more northerly Mediterranean one, which would be in agreement with the overall oceanographic surface circulation pattern in the western Mediterranean. Introduction Liocarcinus depurator (L.) is the dominant brachyuran crab of Mediterranean demersal fisheries down to depths of around 200 m (Abell´o, Valladares & Castell´on, 1988; Abell ´o, Carbonell & Torres, 2002). It ranges in distribution from the coasts of the western Sahara to Norway, including the Mediterranean Sea (Udekem d’Acoz, 1999), where it is one of the most abundant species of continental shelf communities (Ungaro et al., 1999; Abell´o et al., 2002). Liocarcinus depurator can be found on several types of substrata, although it is most commonly encountered on mud and sandy-muddy bottoms (Minervini, Giannotta & Falciai, 1982). Morphometric studies on L. depurator have previously been performed, using linear measurements, in the western Mediterranean (Mori & Zunino, 1987; Abell´o, Pertierra & Reid, 1990) and in the Atlantic coast of Spain (Fern´andez, Gonz ´alez-Gurriar ´an & Freire, 1991). Fern ´andez et al. (1991) found significant differences between the relationship width/ length of L. depurator males and females in R´ıa de Arousa, with females being broader than males, whereas Abell ´o et al. (1990) did not observe any significant differences attributa- ble to gender. Furthermore, the female maturity size of L. depurator was larger in R´ıa de Arousa than in the Mediterranean (Mori & Zunino, 1987; Abell´o et al., 1990; Fern´andez et al., 1991). However, although maturity size was larger in the Galician R´ıa, growth rates were faster, and females attained maturity size faster in the Catalan coast (Abell´o et al., 1990; Fern´andez et al., 1991). Immature individuals of L. depurator did not exhibit growth or ‘size’ differences between sexes, as these arise later with maturity. Males presented higher growth rates than females, which causes a tendency towards greater relative abundance of males as size increases both in Galicia and in the Mediterra- nean (Abell ´o,1989; Fern´andez et al., 1991). Crustaceans have hard exoskeletons, often adorned with obvious spines, which should make them excellent Journal of Zoology 269 (2006) 458–465 c  2006 The Authors. Journal compilation c  2006 The Zoological Society of London 458 Journal of Zoology. Print ISSN 0952-8369