Molecular evidence of male-biased dispersal in loggerhead turtle juveniles Paolo Casale a, * , Luc Laurent b , Guido Gerosa c , Roberto Argano d a via Antonio Calderara 29, I-00125 Rome, Italy b BioInsight, Biologie de la Conservation, B.P. 2132, F-69603 Villeurbanne, France c Chelon, Marine Turtle Conservation and Research Program, Via Val Padana 134/B, I-00141 Rome, Italy d Dipartimento di Biologia Animale e dell’Uomo, Universita ` ‘‘La Sapienza’’, I-00185 Rome, Italy Received 13 June 2001; received in revised form 27 August 2001; accepted 17 September 2001 Abstract Serum testosterone levels and mtDNA haplotypes were obtained from 65 juvenile loggerhead turtles (Caretta caretta, L.) incidentally caught in the central Mediterranean. The group of specimens carrying a haplotype specific for the northwest Atlantic had higher testosterone levels, and so included more males, than the other one. Since primary sex ratios of northwest Atlantic colonies are strongly skewed towards females, results indicate a male bias among Atlantic turtles entering the Mediterranean. This demonstrates for the first time a sex-biased dispersal of specimens in the pelagic phase, an important factor to be considered in conservation programs. D 2002 Elsevier Science B.V. All rights reserved. Keywords: Caretta caretta; Dispersal; Mediterranean Sea; Sex ratio 1. Introduction Sea turtles are endangered species whose biology is poorly known, especially that of males and the juvenile phase of both sexes. While adult females, eggs, and hatchlings are relatively well studied when on reproductive beaches, less is known on life at sea. Mixed stock analyses are revealing that juveniles from different and distant nesting colonies mix together in feeding areas (Laurent et al., 1993, 1998; Bowen et al., 1996), but sex-related aspects of their dispersal are still unknown. 0022-0981/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved. PII:S0022-0981(01)00365-3 * Corresponding author. Tel./fax: +39-06-5245-6820. E-mail address: paolo.casale@tiscalinet.it (P. Casale). www.elsevier.com/locate/jembe Journal of Experimental Marine Biology and Ecology 267 (2002) 139 – 145