RESEARCH ARTICLE A. L. Bilodeau Æ D. L. Felder Æ J. E. Neigel Multiple paternity in the thalassinidean ghost shrimp, Callichirus islagrande (Crustacea: Decapoda: Callianassidae) Received: 29 August 2003 / Accepted: 7 July 2004 / Published online: 1 September 2004 Ó Springer-Verlag 2004 Abstract Adult ghost shrimp, Callichirus islagrande (Schmitt, 1935), are obligate inhabitants of burrow sys- tems that they excavate deeply into beachfront sedi- ments in the northern Gulf of Mexico. Mating presumably occurs in these burrows but has never been directly observed in C. islagrande or any other thalas- sinidean. A variety of possible mating systems is sug- gested by those of other decapods, among which are examples of both internal and external sperm deposi- tion, sperm competition among males, and male adap- tations for paternity assurance. We used genetic markers to determine if clutches brooded by individual female ghost shrimp had been fertilized by multiple males. The two microsatellite loci we employed were sufficiently polymorphic to detect 95% of the occurrences of fertil- ization by two males. Among 40 ovigerous females collected from the Louisiana Isles Dernieres barrier is- land, eight (20%) carried egg masses for which more than two paternal alleles were detected, indicating fer- tilization by multiple males. In two cases of multiple paternity, alleles from one of the males were detected in only a portion of an egg mass. These observations sug- gest several, possibly novel characteristics of the mating system that can be further investigated. Introduction Diverse mating systems are known from the crustacean order Decapoda although they have been well charac- terized for only a few groups. In all decapod species that have been examined sperm are non-motile (Felgenhauer and Abele 1991; Jamiesen and Tudge 2000) and are deposited by males in packets (spermatophores) either externally on the female’s exoskeleton or internally in special receptacles (spermathecae; Bauer 1986; Subr- amoniam 1993). In some taxa (e.g., advanced brachyu- rans) sperm stored in spermathecae are retained through molts and can fertilize eggs months after mating has occurred (Subramoniam 1993). Sperm storage also al- lows females to mate sequentially and store sperm from multiple males, which in turn has promoted adaptations for males either to displace the sperm of a female’s previous mates or to block the deposition of sperm by subsequent mates (e.g. Diesel 1991). For those decapod taxa in which spermatophores are externally deposited, females do not usually store sperm (Subramoniam 1993). Without sperm storage females can collect sperm from multiple males only by mating with them within a brief period of time, either simulta- neously or in succession. Studies of crustacean mating systems have revealed several mechanisms that should increase paternity assurance and decrease the incidence of multiple paternity (Diesel 1991; Koga et al. 1993). These include precopulatory and postcopulatory mate guarding (Hinsch 1968; Watson 1972; Hooper 1986; Murai et al. 1987; Caldwell 1991; Durbaum 1995; Jormalainen 1998; Minouchi and Goshima 1998). However mate guarding is not universal, and in some taxa multiple mating could be the norm. For example, in a mole crab reported as E. asiatica H. Milne Edwards, junior synonym of E. emeritus (Linnaeus, 1767), up to five males have been observed simultaneously depositing spermatophores on a single female (Subramoniam 1977, 1979). Other mechanisms of paternity assurance include repetitive copulation (Bauer 1992), sperm plugs (Elner et al. 1985; Bauer and Min 1993), and increased ejacu- late size (Diesel 1991). However it is difficult to deter- mine the effectiveness of these mechanisms without examination of the actual paternity of egg clutches in natural populations. Communicated by P.W. Sammarco, Chauvin A. L. Bilodeau (&) Æ D. L. Felder Æ J. E. Neigel Department of Biological Sciences, University of Louisiana at Lafayette, Lafayette, LA 70504, USA E-mail: abilodeau@ars.usda.gov Present address: A. L. Bilodeau Catfish Genetics Research Unit, USDA-ARS, 141 Experiment Station Road, Box 38, Stoneville, MS 38776, USA Marine Biology (2005) 146: 381–385 DOI 10.1007/s00227-004-1444-1