ORIGINAL PAPER Genetic differentiation in the squid Moroteuthis ingens inferred from RAPD analysis Received: 26 June 2002 / Accepted: 25 November 2002 / Published online: 16 January 2003 Ó Springer-Verlag 2003 Abstract Randomly amplified polymorphic DNA mark- ers (RAPDs) were applied in a cephalopod population study. Samples of the squid Moroteuthis ingens taken from around the Falkland Islands and Macquarie Island were used to test a null hypothesis that M. ingens forms a single, panmictic population in the Southern Ocean. Six of the 8 arbitrary RAPD primers screened produced a total of 30 reproducible polymorphic bands. Analysis of RAPD allele frequencies demonstrated high levels of variation between individuals but little variation between two sample sites. Although the differentiation between the two sites was low, subtle population structure was de- tected and the null hypothesis was rejected. The implica- tions of low genetic differentiation between the two sites are briefly discussed in terms of possible egg and para- larval drift facilitated via the circumpolar current. Introduction The Southern Ocean contains fast-moving circumpolar currents that form large gyres at their interstices (Tomczak and Godfrey 1994). Movement of some Southern Ocean organisms by these currents may act to homogenize their populations by promoting high rates of gene flow (Ward et al. 1994; McLean and Taylor 2001). For other species, these currents and gyres may act as boundaries that restrict migration, and may have led to genetic differentiation between populations in different regions of the Southern Ocean (e.g. Zane et al. 1998). There have been a small number of studies ex- amining population genetic structure of Southern Ocean species in which patterns of diversity have ranged from homogeneity to cryptic speciation. Genetic homogeneity was found using allozymes in two studies of the krill Euphausia superba (Ayala et al. 1975; Fevolden and Schneppenheim1989). Low levels of population struc- ture were detected in studies of krill using allozymes (Fevolden and Ayala 1981) and microsatellites (Zane et al. 1998), and the Antarctic coastal krill E. crystall- orophias using mitochondrial DNA sequence (Jarman et al. 2002). Microsatellite markers also found low levels of genetic variation in the Antarctic fur seal Arctoceph- alus gazella (Wynen et al. 2000), the Patagonian tooth- fish Dissostichus eleginoides (Smith and McVeagh 2000) and the squid Illex argentinus (Adcock et al. 1999b). Allozymes have revealed high levels of population structure in the octopus Pareledone turqueti (Allcock et al. 1997) and cryptic speciation in the squid Martialia hyadesi (Brierley et al. 1993). The squid Moroteuthis ingens is an important com- ponent of the Southern Ocean ecosystem. It is a vora- cious predator on myctophid fish and krill (Jackson et al. 1998a; Phillips et al. 2001) and an important prey item for many marine vertebrates (Clarke and Goodall1994; Slip 1995; Clarke 1996; Jackson 1997; Moore et al. 1998; Imber 1999). Moroteuthis ingens is also important in transporting energy from epipelagic waters to deeper benthic environments due to an ontogenetic migration as paralarvae develop to adults (Jackson et al. 1998a). The distribution of Moroteuthis ingens is considered to be circumpolar as catches have been documented from around the Falkland Islands, New Zealand, Macquarie Island, Heard and MacDonald Islands and Crozet Island (Fig. 1). However, the continuity of this distri- bution is uncertain due to inadequate sampling over deep ocean areas. Polar Biol (2003) 26: 166–170 DOI 10.1007/s00300-002-0467-7 Chester J. Sands ® Simon N. Jarman George D. Jackson C.J. Sands (&) ® G.D. Jackson Institute of Antarctic and Southern Ocean Studies, University of Tasmania, TAS 7005 Hobart, Australia S.N. Jarman Australian Antarctic Division, Channel Highway, TAS 7050 Kingston, Australia Present address: C.J. Sands Genetics Department, La Trobe University, Bundoora Campus, VIC 3086, Australia. e-mail: c.sands@latrobe.edu.au, Fax: +61-3-94792480