Highly polymorphic microsatellite loci of the heavily fished squid genus Illex (Ommastrephidae).
Ommastrephid squid of the genus Illex form an important trophic component of large areas of the Atlantic ocean, both as prey for fish, seabirds, whales and other cephalopods, and as predators themselves. Three species occupy extensive coastal and offshore distributions in the southwest (Illex argentinus), northwest (Illex illecebrosus) and northeast (Illex coindetti) Atlantic. As for many squid, the biology of Illex is poorly understood because direct observational methods for studying their population biology and behaviour are constrained by logistics and difficulties with traditional morphological techniques. The application of molecular genetic markers in squid has also been problematic, as allozyme (e.g. Carvalho et al. 1992) and mitochondrial (Norman et al. 1994) markers have shown insufficient variability for inferring population structure, migration and mating patterns. The need for suitable markers has become more urgent since the development in 1985 of an intensive fishery targeting I. argentinus, one of the largest (300 000 tons per annum) for any molluscan. The other two species are also the targets of fisheries. A study of another squid (Shaw 1997) showed that microsatellite DNA regions are abundant and highly polymorphic in this group, identifying their potential for population discrimination and individual identification (Shaw & Boyle 1997). We have isolated polymorphic microsatellite markers from I. argentinus, and tested their potential utility for defining population structure and variability in each of the three Illex species, and the wider application of primers to other genera within the Cephalopoda.