GENE TIC VARIATION IN THE NERITIC SQUID LOLIGO-FORBESI (MYOPSIDA, LOLIGINIDAE) IN THE NORTHEAST ATLANTIC-OCEAN

Horizontal starch gel electrophoresis was employed to investigate leve ls of genetic differentiation between 13 samples of the neritic squid species Loligo forbesi Steenstrup obtained from throughout the majorit y of its known geographical range. Six enzyme loci identified in a pre liminary study as being polymorphic were screened for variation betwee n samples. No significant differences in allele distribution were dete cted between any of the samples obtained from the Faroe Bank in the no rth to Lisbon in the south, suggesting that squid throughout this rang e in the vicinity of the continental shelf are able to maintain panmix ia, and effectively belong to a single population sharing a common gen e pool. No clinal variation in allele distribution was detected throug hout this range, a result which complements the findings of a detailed morphological companion study of the same individuals. Comparison of this homogenous European continental shelf population with squid from the Azores revealed highly significant (P < 0.01) differences in allel e distribution at five of the six polymorphic enzyme loci studied. A g enetic identity value (I) equivalent to 0.93 over 33 loci was obtained . Analysis of F-statistics suggested migration rates between sites to be as low as one individual per five generations, a rate deemed insuff icient under most models to prevent divergence by random genetic drift . The large distance and oceanic depths separating the Azores from con tinental Europe seem to present an effective barrier to gene now to L. forbesi, a squid belonging to a family considered to be confined in d istribution to relatively shallow, near coastal waters. The two popula tions of squid in the Azores and along the European continental shelf currently both ascribed to L. forbesi should therefore probably best b e regarded as relative subspecies.