Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

David W. Foltz


Based on restriction fragment length polymorphisms (RFLP) in mitochondrial DNA, the population structures of two species of Loligo squid were analyzed in the context of the classic Gulf of Mexico-Atlantic Ocean phylogeographic pattern. A 709-bp fragment of the cytochrome c oxidase (subunit I) gene was amplified by PCR from 356 L. pealei and 431 L. plei. Between latitudes 25°N and 43°N, each species had three common (>5% frequency) haplotypes and many rare haplotypes. Sequence data from all haplotypes indicated that nucleotide divergence between the two species ranged from 13.7 to 15.0% (transition-transversion ratio of ∼1.5; two inferred amino acid replacements). Within each species, RFLP analyses detected 40 to 45% of the total variability in nucleotide sites ( n = 18 in L. pealei; n = 21 in L. plei). Intraspecific divergences were typically <1%, with transition-transversion ratios of 17:4 for L. pealei and 21:0 for L. plei . Minimum-spanning networks of the sequence data showed two discrete clusters of haplotypes for L. pealei and no discrete clusters for L. plei. Both species were composed of two populations (P < 0.02), according to analyses of their haplotype frequencies by AMOVA (Analysis of Molecular Variance in Arlequin 1.1). L. pealei was divided at Florida, with one population in the northern Gulf of Mexico and another in the Atlantic Ocean; L. plei was divided at the Mississippi River, with one population in the northwestern Gulf of Mexico and another in the northeastern Gulf of Mexico and the Atlantic Ocean. Gene flow within each population of L. pealei was consistent with panmixia, while gene flow within each population of L. plei conformed to an isolation-by-distance model. The different phylogeographic patterns might result from the more offshore position of L. pealei in conjunction with the temperature and salinity tolerances of both species. In addition, the two populations of L. plei might represent annual recolonization from more southern populations. Finally, should fisheries develop for these species throughout the study area, these data provide support for management plans based on multiple stocks.