INFERRING THE GENETIC-STRUCTURE OF MARINE POPULATIONS - A CASE-STUDY COMPARING ALLOZYME AND DNA-SEQUENCE DATA

The genetic structure of natural populations of marine organisms is fr equently inferred from the distribution of alleles at gene loci. Until recently, most investigations relied entirely on protein electrophore tic techniques, with particular emphasis on polymorphic enzyme-coding gene loci (allozyme loci). Over the past few years, increasing use has been made of molecular techniques, including methods that allow the c onstruction of gene genealogies. These later methods provide powerful insight into the evolutionary history of genetic variation and, under some conditions, provide valuable information concerning population st ructure. This paper compares results of both allozyme and DNA sequence studies for a set of populations of the intertidal copepod Tigriopus californicus along the California coast. The comparisons show that: (1 ) Allozyme frequencies distinguish almost all the study populations, w hereas genealogies of the sampled DNA sequences do not. (2) Both nucle ar and mitochondrial DNA sequences reveal strong population differenti ation between central and southern California populations that is not apparent in the allozyme frequencies. (3) Allozymes and DNA sequences are not entirely concordant in the picture they present of population relationships. (4) The most complete analyses of population structure will require multiple genetic techniques.