Abstract

The morphology of "sea squirts" (Urochordata: Tunicata) is highly variable and is expressed in habitat-specific differences intra- and interspecific variation pattern that had hindered the interpretation of such differences as well as their taxonomical, ecological or evolutionary meaning. Here we describe the population genetic structure of three morphotypes (squat, intermediate and tall "sea squirt") observed in populations of the "piure de Antofagasta", Pyura praeputialis by enzyme electrophoresis. The study was carried out in three localities in the northern sac of the Bay of Antofagasta, Chile, and distributed along a wave exposure gradient. A total of 17 enzymatic loci were assayed by horizontal starch-gel electrophoresis, three of which (IDH-1, MDH-1 and PGM-1) were polymorphic. The results showed significant genetic differences among localities, but not among morphotypes. These results are contrasted with similar studies conducted on the same species in Australia, on the base that P. praeputialis has recently colonized Antofagasta from Australia. It is suggested that the differences among the morphotypes from Antofagasta are intraspecifics and those from Australia are interspecifics. The possible explanations for the genetic and morphological differences among localities are discussed.