Strutturazione genetica e pattern di flusso genico in quattro specie di Anfipodi Talitridi sopralitorali dell'area egea

Abstract

Allozymic variation was studied at 2210ci in 5 populations of Talitrus saltator, 6 populations of Orchestia montagui, 5 populations of Orchestia stephenseni and 1 population of Platorchestia platensis from the Aegean area. These data were compared with the well documented allozymic variation within each species at the scale of the whole Mediterranean. Interspecific mean values ofNei's genetic distance (D; Nei, 1978) ranged from 0.495 to 1.410, while the intraspecific mean values of D ranged from 0.007 (F. platensis) ro 0.256 (T saltator). Levels of gene flow (Nm) were calculated by using F st parameter, according to Weir and Cockerham's method (1984). The Slatkin's approach (1993) was used ro analyse the relationship between Nm values and geographic distances ro test for the presence of an isolation by distance pattern in the spatial genetic variation within each species. Different levels of gene flow were detected within each species both at the scale of the whole Mediterranean and of the Aegean area: Nm values 2': 1 resulted among o. montagui and P. platensis populations, while Nm values < 1 were obtained for T saltator and o. stephenseni populations. Interestingly, a pattern of isolation by distance is useful to describe the genetic structuring of the study species in ali Mediterranea areas but Aegean insular ones.