PERFORMANCE OF 18S RIBOSOMAL-RNA IN LITTORINID PHYLOGENY (GASTROPODA,CAENOGASTROPODA)

In the past, 18S rRNA sequences have proved to be very useful for trac ing ancient divergences but were rarely used for resolving more recent ones. Moreover, it was suggested that the molecule does not contain u seful information to resolve divergences which took place during less than 40 Myr. The present paper takes littorinid phylogeny as a case st udy to reevaluate the utility of the molecule for resolving recent div ergences. Two data sets for nine species of the snail family Littorini dae were analyzed, both separately and combined. One data set comprise d 7 new complete 18S rRNA sequences aligned with 2 published littorini d sequences; the other comprised 12 morphological, 1 biochemical, and 2 18S rRNA secondary structure characters. On the basis of its ability to confirm generally accepted relationships and the congruence of res ults derived from the different data sets, it is concluded that 18S rR NA sequences do contain information to resolve ''rapid'' cladogenetic events, provided that they occurred in the not too distant past. 18S r RNA sequences yielded support for (1) the branching order (L. littorea , (L. obtusata, (L. saxatilis, L. compressa))) and (2) the basal posit ion of L. striata in the Littorina clade.