A PHYLOGENETIC PERSPECTIVE ON THE EVOLUTION OF REPRODUCTIVE-BEHAVIOR IN PAGOPHILIC SEALS OF THE NORTHWEST ATLANTIC AS INDICATED BY MITOCHONDRIAL-DNA SEQUENCES

The ice-breeding (pagophilic) habits and relatively short lactation pe riods of several species of ''true'' seals (Phocidae) of the Northwest Atlantic, including the harp seal (Pagophilus), bearded seal (Erignat hus), and hooded seal (Cystophora), usually are assumed to have evolve d in parallel. Current taxonomy regards Pagophilus and ringed seals (P usa) along with harbor seals (Phoca vitulina) as subgenera of Phoca, u nites Phoca (sensu late) together with gray seals (Halichoerus) and Er ignathus in the subfamily Phocinae, and places Cystophora with elephan t seals (Mirounga) in a separate subfamily, Cystophorinae. Cladistic a nalysis of variation in the DNA sequence of the mitochondrial cytochro me b gene identifies three clades among northern seals: Phoca-Pusa-Hal ichoerus, Cystophora-Pagophilus, and Erignathus. Erignathus is the sis ter group to the other species examined. Each clade may be regarded as a tribe of the subfamily Phocinae (the Phocini, Cystophorini, and Eri gnathini, respectively). The phylogeny suggests that the ice-breeding habit and associated brief lactation are ancestral characters for the Phocinae and that instances of fast-ice or terrestrial breeding are co nvergences on the ancestral condition in other phocid subfamilies.