Origins of endemic stickleback from the Queen Charlotte Islands: mitochondrial and morphological evidence

Abstract

Recently, two divergent mitochondrial lineages were described in a survey of 12 scattered populations of the threespine stickleback (Gasterosteus aculeatus) on the Queen Charlotte Islands (QCI), western Canada, one of which, possibly a relict lineage, was subsequently shown to characterize stickleback from the western Pacific near Japan. In the present study, we assayed 985 fish from 85 QCI populations for mitochondrial lineage using a restriction enzyme test. Our data indicate that the relict lineage was largely limited (18 of 20 populations) to adjacent watersheds in the northeast corner of the QCI close to a suspected glacial refugium, but we also found the lineage in two remote lakes on the west coast of the QCI, distant from any known refugia. We obtained a sample of 33 stickleback from the mid-Pacific and found both mitochondrial DNA (mtDNA) lineages, strongly suggesting ongoing dispersal of these fish across the Pacific, and inconsistent with previous suggestions of relict status for one of the lineages. Morphologically derived traits, such as loss of armour and loss of spines, occurred in both lineages, but these were more prevalent in the Japanese lineage. Surprisingly, 19 localities had both lineages, and within each of these there were no significant univariate or multivariate associations between lineages and morphology, suggesting few if any reproductive barriers between the divergent mtDNA lineages.