First report of <i>Daphnia</i> in Hawaiʻi: <i>D. obtusa</i> occurrence and genetic affinities

ABSTRACT We report discovering Daphnia cf. obtusa on Hawaiʻi Island: the first report of the genus Daphnia in the Hawaiian archipelago and the first for nearly all south and central Pacific Ocean islands. Of 21 freshwater bodies sampled on Hawaiʻi Island, D. cf. obtusa was found in four, all lacking fish. Morphology of the Hawaiʻi Daphnia is consistent with D. cf. obtusa described from North America and Europe. Sequencing of 12S rRNA (12S subunit mitochondria ribosomal ribonucleic acid) and COI (cytochrome c oxidase subunit I) genes also identify the species as D. cf. obtusa, most closely related to populations in North America. The sequences from Hawaiʻi are nevertheless distinct at the COI locus, diverging from North America sequences ca. 11 000 years ago, although it is not known if divergence occurred before or after dispersal to Hawaiʻi. Possible dispersal pathways include phoresis via North America–Hawaiʻi waterbird migration routes that have existed for millennia, and recent transport by humans post-European colonization. The novel occurrence of Daphnia in Hawaiʻi provides opportunities for study, inspired by the legacy of Maciej Gliwicz, of the traits that facilitate the transport of small freshwater zooplankton over great distances, and the effects of this ecologically important taxon on plankton communities that have otherwise developed without it.