Intertidal Breeding and Aerial Development of Embryos of a Stickleback Fish (Gasterosteus)

Abstract Males of the newly discovered 'white' stickleback disperse their embryos over the filamentous algae in which they nest and, unlike any other stickleback, they provide no subsequent parental care. Previously known populations of white sticklebacks nest only in shallow subtidal waters where filamentous algae are abundant. Our purpose in this paper is to describe highly divergent populations at Spry Bay, Nova Scotia, Canada, in which males build nests on bare rock in the subtidal and intertidal zones, and disperse their embryos over bare rock. Intertidal embryos are exposed to air and are vulnerable to desiccation at low tide. Field studies reveal that nests are built from locally available materials directly on the rock substrate. They are constructed very quickly and tend to be less substantial than subtidal nests. Internest distances are shorter in the intertidal zone than in adjacent subtidal areas. Dispersed intertidal embryos tend to settle into crevices between stones where the microenvironment remains moist and temperate between tides due to the presence of organic detritus and shade. Such embryos survive, develop, and hatch. Similar behaviours occur at other sites in Nova Scotia, and we know that it has persisted for at least four years at Spry Bay. We conclude that breeding and dispersing embryos over bare rock substrate, and intertidal breeding, are novel but stable breeding repertoires. We hypothesize that they have evolved secondarily to the evolution of emancipation from parental care in the white stickleback.