INTERTIDAL BREEDING AND AERIAL DEVELOPMENT OF EMBRYOS OF A STICKLEBACK FISH (GASTEROSTEUS)

Males of the newly discovered 'white' stickleback disperse their embry os over the filamentous algae in which they nest and, unlike any other stickleback, they provide no subsequent parental care. Previously kno wn populations of white sticklebacks nest only in shallow subtidal wat ers where filamentous algae are abundant. Our purpose in this paper is to describe highly divergent populations at Spry Bay, Nova Scotia, Ca nada, in which males build nests on bare rock in the subtidal and inte rtidal zones, and disperse their embryos over bare rock. Intertidal em bryos are exposed to air and are vulnerable to desiccation at low tide . Field studies reveal that nests are built from locally available mat erials directly on the rock substrate. They are constructed very quick ly and tend to be less substantial than subtidal nests. Internest dist ances are shorter in the intertidal zone than in adjacent subtidal are as. 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 i n Nova Scotia, and we know that it has persisted for at least four yea rs at Spry Bay. We conclude that breeding and dispersing embryos over bare rock substrate, and intertidal breeding, are novel but stable bre eding repertoires. We hypothesize that they have evolved secondarily t o the evolution of emancipation from parental care in the white stickl eback.