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Freshwater threespine stickleback fall along a benthic (bottom feeding)–limnetic (plankton feeding) continuum of ecotypes. Although trophic and courtship behaviour are well-described, the full reproductive cycle has not been characterized in the ecotypes. We provide detailed in situ descriptions of the reproductive cycle of males in one population of each ecotype, and a less detailed description in one oceanic population likely to represent the ancestral form that gave rise to the post-glacial freshwater radiation in southern British Columbia. All populations exhibited typical patterns including: pre-spawning nest building, fanning (which peaked in intensity just before hatching of embryos), and gluing (which was most common from nest building through the early parental phase). These elements of behaviour may be fixed by the physiological requirements of the fry. Males in the benthic and oceanic populations interacted frequently with groups and solitary non-neighbours, reflecting the abundance of bottom-feeding adults. Interactions with groups did not occur in limnetic populations and those with solitary non-neighbours were rare. Interactions were common with neighbours in all populations, but in the limnetic population they were conspicuous and ritualized, rather than the simple chases observed in the other populations. Males in the limnetic population also attended to the nest more, in some cases producing a 3-cm mound of sediment following the completion of spawning and often placing rushes around the pit-nest. The general pattern was one in which males in the cannibalistic benthic and oceanic populations appeared to be constrained in their interactions with neighbours and their attention to the nest by the need for vigilance and nest defense, while limnetic males attended more to nests and neighbours, possibly exhibiting the optimal pattern of nest-directed activities for the fry. [ABSTRACT FROM AUTHOR]