The role of breeding behavior and habitat preferences on the reproductive isolation of three allopatric populations of ninespine stickleback, Pungitius pungitius

Abstract

Earlier studies have shown differences in morphology and reproductive behavior of Mississippi, Bering, and European populations of ninespine stickleback (Pungitius pungitius). In this study, assortative mating was examined experimentally to determine the role of habitat preference and breeding behavior as possible isolating mechanisms. Choice tests in naturalistic and uniform environments showed positive assortative mating in all but one pairing. One-hour latency tests gave similar results, while in the 24-h latency tests, interpopulation mating became prevalent. Although nesting habitat selection differences were found, courtship breakoff appeared to be a more important isolating mechanism. Failure to induce females to court was probably due to differences in male color, size, body proportions, and zigzag display. Failure to lead the female to the nest was probably related to differences in color and leading behavior, while failure to induce the female to enter the nest was probably related to differences in nesting substrate, nest location, and size, type, and number of entrances. The results of this study demonstrate that reproductive divergence among the three populations makes intrapopulation mating more likely than interpopulation mating.