Variation in morphology among populations of threespine stickleback (Gasterosteus aculeatus) from western Newfoundland, Canada

Abstract Freshwater populations of threespine stickleback ( Gasterosteus aculeatus ) have diverged from their marine ancestor and show extensive variation among populations throughout most of their range. However, phenotypes of freshwater populations from the east coast of North America does not appear to demonstrate extensive variability observed throughout the rest of the species’ range. The relative young age of east coast North American populations may explain the apparent lack of freshwater variability. On the other hand, populations in this part of the species’ range have not received the level of attention as have populations throughout the rest of its range and the low level of variability observed may simply reflect lack of data for this region. We examined morphological traits (including linear measurements of body armor and body shape) of stickleback from 52 locations representing marine and freshwater populations along the west coast of Newfoundland, Canada. We found that variability in morphological traits among freshwater populations was much more extensive than previously assumed and similar to patterns observed throughout the rest of the species’ range.