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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 do not appear to demonstrate extensive variability observed throughout the rest of the species' range. The relatively 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 same level of attention as populations throughout the rest of its range have, and the low level of variability observed may simply reflect a 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 for populations in mainland British Columbia, Alaska, and western Europe. [ABSTRACT FROM AUTHOR]

We describe the antipredator armour of a unique population of threespine stickleback (Gasterosteus aculeatus) from Narrows Pond in western Newfoundland and compare traits for this population to nearby populations from marine and freshwater systems. After standardizing for length, Narrows Pond stickleback are shallower bodied and have shorter dorsal spines than stickleback from the other populations. Also, though the number of armour plates for Narrows Pond stickleback is greater than for typical low-plate morphs, the size of the lateral plates for Narrows Pond stickleback is much smaller. Finally, most (nearly 75% of sampled individuals) Narrows Pond stickleback do not have a pelvic structure (bilateral pelvic plate, ascending process, and ventral spine), and the remaining individuals have greatly reduced pelvic girdle, whereas all individuals from the other populations possessed complete pelvic structures. [ABSTRACT FROM AUTHOR]