Habitat and Morphological Correlates to Vertebral Number as Shown in a Teleost, Gasterosteus aculeatus

Abstract

Vertebral counts were made on 3257 Gasterosteus aculeatus (threespine stickleback) from Drizzle Lake, Queen Charlotte Islands, Canada, and their frequency distribution tested for randomness with respect to sex, body length, body depth, and lake habitat (littoral, limnetic). Males had a higher vertebral number than females and had a smaller adult body size, a pattern inconsistent with the phenomenon of pleomerism. Mean vertebral number decreased from juvenile to pre-adult size classes (40-60 mm body length) and then increased among adult fish over 70 mm and reached the highest counts in the largest fish (>80 mm). Vertebral number was inversely correlated to relative body depth independent of sex and size class of fish. These data parallel trends found in higher taxonomic comparisons. Increased frequency of higher vertebral counts in littoral areas was principally the result of a higher proportion of males and larger bodied (older) fish of both sexes occurring in littoral areas. This emphasizes the importance of considering sampling biases before drawing conclusions on small differences in vertebral number between samples from different populations.