Years ago (feels like decades) when I first went after nine-spined sticklebacks (Pungitius pungitius), the original idea was to see if there was anything spectacular in the system (marine vs. lake vs. pond populations) keeping in mind that even if I found nothing surprising, the almost certainly existing morphological variation itself should yield interesting results. Luckily, there were lots of stuff to study including gigantism (1,2), behaviour (3), brain divergence (4,5), social costs of shoaling (5,6), phylogeography & population genetics (7), and metabolic rates & stress response (8), but finally, thanks to Mirva’s efforts, results on morphological variation are also out.
Here, we compared body shape (via geometric morphometrics) and body armour (pelvic structure, lateral plates) between sticklebacks from five marine, four lake and ten pond populations covering whole Fennoscandia. The results were surprisingly predictable: pond fish were different ffrom marine and lake fish, the latter being close to each other. Sticklebacks in ponds have deeper bodies and shorter caudal peduncles (benthic adaptation) together with less body armour (adaptation to negligible predation; in some cases the whole pelvis was absent) than marine or lake sticklebacks (more pelagic life together with heavy predation).
The results are indicative of parallel evolution at two levels: first, we found similar nine-spined stickleback phenotypes in similar habitats in geographically and genetically isolated cases (from Sweden to Russia), and second, the observed paterns were similar to those reported for three-spined sticklebacks (Gasterosteus aculeatus), providing several interesting future lines of study.
Herczeg G, Turtiainen M, Merilä J 2010. Morphological divergence of North-European nine-spined sticklebacks (Pungitius pungitius): signatures of parallel evolution. Biological Journal of the Linnean Society, in press.