In northwestern North America, stickleback in small, shallow lakes have evolved a deep-bodied (benthic) form specialized for feeding on benthic invertebrates, while those in deep, oligotrophic lakes evolved a slender form (limnetic) adapted for feeding on plankton. Research in our laboratory has demonstrated that benthic populations retain ancestral tendencies to form bottom-feeding foraging groups that cannibalize young in nests when they are discovered. Courtship in benthic populations is typically initiated by females who swim to the male and press their abdomens against the male’s dorsal spines initiating the relatively inconspicuous dorsal pricking behavior that makes up most courtship in these populations. In contrast, limnetics have lost ancestral cannibalistic tendencies, and males initiate courtship with the very conspicuous zig-zag dance. In benthic and oceanic populations males are generally drab, a condition that reflects the plastic response of motile chromatophores to the threat of cannibalism – although low settlement abundance on the breeding grounds of oceanic stickleback can lead to the expression of bright nuptial coloration. A primary goal of our research is to understand how ancestral plasticity in coloration and reproductive behavior have influenced subsequent evolution in fresh water, and possibly the very high levels of parallelism in the adaptive radiation along the benthic-limnetic axis.
We are also very interested in the way that the stress response has evolved along the benthic-limnetic axis. Females in benthic and oceanic populations can be forced to retain eggs for long-periods post-ovulation because cannibalistic groups interfere with courtship. On-going research by Ph.D. student Melissa Graham has yielded evidence of ecotypic differences in the female stress response and in egg hormone concentrations that affect growth of offspring – yielding a transgenerational effect of stress in limnetic fish but not in benthic fish, which have retained the ancestral phenotype. Comparison of oceanic and derived phenotypes offers an unusual opportunity to understand the evolution of the vertebrate stress response over a 12,000 year time frame.