Trophic plasticity and fine-grained resource variation in populations of western mosquitofish, Gambusia affinis

Hypothesis: Fish will exhibit morphological plasticity in response to how (food type: live vs. attached food) and where (orientation: surface, mid-water, benthic) they are fed. Fine-grained resource variation (daily rotation of orientations) will produce intermediate morphologies. Population differences will reflect responses to both predators and resources. Organism: Offspring from two populations of western mosquitofish (Gambusia affinis). Experiment: A factorial design of 16 treatments: 4 (3 static orientations + 1 rotating diet) × 2 (food types) × 2 (populations) replicated three times. Methods: We raised fish in the different diet treatments for 60 days. Morphology was characterized using geometric morphometric techniques. Multivariate analysis of covariance, visualizations and multiple regressions were used to assess morphological variation. Conclusions: Responses to how and where fish fed resembled general morphological paradigms across species and may be adaptive. Fine-grained resource variation produced intermediate and unique shape effects. Population differences appeared to be related to trophic and predation ecology.