Meeting Abstract

S11.11  Wednesday, Jan. 6  Morphological selection and tradeoffs between predator escape and climbing in Hawaiian gobies BLOB, R.W.**; KAWANO, S.M.; BRIDGES, W.C.; MAIE, T.; PTACEK, M.B.; JULIUS, M.L.; SCHOENFUSS, H.L.; Clemson Univ.; Clemson Univ.; Clemson Univ.; Clemson Univ.; Clemson Univ.; St. Cloud State Univ.; St. Cloud State Univ. rblob@clemson.edu

Environmental pressures may vary over a species range, exposing different subpopulations to opposing functional demands. How does exposure to competing demands shape fish morphology and influence population divergence? We performed selection experiments on the Hawaiian goby Sicyopterus stimpsoni, an amphidromous fish facing potentially opposing selection on juvenile body shape as a result of (1) avoiding predators in lower stream reaches, and (2) climbing waterfalls to reach adult habitats. Adult fish differ in shape between islands where different pressures predominate: S. stimpsoni from Kaua’i have deep bodies, improving thrust for predator escape in long estuaries on the way to adult habitats, whereas S. stimpsoni from the Big Island have low body heights, reducing drag in waterfalls that juveniles climb shortly after entering streams. To evaluate how competing selection pressures contribute to this divergence, we compared selection imposed on juvenile body shape by (1) predation by the native fish Eleotris sandwicensis, vs (2) climbing an artificial waterfall (~100 body lengths). Fineness ratio (length/height) showed opposing selection patterns that matched predictions: predation survivors had lower ratios than control fish (i.e., greater body depth for a given length), whereas successful climbers had higher fineness ratios (reducing drag) than fish that failed. However, most variables showed significant selection in only one treatment, rather than opposing selection across both. Thus, both predators and flow conditions might influence body shape differences acoss goby subpopulations, but divergence might result from differing, rather than opposing, selection patterns. NSF IOS-0817794, 0817911.