title: Stairway to heaven: evaluating levels of biological organization correlated with the successful ascent of natural waterfalls in the Hawaiian stream goby Sicyopterus stimpsoni.
abstract: Selective pressures generated by locomotor challenges act at the level of the individual. However, phenotypic variation among individuals that might convey a selective advantage may occur across any of multiple levels of biological organization. In this study, we test for differences in external morphology, muscle mechanical advantage, muscle fiber type and protein expression among individuals of the waterfall climbing Hawaiian fish Sicyopterus stimpsoni collected from sequential pools increasing in elevation within a single freshwater stream. Despite predictions from previous laboratory studies of morphological selection, few directional morphometric changes in body shape were observed at successively higher elevations. Similarly, lever arm ratios associated with the main pelvic sucker, central to climbing ability in this species, did not differ between elevations. However, among climbing muscles, the adductor pelvicus complex (largely responsible for generating pelvic suction during climbing) contained a significantly greater red muscle fiber content at upstream sites. A proteomic analysis of the adductor pelvicus revealed two-fold increases in expression levels for two respiratory chain proteins (NADH:ubiquinone reductase and cytochrome b) that are essential for aerobic respiration among individuals from successively higher elevations. Assessed collectively, these evaluations reveal phenotypic differences at some, but not all levels of biological organization that are likely the result of selective pressures experienced during climbing.
authors.affiliation: Aquatic Toxicology Laboratory, Saint Cloud State University, Saint Cloud, Minnesota, United States of America.
authors.forename: Heiko L
authors.initials: HL
authors.lastname: Schoenfuss
authors.affiliation: Department of Biological Sciences, Clemson University, Clemson, South Carolina, United States of America.
authors.forename: Takashi
authors.initials: T
authors.lastname: Maie
authors.affiliation: Department of Biological Sciences, Clemson University, Clemson, South Carolina, United States of America.
authors.forename: Kristine N
authors.initials: KN
authors.lastname: Moody
authors.affiliation: Aquatic Toxicology Laboratory, Saint Cloud State University, Saint Cloud, Minnesota, United States of America.
authors.forename: Kelsey E
authors.initials: KE
authors.lastname: Lesteberg
authors.affiliation: Department of Biological Sciences, Clemson University, Clemson, South Carolina, United States of America.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Blob
authors.affiliation: Department of Food Science and Nutrition, University of Minnesota, Saint Paul, Minnesota, United States of America.
authors.forename: Tonya C
authors.initials: TC
authors.lastname: Schoenfuss
mesh_terms: D000818:Animals; D004579:Electron Transport / Q000502:physiology; D005399:Fishes / Q000378:metabolism*; D005618:Fresh Water; D008124:Locomotion / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D040901:Proteomics
chemical_list: D009124:Muscle Proteins