Sandy M. Kawano

Foraging Behavior Delays Mechanically-Stimulated Escape Responses in Fish

Foraging and the evasion of predators are fundamental for the survival of organisms, but they impose contrasting demands that can influence performance in each behavior. Previous studies suggested that foraging organisms may experience decreased vigilance to attacks by predators; however, little is known about the effect of foraging on escape performance with respect to the kinematics and the timing of the response. This study tested the hypothesis that engaging in foraging activities affected escape performance by comparing fast-start escape responses of silver-spotted sculpins Blepsias cirrhosus under three conditions: (1) control (no foraging involved), (2) while targeting prey, and (3) immediately after capture of prey. Escape response variables (non-locomotor and locomotor) were analyzed from high-speed videos. Responsiveness was lower immediately after capturing a prey item compared with the other two treatments, and latency of performance was higher in the control treatment than in the other two. Locomotor variables such as maximum speed, maximum acceleration, and turning rates did not show statistical differences among the three groups. Our results demonstrate that foraging can negatively affect two fundamental components of the escape response: (1) responsiveness and (2) latency of escape, suggesting that engaging in foraging may decrease an individuals ability to successfully evade predators.

Differences in locomotor behavior correspond to different patterns of morphological selection in two species of waterfall-climbing gobiid fishes

Behavior plays an important role in mediating relationships between morphology and performance in animals and, thus, can influence how selection operates. However, to what extent can the use of specific behaviors be associated with particular types of selection on morphological traits? Laboratory selection analyses on waterfall-climbing gobiid fishes were performed to investigate how behavioral variations in locomotion can affect patterns of linear and nonlinear morphological selection. Species from sister genera (Sicyopterus stimpsoni and Sicydium punctatum) that use different climbing behaviors were exposed to similar artificial waterfalls to simulate a controlled selective regime involving the climbing of a nearly vertical slope against flowing water. Juvenile S. stimpsoni “inch up” waterfalls by alternate attachment of oral and pelvic suckers with little axial or fin movement, leading to straightforward expectations that climbing selection should favor morphologies that improve drag reduction and substrate adhesion. In contrast, juvenile S. punctatum climb using substantial axial and fin movements, complicating expectations for selection patterns and potentially promoting correlational selection. Comparisons of directional, quadratic and correlational selection coefficients for various morphological traits and trait interactions indicated that these species showed different selection patterns that generally fit these predictions. Both directional and correlational selection patterns were different between the species, and on average were stronger in S. punctatum compared to S. stimpsoni. Stronger selection in S. punctatum may be related to its climbing style that requires more integrated movement of the fins and body axis than S. stimpsoni, promoting dynamic interactions among body regions within a complicated hydrodynamic environment.

Contrasting post-settlement selection results in many-to-one mapping of high performance phenotypes in the Hawaiian waterfall-climbing goby Sicyopterus stimpsoni

Natural selection drives adaptive evolution, but contrasting environmental pressures may lead to trade-offs between phenotypes that confer different performances. Such trade-offs may weaken the strength of selection and/or generate complex fitness surfaces with multiple local optima that correspond to different selection regimes. We evaluated how differences in patterns of phenotypic selection might promote morphological differences between subpopulations of the amphidromous Hawaiian waterfall-climbing goby, Sicyopterus stimpsoni. We conducted laboratory experiments on fish from the islands of Kaua‘i and Hawai‘i (the “Big Island”) to compare patterns of linear and nonlinear selection, and the opportunity for selection, that result from two contrasting pressures, predator evasion and waterfall climbing, which vary in intensity between islands. We found directional and nonlinear selection were strongest when individuals were exposed to their primary selective pressures (predator evasion on Kaua‘i, waterfall climbing on the Big Island). However, the opportunity for selection was greater for the non-primary pressure: climbing on Kaua‘i, predator evasion on the Big Island. Canonical rotation of the nonlinear gamma matrix demonstrated that individuals from Kaua‘i and the Big Island occupy regions near their local fitness peaks for some traits. Therefore, selection for predator evasion on Kaua‘i and climbing on the Big Island may be less effective in promoting morphological changes in this species, because variation of functionally important traits in their respective environments may have been reduced by directional or stabilizing selection. These results demonstrate that despite constraints on the opportunities for selection, population differences in phenotypic traits can arise due to differences in selective regimes. For S. stimpsoni, sufficient variation exists in other locomotor traits, allowing for necessary levels of performance in the contrasting selective regime (i.e., climbing on Kaua‘i and predator evasion on the Big Island) through many-to-one-mapping, which may be essential for the survival of local populations in an evanescent island environment.