Functional diversity in extreme environments: effects of locomotor style and substrate texture on the waterfall‐climbing performance of Hawaiian gobiid fishes

Abstract

Juveniles of three species of Hawaiian gobiid fishes climb waterfalls during migration to adult habitats using two kinematically distinct patterns: Awaous guamensis and Lentipes concolor use rapid, intermittent bouts of axial undulation ('powerbursts'), whereas Sicyopterus stimpsoni inches up waterfalls by alternately attaching oral and pelvic suckers to the substrate. Despite the differing kinematics and speed of these behaviors, the extreme demands of locomotion up waterfalls might require similar levels of performance from all climbing goby species. However, the roughness of climbing surfaces might affect performance differently between climbing styles, with rough surfaces decreasing inching performance by impairing the grip of sucking discs on the substrate, but improving powerburst performance by allowing the pectoral fins better purchase as they push against the substrate to start climbing bouts. To test whether species of Hawaiian climbing gobies differ in climbing performance, we filmed multiple individuals of each species as they ascended distances of several body lengths over substrates with three different degrees of roughness. Substantial differences in climbing performance among species were independent of climbing style. For example, the powerburst climber L. concolor always had a faster net climbing speed (speed over 20 cm, including rests between climbing bouts) than the inching climber S. stimpsoni; however, the powerburst climber A. guamensis was similar in net speed to S. stimpsoni, or, on smooth substrates, climbed more slowly. Yet, some differences in performance did emerge between the climbing styles. Substrate roughness did not affect climbing speed in S. stimpsoni, but, as predicted, both powerburst climbers climbed faster on rougher surfaces. In addition, the intermittent motion and rest periods for both powerburst climbers seem of appropriate durations to facilitate an increase in the distance that these species travel before fatigue, but the inching climber S. stimpsoni spent more time in motion than either powerburst climber, and the relative durations of its motion and rest periods seem less likely to convey any performance advantages. These results indicate considerable functional diversity among Hawaiian climbing gobies beyond the two varieties of climbing styles, and show that a wide range of performance capabilities can persist among members of a fauna even under extreme environmental conditions.

Performance and scaling of a novel locomotor structure: adhesive capacity of climbing gobiid fishes

“…Prior to each trial, ambient atmospheric pressure was recorded for 10s, and the average pressure from this period was used to calculate suction pressure differentials (PP ATM -P suction ). For each individual, area of the pelvic sucker was calculated as an ovoid from maximum width and length measurements collected directly [AreaWidthϫLengthϫ/4 (Schoenfuss and Blob, 2003;Blob et al, 2006;Maie et al, 2007)]; pressure differentials were then multiplied by this value to calculate adhesive suction forces generated by the pelvic sucker (ForceAreaϫP). For each individual, we collected 17 to 22 pressure recordings for each inclination, and selected the five highest values at each inclination to represent maximum adhesive capacity.…”

“…Blob et al, 2006;Blob et al, 2007) and placed in a small (15l) tank (Fig.1B). Stream water from a bucket was released over the climbing surface by siphon at 250mlmin -1 , producing a sheet 1mm in depth (Fig.1B).…”

“…Such muscularization indicates an important role for the fin retractor muscles among effectively climbing species, but why do such species not also exhibit positive allometry of sucker size, particularly as the tissues comprising the fins might be expected to be less energetically demanding than enlarged muscles? It is possible that excessively large pelvic suckers might actually impede functional performance in waterfall climbing, if increased drag or mass of the sucker made it more difficult to advance, or if large sucker size increased the chance of encountering a heterogeneous climbing surface, making it difficult for the sucker to form an effective seal on the substrate (Blob et al, 2006). Some support for such hypotheses is indicated by selection experiments that required juvenile S. stimpsoni to climb artificial waterfalls, which found significant selection for suckers that were larger in width, but smaller in length (Blob et al, 2010).…”

Aquatic turning performance of painted turtles (Chrysemys picta)and functional consequences of a rigid body design

“…Whereas the importance of some components of locomotor performance, such as rectilinear sprint speed and endurance, is widely appreciated, many other aspects of locomotion can also be critical to an animal's survival (Biewener and Gillis, 1999;Blob et al, 2006). For example, animals rarely move in a straight line for prolonged durations.…”

Locomotor loading mechanics in the hindlimbs of tegu lizards (Tupinambis merianae): comparative and evolutionary implications

“…Although consistent across the lizard (and crocodilian) species that have been studied, this mechanism appears not to apply for salamanders (Sheffield and Blob, 2011) or turtles (Butcher and Blob, 2008a;Butcher et al, 2008), in which the rotational moment of the GRF induces inward rotation, complementing (rather than opposing) that produced by CFL retractor muscles. Thus, despite the superficially similar body plans and locomotor movements of many sprawling tetrapods, torsional loading of the femur appears to result from differing patterns of torsional moments across lineages, indicating that multiple functional paths can lead to similar ranges of functional performance (Wainwright et al, 2005;Blob et al, 2006).…”