Morphological selection in waterfall-climbing fishes
In addition to my doctoral work, I also conducted considerable work on aspects related to morphological diversity in Hawaiian goby fishes, as part of an NSF-funded research grant awarded to my collaborators Rick Blob (Clemson University), Margaret Ptacek (Clemson University), Heiko Schoenfuss (St. Cloud State University), and Matt Julius (St. Cloud State University). Characteristics of the environment can play important roles in shaping phenotype and performance, and can drive population divergence if strong enough. The waterfall-climbing gobiid system provides the opportunity to understand how biotic (e.g. predation) and abiotic (e.g. selective pressures induced by waterfall climbing) can shape morphology and performance in this taxon. Although these fishes share an amphidromous life history that has allowed them to invade a variety of insular freshwater streams, they exhibit various behavioral and morphological differences, occupy different regions within a stream, and have invaded islands across the globe. We use a combination of linear and nonlinear selection analyses, morphometrics, kinematics, and performance measures in the lab and field to answer a variety of questions including: how behavioral differences of a similar locomotor mode (e.g. climbing) influence patterns of morphological selection, how habitat use induces context-dependent locomotor behaviors and performances, and how functional trade-offs influence selection on morphology. See Rick Blob's website for more info.
Differences in locomotor behavior correspond to different patterns of morphological selection in two species of waterfall-climbing gobiid fishes
Behavior can influence the relationship between morphology and performance, and can affect how organisms respond to particular agents of selection. Waterfall-climbing goby fishes were used to investigate this aspect since climbing waterfalls is a brief yet intense agent of selection. But there's more than one way to climb a waterfall. Laboratory selection analyses were conducted on two species of waterfall-climbing goby fishes, Sicyopterus stimpsoni from Hawai'i and Sicydium punctatum from Dominica, to determine how locomotor differences between waterfall-climbing behaviors could influence patterns of morphological selection. Sicyopterus stimpsoni climbs like an inch worm using its mouth and pelvic sucker ("inching" climbing) whereas S. punctatum climbs by pushing off with its pectoral fins and undulations of its body axis ("power-burst" climbing). We found that these different locomotor strategies for climbing a waterfall can result in different patterns of morphological selection that relate to the biomechanics of each locomotor behavior. Stronger selection was also observed in S. punctatum, which may result from the power-burst climbing mode imposing greater constraints for a more integrated locomotor system.
Results were published in Kawano et al. (2013). Data are available via Clemson Tiger Prints.
Photo is an example of one of the fitness surfaces for S. stimpsoni.
Results were published in Kawano et al. (2013). Data are available via Clemson Tiger Prints.
Photo is an example of one of the fitness surfaces for S. stimpsoni.
Intraspecific variation in the patterns of morphological selection in the waterfall-climbing fish, Sicyopterus stimpsoni
Selection is the primary driver of adaptive evolution, and local adaptation can occur when selection is stronger than gene flow. The Hawaiian freshwater goby fish,Sicyopterus stimpsoni, exemplifies how the interplay between selection and gene flow can result in population differentiation. The pelagic larval stage during their amphidromous life cycle allows for gene flow across islands, with returning juveniles facing differing selective pressures: 1) escaping from predators in the lower stream reaches, and 2) climbing waterfalls to reach breeding habitats. However, the primary selective agents between Hawai’i and Kaua’i (climbing vs. predation, respectively) may be driving subpopulation differences since adult morphologies match predictions for improving streamlining and thrust production, respectively. We conducted selection analyses to assess whether juveniles recruiting to Hawai'i and Kaua’i exhibit different patterns of morphological selection in response to a brief, yet intense selective agent: waterfall climbing. Our study found that the Hawaiian subpopulation had greater climbing success, and that nonlinear selection patterns were more similar between two Kauaiian subpopulations than between island subpopulations. Quadratic selection was also ~2x stronger on Kaua’i. Traits under selection generally matched predictions for the primary selective agent on each island: taller body heights that could improve predator evasion on Kaua’i, and shallower bodies that improve streamlining during climbing on Hawai’i. These data provide insight into how patterns of morphological selection can contribute to local adaptation despite gene flow.
This work was conducted in collaboration with Kristine Moody (Tulane University), Billy Bridges (Clemson University), Margaret Ptacek (Clemson University), Heiko Schoenfuss (St. Cloud State University), and Rick Blob (Clemson University).
Results were published in Moody, Kawano, et al. 2017.
This work was conducted in collaboration with Kristine Moody (Tulane University), Billy Bridges (Clemson University), Margaret Ptacek (Clemson University), Heiko Schoenfuss (St. Cloud State University), and Rick Blob (Clemson University).
Results were published in Moody, Kawano, et al. 2017.
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Schoenfuss HL, Maie T, Kawano SM, Blob RW. 2011. Performance across extreme environments: comparing waterfall climbing among amphidromous gobioid fishes from Caribbean and Pacific Islands. Cybium 35(4): 361-369. Paper available HERE.
Blob RW, Kawano SM, Moody KN, Bridges WC, Maie T, Ptacek MB, Julius ML, Schoenfuss HL. 2010. Morphological selection and tradeoffs between predator escape and climbing in Hawaiian gobies. Integrative and Comparative Biology 50: 1185-99. Paper available HERE.
Blob RW, Kawano SM, Moody KN, Bridges WC, Maie T, Ptacek MB, Julius ML, Schoenfuss HL. 2010. Morphological selection and tradeoffs between predator escape and climbing in Hawaiian gobies. Integrative and Comparative Biology 50: 1185-99. Paper available HERE.
