Date of Award

8-2007

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Biological Sciences

Advisor

Blob, Richard W

Committee Member

Ptacek , Margaret B

Committee Member

Schoenfuss , Heiko L

Abstract

Distributions of Hawaiian stream fishes are typically interrupted by waterfalls that divide streams into lower and upper segments. Larvae hatched upstream are flushed into the ocean, and must climb these waterfalls to reach adult habitats when returning back to freshwater as part of an amphidromous life cycle. Stream surveys and studies of climbing performance show that Lentipes concolor can reach fast-flowing upper stream segments, but that Awaous guamensis reaches only slower, lower stream segments. Gut content analyses for these two species indicate that diet differs between them only by 10% or less dry weight for most major components (mostly green algae and invertebrates). This might suggest that feeding kinematics and performance of these two species would be similar. Alternatively, feeding kinematics and performance of these species might be expected to differ in relation to the different flow regimes where they live (faster feeding for L. concolor, slower feeding for A. guamensis). To test for such differences, we compared suction feeding kinematics and performance between A. guamensis and L. concolor through analysis of high-speed video footage and geometrical modeling. L. concolor showed significantly faster jaw opening performance than A. guamensis, which may facilitate suction feeding in the fast stream reaches L. concolor typically inhabits. Additionally, performance of jaws during feeding could depend on the proportions and configurations of jaw muscles, like all anatomical lever systems. Differences in feeding behavior and performance among all five native Hawaiian goby fishes (Sicyopterus stimpsoni, Lentipes concolor, Awaous guamensis, Stenogobius hawaiiensis, & Eleotris sandwicensis) were explored using a mathematical model of muscle function to provide further ecological and evolutionary insight into their natural history. Simulations of jaw closing indicate that several differences in functional performance correlate well with morphological differences. For example, high output force in adductor mandibulae muscles (A2 and A3) of both A. guamensis and E. sandwicensis matches expectations from morphology because these muscles are larger in these species than in the other Hawaiian stream gobies. Stenogobius hawaiiensis exhibited an alternative morphological strategy for achieving high relative output forces of both muscles, which the placement and configuration of the muscles conveyed high mechanical advantage. The multiple anatomical pathways to similar functional performance in the feeding systems of Hawaiian gobioid fishes reflect a pattern of many-to-one mapping of morphology to performance. In addition, a similar functional differentiation between A2 and A3 was evident for all species tested in which A2 was better suited for forceful movements and A3 for rapid movements. Thus, diversity of feeding performance of Hawaiian stream gobies does not show simple correlations with their habitats but, rather, seems to reflect a combination of maintenance of functional breadth with retention of some primitive traits, in addition to novel functional capacities in several species.

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