DISSERTATION RESEARCH: Experimental miniaturization of guppy offspring

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This project will examine which of two possible causes, difficulty in feeding or constraints on development, are responsible for setting the lower limit for the size of fish. The findings will help test theories of life-history evolution, and provide developmental and functional insights into limitations on recruitment in marine fisheries. The size of individuals spans many orders of magnitude, but is constrained at the large and small extremes by principles of physics. As organisms become smaller, the world surrounding them becomes more resistive to their movements, which are thought to limit the size of fish offspring to no smaller than 4.5 mm. At this size, fish larvae experience difficulty feeding. Alternatively, size at birth is also related to the time it takes to reach maturity. This project will test these alternatives using guppies as a model system. The project incorporates undergraduate mentoring and research training. Additionally, the project will utilize the guppy as a model for the teaching of evolution and ecology within local high school classrooms. This project involves two miniaturization manipulations: hydrodynamic and developmental. In the first manipulation, the researchers will increase the viscosity of water using dextran, thereby effectively miniaturizing the offspring in size, but not development. In the second manipulation, the researchers will remove yolk from the eggs of developing embryos, thereby miniaturizing and prematurely delivering the young. Because guppies are live bearing, the yolk manipulation requires culturing guppy embryos in vitro in order to access the yolk sac. With a pulled capillary tube, yolk will be removed such that guppy embryos will be forced to feed exogenously at approximately 4.4 mm. Feeding rates will be compared between the hydrodynamic and developmental manipulations to determine if size or maturity is the limiting feature when feeding on suspended food items. Feeding trials will be filmed using high-speed video to measure jaw kinematics and determine the Reynolds number under which the feeding apparatus is operating during suction feeding.