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The highly variable male color morphsof the guppy (Poecilia reticulata) havebeen studied for more than 80 years,and the guppy was one of the firstvertebrates in which sex-linked inheritance of color loci was demonstrated(Winge, 1927). More recently, theguppy has become a model organismfor studying behavioral traits such ascourtship and mate choice (Evans etal., 2003; Magurran and Henderson,2003), as well as for understandingecogeographic adaptation (Endler,1991, 1995; Reznick, 1997).Guppies are live-bearers, who retain their fertilized eggs within thefollicle throughout gestation (Turner,1940; Lambert, 1970). The synchronously growing diplotene oocytesstore nutrients in oil droplets andyolk, before their maturation andfertilization. This developmentalprogram is termed lecithotrophic,and it contrasts matrotrophic programs where nutrients are providedby means of the maternal circulationthroughout gestation. Matrotrophyand lecithotrophy can contribute simultaneously to embryonic nutritionin other species of poeciliid fish(Reznick et al., 2002). In guppies, theinterface between the embryonicyolk portal system and the maternalfollicle allows for efficient gas exchange and waste disposal, whilematernal food provisioning does notseem to be required after fertilization (Turner, 1940; Thibault andSchultz, 1978).Unfortunately, studying the earlydevelopment of live bearers is morecomplicated than that of oviparousspecies, due to the inaccessibility ofdeveloping embryos for experimentalmanipulation. Therefore, despite awealth of classic genetic studies on themale color polymorphism found inguppies, knowledge of both the ontogeny and the molecular mechanismsunderlying this polymorphism is virtually nonexistent.In vertebrates, trunk neural crestcells (NCCs), which become precursors of pigment cells, most likely starttheir migratory pathways at neurulaand tail bud stages (Jacobson, 1991)
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