Egg size, yolk content and gastrulation in the polychaete, Streblospio benedicti webster
LE3 .A278 2007
Gibson, Glenys D.
Bachelor of Science
Gastrulation is a critical period in development where an animal’s body plan (e.g., germ layers, body axes) is established. The objective of my study is to investigate the influences of egg size and yolk content on gastrulation in Streblospio benedicti, an unusual polychaete that produces eggs that are dimorphic in size. Small eggs (~90 μm) develop into feeding, dispersive larvae (i.e., planktotrophy) while large, yolky eggs (~110 μm) develop into non-feeding advanced young with restricted dispersal potential (i.e., lecithotrophy). Broods of both morphs were examined in 1 μm sections and also with scanning electron microscopy (SEM). For the planktotrophic morph, the mouth and gut form and are fully functional before the larva is released into the water. In the lecithotrophic morph, the cell migration of gut formation is impeded by the amount of yolk in the egg and thus overall gut formation is delayed. Epiboly of the ectoderm was documented during all three stages (early, mid, late) of gastrulation for both morphs. The formation of the mouth was not observed during gastrulation in either morph. It is expected that the mouth and gut are not completed in lecithotrophic morphs until after the embryos have been released into the water. Based on the findings of this study, more information concerning this species and the process of gastrulation will be determined which has been lacking in the past.
The author grants permission to the University Librarian at Acadia University to reproduce, loan or distribute copies of my thesis in microform, paper or electronic formats on a non-profit basis. The author retains the copyright of the thesis.