LE3 .A278 2007

2007

Gibson, Glenys

Acadia University

Bachelor of Science

Honours

Biology

Biology

Egg size and yolk content influence early larval development in the polychaete Streblospio benedicti, a tube-dwelling marine invertebrate that produces two size classes of eggs. Some females produce small eggs that hatch as feeding, dispersive larvae (i.e., planktotrophy) while others produce slightly larger eggs that hatch as advanced, nondispersive young (i.e., lecithotrophy). My objective was: 1) to examine the developmental morphology of planktotrophic larvae from segmentation to metamorphosis based on bright field (live larvae and in 1μm section) and scanning electron microscopy; and 2) compare these data to those of the lecithotrophic morph (data collected by M. Coxhead). Relative to the lecithotrophic morphs, planktotrophic larvae had more rapid differentiation of the three germ layers throughout larval development. The ectoderm had greater differentiation of external structures such as swimming chaetae and ciliary bands (prototroch, gastrotroch and telotroch), and glandular development. Mesodermal differentiation also began earlier in the planktotrophic morph and gave rise to bands of muscle and blood vessels. Endodermal differentiation and gut formation occurred much earlier in the planktotrophic morph as well. These results suggest that development in planktotrophic larvae is accelerated relative to lecithotrophic morphs which has important consequences for supporting planktonic life with well developed dispersal (chaetae, cilia) and feeding (gut) structures. Delayed cellular differentiation of the lecithotrophic morph may support rapid growth, allowing the young to metamorphose into adults immediately following release. Variation of developmental traits (i.e., heterochrony in morphogenesis and also allocation of energy reserves) in the two morphs generates intraspecific diversity in young, perhaps increasing availability of these traits to natural selection.

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https://scholar.acadiau.ca/islandora/object/theses:515