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Offspring of lecithotrophic mothers receive all their nutrients from a yolk reserve produced before fertilization has occured (Trexler and DeAngelis, 2004). The mother collects and stores her resources for reproduction in advance and later uses this store in a single, yet substantial, energy investment to her offspring (Trexler and DeAngelis, 2004) (Jonsson, 1998). The female uses her liver to convert huge lipid stores into the yolk precursor, vitellogenin (Lucifora et al., 2002). Vitellogenin is then stored in ovulated ova during oogenesis where it can be used for the future growth and development of an embryo (Wourms, 1993).
There are two types of lecithotrophic organisms: oviparous and ovoviviparous.
Oviparous lecithotrophs lay fertilized eggs that spend months to a year developing independently of the maternal uterus (Hamlett, 1998) (Lombardi, 1996). Oviparous Elasmobranchs, such as Scyliorhinus caniculus (catshark), enclose their embryos in permanent, leathery egg cases made of collagen (Wourms,1993). Inside the egg capsules, the embryo feeds off yolk platelets that cilia move from the external yolk sac into the yolk stalk and to the intestine of the embryo (Hamlett, 1998). Even though the mother does not contribute anything more than this initial yolk reserve it is enough to provide the embryo with food throughout gestation and even a few weeks following its hatching (Hamlett, 1998).
Ovoviviparous lecithotrophs are similar to oviparous lecithotrophs in that they do not have a nutritive relationship with their mother and depend solely on yolk reserves for sustenance (Wourms, 1993) (Lombardi, 1996). Ovoviparous lecithotrophs are different from oviparous lecithotrophs in that ovoviparous organisms retain their embryos inside the uterus during gestation and give birth to live young. In ovoviviparous species such as, Squalus acanthias (Atlantic Spiny Dogfish), the egg capsule is a temporary structure. Halfway through gestation the embryo breaks out of its egg capsule and completes development in its mother’s uterus (Wourms,1993) (Hamlett, 1983). Although the uterus regulates the ionic and osmotic environment of the embryo, it does not form an exchange organ with the embryo or provide any more nutrition (Hamlett, 1998). For this reason ovoviparity can also be called aplacental viviparity (Hamlett, 1998).
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