OVIPARY, OVOVIVIPARY, VIVIPARY Introduction: Result of fertilisation is a diploid zygote (called egg) Three different reproductive strategies in vertebrates which are based on the relationships between zygote and parents / female (protection, nutrition and development of embryo) are called ovipary, ovovivipary and vivipary.
Ovipary OVIPARY: The fertilised eggs develop and hatch outside the mother's body. • The female releases her fertilised eggs into the environment (outside the body of female). • The fertilised egg / zygote is enclosed by a protective shell. • Egg yolk provides nutrition for the embryo. • Fertilisation can be internal or external
OVIPARY in aquatic conditions • Most fish, amphibians and lower aquatic forms. • Needs large numbers of eggs. • Larval stage self-sufficient; don’t compete with parents – use different food sources. • External fertilisation. • Fertilised eggs and larvae easily dispersed by sea currents.
OVIPARY in terrestrial (land) environments – maximising reproduction • Protective shell (leathery shell in case of reptiles) prevents embryo from drying out. Shell of embryo of birds is hard and brittle (breaks easily). • Fewer eggs in e.g. birds and reptiles – energy can be used for more food in large egg (yolk and albumin), hatching and protection, parental care. • Female reptile makes a hole in soil to lay her eggs in it. The sun incubates them. Birds: Parent(s) sit on the eggs to keep them warm. Birds feed young one’s. • Young reptiles are very vulnerable to predators. • Development of amnion important factor in success. See the amniotic egg.
Hard shell good protection for developing embryo; prevents embryo from drying out.
OVOVIVIPARY OVOVIVIPARY refers to the development of a fertilised egg enclosed with a soft shell that is retained (kept) in the mother's body. The young hatch within the mother's body and are then born. The developing young obtain nutrients from the yolk of the egg. Parents take no part in feeding the embryo. Ovovivipary occurs in some insects, some fish and some reptiles. Specific examples puff adder, Cape chameleon. Internal fertilisation, egg shell is soft, eggs hatch inside body, appears to be born alive, egg yolk nutrition, mother for protection. (ovo+vivi+parity (a noun), egg-live-birthing)
OVOVIVIPARY – how is reproduction maximised? • Fewer eggs needed – higher survival rate of offspring. • Developing embryo much less vulnerable to predators. • Developing embryo not subject to environmental changes e.g. temperature. • Young born fully developed, can feed and escape predators more easily. • Occurs in some fish and reptiles.
Young puff adder being “born alive” after hatching inside mother; note position of cloaca. Lorraine Kuun, July 2011
VIVIPARY Vivipary refers to the development of the embryo in the female’s body uses nutrients from her body. Internal fertilisation, no egg shell, covered by membranes Nutrition via placenta from the mother to the embryo. Waste is also passing through the placenta from the embryo to the mother. Young one’s have parental care. Study the detail during human reproduction.
VIVIPARY maximising reproduction • Occurs in placental mammals, some sharks and scorpions • Fertilisation internal, no shell • Placenta responsible for nutrition – young born alive • fewer eggs necessary • energy available for nourishment and protection of embryo, as well as parental care