REPRODUCTION IN VERTEBRATES

• takes place outside the female body • very little cooperative behaviour is required • courtship and specific mating behaviour ensure that ova and sperm are released at the same time and place to increase the possibility of fertilisation • gametes are released into the water where fertilisation occurs. the water prevents gametes from drying out • large numbers of gametes are produced and released to increase the chances of fertilisation and the number of offspring. • the zygote develops into an independant larva that lives on yolk or plankton. • the offspring are easily dispersed by water currents, away from the parents to minimise competition.

• takes place inside the females body • does not require water • fewer gametes produced, because the possibility of fertilisation is much greater. • during mating the sperm are released directly into the females body. the sperm swim to the ovum to fertilise it. • specific mating strategies and cooperative behaviour are required between male and female individuals. • much fewer offspring produced • in reptiles and birds the developing embryo is nourished by the yolk and enclosed in a protective shell. • in mammals, the developing embryo remains inside the female where it receives protection and nutrition from the placenta

in oviparous animals the embryo develops in an egg outside the females body

• internal fertilisation takes place and eggs are retained inside the body • the embryo is surrounded by a thin, membranous shell inside the female’s body • the developing embryo receives nutrition from the yolk in the egg • the egg is retained inside the female’s body until the newborn hatch and are then born live

• internal fertilisation • the ovum develops into an embryo without the protection of the shell

the amniotic egg consists of: 1. the developing embryo 2. a fluid filled amnion surrounds the emnryo. the amniotic fluid protects it against shocks, injuries, temperature changes and dehydrating 3. the allantois is a sac that grows from the embryo’s intestines, collects wasre products and exchanges gases. 4. the chorion is the outermost membrane that surrounds all the membranes 5. the yolk sac, filled with energy-rich yolk, provides food for the developing embryos 6. the albumen, between the chorion and the shell, serves as reserve food 7. the hard, calcareous or leathery shell is porous to allow gaseous exchange. it also protects the embryo and prevents dehydration

• precocial refers to species where the young are practically fully developed and immediatly mobile when they are hatched/born • in general, fewer offspring are produced, as each individual has to develop to a relatively advanced stage before it is born or hatched • in precocial animals, most of the energy is expended on prenatal development. the mothers are far less involved after the young are born or hatched • most precocial species show little parental care

• altricial refers to species where the young are not fully developed and cannot move around immediatly after being born or hatched • in general, more offspring are produced and the young are born or hatched at an early stage • altricial animals spend most of their energy on postnatal development. the parents are involved in feeding the young and protecting them against predators for a long time after birth • altricial species show high parental care

• parental care is any behavioural pattern where patterns spend time and/or energy on the feeding and protection of their offspring • in animals where most of the energy input of parents is prenatal, there is usually very little or no parental care • in animals where prenatal energy input is less, postnatal parental care is intensive, requiring much more energy

• guarding of eggs • incubation of eggs • keeping the young warm • feeding the young • protection from predators