Reproductive Strategies in Vertebrates
Introduction
● It ensures the continued existence of a species
● Reproduction strategies differ in:
○ The number of eggs produced by the female
○ The site of fertilisation, inside or outside the body of the female
○ The place of development of the embryo and it’s nourishment
○ How quickly the young can fend for themselves
○ The type of parental care given to offspring
Difference between pregnancy vs gestation:
Reproduction Structural, functional + behavioural adaptations that improve the chances of
Strategy fertilisation + the survival of offspring
External Fertilisation that takes place outside the female’s body, usually in water
Fertilisation
Internal Fertilisation that occurs inside the female’s body where the male has deposited
Fertilisation it’s sperm
Ovipary Eggs are laid; the embryo develops outside the mother’s body
Ovovivipary Young develop from egg fertilised internally + retained within the mother’s
body after fertilisation until they hatch
Vivipary The young develop inside the uterus of mother after eggs are fertilised
internally; young are nourished through the placenta
Amniotic egg The embryo inside the egg = protected by a hard shell; the egg consists of many
extra-embryonic membranes that serve different functions
Extra-embryonic Membranes that surround the developing embryo inside the amniotic egg or
membranes uterus
Amnion Produces amniotic fluid which cushions embryo + protects it from mechanical
injury, temperature changes, dehydration
Allantois Collects the embryo’s nitrogenous waste + assists in the exchange of gases
Chorion Allows for gaseous exchange in the amniotic egg + forms the placenta in
mammals
Yolk sac Contains the food reserves for the developing embryo
Precocial When hatchlings are underdeveloped as they hatch, able to move and feed
development themselves, with eyes open - limited parental care
Altricial When hatchlings are underdeveloped as they hatch, unable to move/feed/fend
, development for themselves - young require more parental care
Parental care Includes the building of nests, protection, teaching of young + feeding - the
care, or lack thereof, directly influences the survival of the young
External and Internal Fertilisation
● Fertilisation occurs when a sperm cell and egg cell fuse to form a zygote
● Fertilisation can either occur outside/inside the female’s body + varies in it’s water
dependency
External Fertilisation
● Takes place outside the female’s body and water is required for fertilisation
Internal Fertilisation
● Takes place inside the female’s body and no water is required
Comparison:
External Fertilisation Internal Fertilisation
● Requires water for fertilisation ● No water is required for fertilisation
● Gametes (sperm + egg cells) = ● Sperm cells = released into the female’s
released into water body
● Many gametes released ● Fewer gametes released
● High mortality rates among young, ● Lower mortality rates among young -
due to lack of protection. Eggs can protection provided by the mother’s
easily desiccate or be predated on body/a hardened calcareous/leathery shell
● E.g. fish and amphibia ● E.g. reptiles; birds + mammals
Ovipary, Ovovivipary and Vivipary
They differ in reproductive strategies by:
● The site where the zygote is formed
● The site where development occurs
● How the embryo receives it’s nutrients
● The type of egg or it’s presence or absence
Introduction
● It ensures the continued existence of a species
● Reproduction strategies differ in:
○ The number of eggs produced by the female
○ The site of fertilisation, inside or outside the body of the female
○ The place of development of the embryo and it’s nourishment
○ How quickly the young can fend for themselves
○ The type of parental care given to offspring
Difference between pregnancy vs gestation:
Reproduction Structural, functional + behavioural adaptations that improve the chances of
Strategy fertilisation + the survival of offspring
External Fertilisation that takes place outside the female’s body, usually in water
Fertilisation
Internal Fertilisation that occurs inside the female’s body where the male has deposited
Fertilisation it’s sperm
Ovipary Eggs are laid; the embryo develops outside the mother’s body
Ovovivipary Young develop from egg fertilised internally + retained within the mother’s
body after fertilisation until they hatch
Vivipary The young develop inside the uterus of mother after eggs are fertilised
internally; young are nourished through the placenta
Amniotic egg The embryo inside the egg = protected by a hard shell; the egg consists of many
extra-embryonic membranes that serve different functions
Extra-embryonic Membranes that surround the developing embryo inside the amniotic egg or
membranes uterus
Amnion Produces amniotic fluid which cushions embryo + protects it from mechanical
injury, temperature changes, dehydration
Allantois Collects the embryo’s nitrogenous waste + assists in the exchange of gases
Chorion Allows for gaseous exchange in the amniotic egg + forms the placenta in
mammals
Yolk sac Contains the food reserves for the developing embryo
Precocial When hatchlings are underdeveloped as they hatch, able to move and feed
development themselves, with eyes open - limited parental care
Altricial When hatchlings are underdeveloped as they hatch, unable to move/feed/fend
, development for themselves - young require more parental care
Parental care Includes the building of nests, protection, teaching of young + feeding - the
care, or lack thereof, directly influences the survival of the young
External and Internal Fertilisation
● Fertilisation occurs when a sperm cell and egg cell fuse to form a zygote
● Fertilisation can either occur outside/inside the female’s body + varies in it’s water
dependency
External Fertilisation
● Takes place outside the female’s body and water is required for fertilisation
Internal Fertilisation
● Takes place inside the female’s body and no water is required
Comparison:
External Fertilisation Internal Fertilisation
● Requires water for fertilisation ● No water is required for fertilisation
● Gametes (sperm + egg cells) = ● Sperm cells = released into the female’s
released into water body
● Many gametes released ● Fewer gametes released
● High mortality rates among young, ● Lower mortality rates among young -
due to lack of protection. Eggs can protection provided by the mother’s
easily desiccate or be predated on body/a hardened calcareous/leathery shell
● E.g. fish and amphibia ● E.g. reptiles; birds + mammals
Ovipary, Ovovivipary and Vivipary
They differ in reproductive strategies by:
● The site where the zygote is formed
● The site where development occurs
● How the embryo receives it’s nutrients
● The type of egg or it’s presence or absence
