Mating Systems

Monogamy Pair bonds with one male and one female for one or more breeding seasons or for life Estimated that 90% of bird species are monogamous

Emperor Penguins form pair bonds for one breeding season

 Where the survival of the young requires the care of both parents for tasks, the species is usually monogamous  Defending the nest  Incubating eggs  Feeding offspring The young of many but not all monogamous bird species are born featherless, blind and helpless – altricial development mode.

Polygamy Either one male or one female has multiple partners during a breeding season Often seen in bird species living in habitats with plentiful and reliable food resources; where one parent can ensure survival of the young

Mating Systems - Polygamy Polygyny (poly – many, gunos – woman) When one male has multiple female partners during a breeding season Polyandry (poly – many, andro – male) When one female has multiple male partners during a breeding season

Polygyny Occurs in about 2% of bird species Harem Polygyny – occurs when one dominant male lives with a group of females and mates with each of them during the breeding season. Example – magpies, gorillas, lions Mating Systems - Polygamy

Polygyny Serial polygyny – one male attracts passing females in turn for mating. Males must advertise themselves through visual or vocal signals, hence males often appear quite different in colour to the female. Examples – lyrebird, bower bird, walruses, fallow deer.

Mating Systems - Polygamy Polygyny Serial polygyny sometimes involves lekking. Many males gather in a communal area (a lek) to perform displays and attract passing females

The Bower bird attracts passing females with his excellent bachelor bower pad.

Polyandry When one female mates with two or more male. This mating system is rare, less than 1% of bird species Female is often larger and more brightly coloured Examples – cassowary, jacana

Polyandry Examples – a female Jacana will mate, lay eggs in a nest he has built, then leave him to incubate the eggs while she looks for another mate. - the female cassowary does the same, leaving the male to incubate the eggs then care for the young for several months

Promiscuous Mating Systems - males and females within a social group engage in multiple and indiscriminate matings. - all males are about equally successful in producing offspring What are the survival advantages and disadvantages of this system compared to polygamy and monogamy?

Offspring: How many? How often? Two reproductive strategies commonly identified in animals are; - ‘quick and many’ known as r-selection - ‘slower and fewer’ known as K-selection Many species cannot be pigeon-holed into either category. These two are at either end of the continuum. Plants – generally -shorter-lived plants often produce large numbers of minute seeds - longer-lived plants often produce fewer but larger with food reserves for developing the plant embryo

r-selection Typical of species that reach sexual maturity quickly, produce large numbers of offspring or breed more frequently and may put little or no care into offspring. Fecundity – refers to the number of eggs produced by each female on an annual basis Offspring often have higher mortality rates so few survive to adulthood

r-selection A common female octopus lays from 100,000 to 400,000 eggs in clusters and deposits them in crevices in a coral reef She keeps her eggs supplied with oxygen by squirting them with water and keeps them clean by gently wiping the eggs with her arms.

 These species mature slowly, breed later, produce fewer and larger offspring and may care extensively for their offspring  Often have a longer lifespan and typically have more than one breeding season during their lifetimes.

 Sexual maturity does not occur until whales are about 5  Gestation lasts about 11.5 months  Female gives birth to one calf every two years  Calf suckles for an average of 10 months  Life span is up to 50 years

Eggs or liveborn young? Oviparity – eggs released by the mother so embryos develop outside mother’s body with nutrients for the embryo coming from the egg yolk Viviparity – embryos develop within the mother’s body and are born as miniature copies of the adult. Nutrition of the developing embryo within the mother occurs in different ways.

Oviparous Animals The size of the newly hatched young is determined by the yolk supply in the egg – the larger the yolk, the larger the young. Examples – some sharks, all rays, bony fish, amphibians, monotreme mammals

 The eggs of bony fish and amphibians (eg frogs) do not have shells; they dry out if they are not released into water.  Embryonic development occurs outside the female body  The embryo obtains all its nutrients from the yolk and releases wastes into the water. Egg case of the Port Jackson shark

 The eggs of reptiles and birds are known as amniote eggs. Features include:  An outer shell for protection, gas exchange, an thin membrane under the shell also allows gas exchange.  A series of membranes inside the egg, including;  A membrane (amnion) that surrounds the embryo and secretes a fluid that bathes and protects the embryo from drying out.  A membrane (allantois) that stores embryo wastes in a solid form  A membrane that forms a yolk sac for food

 Amniote eggs can be laid on land as they have their own supply of water  Oviparous animals can either put energy into producing smaller numbers of large eggs or larger numbers of small eggs  Larger eggs have larger food stores (yolk)  Young hatching from larger eggs have longer periods of embryonic development and are bigger at the time of hatching.  The larger the eggs, the fewer the number of eggs

 Instead of laying eggs, some vertebrate animals produce miniature live-born young Examples – most sharks, some snakes, mammals (except monotremes)  Viviparity increases the chance of survival by protecting the young within a female’s body rather than leaving them exposed to predators

 Three types of viviparity have been identified, depending on the source of nutrients for the embryo. Nourished by the yolk (egg yolk viviparity) Nourished by the placenta (placental viviparity) Nourished by other sources

 Some sharks – eg the nurse shark gives birth to 30 – 40 pups, each about 30cm long  About 20% of snakes – eg copperhead produce up to 20 young  Research shows that the snakes are better able to regulate temperatures of the eggs in their bodies (suited to cooler climates)

 All mammals (except monotremes) produce tiny eggs with very little yolk.  Mammalian embryos are enclosed in fluid filled sacs and develop within the mother’s uterus.  Nutrients are delivered from the maternal bloodstream via the placenta to the embryo.  The placenta is where the bloodstream of the mother and the embryo come into close contact allowing for nutrient and waste exchange.

Viviparity – Nutrients from other sources  Some sharks give birth to a few very large young. These young grow after the eggs hatch but while they are still inside their mother.  Nutrition via shark placenta – eg hammerhead shark  Nutrition via extra eggs – eg porbeagle shark. Extra yolky eggs produced just for feeding  Nutrition via intrauterine milk – eg bat rays. A protein rich milk secreted to nourish the embryo after the yolk is used.

Parental Care or Not? Different animal species vary in the energy they put into the care of their eggs or their young. Eg most reef fish, all turtles, most frogs and toads give no care to their eggs or young after laying All mammals and most birds give great care and protection to their young and eggs.

Parental Care or Not? Caring for eggs after laying EEg clownfish guard their eggs EEg seahorse – the female seahorse lays her eggs in a pouch in the male. The male gives birth to live young about 1cm long. EEg Some oviparous snakes. Australian diamond python guards her eggs until they hatch. Children’s python coils around her eggs until they hatch EEg some cephalopods (octopus, squid, etc) attach their eggs to ‘safe’ locations, then cleans and protects them EEg spiders wrapping their eggs in a silken cocoon.

Parental care of young ▫M▫Most bird species, both parents care for the young ▫P▫Polygynous species – who cares for the young? ▫P▫Polyandrous species – who cares for the young? ▫M▫Mammals care for their young for some period after birth through the young suckling from the mammary glands. ▫P▫Primates care for their young for considerable periods after they are weaned

C ASE STUDIES IN P ARENTAL C ARE Emperor Penguin – page 389 Monogamous or polygamous? Who cares for the egg? For how long? Have you seen ‘Happy Feet ’?

C ASE STUDIES IN P ARENTAL C ARE Australian Mallee Fowl Who builds the nest? Laying 12 – 24 eggs, would they be large or small? Who cares for the eggs? Polygynous or Polyandrous?

C ASE STUDIES IN P ARENTAL C ARE Emu Who cares for the eggs? Who cares for the hatchlings? For how long? How does the mating system of the emu assist in survival of the species?