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Chapter 12 KEY KNOWLEDGE: •Extend your knowledge of the variety of reproductive strategies in animals and plants •Develop understanding of how various strategies assist successful reproduction in particular environments What are reproductive adaptations? Reproductive adaptations are those directly related to the animal's need to reproduce. They may include behavioural adaptations such as courting behaviour, or structural adaptations such as special colouration designed to attract the opposite sex. The main goal for organisms in the wild is to survive and reproduce For example, rabbits breed all year round so the chances of some of their offspring surviving are higher. ANIMAL REPRODUCTION Producing eggs and sperm Making displays to attract mates Size and number of eggs produced Care of eggs and offspring Energy investments Boxfish all energy into producing many eggs, no energy into their care Clownfish fewer eggs produced, but increased energy put into their care Sexual Reproduction Lends itself to greater genetic diversity Allows organisms to evolve and adapt, but requires more energy than asexual reproduction Tends to happen in changing or less stable environments and where there is more competition Broadcast Spawning p 374 Simultaneously releasing sperm and eggs into the water where fertilisation will occur Usually occurs in regions of the reef affected by strong currents and when an outgoing tide is flowing Fertilised eggs are quickly carried away from the reef and predators living in this habitat Eggs which float within the water column are pelagic eggs Most reef fish use broadcast spawning Fish that are broadcast spawners include boxfish, butterfly fish, coral trout (reef fish) and mackerel, tuna and cod (open ocean fish) Many gather in large groups at one location and release their eggs and sperm simultaneously = mass spawning Broadcast spawners but all their energy into egg production to produce large numbers of eggs Fertilised eggs are ‘on their own’ as the current takes them away – they depend upon their yolk sacs for nutrition until they are strong enough to find food Demersal spawning p 375 Demersal eggs do not float. The female fish that produces them may lay them in a nest in the sand or in a crevice in the reef After being laid, the eggs are fertilised by sperm released by the male Unlike broadcast spawners, demersal spawners typically give some care to their eggs by guarding them until they hatch or keeping them clean Energy is invested in guarding and cleaning their eggs, these fish produce fewer and larger eggs than broadcast spawners Monogamy 1 male + 1 female for 1 or more breeding seasons (or for life!) Some bird species for ‘pair bonds’ which breed together monogamously for a breeding season, while others breed together exclusively for a lifetime Seen in species where survival of offspring depends upon care of both parents for tasks such as: Defending the nest site Incubating eggs Providing warmth Feeding offspring The young of many monogamous birds are born featherless, blind and helpless = Altricial development mode Polygamy 1 male + multiple female partners in one breeding season (polygyny) OR 1 female + multiple male partners during a breeding season (polyandry) Polygamy is seen in habitats with plentiful and reliable food sources and where one parent can ensure survival of the offspring Harem Polygyny 1 male mates with each of the females in his Harem during the breeding season (eg. magpies, lions, gorillas) Serial Polygyny 1 male attracts passing females in turn for mating must advertise self through visual/vocal signals Males of polygynous species often differ markedly in colour and feather length from the females (eg. Lyrebird, bowerbirds) ○ These males put all their energy into producing long feathers etc, and no energy into the care of the young. The female is responsible for caring for the offspring The female chooses who she mates with, usually based on his genetic potential, strength, fitness or other survivalrelated traits Polyandry (promiscuous female) is rare and occurs in less than 1% of bird species In Cassowary, once the female has laid the eggs, she leaves them to go and find another partner the male is left to incubate the eggs for 47+ days and chicks then stay with the father for a number of months Promiscuous mating = multiple and indiscriminate mating more common in male birds Females tend to be selective in their choice of partner r – selection p 381 Quick and many Typical of species which sexually mature quickly Produce large numbers of offspring or breed more frequently Parents put little or no care into their offspring High fecundity = High number of eggs produced annually Eggs produced in larger numbers but have higher mortality rates few survive to adulthood Animals include: reef fish, squid, oysters, scallops, many insects, cane toads, mice and rabbits r-selection species are suited to rapid spread in habitats where the population density is low K-selection p 382 Slower and fewer Animals mature slowly, breed later, produce fewer and larger offspring Generally put extensive care into their young Animals include: some birds, gorillas, elephants, whales and humans Longer lifespan = typically more than one breeding season during their lifetimes r- and K-selection Two reproduction strategies At opposite ends of a continuum Some species show features of both strategies Eggs or live-born young? p 383 Oviparity = eggs are released by the mother so that embryos develop outside the mother’s body, with nutrients coming from the egg yolk Oviparous = egg bearing Sharks, all rays, bony fish, amphibians (incl frogs & toads), most reptiles (incl. turtles, crocodiles, goannas but only some snakes) and all birds; monotreme mammals (echidna and platypus) Size of newborn hatchling depends upon yolk supply in egg REFER TO p 384 for how the eggs are produced internally Eggs of birds and reptiles are called amniote eggs They have their own protection from drying out, own waste removal system and energy supply These eggs can be laid on land since they carry their own supply of water (fish and amphibians rely on water to reproduce, however this adaptation of birds and reptiles enables reproduction to occur away from water) The success of reptiles in arid habitats is due in part to the fact they produce amniote eggs Oviparous animals can concentrate energy on producing a small number of large eggs (bigger the egg, bigger the food source and therefore the offspring) or large numbers of small eggs (these young have a shorter embryonic development) Viviparity = eggs develop within the mother’s body and are born as miniature copies of the adult Viviparous = live bearing Contributes to an increased chance of survival for a developing embryo (protection from within mother rather than exposure to predation) Egg-yolk viviparity Eggs remain within the mother, embryos nourished by yolk within the uterus before and after hatching, then born as mini-adults Mother can maintain temperature of embryos better by retaining eggs inside her Placental viviparity all mammals except monotremes produce tiny pin-head sized eggs with very little yolk. Embryos contained within a fluid-filled sac and develops within the uterus, with nutrition coming from the mother’s bloodstream via the placenta (also acts to remove wastes from the embryo) Caring for eggs after laying p 388 Caring for eggs after hatching increases their survival Male seahorse incubates and protects his young for ~5 weeks (1cm long) in his pouch Certain snakes wrap themselves around their eggs until they are hatched, monitoring the temperature and shivering to increase heat if the temperature drops Some sea creatures attach their parcel of eggs to ‘safe’ locations within reefs Certain species of spiders wrap hundreds of eggs within egg sacs and stay with them until they hatch within the sacs One or both parents may care for the young All mammal babies suckle milk for some period after birth Features of marsupial reproduction Marsupials have developed strategies that equip them for successful reproduction in the drought-prone and unpredictable environments in Australia Marsupial mammals = pouch Marsupial embryos have a very short period of development in the uterus before being born further extended development occurs in the pouch Use a ‘stay-on-the-nipple’ approach to early development whereas mammals use a ‘stay-in-the-uterus-longer’ approach. ALL mammals (monotreme, marsupial and placental) produce milk for the nutrition of their young Reproduction in kangaroos and wallabies is influenced by environmental conditions They can suspend embryonic development Immediately after giving birth and having young in her pouch, a female kangaroo conceives again held in arrested development as long as other young are feeding on milk in pouch Occurrence of mating p 393 In many species, mating occurs just before each fertilisation event because sperm typically does not live long after they are released by a male Sperm release can be into the environment = external fertilisation OR into the female’s reproductive tract = internal fertilisation In some animals (eg, honeybees) sperm can be stored by the female, depending upon the needs of the hive, and produce fertilised eggs at a later time Patterns and breeding times Eggs and sperm must be available at the same time in members of a population Breeding season = time when members of population have sperm and eggs ready for release Called Spawning season in animals that have external fertilisation (aquatic animals) Mating season for animals that have internal fertilisation Production of sex cells influenced by hormones, temperature and day length Some species don’t breed until almost the end of their lives, then fertilise and release the eggs, and die.