2 How many, and how often? r Selection (aka. Quick-and-many) K selection (aka. Slower and fewer)Age of maturationYoung – usually before the next breeding seasonOlder – usually many seasons after birthNumber of offspringManyFewFrequency of breedingUsually frequently (many times a season) – high fecundity = many eggs produced per breeding seasonGenerally once a season. Low fecunditySize of offspringUsually smallGenerally largerMortality ratesHigh – many offspring do not live to sexual maturityLow – offspring generally surviveExamples of speciesMice, rabbits, most insects, cane toads, octopus, mass spawning organismsHumpback whales, elephants, humans, some birds
3 Eggs or liveborn young? Oviparity Viviparity Literally means Ovum = egg, parus = bearingVivus = living, parus = bearingDescriptionEggs released by mother, embryos develop outside mother’s body, nourished by egg yolkEmbryo develops in mother, born as young. Mode of nutrition variesBenefitsReduced energy use in care of youngYolk provides good nutrient sourceMore likely for offspring to survive to birthDrawbacksEggs may need to be incubatedLess chance of survival to birth due to eg. Eggs desiccating, predators, poor environmentEnergy expenditure for female carrying offspringExamplesBirds, sharks, reptiles, monotremesHumans, some snake species, most mammals
4 Oviparity Bony fish and frogs Birds and reptiles Known as Shell -Amniote eggsShellNone, or leathery membraneUsually a hard, calcerious shellBenefitsWedge into safe crevicesBetter protected from desiccation – do not have to reproduce in waterDangersDesiccationDamageCannot be hidden in crevicesExamplesPort Jackson shark, amphibiansHens, monotremes, crocodiles
5 Viviparity Egg yolk viviparity Placental viviparity Types of viviparity are recognised by the nutrient source for the developing embryoEgg yolk viviparityPlacental viviparityOther source of nutrientMore notesCool habitat – kept warmer within bodyLargish eggsAny – nutrient sent via blood stream to embryoVery small eggsFeed them unfertilised eggsFeed them “uterine milk” – secretion from uterusExamplesSome sharks and snakes. Sea snakes – so that they do not have to return to land to breedMammals except monotremes, hammerhead sharkPorbeagle shark (feeds with eggs), Bat rays (feed with “milk”)
6 ActivitiesGlossary: r selection, K selection, fecundity, oviparity, viviparity, amniote, placenta, mortality, monotremeQuick check questions: pg 383, 387.
7 Parental care or not? No parental care Care of laid eggs Care of young What is it?No contact with offspring after eggs are laidGuarding and/or incubating eggs to hatchingCare of young after hatching/birthBenefitsFree to mate moreNo energy expenditureEggs have protection from predators/ harsh conditionsHigh chance of offspring survivalDrawbacksHigh levels of mortalityEnergy expenditureSome mortality after hatchingVery high levels of energy expenditure – may not be able to mate for many years after offspring birthExamplesReef fish, frogs, turtlesSeahorse, diamond python, cephalopods (eg. Octopus, squid), spidersHumans, primates. Mammals (milk), emperor penguins, emus
8 Case studies – 1. Australian Mallee Fowl Male invests energy into nest building – incubation mound made of rotting plant matterFemale invests energy into laying 12 to 24 eggs at onceMale incubatesChicks hatch, do not require further care
9 Case studies – 2. Emu Polyandrous Male is caregiver He builds nest, incubates eggs, guards youngFemale lays eggs and leaves to mate again
11 Australian Marsupials Placental mammals (not marsupials) have a long period of uterine developmentIn contrast, marsupials have a short period within the uterus, and a long period developing in the pouchTURN TO PAGE 391 IN YOUR TEXT BOOK
12 Australian Marsupials – arrested development Kangaroos and wallabies can suspend development within the uterusIf kangaroo conceives while young is in pouch, she stops uterine development until pouch young is off the nipple in the pouch.
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