Presentation on theme: "Cleidoic, Amniotic Egg – Amazing Life Support System"— Presentation transcript:
1 Cleidoic, Amniotic Egg – Amazing Life Support System “I think that if required on pain of death to name instantly the most perfect thing in the universe, I should risk my fate on a bird’s egg” Higginson 1863Handling all metabolic requirements and byproducts independent of parent except temperature regulationEgg Size, Shape and Color shaped by:Morphology – grebes versus owlsLife History – cavity versus cup vs groundChick development – precocial vs altricial
2 Energy – YolkProtein – yolk and albumenCalcium/phosphorous – shellWater – AlbumenOxygen – Air Cell in partWaste – uric acid (allantois)CO2
4 Shell porosity adaptations Length of incubationShearwater – incubation2.5X longer than chicken2 x fewer poresBurrow-nesting seabirdsMore poresNest microclimateBlack tern- wet nestsFewer pores
5 Fertilization, Egg production, Early Development All Birds Internal Fertilization and Oviparous -Sex Organs – Male – Homogametic ZZTestis and Penis/Cloacal Protuberance CPFemale – Heterogametic WZOvary (ovaries)Copulation3) Internal FertilizationOva (Ovum) released via LHYolk = 1/3 Lipid, ¼ Protein, Water +Associated compounds (androgens, carotenoids) =Maternal Effects
6 Usually 1 egg/24 hrs. Laid in AM - Why? FertilizationMagnum – 3hrsIsthmus 1 hrUterus 19-20hrsCloaca minutesUsually 1 egg/24 hrs. Laid in AM - Why?
7 Incubation of eggs – provide heat (below 26 devpt stops) and shade (>40 fatal)Brood patches – Prolactin, estrogen and progesterone in either or both sexesIncubation periodsTime on nestTime off nest
8 Given that 1 egg laid/day, brooding of multiple egg clutches can: Begin immediately after first egg – asynchronous hatching of youngFalconiformes, Strigiformes, Ciconiiformes, Pelecaniformes, PsittaciformesDelay incubation until clutch is laid – synchronous hatching
9 Megapodes and Incubation via external heat sources - geothermal/biotic decay Australian mallee fowl
12 Contrasts of precocial vs altricial development Precocial advantageous because once hatched, chicks can immediately fledge(nidifigous) feed on own and escape nestling predators.Disadvantage – eggs take longer to develop, longer exposure to egg predatorsAltricial allows greater growth (esp of brain) before maturation, so larger brain sizeDue to trade –off between organ growth and differentiation (maturation)Disadvantage – although egg stage shorter, nestling phase longer, greater nestlingpredation risk, increased demands of parental feeding of nestlingsFig maturation of quail legmuscles reduces energy for growthearly on, then costs of locomotion andfeeding do so slower to reach adult size
14 Extremes of parental care NoneHelpersParents plusPrevious broodsAbiotic incubationBrood ParasitismSingle parentBothIntraspecific brood parasitism“Egg dumping”Ducks, colonial swallowsInterspecific brood parasitismCowbirds, cuckoos, honeyguides
15 Evolution of brood parasites Increasing adaptationsIncreasing # host speciesFaster devpt, In utero incubation, earlier hatching,Egg ejection and host killing behaviorsFigure 19-5Common Cuckoo egg mimicry (on W chromosome)
16 Helper’s at the Nest - why forego reproduction and help? Offspring perspective:Direct benefits:Indirect benefits:Ecological Constraints
17 Clutch SizeDeterminate vs. Indeterminate Layers - will a bird replace eggs?Clutch size variation: Correlated variablesLower latitude, lower altitude, body size, ageEvolution: Lack (1947) maximum # parents can feed and nourishAlternatives: Trade-off hypothesis – long-term repro outputreduce clutch to inc adult survivalPredation – reduce time exposed , attractiveness and cost of loss where predation high (tropics)Seasonality – greater the pulse in resources overbaseline, the greater the clutch (latitude)
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