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Cleidoic, Amniotic Egg – Amazing Life Support System I think that if required on pain of death...

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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 birds egg Higginson 1863 Handling all metabolic requirements and byproducts independent of parent except temperature regulation Egg Size, Shape and Color shaped by: Morphology grebes versus owls Life History cavity versus cup vs ground Chick development precocial vs altricial Slide 2 Energy Yolk Protein yolk and albumen Calcium/phosphorous shell Water Albumen Oxygen Air Cell in part Waste uric acid (allantois) CO 2 Slide 3 Outside Chorion or Chorioallantois Slide 4 Shell porosity adaptations Burrow-nesting seabirds More pores Black tern- wet nests Fewer pores Shearwater incubation 2.5X longer than chicken 2 x fewer pores Nest microclimate Length of incubation Slide 5 Fertilization, Egg production, Early Development 1)Sex Organs Male Homogametic ZZ Testis and Penis/Cloacal Protuberance CP Female Heterogametic WZ Ovary (ovaries) 2)Copulation 3) Internal Fertilization Ova (Ovum) released via LH Yolk = 1/3 Lipid, Protein, Water + Associated compounds (androgens, carotenoids) = Maternal Effects All Birds Internal Fertilization and Oviparous - Slide 6 Fertilization Magnum 3hrs Isthmus 1 hr Uterus 19-20hrs Cloaca minutes Usually 1 egg/24 hrs. Laid in AM - Why? Slide 7 Incubation of eggs provide heat (below 26 devpt stops) and shade (>40 fatal) Brood patches Prolactin, estrogen and progesterone in either or both sexes Incubation periods Time on nest Time off nest Slide 8 Given that 1 egg laid/day, brooding of multiple egg clutches can: A)Begin immediately after first egg asynchronous hatching of young Falconiformes, Strigiformes, Ciconiiformes, Pelecaniformes, Psittaciformes B)Delay incubation until clutch is laid synchronous hatching Slide 9 Megapodes and Incubation via external heat sources - geothermal/biotic decay Australian mallee fowl Slide 10 Hatching - Slide 11 Developmental Mode Precocial (ancestral) Altricial Table 18-6 Cute Ugly! Slide 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 predators Altricial allows greater growth (esp of brain) before maturation, so larger brain size Due to trade off between organ growth and differentiation (maturation) Disadvantage although egg stage shorter, nestling phase longer, greater nestling predation risk, increased demands of parental feeding of nestlings Fig 16-4 maturation of quail leg muscles reduces energy for growth early on, then costs of locomotion and feeding do so slower to reach adult size Slide 13 Slide 14 Extremes of parental care None Abiotic incubation Brood Parasitism Single parent Both Helpers Parents plus Previous broods Intraspecific brood parasitism Egg dumping Ducks, colonial swallows Interspecific brood parasitism Cowbirds, cuckoos, honeyguides Slide 15 Figure 19-5 Evolution of brood parasites Increasing adaptations Increasing # host species Common Cuckoo egg mimicry (on W chromosome) Faster devpt, In utero incubation, earlier hatching, Egg ejection and host killing behaviors Slide 16 Helpers at the Nest - why forego reproduction and help? Offspring perspective: Direct benefits: Indirect benefits: Ecological Constraints Slide 17 Clutch Size Determinate vs. Indeterminate Layers - will a bird replace eggs? Clutch size variation: Correlated variables Lower latitude, lower altitude, body size, age Evolution: Lack (1947) maximum # parents can feed and nourish Alternatives: Trade-off hypothesis long-term repro output reduce clutch to inc adult survival Predation reduce time exposed, attractiveness and cost of loss where predation high (tropics) Seasonality greater the pulse in resources over baseline, the greater the clutch (latitude)

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