1. Bellwork: How do some offspring of animals survive when parents provide little – no parental care? Why is maternal care an important mammalian characteristic?

2. Reproduction
Section 28.3

3. Do some animals reproduce asexually?
Yes!
Some cnidarians cane divide in two
Some animals reproduce through budding
Some lizards can produce eggs that don’t need to be fertilized
Process called parthenogenesis – DNA only from Mother
Rare in vertebrates
Asexual reproduction only requires one parent
Well suited for favorable environmental conditions, but less genetic diversity

4. What cellular process is the basis of sexual reproduction?
Meiosis!
Haploid gametes formed with half the number of chromosomes
Sexual reproduction maintains genetic diversity, by essentially shuffling genes
Populations are better evolved to adapt and respond to changing environments
Normally involves a male and a female, although some animal species are hermaphroditic (certain annelids, mollusks and fishes)
Some produce egg and sperm at the same time, but don’t fertilize their own eggs – why?
Some species change sex as they mature - clownfish

5. Can organisms reproduce both sexually and asexually?
Yes!
Common with parasitic worms and cnidarians
Parasitic worms infect a person and reproduce sexually
Embryos released into feces
In fresh water they develop into larvae and infect snails
They reproduce asexually in the snail
Larvae released, infect another person to reproduce sexually – process repeats

6. With Jellyfish it’s a bit different

7. Does fertilization of an egg have to take place inside a body
No, there are two types of fertilization, internal and external
Many aquatic and virtually all terrestrial animals reproduce via internal fertilization
Invertebrates – can be mating, or in the case of sponges, sperm is absorbed from surrounding water
Chordates – most involve a male external sexual organ, but in some amphibians males excrete sperm packets
External fertilization – more common in aquatic vertebrates and invertebrates
Large numbers of eggs and sperm often released into the water
In some cases, you can still have fish and amphibians spawning in pairs

8. Where do Embryos develop?
It depends on the organism

9. Development of young
Most newborn mammals, and hatched birds and reptiles look like miniature adults
For some other groups of animals, when you look at an infant, it is not clear what it is
This is because the animal will undergo metamorphosis
In Aquatic invertebrates there is a larval stage
Invertebrates - more complex
Incomplete and complete metamorphosis

10. What controls metamorphosis in arthropods?
Hormones! What is a hormone?
A hormone is a chemical produced in one organ of an organism that affects the organisms other tissues and organs
If an insect undergoes complete metamorphosis, high levels of juvenile hormone keep the insect in it’s larval form
As the insect matures, production of juvenile hormone decreases
Amphibians go through a similar metamorphosis controlled by hormones

11. Do all animals care for their offspring?
No! Caring for offspring if highly variable, from no care to years of nurturing
Aquatic Invertebrates, fish and amphibians ordinarily release their eggs, and that is parenting done!
Works when population disperses and grows rapidly
Other animals care for offspring, with both parents helping out
This intense parental care helps animals to survive in crowded, competitive environments
Species that provide intensive, or long term care typically give birth to fewer young

12. Reproductive diversity in chordates
All chordates originated in water - so early chordate production was suited to aquatic life
Fish and amphibian egg ordinarily still need water to develop
Reptiles, birds and a few mammals evolved amniotic eggs, which allow the embryo to develop outside of the mother without drying out

13. What adaptations have mammals evolved for reproducing and caring for their young?
Monotremes – lay soft shelled, amniotic eggs that are incubated outside of the body. Eggs hatch quickly (10 days), but mother has mammary glands that produce milk, secreted through pores on the surface of the abdomen. Example Echidna.
Marsupials – birth live young, but development finished in an external pouch. Often spend months in the pouch, drinking milk
Placentals – Placenta allows exchanges of nutrients, oxygen, carbon dioxide and waste between mother and child. Embryo develops for a long time inside mother, and is born at a fairly advanced stage of development

14. Key point questions
Compare asexual and sexual reproduction in terms of genetic diversty
Why might sexual reproduction produce populations better suited for surviving environmental changes?
What are the two types of fertilization? Why is water needed for one of these types?
What are the three ways that embryos can develop?
How does an amniotic egg allow reproduction outside of water?