Animal Reproduction Flashcards
What is Asexual reproduction?
Creation of new individuals without fusion of gametes
» Relies on mitosis at the cellular level
What are three different types of Asexual reproduction?
- Budding
- Fission
- Fragmentation and regeneration
What is Parthenogenesis?
A form of Asexual reproduction where an egg develops without being fertilised
» Offspring can be haploid or diploid
What animals are capable of Parthenogenesis?
» Inverts: bees, wasps, ants, crustaceans, rotifers …
» Rarer in vertebrates (about 0.1% of species)
• Komodo dragon
• Hammerhead shark
What species is Parthenogenesis most important to and why?
Some species of lizards are exclusively females and reproduce entirely asexually by parthenogenesis
» Oddly enough, more eggs laid if mounted at ovulation … historical artefact? (evolved from sexual species?)
What is sexual reproduction?
Fusion of haploid gametes (sex cells) → diploid (“zygote”), which divides by mitosis to produce multicellular embryo
» Female gamete = egg: large, nonmotile
» Male gamete = sperm: small, motile
What are the advantages and disadvantages of Asexual reproduction?
Advantages:
- No need to locate a mate
- Asexual products usually large (↑ survivorship)
- Rapid development to adult (limited vulnerable juvenile stage)
- May occur throughout the year
Disadvantages:
- No genetic recombination (offspring is genetic copy of parent)
- Offspring usually locally dispersed
What are the advantages and disadvantages of Sexual reproduction?
Advantages:
- Genetic recombination (→ adaptive)
- Offspring often widely dispersed (eg larvae in ocean currents)
Disadvantages:
- Need a mate
- Sexual products usually small (↓ survivorship)
- Delay to reach sexual maturity (longer vulnerable juvenile stage)
- Usually occurs seasonally (when environmental conditions favour survival of offspring)
What is the sexual reproductive cycle?
Environmental cues (eg temperature, day length) → sex hormones → reproductive status
What is the reason for a sexual reproductive cycle and what impacts might be affecting it?
» So that offspring are born in most favourable conditions (eg Spring)
» Impact of climate change?
- eg Caribou in Greenland: mismatch between onset of migration (day length) and plant growth (temperature)
What adaptions have some animals formed when there is a scarcity of mates?
Finding a mate can be challenging, so some animals are hermaphrodites (have both male and female reproductive systems) → any two individuals can mate
» Some species can even self fertilise
What is Sequential hermaphroditism?
In some hermaphrodites, the animal starts out as one sex and switches to the other sex later in its life.
What are the two types of sequential hermaphroditism?
» Protogynous: female first (most common)
» Protandrous: male first
Provide a summary of fertilisation
- Once found a mate, male gamete needs to fertilise the female gamete
- Fertilisation = union of sperm and egg
- Can be external or internal
Where does external fertilisation happen?
Requires moist habitat (avoid gametes from drying out, allows sperm to swim to eggs)
How does External Fertilisation work?
Gametes released into water
» Asynchronous (→ courtship)
» Synchronous (broadcast spawning)
What is Internal Fertilisation?
Adaptation that enables sperm to reach the egg even in dry environment
- Requires cooperative behavior (copulation) and compatible reproductive systems
What are the advantages and disadvantages of External Fertilisation?
Advantages:
- No need to move to mate (common in sessile organisms)
- Can produce many offspring
Disadvantages:
- Reduced rates of fertilisation
- Can only occur in aquatic environments
What are the advantages and disadvantages of Internal Fertilisation?
Advantages:
- Increases rates of fertilisation success
- Can occur in terrestrial or aquatic environments
Disadvantages:
- Need to locate a mate
- Requires cooperative (often complex) behaviour
- Requires specialised reproductive systems to transfer sperm from males to females
- Fewer offspring produced
What are the different modes of giving birth?
If internal fertilisation, need to “give birth”
» Oviparous: female lays zygotes as eggs
» Viviparous: embryo develops within mother’s body (generally fed by placenta, but in some species as eggs fed by yolk)
What are Placental mammals?
Placenta feeds the developing embryo
» Exchange b/w maternal and embryo’s blood capillaries (nutrients in, waste out)
What level of parental care is given to the offspring of externally reproductive organisms such as coral?
None – gametes released
What level of parental care is given to the offspring of Oviparous organisms?
Some – guard fertilised eggs
What level of parental care is given to the offspring of Viviparous organisms?
Extensive – protect & nurture until adulthood
