LIFE CYCLES, LARVAE AND REPRODUCTION Flashcards
What is external fertilisation?
Include pros and cons
Union of male and female gametes outside the bodies of individuals from which they spawned.
Pros: - Increased genetic diversity
- Favours dispersal
- requires little parental investment time
Cons: - gametes are nutritious and often eaten
Distinguish between broadcast and non-broadcast spawning
Broadcast- both gametes released into sea
Non- broadcast- next to each other
How to maximise success in external fertilisation
- produce loads of gametes
- make sure gametes are cheap (yolk is expensive)
- spawn in calm conditions
- spawn in close contact (<1cm)
- synchronous spawning
What is internal fertilisation?
Led to the evolution of…
Include pros and cons
Union of male and female gametes inside of individuals from which they originated. Usually inside female.
Copulatory structures
Advantages: - mate choice develops
- greater success in fertilisation
- planktonic egg stage can be avoided
- planktonic larval stage can be avoided
Disadvantages: - finding a mate
- can limit no. of offspring as brooding young is spenny
- expensive gametes
- predation risk increased
Coral reef reproduction
Have asexual and sexual parts to lifestyle with synchronised spawning
Phyla with planktonic larvae (most benthic animals)
Crustacea
Echinodermata
Annelida
Mollusca
Describe planktonic larvae
Include pros and cons
larval stage spent feeding on plankton
PRO: -small eggs, so loads produced
- have access to food in plankton
- large dispersal
CON: - variable food supply and conditions in the plankton
- vulnerable to predation in plankton
Describe lecithotrophic larvae
Include pros and cons
shorter time in the plankton as the larvae are fairly well provisioned
- mainly used for dispersal
PRO: - less exposed to predation in plankton
- less influenced by variable food supply in plankton
- still some dispersal
- better chance of survival
CON: -yolky eggs are expensive
Describe Non-pelagic development
Include pros and cons
Direct development (hatch as juveniles)
PRO: - less exposed to the predation in plankton
- not influenced by the variation in food supply in plankton
- best chance of survival
Con: - yolky eggs are spenny
- limited dispersal so competition not removed
Why disperse?
- reduction in intra specific competition
- exploit new areas
- promote outbreeding
Why is survival so poor in pelagic larvae?
- predation
- drift away
- settle in unsuitable environments
How do larvae know when to settle?
- conspecifics
- suitable substrate
- food supply
- environmental cues
Gonochorisitic
sexes are separate and determined for life
Simultaneous hermaphrodite
Adults where both male and female sexual organs present at same time
Sequential hermaphrodite
Adults where male and female sexual organs present at different times during their life
