lecture 20: life history & metamorphosis

Question 1

Three Basic Life History Patterns

Answer 1

1. Planktotrophic larvae - (indirect)
   - look like larvae
   - feed in water column
   *high fecundity
2. Lecithotrophic larvae - (indirect)
   - look like larvae
   - feed from yolk
   *low fecundity
3. Aplanktonic (direct)
   - look like mini adult
   - brooded
   ** very low fecundity

Question 2

Facultative planktotrophic development

Answer 2

switching behaviour

provisioned w enough yolk by mother, but can feed if needing to

when at a point to metamorphosize

why is this beneficial?
- if theyve reached a time where theyre undergoing metamorphosis, they have an option to switch (extent larval lifespan)

Question 3

why is Facultative planktotrophy beneficial?

Answer 3

• Extend larval lifespan in the absence of suitable settlement substrate
• Maintain high threshold stimulus for metamorphic induction - can continue to be choosy
• Increase energy content of larva

Question 4

nurse eggs

Answer 4

will have nurse eggs and one or few viable embryos so they feed on yolk of nurse eggs

if more nurse eggs, more competition and less resources avail –> smaller hatchlings

Question 5

Larval Defensive Strategies
(types and examples)

Answer 5

types:
structural, behavioural,
chemical

structural - making spikes or chaetae which make you bigger (harder to get predator mouth around)

behavioural - shadow reflex - arrest swimming motion

chemical - brightly coloured indicating toxicity

Question 6

what is metamorphosis?

Answer 6

the big irreversible change from larva to adult body form

Question 7

settlement vs metamorphosis

Answer 7

settlement:
A behavioural process that involves cessation of swimming and adherence to a substrate.
**REVERSIBLE

Metamorphosis:
A developmental process that involves loss of larval characters and emergence of juvenile characters.
**NONREVERSIBLE

Question 8

what is metamorphogenesis?

Answer 8

encompasses the changes before big change to adult (happen during larval stage)

• EXAMPLE : like slipper limpet develops radula, internal anatomy, and foot to be ready for locomotion
• EXAMPLE : marine annelid developing metameres

**necessary things to survive before loss of larval body - METAMORPHIC COMPETENCE

Question 9

two types of induction of settlement and metamorphosis and explanation

Answer 9

1. associative
   - Environmental induction cue (chemical factor) comes from an organism (plant or animal) of a different species.
   * post-metamorphic prey e.g. nudibranchs
   * good habitat indicator
   e.g. abalone
2. gregarious
   - Environmental induction cue (chemical factor) comes from conspecifics (same species).
   * Aggregation of sessile organisms for sexual reproduction
   * Good habitat indicator
   * Protection of new recruits