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Summary BIOL1310 Organisms to Ecosystems Lecture Notes
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BIOL1310 Organisms to Ecosystems detailed lecture notes (Lectures 27-35).
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WEEK 10: LECTURE 27: DEVELOPMENT AND LIFEHISTORY
LECTURE OUTLINE
Developmental stages in plants and animals
Life history strategies
Some unusual developmental pathways
- Change of sex
- Sexual reproductive cycles
WHAT IS DEVELOPMENT
Progressive differentiation
Allows organisms to perform different activities at different times
- For example; growth at early stage, reproduction at later stage
DEVELOPMENT DOES NOT EQUAL GROWTH
Development and growth may occur simultaneously
A certain developmental stage can have a range of sizes
BUT individuals can only perform some functions at certain developmental stages
- For example: Adult and chick birds, same size but different age
PLANT DEVELOPEMNT
Developmental stages – angiosperm
- Pollination (fertilisation – actually double fertilisation)
- Zygote (2n)
- Embryo and seed development (3n endosperm in angiosperm)
o No seed in mosses or ferns
- Seed dormancy
- Germination
PLANT EMBRYOS
Plant species invest varying amounts of nutrients and energy in embryo
- Seedless plants little investment
- Seed plants more investment via seed
Autotrophic embryo must soon obtain its own energy and nutrients
- For example: Dicotyledon (common garden bean as example)
- Monocotyledon (maize as example)
1
,MONOCOT AND DICOT
Ancestorial plants where all dicots
ANIMAL DEVELOPMENT
The question of how a zygote became an animal has been asked for centuries
As recently as the 18th century, the prevailing theory was called pre-formation
Pre-formation is the idea that the egg or sperm contains a miniature infant, or
“homunculus” which becomes larger during development
Early development stages
Fertilisation
Cleavage – rapid cell division
Gastrulation – formation of gut
Organogenesis – formation of organs
EMBRYO DEVELOPMENT
Parental investment – nutrients and energy in embryo
Female often invests more nutrients and energy
Embryo’s development is guided by its genes
- Hox genes in animals
Growth is supported by nutrients and energy
2
,ANIMAL EMBRYOS
Variable investment of nutrients and energy in embryo
- E.g. toothcarp fish little investment
- Large mammals more investment
Animal embryo can receive energy and nutrients
- Externally to female (e.g. laid egg)
- Internally to female (e.g. placenta)
EMBRYOS ARE TYPICALLY SMALL AND VULNERABLE TO MANY THREATS
Predators
Environmental fluctuations
High surface to volume ratio
- Smaller organisms have comparatively more surface for a certain volume
- Larger organisms have comparatively less surface for a certain volume
Malnutrition
PARENTAL PROTECTION OF EMBRYO
Plants
- Usually none, occasionally minor protection
o Sheltering, rhizome
Animals
- Non: egg scattering / spawning
- Moderate: selective egg deposition
- High: extended egg incubation
o For example: Giant water bug Female lays eggs on top of male, males aerate
and protect eggs
PROTECTING THE EMBRYO
Can be fairly unprotected in aquatic environment (plenty of moisture)
Must be protected on land
- Hard shell
- Parental care
- Retained within females
PARENTAL SACRIFICE
Hump Earwig
Eggs laid during early spring when food is scarce
THE JUVENILE (SUB-ADULT) STAGE
Growth and consolidation of resources
- Accumulation of energy and nutrient reserves
o Withstand famine in drought
o Fat reserves for later reproduction as an adult
Development of new behaviours
Development of new structures
- Locomotive: e.g. mobility to find more food
DEVELOPMENT OF NEW STRUCTURES EXAMPLE GRASSHOPPER
3
, Hemimetabolism (egg, nymph, adult)
- Grasshopper nymphs grow larger (1st-5th instar)
- Develop wings and genitalia (6th instar)
- Later stages develop swarm behaviour
HOLOMETABOLISM
Complete metamorphosis e.g. Mosquito
4 life stages:
- Egg
- Larva
- Pupa
- Adult
JUVENILES LEARN AND REHEARSE BEHAVIOURAL STRATEGIES
Experimentation
Practice and retention of some behaviours
Abandonment of unrewarding / unsatisfactory behaviours
‘Play’ behaviour to practice skills
- Competition, interaction, predator avoidance, social status, courtship
ADULT LIFE HISTORY STAGE
When the organism is capable of reproduction
Slower, minimal or no growth
Energy and nutrients largely devoted to metabolism and reproduction
TIMING OF REPRODUCTION
Semelparity
- Latin: semel ‘once’ parere ‘to beget’
- One reproductive event in lifetime
o For example: Antechinus, century plant which only reproduces once
Iteroparity
- Latin: iterare ‘to repeat’
- Many reproductive events in lifetime
o Have offspring every year, e.g. birds
REPRODUCTIVE STRATEGY
Reproductive strategies have three components:
- Age of first reproduction
- How often the organism reproduces
- How many offspring are produced each time the organisms reproduces
- All highly variable between species
TRADE OFFS
Why not reproduce early, often and produce many offspring?
- Time, energy and nutrients limited
- Need a balanced strategy that maximises chances of successful reproduction
R AND K SELECTED LIFE HISTORY STRATEGIES
4
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