Summary BIOL1310 Organisms to Ecosystems Lecture Notes

WEEK 10: LECTURE 27: DEVELOPMENT AND LIFE
HISTORY
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)




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,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


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,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
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,  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
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