Outline

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Outline

• Introduction to Ecology
• Evolution and Natural Selection
• Physiological Ecology
• Behavioural Ecology

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Behavioural Ecology
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Behavioural Ecology

• The study of ecological and evolutionary
  processes that explain the occurrence and
  adaptive function of behaviour
• Examples of potential questions
• Why do birds migrate?
• Why do grazing animals condense into herds?

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Behaviour

• Affects an individuals ability to survive and
  reproduce in a particular environment
• Develops under the influence of both genetic
  inheritance and environmental experience
  (learning)
• the genetic component of behaviour is subject to
  natural selection

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Behaviour to maintain internal conditions
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Behaviour to get food or prevent becoming food
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Behaviour to reproduce
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Plants manipulate behaviour
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Outline

• Reproduction Why have sex?
• Life histories and mate choice
• Predation
• Optimal foraging
• Applications to fisheries management

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Outline

• Reproduction Why have sex?
• Life histories and mate choice
• Predation
• Optimal foraging
• Applications to fisheries management

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Why have sex?
Ch. 7.1-7.2, Bush
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Outline

• The basics of sex
• The evolution of sex
• Variations in sexual systems

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Outline

• The basics of sex
• The evolution of sex
• Variations in sexual systems

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Reproduction

• The goal of reproduction, for any organism, is to
  ensure the survival of its genetic lineage
• Two ways to do this
• ASEXUAL offspring are exact (almost) genetic
  copies of a single parent
• SEXUAL chromosomes of two parents are segregated
  and recombined so that no two offspring are
  identical to each other or to either parent

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Most organisms are sexual

• Of the 1.8 million known species only 2000 of
  them are totally asexual

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Asexuality is concentrated among the basal
organisms
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Asexual reproduction

• The cell divides to produce two daughter cells
• This type of reproduction can be very rapid
  several generations can be produced each hour

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Sex meiosis

• Meiosis is the process whereby gametes are made
  with half the number of chromosomes
• The original number of chromosome is reformed
  when two gametes come together

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Meiosis versus mitosis
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Outline

• The basics of sex
• The evolution of sex
• Variations in sexual systems

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Why did sex evolve?

• Life originated without sex (as best we can tell)
  so sexual reproduction is something that had to
  evolve
• There are a large number of disadvantages to
  sexual reproduction which makes the evolution of
  sex a conundrum

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Sex is not necessary for all life

• Some plants and animals have entirely abandoned
  sex
• Others have sex only when its convenient and are
  asexual most of the time (facultatively sexual)

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Sex in the news
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Ancient asexuals Bdelloid rotifers

• bdelloid rotifers date back 100 million years
• Despite bdelloids' asexuality, they've
  diversified into 380 species

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Facultative sexuality in animals

• In some animals, such as Hydra, asexual
  reproduction can occur through budding
• These animals are still capable of reproducing
  sexually as well
• Sexual and asexual processes are governed by
  environmental conditions

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Parthenogenesis offspring from unfertilized eggs
Cnemidophorus velox, a parthenogenic lizard
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Aphids asexual and sexual

• Females give birth to live females during the
  summer months
• As winter approaches, both males and females are
  produced, which mate to produce eggs

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The Cost of Sex

• The cost of males
• The cost of recombination
• The cost of mating

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The Cost of Males
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Passing on genes is like tossing coins

• Two copies exist for each gene
• Whether you pass on a certain copy of a gene is
  an independent event for each child
• If you have two children, sometimes you will pass
  on the same copy to both children (leaving the
  second copy passed on to neither child)

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Fitness

• FITNESS
• the number of offspring an individual produces
  that survive to reproduce themselves
• Fitness 1.0 means that individuals of this
  phenotype are successfully passing on 100 of
  their genes, on average

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How is fitness calculated

• Fitness the number of genes passed on to the
  next generation
• Because diploid organisms (I.e., most organisms)
  only pass on half of their genes to each child,
  they must have two offspring living to
  reproductive age to have Fitness 1
• Fitness 1 does not exactly mean that you have
  passed on 100 of your genes to the next
  generation (Remember sometimes you send two
  copies of the same gene and zero copies of the
  other)

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Cost of recombination

• Asexual Sexual
• F F
• F F F F M M
• Fitness 2 1
• of females

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The Cost of Mating

• Cost of sexual mechanisms
• Chemical attractants
• Sexual organs
• Flowers
• Cost of mating behaviour
• Courtship is costly
• Potential exposure to predators
• Injury
• Disease Transmission

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Sexual Mechanisms
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Mating Behaviour
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Injury to females - unintentional

• When males are much bigger than females, the
  females can be injured by intercourse

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Injury to females - intentional!
Callosobruchus maculatus
Male genitalia
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Why hurt the female?

• Reducing the fitness of your mate ought to reduce
  the fitness of yourself as well
• Copulation is not always a cooperative venture
  between the sexes.
• In C. maculatus, females mate repeatedly
• genital wounding could increase the fitness of
  male C. maculatus if
• it causes females to postpone remating (less
  sperm competition)
• increase immediate oviposition (egg-laying) rates
  because females perceive damage as a threat to
  survival and invest more in current reproduction

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Costs of mating are widespread

• Female Drosophila melanogaster that mate more
  often die more often
• seminal fluid increases female death rate
• Fluid is also responsible
• in elevating the rate of female egg in elevating
  the rate of female egg-laying,
• in reducing female receptivity to further matings
• in removing or destroying sperm of previous mates
  

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Birds, bees, and STDs

• Most organisms are plagued by a few
  sexually-transmitted diseases
• E.g., earwigs, frogs, koalas, or humans
• Ustilago violacea (smut fungus) infects flowers
  of Silene alba and is transferred via pollinators

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Sexuality must have its advantages

• Hardly any asexual lineages seem old, and fossil
  evidence has suggested that asexuality is a dead
  end
• The prevalence of sexuality amongst species is
  caused not because asexual species don't evolve,
  but because they don't last

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Sex increases variation
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Sex increases variation

• Genes from maternal and paternal parent get
  shuffled up when gametes are made
• Causes some gametes to have superfit genotypes
  and others to have superunfit genotypes

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Sex leads to more variation in offspring
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Sex and speed of evolution

• More variation leads to natural selection
  operating faster
• Most selection, however, is stabilizing
  selection, as individuals are well-adapted for a
  given environment and try to stay that way

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Sex and speed of evolution

• What aspect of the environment is so variable
  that the production of variable offspring could
  offset the cost of sex? - Parasites and
  pathogens
• Hosts are constantly evolving to protect
  themselves from parasites and parasites are
  constantly evolving to overcome their hosts
  defenses
• Parasites and hosts are locked in a host-parasite
  arms race

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Red Queen Hypothesis

• "Well in our country," said Alice, still panting
  a little. "you'd generally get to somewhere
  else-if you ran very fast for a longtime as weve
  been doing.
• "A slow sort of county!" said the Queen. "Now,
  here, you see, it takes all the running you can
  do to keep in the same place."

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Evidence for Red Queen Hypothesis

• In top minnows, sexual and asexual lineages
  coexist
• Sexual lineages are the least susceptible to
  parasites
• Genetic variation needed to keep up with
  evolution of parasites

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Mullers Ratchet

• Vast majority of mutations are detrimental
• Mutation acquisition is a one-way process in the
  genomes of asexuals
• In Salmonella typhimurium 444 lineages started
  from a single colony
• After 1700 generations, 1 of lineages showed
  decrease in fitness (growth rate) but no lineages
  showed increased fitness

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Outline

• The basics of sex
• The evolution of sex
• Variations in sexual systems

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Variations in the sexual theme

• Are there always two separate sexes?
• Do females always have the offspring?
• Do females control who fathers their offspring?

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Sexual systems

• Depends on the sexual system of the organism
• Hermaphroditic
• Dioecious (Latin for two houses)

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Flowering plants

• Wide diversity of sexual systems ranging from
  strict hermaphroditism to dioecy
• Hermaphroditism is the most common (90 of all
  flowering plants)

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Hermaphroditic animals
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Snail copulation

• Copulation involves a two- to six-hour marathon
  that is actually an exchange of sperm between two
  individuals, combined with plenty of rubbing,
  biting and "eye-stalk" waving
• shoot centimetre-long darts out of their bodies
  and into the genital area of the other (which
  happens to be just behind the head on the right
  side).

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Helix aspersa
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Why only two sexes at most?

• If we describe the individuals that have the
  offspring as females, then the other sex is male
• If we introduce another sex that also does not
  have offspring (i.e., males) then we increase the
  cost of males
• a higher cost of males would be maladaptive

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Seahorse anatomy
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Mating and Males Giving Birth
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Sperm storage in female insects
Many female insects have the ability to store
sperm from many males, only choosing the best to
fertilize her eggs when the reproductive season
is over
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Male Drosophila flies

• Drosophila flies have sperm cells that are up to
  6 centimetres long!
• Their testes take up 11 of their body mass

Male Drosophila bifurca
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Summary

• Considering the short-term advantages of
  asexuality, it is not entirely clear why so many
  organisms are sexual
• Although the exact reason why sex is advantageous
  has not been determined, the increase in
  variation that sex brings is thought to play a
  large part
• A wide variety of variations in sexuality have
  evolved in terms of the separation of sexes, the
  placement of parental care, and the timing of
  sexuality

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