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Outline. Introduction to Ecology Evolution and Natural Selection Physiological Ecology Behavioural Ecology. Behavioural Ecology. Behavioural Ecology. The study of ecological and evolutionary processes that explain the occurrence and adaptive function of behaviour

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  • Introduction to Ecology
  • Evolution and Natural Selection
  • Physiological Ecology
  • Behavioural Ecology
behavioural ecology1
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?
  • Affects an individual’s 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
  • Reproduction: Why have sex?
  • Life histories and mate choice
  • Predation:
    • Optimal foraging
    • Applications to fisheries management
  • Reproduction: Why have sex?
  • Life histories and mate choice
  • Predation:
    • Optimal foraging
    • Applications to fisheries management
why have sex
Why have sex?

Ch. 7.1-7.2, Bush

  • The basics of sex
  • The evolution of sex
  • Variations in sexual systems
  • The basics of sex
  • The evolution of sex
  • Variations in sexual systems
  • 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
most organisms are sexual
Most organisms are sexual
  • Of the 1.8 million known species only 2000 of them are totally asexual
asexual reproduction
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
sex meiosis
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
  • The basics of sex
  • The evolution of sex
  • Variations in sexual systems
why did sex evolve
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
sex is not necessary for all life
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)
ancient asexuals bdelloid rotifers
Ancient asexuals: Bdelloid rotifers
  • bdelloid rotifers date back ~100 million years
  • Despite bdelloids' asexuality, they've diversified into 380 species
facultative sexuality in animals
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
parthenogenesis offspring from unfertilized eggs
Parthenogenesis – offspring from unfertilized eggs

Cnemidophorus velox, a parthenogenic lizard

aphids asexual and sexual
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
the cost of sex
The Cost of Sex
  • The cost of males
  • The cost of recombination
  • The cost of mating
passing on genes is like tossing coins
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)


    • 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
how is fitness calculated
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)
cost of recombination
Cost of recombination

Asexual Sexual



Fitness 2 1

of females

the cost of mating
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
injury to females unintentional
Injury to females - unintentional
  • When males are much bigger than females, the females can be injured by intercourse
injury to females intentional
Injury to females - intentional!

Callosobruchus maculatus

Male genitalia

why hurt the female
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
costs of mating are widespread
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
birds bees and std s
Birds, bees, and STD’s
  • 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
sexuality must have its advantages
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
sex increases variation1
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
sex and speed of evolution
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
sex and speed of evolution1
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 host’s defenses
  • Parasites and hosts are locked in a host-parasite arms race
red queen hypothesis
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 we’ve 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."

evidence for red queen hypothesis
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
muller s ratchet
Muller’s 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
  • The basics of sex
  • The evolution of sex
  • Variations in sexual systems
variations in the sexual theme
Variations in the sexual theme
  • Are there always two separate sexes?
  • Do females always have the offspring?
  • Do females control who fathers their offspring?
sexual systems
Sexual systems
  • Depends on the sexual system of the organism:
    • Hermaphroditic
    • Dioecious (Latin for “two houses”)
flowering plants
Flowering plants
  • Wide diversity of sexual systems ranging from strict hermaphroditism to dioecy
  • Hermaphroditism is the most common (~90% of all flowering plants)
snail copulation
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).
why only two sexes at most
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
sperm storage in female insects
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

male drosophila flies
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

  • 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