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 Examples of potential questions: Why do birds migrate? Why do grazing animals condense into herds?

Behaviour 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

Behaviour to maintain internal conditions

Behaviour to get food or prevent becoming food

Behaviour to reproduce

Plants manipulate behaviour

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

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

Why have sex? Ch. 7.1-7.2, Bush

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

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

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

Most organisms are sexual Of the 1.8 million known species only 2000 of them are totally asexual

Asexuality is concentrated among the basal organisms

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 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

Meiosis versus mitosis

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

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

Sex in the news…

Ancient asexuals: Bdelloid rotifers bdelloid rotifers date back ~100 million years Despite bdelloids' asexuality, they've diversified into 380 species

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 Cnemidophorus velox, a parthenogenic lizard

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 males The cost of recombination The cost of mating

The Cost of Males

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)

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

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

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

Sexual Mechanisms

Mating Behaviour

Injury to females - unintentional When males are much bigger than females, the females can be injured by intercourse

Injury to females - intentional! Callosobruchus maculatus Male genitalia

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 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 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 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 variation

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 leads to more variation in offspring

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 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 "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 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 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

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

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 Depends on the sexual system of the organism: Hermaphroditic Dioecious (Latin for “two houses”)

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

Hermaphroditic animals

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).

Helix aspersa

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

Seahorse anatomy

Mating and Males Giving Birth

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 bifurca 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

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