Ecology Lecture Notes - Reproduction PDF

Ecology Week 6 Lecture 10 – Reproduction  Reproduction How does an organism pass its genes on to the next generation? 2  Reproduction Sexual reproduction: fusion of male and female gametes to form a zygote. Human dip...

Ecology Week 6 Lecture 10 – Reproduction  Reproduction How does an organism pass its genes on to the next generation? 2  Reproduction Sexual reproduction: fusion of male and female gametes to form a zygote. Human diploid genome: 3 Sexual Reproduction  Reproduction Sexual reproduction: fusion of male and female gametes to form a zygote. Asexual reproduction: production of spores or other reproductive bodies by one individual. (Clones) – Vegetative reproduction: Production of new individuals through growth. 5 Walking fern (Asplenium rhizophyllum) 6  (Parthenogenesis) Whiptail Lizards (some species 100% female) 7  Selfing Pollen fertilizes own ovules (in plants) Which would be ‘worse’ for offspring, clones or selfed? 8  Sexual reproduction Sexual reproduction is costly. Why? 9  Sexual reproduction Sexual reproduction is costly. Why? – Have to attract/find mates – Courtship displays, secondary sexual characteristics (e.g., peacock’s tail, floral displays), reproductive systems (e.g., gonads) 10  Sexual reproduction Sexual reproduction is costly. Why? – Cost of meiosis: Parents contribute only half the number of genes when producing sexually as they do when reproducing asexually. – Evolutionarily, halves fitness, b/c halves contribution to next generation 11 12 13  Sexual reproduction Sexual reproduction has benefits. 14  Sexual reproduction Sexual reproduction has benefits. – Ability to purge mutations (can accumulate in generations of clones) – Genetic diversity in the face of changing environment (abiotic & biotic) 15  Genetic diversity in the face of changing biotic conditions. Red queen hypothesis: Reproduction confers advantages in the arms race against pathogens. Offspring genetically different from parent and less susceptible to pathogens – “moving target”. 16  Genetic diversity in the face of changing biotic conditions. Red queen hypothesis: Reproduction confers advantages in the arms race against pathogens. Offspring genetically different from parent and less susceptible to pathogens – “moving “Now here, you see, it takes all target”. the running you can do to stay in place” 17 Sexual Reproduction Review Ted Talk – DNA Tests 18  Sexes Female function: produces larger gamete (thus fewer gametes for a given allocation) Male function: produces smaller gamete (thus more gametes for a given allocation) 19  Sexes Female function: produces larger gamete (thus fewer gametes for a given allocation) – often limited by number of gametes she can produce and offspring she can raise (resources) Male function: produces smaller gamete (thus more gametes for a given allocation) – often limited by number of eggs he can fertilize (mating) 20  Sexuality In animals: Individual organisms may be – unisexual (male or female) – hermaphrodite (male and female functions in the same individual). 21  Sexuality In animals: Individual organisms may be – unisexual (male or female) – hermaphrodite (male and female functions in the same individual). In hermaphrodites, female and male function may be – simultaneous: snails, worms – sequential: » male first (molluscs, echinoderms) » female first (some fishes) 22  Sexuality In plants: – dioecious (two-houses) different sexes on separate plants – monoecious (one-house) individual plants bear distinct male and female flowers. – perfect flowers: both male and female parts, i.e. hermaphrodites (common - 2/3 of plants) 23  Monoecious, dioecious, or perfect? 24  Monoecious, dioecious, or perfect? 25  Sexuality If most are perfect, how to deal with selfing? Self-incompatibility Sequential hermaphroditism Heterostyly 26  Sex ratio Ratio of # of individuals of one sex relative to # of individuals of other sex in the population – Typically rarer sex has a fitness advantage. Why? 27 Sex ratio 28  Mating systems Pattern of matings between males and females in a population 29  Mating systems Promiscuity: When one finds as many mates as possible (no pair-bonds, and typically no parental investment) – Most common system in animals and universal in outcrossing plants 30  Mating systems Polygamy: one individual forms a long-term bond with more than one of the opposite sex – Polygyny: one male with a number of female mates (harem). – Polyandry: one female mates with several males. Gorilla beringei 31  Mating systems Monogamy: Pair-bond that is formed between a male and female and lasts long enough to raise offspring from the union. more common in birds or mammals? 32  Mating systems Monogamy: Pair-bond that is formed between a male and female and lasts long enough to raise offspring from the union. more common in birds: male parental care; contribute to egg incubation & feeding chicks. 33  Genetic work on monogamous birds shows frequent cheating (extra- pair copulations). DNA fingerprinting Layson Albatross (paternity tests) -Mate for life, but 1/3 are EPCs 34  Sexual selection All mating systems involve choosing a mate. Females usually do the selection. Why? 35  Sexual selection All mating systems involve choosing a mate. Females usually do the selection. Why? – Males limited by mating; benefit by mating with many females. – Females limited by resources; benefit by mating with quality males. 36  Sexual selection All mating systems involve choosing a mate. Females usually do the selection. Why? – Males limited by mating; benefit by mating with many females. – Females limited by resources; benefit by mating with quality males. Resources/ parental care Good genes 37  Sexual dimorphism A common result of sexual selection is sexual dimorphism: – Phenotypic differences between the sexes 38 39  Sexual dimorphism Sexual dimorphism may arise in three ways: 40  Sexual dimorphism Sexual dimorphism may arise in three ways: 1) Differences resulting from reproductive function: Females larger than males because they produce eggs (larger gamete) or carry the offspring. More, larger gametes are produced by larger individuals therefore tendency leads towards an increase in size. 41 42  Sexual dimorphism Sexual dimorphism may arise in three ways: 2) Male-Male competition: Males larger than females: contests between males favor the evolution of large body size or weapons such as antlers. 43 Reindeer (Rangifer tarandus) 44 Sexual dimorphism  Sexual dimorphism Sexual dimorphism may arise in three ways: 3) Mate choice: Females benefit by selecting quality males; leads to larger/showier males. 46  http://www.youtube.com/watch?fea ture=player_embedded&v=z- _abWX65a8 Peacock Spider mating dance 47  Secondary sexual characters in males 48  Secondary sexual characters in males Why should females select for extreme preferences when can be detrimental? Two main hypotheses: 1) Handicap Principle (“Good Genes”) 2) Runaway Sexual Selection (“Sexy Sons”)  The Handicap Principle Also called “Good Genes” hypothesis: A male with exaggerated features may have difficulty foraging or avoiding predators. Surviving with such a handicap would signal to a female a superior genotype.  Average damage from lice Heavy damage Normal Parasite/pathogen mediated?  Runaway sexual selection Also called “Sexy Sons” hypothesis: May originally have indicated high-quality males, but becomes runaway ‘self-fulfilling- prophecy’- sons of choosy females will do better when they eventually mate No support for ‘good genes’: Support for ‘runaway’: 55