Reproductive Ecology & Sexual Selection REPRODUCTIVE ECOLOGY REPRODUCTION & SEXUAL SELECTION • Asexual • Sexual – Attraction, Courtship, and Mating – Fertilization – Production of Young The Evolutionary Enigma of Benefits of Asex Sexual Reproduction • Sexual reproduction produces fewer reproductive offspring than asexual reproduction, a so-called reproductive handicap 1. Eliminate problem to locate, court, & retain suitable mate. Asexual reproduction Sexual reproduction Generation 1 2. Doubles population growth rate. Female Female 3. Avoid “cost of meiosis”: Generation 2 – genetic representation in later generations isn't reduced by half each time Male 4. Preserve gene pool adapted to local Generation 3 conditions. Generation 4 Figure 23.16 The Energetic Costs of Sexual Reproduction Benefits of Sex • Allocation of Resources 1. Reinforcement of social structure 2. Variability in face of changing environment. – why buy four lottery tickets w/ the same number on them? Relative benefits: Support from organisms both asexual in constant & sexual in changing environments – aphids have wingless female clones & winged male & female dispersers – ciliates conjugate if environment is deteriorating Heyer 1 Reproductive Ecology & Sexual Selection Simultaneous Hermaphrodites TWO SEXES • Advantageous if limited mobility and sperm dispersal and/or low population density • Guarantee that any member of your species encountered is the • Conjugation “right” sex • Self fertilization still provides some genetic variation – Ciliate protozoans with + & - mating types. • Or prevent self-fertilization by • Monoecious: both sexes in one individual. § copulation § producing sperm or • Dioecious: separate sexes eggs at different times – one sex makes small haploid gametes (sperm) sponges, flatworms, snails, – the other makes big ones (eggs) earthworms 8’ long earthworm from Ecuador Simultaneous sperm exchange Sequential Hermaphrodites Determinate (fixed) Gender • Protandry: when all else equal • Gametic determination – make sperm when small – Heterogenic male determination (XY male) • you still make more than needed – Heterogenic female determination (XY female) – make eggs when large – Haplotypic male determination (XO male) • costlier & bigger • Environmental determination • Protogyny: when all else isn’t equal – Temperature – especially if big individuals get more mates – Intrauterine position • be a big male: wrasses. Determinate Gender, Biased Sex-ratios yet Biased Sex Ratios in Red Deer Dominant does • Primary Sex Ratio: Ø Sex ratio at fertilization Non-dominant does • Secondary Sex Ratio: Ø Sex ratio at birth • Tertiary Sex Ratio: Ø Sex ratio at sexual • ↑ frequency of male calves to dominant mothers – Dominant moms more likely to yield dominant bucks → ↑ odds of perpetuating maturity her genes • Quaternary Sex Ratio: – Δ ratio probably from pre-implantation events Ø Sex ratio of adult • ↓ frequency of male calves in poor conditions (E.g., ↑density) population – Males larger → more expensive to raise – Δ ratio probably from post-implantation events Heyer 2 Reproductive Ecology & Sexual Selection External Fertilization Broadcast Spawning • Only in water • E.g. marine inverts - larval mortality is high. – gametes must be moist. • Release in response to: • Gamete release is – smell of other gametes synchronized. – environmental cues • Palolo Worm Courtship Behavior Mate Attraction — Courtship • Auditory • Chemical • Pheromones • Visual • Colors • Bioluminescence • Behaviors Internal Fertilization Courtship Spawning • Terrestrial forms need internal fertilization so gametes don't dry out • In fish, amphibians, & some marine inverts • Decreases energy spent on sperm production • Ensure large amounts of your sperm are on target • Behaviors stimulate gamete release • Allow females to store concentrated sperm • Produce fewer eggs but may add in parental care • Spermatophores are – it’s a balance of investment strategy sperm packages – spiders, squid. salamanders • Adpressed Cloacas – birds lack intromittive organs Heyer 3 Reproductive Ecology & Sexual Selection Estrogens & Ovulation Copulatory Organs Ovulation triggered by a sharp rise in estrogens • Legs – squids & spiders Insert fig. 20.35 • Claspers – sharks & rays • Penises – insects – turtles, crocodiles — protrusable – lizards, snakes w/ paired hemipenes — eversible Estrogen rise and female reproductive behavior – marsupials w/ bifurcated penis • Proceptive behavior: “flirting” — advertising sexual state – eutherian mammals w/ penis & bacculum. • Receptive behavior: attentive to male courting • Conceptive behavior: accepting copulation Oviparity: Egg Laying Oviparity • Yolk w/ protein & fats • Birds – Energetically very expensive! • Protective Coating – jelly-like substance in aquatic forms – earthworm's cocoon – horny egg case of some sharks – calcareous or leathery shell of birds & reptiles Ovoviviparity: Retain Eggs Internally Continued Parental Investment • Nest guarding • Brooding • “Mobile nest” • Resource allocation Dogfish shark “candle” from – Less energy spent on • Keeping eggs warmer female’s uterus egg production speeds development. – Use energy insuring development of fewer – Cold climate reptiles offspring retain eggs rather than – Often, females spend laying them. energy on egg production – Males do the parental care “Candle” opened to show small embryos with large yolk Heyer 4 Reproductive Ecology & Sexual Selection Viviparity: Maternal Nourishment Viviparity: Maternal Nourishment • Maternal Nourishment • Maternal Nourishment – Spreads maternal energy demand over longer time period – Spreads maternal energy demand over longer time period – Allows embryo to grow beyond original egg size – Allows embryo to grow beyond original egg size • Placenta connects embryo to mother for nutrition & • Aplacental viviparity: intra-uterine feeding. gas exchange. – “Uterine milk” – rays – Placental mammals – Oophagy (& adelphophagy!) – mackerel sharks – Reptiles (rattlesnakes Gill filaments for & sea snakes) absorbing uterine milk in river stingray – Fish (sharks, guppies, pup. (Later, will drink surf perch) by bucchal pumping.) Swollen bellies of oophagous porbeagle shark pups Aphids — a little bit of everything! Aphids — a little bit of everything! 1. .Asexual (parthenogenic) viviparity “ ” – And telescoping generations (born pregnant!) • Aphid yearly cycles 2. Seasonally alternating with a dioecious generation having: Sexual oviparity • Parthenogenic live birth (all females) • And the baby being born already has a baby! EVOLUTION OF POPULATIONS “Survival of the fittest” • Genetics & Variability • Non-Adaptive Evolution • Adaptive Evolution: Natural Selection “Reproduction • Sexual Selection of the fittest” Heyer 5 Reproductive Ecology & Sexual Selection Sexual Selection Sexual Selection • Even though some variations may increase survival, health, competitive success, etc., … • Natural Selection (NS): differential • they will not increase in frequency in the gene reproduction due to differential survival. pool if they are not also associated with increased reproductive success! • Sexual Selection (SS): differential reproduction due to increased Reproductive • Even though some variations may decrease Success (RS) despite possible decreased survival, health, competitive success, etc., … survival. • they will increase in frequency in the gene pool if they are also associated with increased reproductive success! Sexual Selection and the Sexual Selection Energetic Costs of Reproductive Success • Increased Reproductive Success comes at increased energetic costs → decreased survival Mating calling in frogs the most energetically expensive activity in their life. • Aerobic metabolism up 25x for several hours • Sexual Selection: differential reproduction due to 1. Advertising calls (chorus) increased Reproductive Success despite possible 2. Aggressive calls decreased survival. 3. Courtship calls (solo) – Louder vocalizations → stronger attraction for mates – Louder vocalizations → stronger attraction for predators! Social Sex Sexual Selection • Promiscuous • No social bonding • Observed sexual dimorphism – sexes differ in size, color, or behavior • Monogamous • One female + one male • Some differences don’t aid survival – dimorphic feature makes animal more obvious • Polygamous (sexually dimorphic) – Polygynous • One male + multiple females – Polyandrous • One female + multiple males Heyer 6 Reproductive Ecology & Sexual Selection Sexual Selection Sexual Selection • Game Theory (rock-paper-scissors) • Frequency-dependent • Intrasexual Selection: Intrasexual Selection: – competition among members of one sex for – Oscillating frequencies access to members of the other sex. • Side-blotch lizard – Orange-spotted males – a.k.a. Male-Male Competition. • Aggressive, large harems – Blue-spotted males • Less-aggressive, small harems DISPLACES – Yellow-spotted males • Non-aggressive, no harems DISPLACES DISPLACES Sexual Selection Female Choice • Intrasexual Selection • Intersexual Selection: – ability of one sex to woo the opposite sex. – a.k.a. Female Choice. Female Choice in New Guinea Female Choice Birds of Paradise & Hills Tribes • Bowerbirds: display is separate from bird. https://www.youtube.com/watch?v=KIYkpwyKEhY https://www.youtube.com/watch?v=DU-V3OYwwQU Heyer 7 Reproductive Ecology & Sexual Selection Social Learning & Mate Choice Why Females Choose and Males Fight: Parental Investment & Sexual Selection • Sex w/ most invested has most to loose: • Female guppy introduced to – Eggs more “expensive” than