J.SexSelect09b

J.SexSelect09b - Reproductive Ecology& Sexual Selection...

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Unformatted text preview: Reproductive Ecology & Sexual Selection REPRODUCTIVE ECOLOGY & SEXUAL SELECTION REPRODUCTION • Asexual • Sexual – Attraction, Courtship, and Mating – Fertilization – Production of Young Benefits of Asex 1. Eliminate problem to locate, court, & retain suitable mate. 2. Doubles population growth rate. 3. Avoid “cost of meiosis”: – The Evolutionary Enigma of Sexual Reproduction • Sexual reproduction produces fewer reproductive offspring than asexual reproduction, a so-called reproductive handicap Sexual reproduction Asexual reproduction Female Generation 1 Generation 2 genetic representation in later generations isn't reduced by half each time 4. Preserve gene pool adapted to local conditions. Female Male Generation 3 Generation 4 Figure 23.16 The Energetic Costs of Sexual Reproduction • Allocation of Resources Benefits of Sex 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 Fission • Divide in two – protozoans, anemones, flatworms Parthenogenesis • Eggs develop w/o fertilization – some rotifers, fish, crustaceans, insects, & lizards. • Obligatory Cloning • Grow cells – Gemmules of sponges. Parthenogenesis • Derived parthenogenesis & pseudocopulation in whiptail lizards – Whiptails • Facultative – Snakes – Aphids Whiptails — C nemidophorus uniparens TWO SEXES • Conjugation – Ciliate protozoans with + & - mating types. • Monoecious: both sexes in one individual. • Dioecious: separate sexes – one sex makes small haploid gametes (sperm) – the other makes big ones (eggs) Simultaneous Hermaphrodites • Advantageous if limited mobility and sperm dispersal and/or low population density • Guarantee that any member of your species encountered is the “right” sex • Self fertilization still provides some genetic variation • Or prevent self-fertilization by copulation producing sperm or eggs at different times sponges, flatworms, snails, earthworms 8’ long earthworm from Ecuador Heyer Simultaneous sperm exchange 2 Reproductive Ecology & Sexual Selection Sequential Hermaphrodites • Protandry: male ➔ female – anemonefish • Protogyny: female ➔ male – wrasses Sequential Hermaphrodites • Protandry: when all else equal – make sperm when small • you still make more than needed – make eggs when large • costlier & bigger • Sequential Hermaphrodites Protogyny: when all else isn’t equal – especially if big individuals get more mates • be a big male: wrasses. Biased Sex-ratios in Red Deer Determinate (fixed) Gender • Gametic determination – Heterogenic male determination (XY male) – Heterogenic female determination (XY female) – Haplotypic male determination (XO male) • Environmental determination – Temperature – Intrauterine position External Fertilization Dom inan t do es • Only in water Non-dominant does – gametes must be moist. • Gamete release is synchronized. • ↑ frequency of male calves to dominant mothers – Dominant moms more likely to yield dominant bucks → ↑ odds of perpetuating her genes – Δ ratio probably from pre-implantation events • ↓ frequency of male calves in poor conditions (E.g., ↑density) – Males larger → more expensive to raise – Δ ratio probably from post-implantation events Heyer 3 Reproductive Ecology & Sexual Selection Broadcast Spawning Mate Attraction —Auditory • E.g. marine inverts - larval mortality is high. • Release in response to: – smell of other gametes – environmental cues • Palolo Worm Mate Attraction —Chemical • Insect pheromones • Vertebrates too – snakes – mammals Courtship Behavior Mate Attraction —Visual • Displays include – colors – behaviors Courtship Spawning • In fish & some marine inverts • Behaviors stimulate gamete release • Produce fewer eggs but add in parental care – it’s a balance of investment strategy Heyer 4 Reproductive Ecology & Sexual Selection Internal Fertilization • Terrestrial forms need internal fertilization so gametes don't dry out • Decreases energy spent on sperm production • Ensure large amounts of your sperm are on target • Allow females to store concentrated sperm • Spermatophores a re sperm packages –spiders, frogs • Adpressed Cloacas –birds lack intromittive o rgans Copulatory Organs Copulatory Organs • Legs – squids & spiders • Claspers – sharks & rays • Penises – – – – – insects turtles, crocodiles lizards, snakes w/ hemipenes marsupials w/ bifurcated penis eutherian mammals w/ penis & b acculum. Estrogens & Ovulation Ovulation triggered by a sharp rise in estrogens • Insects Insert fig. 20.35 Estrogen rise and female reproductive behavior • Proceptive b ehavior: “flirting” — advertising sexual state • Receptive behavior: attentive to male courting • Conceptive behavior: accepting copulation Oviparity: Egg Laying • Yolk w/ protein & fats – 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 Heyer Continued Parental Investment • Nest guarding • Brooding • Resource allocation – Less energy spent on egg production – Use energy insuring development of fewer offspring – Often, females spend energy on egg production – Males do the parental care 5 Reproductive Ecology & Sexual Selection Ovoviviparity: Retain Eggs Internally Viviparity: Maternal Nourishment • Maternal Nourishment – Spreads maternal energy demand over longer time period – Allows embryo to grow beyond original egg size • “Mobile nest” • Keeping eggs warmer speeds development. Dogfish shark “candle” from female’s uterus • Placenta connects embryo to mother for nutrition & gas exchange. – Placental mammals – Reptiles (rattlesnakes & sea snakes) – Fish (sharks, guppies, surf perch) – Cold climate reptiles retain eggs rather than laying them. “Candle” opened to show small embryos with large yolk Aphids — a little bit of everything! 1. .Asexual (parthenogenic) viviparity – And “telescoping generations” (born pregnant!) 2. Seasonally alternating with a dioecious generation having: Sexual oviparity Aphids — a little bit of everything! • Aphid yearly cycles •Parthenogenic live birth (all females) Parthenogenic live •And the baby being born already has a baby! EVOLUTION OF POPULATIONS • • • • Heyer Sexual Selection Genetics & Variability Non-Adaptive Evolution Adaptive Evolution: Natural Selection Sexual Selection • Natural Selection (NS): differential reproduction due to differential survival. • Sexual Selection (SS): differential reproduction due to increased Reproductive Success (RS) despite possible decreased survival. 6 Reproductive Ecology & Sexual Selection Sexual Selection Sexual Selection • Observed sexual dimorphism – sexes differ in size, color, or behavior • Some differences don’t aid survival – dimorphic feature makes animal more obvious animal • Sexual Selection (SS): differential reproduction due to increased Reproductive Success (RS) despite possible decreased survival. – Louder vocalizations → stronger attraction for mates – Louder vocalizations → stronger attraction for predators! Social Sex Sexual Selection • Promiscuous • No social bonding • Intrasexual Selection: • Monogamous – competition among members of one sex for access to members of the other sex. – a.k.a. Male-Male Competition. • One female + one male • Polygamous (sexually dimorphic) – Polygynous • One male + multiple females – Polyandrous • One female + multiple males Sexual Selection Sexual Selection • Game Theory ( rock-paper-scissors) • Frequency-dependent Intrasexual Selection: • Intrasexual Selection • Intersexual Selection: – Oscillating frequencies • Side-blotch lizard – Orange-spotted males – ability of one sex to woo the opposite sex. – a.k.a. Female Choice. • Aggressive, large harems – Blue-spotted males • Non-aggressive, no harems ES AC PL S DI ES LAC DISP • Less-aggressive, small harems – Yellow-spotted males DISP LAC ES Heyer 7 Reproductive Ecology & Sexual Selection Female Choice Female Choice in New Guinea Birds of Paradise & Hills Tribes Social Learning & Mate Choice Female Choice • Bowerbirds: display is separate from bird. • Female guppy introduced to unaccompanied males Choose most brightly o rnated • Female guppy introduced to one accompanied male + unaccompanied males Choose whichever color-pattern the accompanied male has Why Females Choose and Males Fight: Parental Investment & Sexual Selection • Sex w/ most invested has most to loose: Reversed Dimorphism Where the female is the pursuer because she invests less. • Phalarope females are bigger and brighter. – Eggs more “expensive” than sperm – Females must be selective • Female RS limited by # of young they raise. • Male RS limited by # of females they mate. • Females lay a clutch every 10-12 days • Male clutch care takes 3 months • Females will destroy eggs to free up a male Ala lions, primates, mice Heyer 8 ...
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This note was uploaded on 09/02/2011 for the course BIOL 6C taught by Professor Sundram during the Spring '09 term at DeAnza College.

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