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

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

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 ...
View Full Document

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.

Ask a homework question - tutors are online