Sexual Selection Notes PDF

Mate competition → intrasexual selection Mate choice → intersexual selection Why 2 sexes? - Males → many small gametes (proto-males) - Females → few larger (proto-females) Isogamy: ancestral form - All same sized gamete - Algae, fungi, etc Geoff Parker Model: how did anisogamy evolve?...

Mate competition → intrasexual selection Mate choice → intersexual selection Why 2 sexes? - Males → many small gametes (proto-males) - Females → few larger (proto-females) Isogamy: ancestral form - All same sized gamete - Algae, fungi, etc Geoff Parker Model: how did anisogamy evolve? Assumptions: 1. Ancestral env: diff reproductive compatibility → diff sized gametes 2. Each parent has fixed E for gametes → size-number tradeoff a. Inc size, less gametes prod 3. Zygote viability correl w size Small gametes → numerical advantage Larger → survival advantage - Disruptive selection against intermediate gametes Bateman’s hypothesis and parental investment Fruit flies: - Males have inc variation of reproductive success → inc intensity of sexual selection (comp) - Success correl w number of mates Bateman’s hypothesis: female reprod lim by egg production; male lim by number of mates Robert Trivers Parental investment theory: sex that pays highest cost investing should be choosier; other sex faces intense sexual selection Operational sex ratio: sexually receptive males : sexually receptive females Weapons and ornaments: Dung beetles: - Larger male/larger horn won more fights - Weapon Pea fowls: - Competition for leks - Females prefer male w most display and most ocelli  - Not body size - Likelihood of displaying correl w body size and tail length Male mate choice: Pipefish: - Sex role-rev species - Females secondary trait = striped pattern - Display only during competition and courting - Costly - Males prefer ornament Sensory bias hypothesis: female pref = byproduct of pre-existing biases in female’s sensory system - Ie. evolved in nonmating context - Male traits co-evolve to match Guppies: - Females prefer orange colour - From carotenoids - Nat selection and sex selection - Innate pref for orange objects - Predation risk high: preference is reduced Benefits: Butterflies: - Nuptial gifts (larger male → larger gift) - Spermatophore (protein) Fireflies: - Longer flash → larger spermatophore → inc female response Lizards: - Territory quality - Rockier = better for micro-climates (thermoreg) - Large dom males - Females prefer rockiest regardless of male - Laid eggs sooner and larger Fisherian runaway and good genes: Fisher model: - Female choose males based on trait - Could evolve indep of female choice - Trait correl w male quality Runaway process: male trait should co-evolve w female pref and become inc exaggerated Russell Lande: - Runaway process occurs thru linkage disequilib - Trait and preference = genetically linked Zahavi’s handicap principle: good secondary traits are costly bc they handicap male’s survival; good indicator of male quality (good genes) Tree frogs: - Good genes - Select males based on vocalizations - Weak male competition - Offspring growth correl w male’s attractiveness Hamilton-Zuk Hyp: females pref males w inc expression of second traits bc indicates inc levels of immunocompetence - Parasites and pathogens Red jungle fowl: - Infected half males - Uninfected → larger combs → female prefer Field crickets: - HF and LF ticks in courtship songs - HF + inc duration → better immune sys function (inc encapsulation rate) - Indirect benefit Spiders: - Pheromones - Females use male pheromone to choose mate - Convey info ab quality - Females mated w preferred mate → larger and heavier eggs and more eggs - Indirect benefit Sexual selection after mating: Warblers: - Mate guarding - Red EPC; doesn’t prevent tho - Effective strategy Tree swallows: - Sperm comp - Inc freq of copulations swarms sperm → inc paternity - Males spend more parental care - Type of mateguarding Cryptic female choice: - Female influences success of fertilization - Close relative → low quality → dec offspring fitness (inbreeding depression) Spiders: - Inbreeding avoidance by cryptic choice - Female has two storage sperm - First male: sibling or nonsibling doesn’t matter - Second male: store more sperm from NS Alternative reproductive tactics: Satellite: stay near dom Sneaker: hide and fertilize Evolution: - Conditional strategy: choose strat based on condition - Coexist in ESS: equal fitness - Negative frequent dependent selection Tree frogs: - Satellite males (conditional strategy) - Females pref energetic calls and LF - Only large can produce - Humfeld’s hypothesis: - Unattractive males → inc likely to be satellite - Satellite should have same pref as females Sunfish: - ESS - Parentals → bourgeois - Younger/smaller → sneaker - More rare, less percent offspring sired; but in proportion Hormone profiles in sunfish: parasitic (ie. sneaker) → inc testost and cortisol, dec 2-ketotest Mate choice copying: Guppies: - Females spent more time near male near female model Fruit flies: - Copied model (even if male was low quality) Benefits: - No worse off if can’t discriminate - Discrimination inc w age and experience Nonindependent mate choice: - Males should avoid mating w females seen recently mated - To minimize sperm comp Mosquitofish: - Males pref same female in Stage 1 and 3 if rival is near unpref female - If observe rival near preferred → dec time spent in Stage 3 Mating systems: Polygyny: 1 male → multiple females Polyandry: 1 female → multiple males - Role-reversed Polygynandry (plural breeding)/promiscuity: more than 1 each - When group defense = beneficial Emlen and Oring model: - Mating system has 2 factors - Evolutionary: sexual conflict/selection - Ecological: resource distribution → fitness Model assumes: - Female fitness lim by resources - Male fitness lim by number partners Resource poor conditions + high predation → monogamy and biparental care Polygyny evolution: Because: 1. Aggreg of females → female defense pol 2. Resources = clumped → resource defense pol Female defense polygyny: males monopolize females directly - Dec predation Resource defense polygyny: males monopolize females by defending resources Leks: - Male dominant polygyny: males on lek mate w many females - Uniform distribution of resources Polyandrous evolution: - When advantageous that women is free from parenting - Ie. high predation of offspring → can reprod quickly Promiscuous benefit:  - When social living = low or defense = uneconomical - Ie. uniform distribution - Cannot forgo feeding time Reed warblers: - Females = care - Poor habitat quality → monogamy and inc male care (biparental) - Polygyny evolved independently - Evolve w habitat quality - Ie. good quality → polygyny California mouse: - Monogamy - Father removed → no diff in number offspring; diff in survival Poision frogs: - R. imitator → small pools → monogamous and bip care - R. variabilis → lare pools → promiscuous; male care (defense) - No parental care: both species inc growth rate in large > small - Control: R. imitator in small = inc growth rate (bip care) Snapping shrimp: - Monogamy without bip care - Territorial coop hyp: 2 inds defend better than 1 → pair formation - Mate guarding hyp: male can monopolize 1 female - Assumptions for both: - Intense competition + high predation outside territory - Male encounter is low - Female short window of sexual receptive - Male guarding for high qual (close to reception) females - Pair guarding more effective Horses: - Female defense polgyny - Social bands → males defend bands (ie. females- direct), not territories Blackbirds: - Resource defense polygyny - Polygyny threshold model: fems should mate polgynyoulsy if benefits outweigh costs of sharing resources - Nesting over water = better quality + dec predation → female mate polygynously - Con: less food - Pros outweigh cons - No water → monogamous - Consequence of poly mating → inc variation in male mating success Carrion beetles: - Resource defense pol  - Males defend carcass (clumped source) → polygyny - Aggression → dom more success Leks: - Male dominant polygyny Hotspot hyp: males aggreg where they can encounter many females; ie. near resources Hotshot: dom males display, minimize cost of searching; subordinates stay near male Removal of males: - Hotspot: remove dom male, subordinate fill his spot - Female attracted regardless (no influence of female) - Hotshot: remove dom male, everyone leaves - Dec attraction to everyone Great snipe: - Hotshot lek - Dom males w inc display rates → removed → neighbours move away - Subordinate removed → neighbours take their place to be near Peafowl: - Hotspot - Dom males and floater males - Dom male removed → floaters move to opening and display - Just as attractive to females Polyandry and sex role-rev: Andersson 3 step hyp: benefits of polyandry 1. Male-biased parental care favoured in resource poor or high predation 2. Evolution of inc female fecundity a. Lay more eggs than male can raise b. Female fitness lim by number of mates 3. Females compete for mates Polygynandry: Badgers: - Mating year round → reduced mate guarding - Females benefit by ensuring fertilization; red male harassment, inc genetic diversity Promiscuity: Scramble competition: indirect comp of individuals to get multiple copulations Seaweed flies: - No courtship; mate whenever encounter Red squirrels: - Each sex defend large territory → male can’t defend both territories - Males → mating chases when sex receptive female EPC: - Male benefit: inc reproductive success - Female benefit: inc genetic quality, protect from dom males who kill unrelated offspring Monogomous females + low-quality males = inc levels of stress Juncos: - EP offspring = inc fitness - Benefit in F2 generation - F1 → no diff in fledging success - F1→ more offspring (grandoffspring) Marmot: - EPC = inc survival and inc likelihood of dom status - Correl w heterozygosity