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32 Cards in this Set
- Front
- Back
Sexual Dimorphism (vs other groups) . . . |
More noticeable in birds than any other group |
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Natural Selection |
1. Individuals within a population vary 2. Some of this variation is inherited 3. Some individuals are more successful at surviving and reproducing 4. Survival and reproduction is tied to the inherited characteristics of individuals. Those with most favorable variations are naturally selected – they are disproportionately represented in future generations |
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Directional Selection |
mode of natural selection extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype. Daphne birds - drought - seed size change - increase of beak depth |
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Why can't natural selection explain the sexual dimorphism (the long tail of males) of Long-tailed Widow Birds |
If long tail was adaptive both male and females would have it long tail easier to be caught more energy for growht |
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Fitness (according to natural selection) really equals . . . |
Reproduction (Failing to mate = Die young) |
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What is needed for success in fitness (aka reproduction)? What part involves "sexual selection"? |
1. Survival to reproductive age 2. Finding a Mate (Involves sexual selection) 3. Reproducing successfully Different Bird Species Vary in ALL 3 parts |
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What is sexual selection? |
heritable variation in a trait that affects mate acquisition This successful trait will increase in frequency over time Leads to sexual dimorphism |
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Why does sexual selection lead to sexual dimorphism? |
Eggs are more expensive than sperm Reproduction is more expensive for females Females then mate with few(one) male (vs males who can mate with many) Females must choose only ones of high fitness (higher cost with failed reproduction) Are very picky Males must then compete (against other males) Male trait (normally) become more elaborate |
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Traits selected for via sexual selection (that lead to sexual dimorphism) are called . . . |
Secondary sexual characteristics |
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Two possible ways sexual selection occurs? |
1. Intersexual Selection (Female choice) 2. Intrasexaul Selection (Male choice) Either can lead to sexual dimorphism |
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Intersexual Selection: Pheasants |
VIDEO |
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How does Intersexual Selection lead to Sexual Dimorphism? |
1. Models of arbitrary mate choice (aesthetic) (Doesn't mean quality) 2) Honest advertisement models (“good genes”) i.e. must be a cost associated with development and/or maintenance of trait |
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Runaway Sexual Selection (Fisherian) |
Extreme male traits can evolve through a process in which the male trait and the female preference for that trait become genetically linked. (Even if a disadvantageous trait according to natural selection) |
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Sensory Bias Model of Sexual Selection |
Females are attracted to traits in males that stimulate their sensory systems (Preferences are due to biases in their sensory system) The 'preference' exists before the male trait does When male trait does exist it spreads quickly due to preference |
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Sensory Bias Model of Sexual Selection
Example: Least Auklet |
some ornaments are likely to be favored by sexual selection because mutual male and female mating preferences benefit individuals with the most elaborate expression of these traits. Naturally crestless least auklets have a mating preference for foreheaded crests like those of other auklet species even though not naturally expressed This means the crests are not just for species recognition |
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"Good Genes" Model of Sexual Selection |
mates are chosen based on characteristics that reflect "good genes" of the mate and the viability of that mates potential offsprings' genes Females choose males that are older/experienced, with better territories, good providers, healthy, sexy, more successful |
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"Sexy Sons" Hypothesis |
Females choose the attractive males so they can have attractive sons and therefore more grandchildren (Other benefits such as caregiving, territory, gifts given are irrelevant) Not well supported (yet) |
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Hamilton-Zuk Hypothesis |
Certain secondary sexual characteristics expressed in males (like certain bright colours) = higher resistance to parasistes Bright coloured males = chosen by females |
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What hypothesis do Wild Turkeys' Snood/beard/spurs/tail fan traits support? (Females are attracted to these traits) |
Good Genes Hypothesis Large/extensive versions of these traits means the male has high energy reserves (can afford it) OR Hamilton-Zuk Hypothesis Increase snood length, and the width of skull caps = decrease the coccidian oocyst loads in feces |
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Handicap Principle (eg Long tailed widow bird) |
Secondary Sexual Characteristics that are costly and wasteful or energy But it shows to the female that the male is of high quality because (unlike low quality males) they can afford the disadvantage it creates |
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Preference for Symmetry (eg Barn Swallows) |
Assymetry Environmental stress (habitat disturbance) Or both environmental and genetic factors |
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Intersexual Selection: Sexual Dimorphism of Coloration in House Finches |
Males' colour type/amount/brightness = amount of carotenoids ingested = better quality Better quality = Better parental care and genotypic quality Naturally bright males = High nest attentiveness, parental care and overwinter survival (not age related) (These traits are passed on to sons) Artificially brightened males = Paired more quickly Females chose Better providers Healthiest males Sexiest males UNKNOWN WHY |
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Intersexual Selection: Sexual Dimorphism of Coloration in Barn Swallows |
Males are more colorful and have longer, more deeply forked tails Longer tails lengths = get mates more quickly Symmetrical tail = Get mates more quickly than any other asymmetrical tails |
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Red-backed Fairy Wrens: Two possible male strategies |
Bright Males:actively pursue extra-pair copulations, resulting in increased reproductive success Dull Males: invest in mate guarding, parental care, nest helpers and experience reduced aggression, which may increase within-brood paternity and survival |
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What would a smart red-back fairy wren do? |
pair w/dull male but solicit copulations from bright male |
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Male-Male Interactions |
compete for access and prevent other males from mating Combat (lekking) Sperm Competition Infanticide |
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Lekking |
eg Greater Prairie Chickens |
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Capercailie Lekking |
VIDEO |
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Why is it hard to separate the two types of sexual selection (Intersexual and Intrasexual selection)? |
Secondary Sexual Trait = Trait x Trait x could be helpful for male-male interactions and make them more attractive for females (those with the trait give female's better repoductive success) |
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What types of females chose males by secondary sexual characteristics and why? |
Females that don't require males to have parental care choose by SS characteristics because they show genotypic quality (that can be passed to children) |
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Common Yellowthroat Coloration correlated to mating success? |
Mask size not yellowness mattered to females |
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Jack-Pine Warbler Coloration correlated to mating success? |
Increased mask size = increased male mating success because it helped with male-male competition not female choice |