Sexual Selection

Question	Answer
Lekking	Area, bird, displays. Females can check out many males of small time/area. Most costs are minimal but still exists. Paradox. RUFF
Traits Through Intersexual Selection	PEACOCK's TAIL. Evolved through a selection of direct benefits model, indirect benefits model & sensory bias model. Fisher's Runaway Hypothesis.
Human Sexual Selection	Wodaabe Tribe. Polygynous mating system. Can have up to 4 wives - 1 = relative. 2 = love marriage. Very structured system. They have a beauty criteria - 'Perfect symmetry, eyes like a gazelle, skin as clear as water' etc. 3 female judges so 3 'best' males are chosen. They carry out a display of 3 dances and paint their faces etc. and then the 3 best are chosen. The daughters of prev. choices choose the next 3 men - so this is the runaway effect - best genes are choosing best genes.
Examples of Intrasexual Selection	GRASSHOPPER - Strong assortative mating large males mated with female but only possible through male-male fighting before and during copulation. BLUEGILL SUNFISH - Parental males (large) & sneaker males (small). Competition between males through different mating strategies. Sneaker males have many low quality sperm, parental males have few high quality sperm.
Good Genes Hypothesis	The preferred male trait INDICATES high viability as the trait is often detrimental. This high viability is inherited. E.g. Grouse with parasite load & red combs.
Sensory Bias Hypothesis	This assumes that females initially prefer a male trait due to a mating benefit associated with the trait because it is also associated with a benefit outside of mating. E.g. preferring red berries because others are toxic, so red-billed males are preferred too. This is selected for & leads to sexual dimorphism.
Remember!!	A = Relationship between PHENOTYPE & GENOTYPE. B= Relationship between PHENOTYPE & FITNESS. A&B establish a relationship between fitness and genotype to determine whether or not evolutionary change occurs. BUT... Selection will only drive evolution of traits if your own offspring reproduce successfully (INHERITANCE
What is the Driving Force?	SS is based on the same principles as NS but the driving force is different - in the case of SS it is the opposite sex. SS is the result of competition within the species between indivs. of the same sex, but where the SELECTION FACTOR is the opposite sex.
Intersexual Selection	Indivs. or 1 sex select among indivs. of the other. E.g. female choice & her selection of attractive traits in males.
Intrasexual Selection	Members of 1 sex competing with each other. E.g. male-male competition. There is pre-copulatory traits (sperm comp. & infanticide etc.) and post-copulatory traits (weaponry and mate guarding etc.)
Mating Strategies	Monogamy = 1M & 1F. Polygyny = 1M & +++F. Polyandry = 1F & +++M. Polygynandry = +++MF Mating strategy is a major component of the evolution of phenotypic divergences of behavioural and secondary sexual character traits.
Dunnocks!	The Victorian symbol of fertility. HA! Dunnocks are polyandrous. The males & females are nearly identical but females try to get 2 fathers to double the parental care. There are alpha & beta fathers. The female mates with beta male on the sly, but then alpha male pecks at her genitalia until she ejects the sperm. She then mates with alpha male. Beta male is none the wiser so still offers parental care & alpha male ensures paternity. Increase in absolute fitness (reproductive success)
Wallace's View	He believed that SS & NS were essentially the same thing. The F was just the resource being competed for.
Importance	Sexual reproduction leads to recombination which maintains genetic diversity. It can select against deleterious mutations & select for advantageous ones.
Ansiogamy	Ansiogamy = different sized gametes. It is a product of sexual selection. Disruptive selection favours parents with many & small gametes (sperm) and few & large gametes (eggs). Assuming fitness increased with size/number of gametes, an equilibrium formed.
Ansiogamy Leads to Conflict	Ansiogamy leads to sexual conflict between the sexes. Sperm is cheap so males are interested in mating with as many females as possible. But eggs are costly, so females want the best possible outcome from it and so are interested in finding the best mate. Male RS increases with the no. of mates, but female RS is dependent on quality of mate (& survival of offspring). This leads to divergent phenotypic behavioural traits
Exaggerated Traits	Intersexual selection is believed to be the origin of exaggerated characters which are often ecologically disadvantageous.
Direct Benefits Model	The male provides a direct benefit to the female or offspring in terms of survival. E.g. 2 males father 1 brood of Dunnocks = extra food, territory & protection for female & offspring.
Indirect Benefits Model	Male provides no direct benefits so alleles affecting female choice increase or decrease in freq. depending on the fitness offspring. E.g Fisher's Runaway Model & Good Genes Hypothesis
Fisher's Runaway Hypothesis.	Sexy-Sons Model. the sons of females that choose a male trait have improved mating success because they have inherited the trait that made their father appealing to their mother

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	Created by Alice Burke over 11 years ago