sexual selection Flashcards
whats ecological competition
-the consequence of limited amounts of resources
-Resources can include food, water, shelter, space or mates
-There is a direct relationship between amount of resource captured and fitness
whats the mating system
-Competition for mates has led to a diversity of outcomes in terms of mating systems
-Monogamy - 1 male & 1 female
-Polygamy - male and female have multiple partners
-Polyandry - female has multiple partners
-Polygyny - male has multiple partners.
is monogamy rare in nature normally
yes
exception to monogamy in nature
-albatross
-find each other during mating
-mate for life
-spend most of the year apart from each other whilst looking for food
-no sexual dimorphism
whats Extra-pair paternity
-Discovered in 1990s with advent of genetic fingerprinting
-Surprisingly high rates in supposedly monogamous species
whats extra-pair paternity
-Dunnocks (Prunella modularis)
-Very variable mating systems
-Frequently polyandrous, despite appearing monogamous
-However, females frequently mate with unpaired males
-sneaky fucker- when male turns his back, another male sneaks in to copulate very quickly with female
-male copulates 100x a day to ensure their sperm gets passed on
extra-pair paternity percentages
-Chaffinch: 17%
-Tree Swallow: 38-76%
-Blue Tit: 10-15%
-Dunnock: 0-36%
-Superb Fairy Wren: 75-85%
whats polygamy
-Multiple partners optimal
-Sexual selection
-Sexual dimorphism
whats Intrasexual Competition
-In polygamous mating systems, there are a few winners and a lot of losers -> intense competition for mates
-Competition between members of the same sex is called intrasexual selection
-This has led to the evolution of several behaviours as a consequence
whatsa Intrasexual Competition
-Male-male competition - “Fighting”
what kind of competion is mate guarding
-intrasexual
what kind of selection is sperm collection
-intrasexual
-looks at adaptation of organism pre and post copulation
whats lek competition
-intrasexual selection
-A gathering of males that compete with each other
They display with each other and females observe the lek
The females choose the ‘best males’
Lekking is costly for males
May be less costly for females
examples of lekking
-Paper wasp
-Fruit flies
-Capercaillie
-Red Grouse
-Manakins
intersexual selection and how females chose mates
-In Lek species, females choose one male
-Other species, males display to females
-Typically in polygynous mating systems (females mate with one male)
-But reverse can happen – polyandrous mating system
what do females gain by intersexual selection and female choice
-access to resources - courtship feeding
-access to good genes - Females choose genes that confer high survival to offspring: resistance to parasites
-access to good genes (attractiveness)- Females choose attractiveness genes that make male offspring more attractive to females
whats Runaway Sexual Selection
-Anderson (1982):
-Experimentally altered tail length of males
-Reduced tail –> lower mating success
-Increased tail -> more mating success
-variation in males in population, females evolve a preference
definition of runaway sexual selection
-Selection on survival and reproduction operating in different directions
whats Sexual vs Natural selection
-Comparative evidence: look at patterns across multiple species to see whether traits vary as we would predict
-Prediction: in species that experience stronger natural selection, sexual selection should be weaker
-Strength of sexual selection is correlated with sexual dimorphism: i.e. males are more different from females when sexual selection is stronger
-E.g. predation pressure: species in habitats that are more prone to predation should have less dimorphism
-These examples also exemplify the importance of gene level selection
-In species in which males are brightly coloured, genes for attractiveness spread because they confer advantages in terms of reproduction
-Not because of survival of individual
is offground nesting more or less predator risk
-less
Runaway Sexual Selection
-Eaxaggerated traits can evolve through sexual selection
-However, as selection proceeds, genetic variation becomes used up
-In the extreme, in a strongly selected population, variations between individuals are not due to genetics but random (additive genetic variation is low)
-Although this is expected, the reverse is actually observed
-Sexually selected traits have high variability and additive variance
-‘The Lek Paradox’ – many theories
