Lecture 10 - sexual selection Flashcards
What is a rule for evolution?
- selection acts on replicators
- these are individual units that replicate themselves
- those that leave most copies are the most successful
(species & individuals aren’t replicators)
What are the ingredients for natural selection & competition?
- ecological competition is 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 & fitness
What is sexual selection?
- intrasexual selection
- intersexual selection
What is fecundity?
the amount of offspring
What is fertility?
the amount of gametes
What does sexual selection lead to?
different adaption
What is sexual dimorphism?
- male & female
- they have different adaptions - e.g. male has claws to fight off predators
- sexual selection produces differences between the sexes
What are mating systems?
competitions for mates had led to diversity of outcomes in terms of mating systems
What is monogamy?
1 male & 1 female - one partner, little sexual selection - no sexual dimorphism
What is polygamy?
male & females have multiple partners
What is polyandry?
females has multiple partners
What is polygyny?
male has multiple partners
What is the extra-pair paternity?
- discovered in 1990s with advent of genetic fingerprinting
- surprising high rates in supposedly monogamous species
How is Dunnock an example of extra-pair paternity?
- very variable mating systems
- frequently polyandrous, despite appearing monogamous
- however females frequently mate with unpaired males (sneak)
- mates 100 times a day
- important consequences
Describe extra pair paternity statistics
- chaffinch 17%
- blue tit 10-15%
- dunnock 0-36%
- tree swallow 38-76%
- superb fairy wren 75-85%
What are the characteristics of polygamy, polyandry & polygyny?
- multiple partners optimal
- sexual selection
- sexual dimorphism
What is intrasexual competition?
- in polygamous mating systems, there are a few winners and lot of losers –> intense competition for mates
- competition between members of the same sex is called intrasexual selection
- thus had led to the evolution of several behaviours as a consequence
What are examples of behaviours carried out due to intrasexual competiton?
- male-male competition - fighting
- mate guarding - pre-copulatory & post-copulatory
- sperm competition - direct competition between sperm (led to adaptions in sperm - e.g. being motile)
What is ‘lek competition’?
- a gathering of males that compete with each other
- they display with others and females observe the lek
- the females choose the ‘best males’
- lemming is costly for males
- may be less costly for females
- example (red grouse)
What is intersexual selection?
- females choose 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
Females choose males based on their characteristics
What do females gain from intersexual selection?
- Access to resources
- Access to good genes - utilitarian
- Access to good genes - attractiveness
What access to resources do females gain?
e.g. courtship feeding
What access to good genes (utilitarian) do females gain?
- females choose genes that confer high survival to offspring - resistance to parasites
What access to good genes (attractiveness) do females gain?
- females choose attractiveness genes that make male offspring more attractive to females
