Lecture 6 - Mate Choice and Sexual Selection Flashcards
During mating season what happens to female mallards?
They lose the feathers around their head from male aggression
What do female praying mantis do after mating?
Eat their mate as the male won’t provide any service so gain their nutrient instead
What are the two male mating strategies?
Elaborate courtship and sneaky-mating
What is the trade-off for female guppys?
Accept the cost of being with the predators as males can’t follow them due to their bright colours. They do this to escape the continuous harassment from males
What is anisogamy?
Reproduction between two gametes which differ in size and form
Example of anisogamy
Male pigs have between 20 to 60 billion sperm
Female pigs have less that 20 eggs every cycle
- Females reproductive success is reduces due to her resources as only one large gamete
- Males invest large numbers to invest in getting as many offsprings with females as possible
Why do females make life time investments in offspring?
Males can reproduce and have multiple offspring every year - women can only have one
Explain how sexual conflict can drive an arms race
Reproductive strategies of males and females are no aligned
- Males can maximise success by mating with as many females as possible
How do males maximise reproductive success?
By amount of females they mate with
- males mate with females they have never seen before
How do females maximise reproductive success?
Females aim for quality
- brightly coloured display suggests quality of male and what foods they eat
When is monogamy favoured?
- Input from both parents is needed to raise offspring
- Male has to guard mate to ensure he is father of offspring
- Low change of meeting many females
Example of monogamy when input from both parents is needed to raise offspring
Djungarian hamster males help keep their female and litter warm
- Pups survival decreases when males leaves the group
Example of monogamy when male has to guard mate to ensure he is father of offspring
House sparrow males
Example of monogamy when there is a low chance of meeting many females
Harlequin shrimp
- Once male has found female is is best for him to stay with female and maximise reproduction with her rather than leave and maybe not find another
What are the two kinds of sexual selection?
Intersexual and intrasexual
What is intersexual selection?
One biological sex choose mates of the other sex to mate with
What is intrasexual selection?
compete with members of the same sex for access to members of the opposite sex
Why does sexual selection occur?
Because of conflict over reproductive investment
What is polygyny?
When males have more than one partner and females only have one
What is an example of polygyny?
Killer wales
What does polygyny promote?
Conflict between males and choosiness by females
How does polygyny promote conflict between males?
- Males fight to establish dominance → access to females
- Dominance correlated with mating success
- For control of resources that females require
- For direct control of groups of females
- Male-male conflict favours large, well-armed males
Example of choosiness by females in polygyny?
Guppys - female choice and sexual selection on male traits
- Females choice favours elaborate male behaviour or morphology
Polygyny is favoured when…
- One sex is operationally rare
- Males can control resources or females
- Females can exert free choice
What is polyandyry?
When females have more than one partner and males only have one
Example of polyandry
Sandpipers
How do female sandpipers behave like males?
Polyandry
1. Larger than males
2. Arrive at breeding grounds first
3. Fight for territories
4. Attracts several males to her territory
5. Skewed reproductive success
When is polyandry favoured?
- Females can escape parental care duties
- Females require resources provided by >1 male
- Males biased sex ratio
What is poydynandry?
When females and males both have more than one partner
Example of polygynandry
Barbary macaque
- Females solicit copulation from several males and each male mates with several females
What is the benefits of polygynandry?
- Male gains several females
- Males unable to defend female exclusively
- Females gain access to wide range of resources
- Females confuse males over paternity = increased paternal care, decreased infanticide
- Females gain access to many males and genetic benefits
When is polygynandry favoured?
When males can’t monopolise females and females gain from multiple matings
What does the decision of monogamy or polygyny in females depend on?
Availability of resources and habitats
Why bother choosing what mating option?
Cost in energy and predation
What are the benefits in choosing how many partners to have?
Direct
Female HERSELF gains benefit and so lives longer or produces more offspring
- Territory
- Nuptial food
- Paternal care
- Reduced harassment
Indirect
Female’ OFFSPRING gain benefit and so lives longer or produces more offspring (more attractive?)
How does the female know what benefits are available?
- Male traits signalling direct benefits
- In some matings, a females only gets sperm
Choosy females should…
- Pay attention to signals of available benefits
- Prefer males with exaggerated signals
- Prefer signals that males cannot “fake”
- Maximise their benefits
Example of runaway selection
Fisherian runaway
- Female (trait) choice is established and male traits become more exaggerated.
- Daughters of successful pairings will chose a mate using the same preferences as their mother
- Sons of a successful mating will possess the same features as their father.
- A trait becomes fixed in the population when all females chose it and when all males carry it.
