Mate choice Flashcards
What is mate choice?
A form of intra-sexual selection whereby females preferentially mate with certain males
What is the Sexy Sons hypothesis?
Under Fisherian selection, females select for ‘attractive’ males as they will sire attractive sons, who will themselves be selected by females and maximise the amount of grandoffspring for the mother.
Are the benefits of the Sexy Sons hypothesis direct or indirect for the female?
Indirect, as her offspring will benefit from the father’s good traits
Describe the Sexy Sons hypothesis in terms of alleles p, P, t and T
p = non-choosy females P = choosy females t = boring male trait T = sexy male trait
Can assume P and T become associated, G(PT)
What is the association of alleles called?
Genetic covariance, they vary in response to each other
What happens at low levels of G(PT)?
Female preference and male ornament size are at equilibrium
What happens at intermediate levels of G(PT)?
The costs and benefits of preference cancel out
What happens at high levels of G(PT)?
It becomes unstable and favours ‘runaway traits’ and extreme preferences
Is there a cost to the female for being choosy?
Only if her preference is extreme, as it restricts her chance of mating. Otherwise it is beneficial.
Does the Sexy Sons hypothesis explain the evolution of mate choice?
No, only how it might be maintained, as the benefit of having sexy sons is relatively small for the female
Is the Sexy Sons hypothesis sensitive to the costs of female choice?
Yes; if she is too choosy then she will not get to mate as extreme ornaments are less likely
Is there much empirical evidence for G(PT)? Give an example.
Yes but very little
Bakker (1993):
Sticklebacks, females preferred red colouration. Intense red or dull males were bred to females of same population. Was found that daughter colour preference for intense red correlated to the intense redness of their brothers, positive correlation.
What is the Good Genes hypothesis?
That ornaments indicate male quality; they are costly to produce and so only the males with the best genes can produce them.
Why does the Good Genes hypothesis convey more benefits to females than the Sexy Sons hypothesis?
Sexy Sons hypothesis ensures production of attractive sons
Good Genes hypothesis ensures production of good quality sons AND daughters
Are the benefits of the Good Genes hypothesis direct or indirect?
Indirect
Under the Good Genes hypothesis, who described he Handicap Principle? When? What is it?
Zahavi, 1975
Male ornaments are seen as handicaps as they are costly to produce and reduce male fitness. Males that invest more into their ornaments are more handicapped but are preferred by females.
What are the parameters P, T and Q in the Good Genes hypothesis?
P = female preference T = male investment into trait Q = genetic quality
What are the 2 main problems with the Good Genes hypothesis?
- The Lek Paradox
2. Honesty
What is the lek paradox?
High quality males are consistently chosen by females, meaning the best male will get to mate with all females in a lek. Therefore his good quality alleles will spread to fixation in the offspring and eliminate genetic variation.
If there is no variation in quality, there is nothing for females to choose between and mate choice will not be maintained.
There are three ways to maintain genetic diversity under the Good Genes hypothesis. What are they?
- Red Queen dynamics
- Genic capture
- Mutation bias
How do Red Queen dynamics maintain genetic diversity?
It ensures selection for alleles with different Q values over time.
Who confirmed that Red Queen dynamics are important in host-parasite co-evolution?
Hamilton and Zuk, 1982
What did Hamilton and Zuk (1982) focus on?
North American birds, finding that there was a correlation between blood infection by parasites and fitness-dependent traits like male brightness and song.
Who furthered Hamilton and Zuk’s work by studying the sage grouse?
Boyce (1990)
What did Boyce (1990) find in sage grouse?
Lice caused hematomas (swellings of clotted blood) in the air sacs of male sage grouse causing them to discolour. These are used in courtship display and so females can detect lousy males.
Under Red Queen dynamics, male fitness-dependent traits evolve over time in response to parasite infection. True or false?
True
What is genic capture?
When multiple loci encode a trait (QTL), even small mutations have an effect on phenotype.
What is biased mutation rate?
When mutations are more likely to reduce quality than enhance it.
Who provided two main explanations for the existence of biased mutation rate?
Iwasa et al., 1991
Iwasa et al. (1991):
What are the two main reasons behind biased mutation rate?
- Greatly-exaggerated traits like ornaments are already at their physiological limits, so a mutation is more likely to be detrimental (example they gave was calling in frogs)
- Complex traits involve numerous pathway with delicate interactions, mutations more likely to upset this balance
Why is honesty a problem in the Good Genes hypothesis?
If there is a selective advantage of displaying a handicap, mimics could invade. In this case females would not be able to tell the difference in male quality and preference would not be maintained.
So what two things must be factored into the model to ensure the Good Genes hypothesis works?
Maintenance of genetic diversity and honesty
Who put forward the Good Parent Process?
Hoelzer, 1989
What is an epigamic trait?
One that attracts the opposite sex
What does the Good Parent Process state?
That females choose males based on non-heritable epigamic traits e.g. territory quality.
Is the Good Parent Process directly or indirectly beneficial to females?
Directly; they will get to share the territory of a mate and thus increase their own survival and reproductive output
Why does male ornament size indicate good territory quality?
If males have more resources they can invest them into ornament production
Why does the Good Parent Process cause females to select males based on epigamic traits?
They are used as indicators of the quality or quantity of care a male would provide for a female’s offspring. This would improve the fitness of the offspring.
Why is territory quality an indicator of future male care?
There are abundant resources that can be channelled into the offspring.
Does the Good Parent Process provide explanation as to how mate choice evolved?
Yes; not only are there indirect benefits (increased offspring fitness), there are direct benefits to females
When using territory quality as an example, what is a caveat?
That territory quality can often be assessed without looking at male ornaments.
What does the polygyny threshold model state?
That if multiple females chose the male with the best territory, the benefit of choosing that male is reduced as females must compete with each other for resources. Sets the upper limit of females in a harem.
What is Sensory Exploitation?
The idea that mate choice evolved as females had a pre-existing sensory bias that was exploited by males
In Sensory Bias, is preference preceded by ornamentation?
Yes
Give a referenced example of sensory bias.
Egger et al. (2011)
Mouth-brooding cichlids: females prefer males with orange spots on their anal fins. Female colour preference was tested outside of the mating context, and was found females like orange/red/yellow. This is hypothesised to be because it resembles the colour of their eggs, is an evolutionary response for retrieving eggs floating in the water.
What is Sexually Antagonistic Coevolution (SAC)?
Males and females face antagonistic selection that causes sexual dimorphism.
Females sustain injury through mating and so benefit by restricting mating to as infrequent as possible, e.g. evolution of choosiness.
Selection on males favours persuasiveness as they get to mate more.
Give a referenced example of a) female phenotypes and b) male phenotypes in water striders response to sexually antagonistic selection.
a) Choe and Crespi, 1997
Females evolve pads and spikes to make them hard to grip, as well as genital shields that a female only retracts when she wants to mate
b) Khila et al. 2012
Males have grasping appendages to grasp females in pre-mating struggles. Reduced appendages was found to correlate with reduced mating success.
What family do water striders belong to?
Gerridae
What is the theory or Genetic Compatibility for mate choice?
Whereby females choose males based on their genetic compatibility to ensure healthy and fit offspring
In the context of mate choice, what does ‘adaptive’ mean?
The female gains good genes for her offspring
Which theories for mate choice are obviously adaptive?
The Good Genes hypothesis
Who debated the adaptiveness of Sensory Bias?
Dawkins and Guilford, 1996
Dawkins and Guilford, 1996:
What did the authors say about the adaptiveness of the Sexy Sons hypothesis?
Females do not gain quality genes as in the Good Genes hypothesis, but they do gain genetically through the attractiveness of their son who can mate with many females.
Dawkins and Guilford, 1996:
The authors suggest that Sensory Bias is adaptive. Why is Sensory Bias NOT traditionally seen as adaptive?
Because the female does not benefit, mate choice simply exists due to a pre-existing state of her sensory system
Dawkins and Guilford, 1996:
Why do the authors suggest that Sensory Bias is adaptive? Give reasons.
- Preference is maintained; if there was no benefit to females, bias would have gone extinct.
- SB increases male detectability
- SB avoids heterospecific mating
Dawkins and Guilford, 1996:
Explain how SB can increase male detectability.
Females are able to locate males quickly as their senses are attuned to some aspect of the male phenotype. This reduces costs to the female as she can find mates quickly. Female choice is costly, so even if she finds a mate that is not of the highest quality, she still gets to mate.
Dawkins and Guilford, 1996:
Explain how SB can avoid heterospecific mating.
The benefits of this are low and species-specific biases allow females to search for members of their own species with reduced costs and error. More exaggerated signals make the disparity between species more obvious.
Is the Good Parent Process adaptive?
Not technically as the female does not gain good genes for her offspring but instead good paternal investment and resources (environmental factors).
Which theories explain the maintenance of mate choice?
Sexy Sons, Good Genes
Which theories explain the evolution of mate choice?
Good Parent Process, Sensory Bias, SAC
What does SAC also explain?
The evolution of sexual dimorphism
