7 - Sexual Selection Flashcards
What are the taxonomy generalisations of parental care?
Mammals - 90% female
Birds - Biparental but female emphasis
Fish - Paternal
What is the common, simplified view of the evolution of parental care?
Parental investment costly
Females make large investment in egg so choose mates carefully
Males have low, replenishable investment
Many males return to mate against competition
High variance in mating success means selection for traits that increase mating success
What is anisogamy?
Fusion of dissimilar gamets
Large female egg
Teeny tiny sperm
What is OSR?
Operational sex ratio: ratio of sexually active/receptive m:f
What is ASR?
Adult sex ratio: ratio adult m:f
What is the concorde fallacy?
Past investment = more profitable to continue investing
Wasn’t true with concorde!
Outcome the same whether they continued to invest or not
What is the Fisher condition?
Pre-mating investment affects future reproduction rates (PRR)
PRR rates higher for males
Lower female PRR biases OSR so more males
Males can’t reporoduce enough to fil reproductive potential
IF only difference is male’s lack of mates, it makes sense for MALES to care too
Does investment = parental care?
A fixed amount of parental care needs to result in higher fitness than just initial investment
Return on investment as an increasing function of past investment may not be realistic
Could be in females not sure
Debunk the simplicity of the common view of sex and parental care.
No real reason for more maternal investment
No explanation for males to invest in competition more than caring
Some males mate more than others eg. gorillas, therefore only some produce offspring
Selection acts on parenting traits of successful breeders, which reduces parental care in population as they are around for less time and sire more offspring
Strong sexual selecition required for this
How does genetic variance remain in the male population on a sexually selected trait in the Soay sheep of St Kilda?
Strong male - male competition
Some males have scurs, most have normal horns
Horn size positively correlated with mating success and is highly heritable
RXFP2 gene explains most variation
Ho+ allele, larger horn
HoP allele, smaller horn
50% HoP HoP scurs, they have less reproductive success but live longer (less aggression from fellow males)
Combination of reproductive success and survival means heterogenous are fittest
Frequencies are close to equilibrium
Variation maintained by trade-off of survival and offspring
Summarise Wilkinson, 2015
Genetic models of sexual selection limit adaptation that may be possbile and ignore complexities of natural systems
More integration needed
Differences in sex largely driven by gene regulation, not genome
Difficult to quantify behaviours as they may change depending on circumstance - should try to identify all
Analysis method: locate genes that differ in male/female or ornamented/unornamented individuals
Analysis method: find sequence varients using sequence expression or manipulation (reverse genetics)
Male based genes have higher variance than non-biased genes
Species specific genes tend to be male, could be selection or higher transcription rate
Male traits evolve faster, but code suggests not due to selection
Ability to identify regulation is limited
