Sexual Selection and Mate Choice Flashcards
What is sexual selection?
Darwin (1871) - The advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.
Adaptations generated by intraspecific competition and the struggle to reproduce.
How can sexual selection and natural selection be distinct and be aligned?
Distinct - Traits that are attractive to mates can also constrain survival e.g. horn size increases extinction risk in bovids.
Aligned - Traits that are associated with enhanced survival can also be attractive to mates e.g. lekking success in black grouse correlates with naturally selected survival.
What is intra and inter sexual selection?
Intra - Individuals of the same sex compete for matings.
Inter - Individuals of one sex (usually females) choose mating partners from the other sex.
Intra and inter sexual selection can be inter-related, males can compete intra-sexually for an inter-sexual result e.g. red deer stags.
What is the primary direct benefit of sexual selection?
Conspecific recognition - Avoidance of hybridisations which may be less fertile or completely infertile.
How is parental investment gained from sexual selection?
Polyandry allows females to increase the number and quality of offspring by ensuring parental investment. e.g. the more opportunity beta male dunnocks had to mate with the female, the more he contributes to feeding the brood.
Male redback spiders often actively sacrifice themselves while mating. Females benefit from extra meal and male feeds their own offspring and achieves greater sperm transfer. May have evolved as 80% do not encounter a mate.
Describe runaway sexual selection models
Female preferences for particular, naturally selected, traits.
Genetic link between male trait and female preference.
Sons carrying the trait gain success, so trait fixes in population and female genes for trait choice persist.
Runaway exaggeration of the trait.
E.g. Male ornamentation varies across Trinidadian guppy populations. Naïve females prefer their own population’s male ornamentation characteristics. Evidence that female preference genes co-evolved with the trait.
Describe good gene models
Traits are costly to develop/carry - they are a handicap and carrying the handicap is a signal of male quality.
Either handicap is standard and acts as a survival filter, OR
Better males carry bigger handicaps.
Being fathered by males that can carry the handicap will capture better genes.
E.g. improved growth and survival of peacock offspring with more elaborate traits. Peacock tails are extravagant, females prefer bigger eyespots. Sons and daughters grew bigger when fathered by males carrying bigger eyespots and had better survival.
What is the parasite model?
Parasite load is a major problem, signal linked to parasite resistance.
Being fathered by males with evident signals will capture better resistance genes.
E.g. swallows and mites, males with longer and more symmetrical tails find mates quicker and have fewer mites - even when translocated to other nests. More mites in one year leads to a shorter tail the next year.
What is the model for compatible genes?
Mate choice benefits choosing genotypes that complement self.
General benefit to avoid outbreeding - similar to self to avoid hybridisation, and avoid inbreeding - different to self.
E.g. mate choice at the major histocompatibility complex (MHC). Large chromosomal region of 200 genes plays a role in immune recognition - difference between self and non-self. Highly polymorphic due to heterozygote advantage/selection for rate types. Mice produce more heterozygous offspring that one would expect from random, suggesting mate choice for heterozygous offspring.
How are all four theories linked?
All four theories fundamentally signal good genes:
- Attractive sons
- General quality
- Parasite resistance
- Combability
What are the wider population benefits of sexual selection?
Helps purge mutations from lineages if mutations influence male mating success in the face of competition or if they are more deleterious in males than females because of sexual selection.
Average successful father should carry less mutations than the average male.
Protects populations against extinction.
