EE Lecture 6: Sexual Selection Flashcards
define sexual dimorphism
phenotypic differences between males and females of the same species
what is the state of having phenotypic differences between males and females of the same species
sexual dimorphism
define sexual selection
natural selection where some individuals outreproduce others of a pop because theyre better at securing mates
what does sexual selection favour
any heritable trait that increases reproductive success
what is Bateman’s principle
variance in reproductive success is generally greater in males than in females a consequence of anisogamy females invest greater in offspring females compete for resources males compete for access to females females are more choosy
what is Triver’s theory
theory of parental investment
what are females reproductive rates limited by
the number of offspring they can birth in a lifetime
whate are male reproductive rates limited by
number of females they can impregnate
which sex invests greater in offspring
females
which sex competes for mates as opposed to resources (mostly)
males
which sex are more choosy
females
why is there variance in reproductive success
females are limited by number of births in a lifetime and males arelimited by the number of females they can impregnate
what are male strategies for reproductive success
max no. copulations direct contest comp for female provide evidence of good genes to female provide female with good resources invest in offspring if parent certainty is high
under what circumstances will males invest in offspring
if parent certainty is high
what are female strategies for reproductive success
invest in offspring
choose males with good genes
choose males who’ll invest in offspring
what is Fisher’s hypothesis
runaway selection hypothesis
who thought of the runaway selection hypothesis
Fisher
what is Fisher’s runaway selection hypothesis
females who mate with attractive males produce attractive sons
genes for the male trait and female preference become associated
preference and the trait become magnified over time
eventually all males have the trait
what is Fishers runaway selection hypothesis halted by
natural selection
what is the hypothesis called where genes female preference and male traits become associated
Fishers runaway selection hypothesis
what is Zahavi’s hypothesis
Zahavi’s handicap hypothesis
what is Zahavis handicap hypothesis
exaggerated secondary sexual traits are an honest indication of good genes
low quality males cant fake the signal because they aren’t strong enough to overcome the handicap
what is the MHC
major histocompatibility complex 3.6Mb region on short arm of chrom 6 encodes immune system proteins repsonsible for transplant rejection most variable part of genome
how many bp is the MHC
where is it found
3.6Mb region on short arm of chrom 6
what does MHC encode
immune system proteins
what is the function of the MHC
recognise foreign proteins
present antigens to T cells
T cells recruit B cells
B cells produce antibodies
how many types of molecules do MHC makes
class 1 and class2
what can class 1 MHC molecules hold - why
class 1 MHC molecules can only hold short peptides because the binding site is closed off
what effect does MHC class 1 binding site being closed off have
class 1 MHC can only hold short peptides
which type MHC can hold short peptides
class 1 MHC can only hold short peptides
what molecules can MHC class 2 bind to
class 2 MHC molecules can bind to peptides of different lengths because the binding site is open at both ends
which MCHC molecule has a binding site open at both ends
MHC molecule class 2 has a binding site open at both ends
what effect does an open binding site on MHC molecule have
MHC Class 2 has an open binding site at both ends, means that peptides of different (longer) lengths can bind
what determines the number of peptides that can be recognised
the number of MHC alleles determines the number of peptides that can be recognised
what does the number of MHC alleles determine
the number of peptides that can be recognised
which type of MHC carriers are more disease resitant
MHC heterozygotes are more disease resistant
what is the effect of being a MHC heterozygote
you are more disease resistant as it may increase the diversity of antigens resented to T cells, creating a diverse T cell repertoire
why is it hypothesized that MHC heterozygotes are more disease resistant
MHC variants will have associations with specific pathogens - therefore less susceptible to disease
which MHC alleles are associated with disease resistance
HLA alleles - infectious diseases
what does MHC heterozygosity confer a selective advantage against
multiple strain infections
what do MHC class 1 and 2 molecules do
they present peptide antigens to T cells, initiating immune recognition of foreign antigens
name a disease that MHC hetrozygosity is effectively associated with
Hep B
what experiments have been done to show MHC heterozygosity does confer disease resistance
Salmonella in MHC heterozygote mice
what is the sexual selection hypothesis
females should prefer mates that produce favourable MHC genotypes for their offspring
- requires that females can know MHC type of potential mates and females maximize the heterozygosity of offspring
which hypothesis states females should prefer mates that produce favourable MHC genotypes for their offspring
sexual selection hypothesis
what is assortative mating
non random mating pattern in which individuals with similar genotype+/phenotypes mate with one another more frequently than would be expected under random mating
what type of mating is mating where two individuals mate more than would be expected under random condns
assortative mating
give an example of MHC-dependent disassortative mating
cycling women prefer the scent of MHC dissimilar men - but this wasnt the case for females on the pill
discuss the T-shirt study
females significantly prefer the odor of T-shirts worn by MHC-dissimilar males, although such preference was not found among females taking the contraceptive pill
what is the upsuck study
female orgasms help retain sperm by sucking it up into the uterus
how does sharing MHC alleles affect time to conception
sharing MHC alleles increases time to conception
