Sex Flashcards
What is the difference between anisogamy and isogamy?
Anisogamy is when there are two strict sexes with different sized gametes. Isogamy is when there are no sexes and gametes are the same size. The gametes will fuse with those that have a different marker to their own.
What is the difference between simultaneous and sequential hermaphroditism?
Simultaneous hermaphroditism is when an organism has both male and female parts e.g. Hamlet fish take turn playing the male and female roles when mating. Sequential hermaphroditism is when an organism changes sex during its lifetime.
What did John Maynard Smith propose was the two-fold cost of sex?
A sexual female will spend 20 units of energy but only produce 50% of her genome in the next generation, whilst an asexual female spends the same amount of energy and produces 100% of her genome in the next generation.
How can a mutation impact asexual lineages?
When a mutation occurs in an asexually reproducing female, she will pass it down to all her offspring and their offspring etc. If there is selection against the mutation, the whole lineage will loose in competition to other lineages without the mutation and go extinct.
Describe the Red Queen hypothesis using an example.
The hypothesis states that individuals directly benefit from being different from their parents. Parasites are constantly evolving to be more efface tat infecting the host, so having a different biochemical makeup to others in the pop might make you less vulnerable to infection.
E.g. water snails from different lakes were exposed to parasites either from their own lake or the other lake. Parasites were best at infecting snails they had co-evolved with. The more parasites there were, the more common sexual reproduction in snails was.
How does MHC act as evidence for the Red Queen hypothesis?
Animals tend to prefer mates with genetically dissimilar MHC, which makes their offspring more different to them at the MHC and gives them an advantage to parasite resistance.
What is the difference beween the efficacy of selection (EOS) hypothesis and the red queen hypothesis (RQH)?
The EOS suggests that the variance in reproductive success of sexual offspring must be greater than that of asexual offspring. The RQH suggests that average reproductive success must be higher for sexual compared to asexual offspring.
Outline the process of the evolution of anisogamy.
- Two mating types of equal gamete size
- Larger than average gametes have some advantage (e.g. more likely to be found by another gamete)
- An individual will produce less larger gametes due to taking up more energy
- There is some random, heritable variation in gamete size that starts the process
Define sexual dimorphism. What is Darwin’s explanation for this?
Sexual dimorphism is the difference between male and female forms in the same species. Darwin suggested this was due to sexual selection - natural selection on the ability to gain mates (even when t is detrimental to other aspects of fitness).
What is Bateman’s principle?
It suggests that male reproductive success increases with each additional partner to a greater extent than for females.
How does varinace in reproductive success differ for males and females?
variance in reproductive success is greater for male than females - females will always find a partner to mate with but the number of offspring produced is limited. There is no limit for males, but females are choosy and will only mate with the best.
How does Bateman’s principle explain intrasexual competition?
Fighting should only occur when C
Describe Moller’s (1988) study on onrnamentation.
Moller (1988) either lengthened or shortened the tails of barn swallows. The birds with shorter tails took longer to find a mate.
The tails of the lengthened group were longer than any naturally occurring tails, but males don’t grow tails to this length because it is costly.
Males elfvoud tail elongation to the point where any extra mating they gain from growing the tail any more would be too costly.
Describe how the sexy son hypothesis works in relation to elongated tails in birds.
if there is an initial slight preference for longer tails, the preference for the long tail and the length of the tail will co-evolve to be greater over time. Females with strongest attraction to long tails will mate with males with the longest tails - creates genetic correlation between preference for trait and the trait. Selection favours a stronger preference because this produces sexier sons. As tails get longer, the sons get sexier, and the fitness payoff for having a greater preference increases.
