Sperm Competition Flashcards
What is sperm competition?
The competition within a single female between the sperm from two or males over the fertilisation of the ova.
Selection arises, from the product of polyandry.
Overt male:male competition ultimately functions to…
Avoid sperm competition
Enhance the success of self’s sperm
What are the behavioural adaptations for sperm competition?
Mate guarding - Natural soapberry bugs show plasticity in mate guarding duration depending on risk of sperm competition from OSR.
Female mate manipulation - Anti-aphrodisiacs, seminal fluids and mating plug.
Rival sperm removal - Sperm removal allows fertilisation to be almost 100% in some odonates, interrupted mating experiments show different stages of copula in Mnais pruinose
How does spermatogenesis affect sperm competition?
Multi male primates have testes sizes that are greater than pair-living or single male species.
Polyandry goes up with adult density (OSR).
Males divert resources into making more sperm, males produce and ejaculate more sperm.
How does sperm number influence sperm competition?
Copula duration = number of sperm transferred
More sperm transferred = more fertilisations
Means relative sperm number important
Raffle principle
How does sperm size influence sperm competition?
Sperm competition drives up the evolution of sperm length - conflict with anisogamy theory.
Sperm quality traits evolving within quantity.
Flour beetles evolved for 77 generations under either female biased OSRs (low sperm competition) or male biased OSRs (high sperm competition)
Male biased OSRs became more competitive and sperm got bigger.
How does sperm mobility influence sperm competition?
Males with faster sperm win
How does sperm cooperation affect sperm competition?
Sperm heads are hooked in wood mice, which form sperm trains and allow for greater velocity.
How does sperm gigantism affect sperm competition?
Significant association between sperm length and female sperm storage site size across Drosophila species.
Females evolved with long and short tracts and males with long and short sperm.
Compete L vs S males in L v S female tracts
Long sperm males more competitive in long female tracts and short sperms more competitive in short female tracts.
What is the sperm competition paradox?
Anisogamy selects for lots of tiny sperm, but sperm competition selects for larger sperm.
