invert sex + reproduction 2 Flashcards
lecture 10
how is sexual cannibalism possibly be adaptive for males
males eaten by females go onto fertilise 2x many of her eggs as those not eaten by her
he’s effectively fertile if he’s used up both of his palps and 80% of males never find a receptive adult female
how does this behaviour function in sexual cannibalism
copulation is twice as long in cannibalism cases but sperm transfer is quick and happens early
females are more likely to reject future mates if they’ve eaten a previous mate already
what is males response to the cannibalism
males have evolved to target ‘one moult before adulthood’ females, tearing away a section of their cuticle to access their spermathecae. they store the sperm and use it later
damage doesn’t reduce females reproductive success and in the wild, mating early may increase average reproductive success
how sperm characteristics are selected for by sexual selection
aiming for them to be very cheap and very abundant
there are remarkably complex genitalia in males and females so why are male genitalia so complex
lock and key hypothesis
sexual selection
sperm competition
with female insects storing for up to 28 years, sperm competition and cryptic female choice is a major problem for males
solutions for sperm competition
mate guarding
scraping previous males sperm out of the females spermatheca
toxic sperm
mating plugs
sperm competition - mate guarding in damselfies
males scrapes out as much as possible of any previous males sperm and injects his own
he hangs onto female long after copulation until after she’s laid eggs so no male can remove his sperm
once the eggs are laid, he can do no more to ensure paternity so leaves
Parker 1970 mate guarding
allowed females to mate with 2 males each but 1 had irradiated - could fertilise eggs but not hatch
1st male normal, 2nd male irradiated - 20% eggs develop
1st male irradiated, 2nd male normal - 80% eggs develop
problems with mating plugs
often removable
leaving parts of your body behind when you leave can be bad for your health
battle of the sexes - haplodiploidy
aim of each individual is to maximise genetic contribution to next generation
haploidiploidy may evolved as result of females trying to achieve this with their sons
females develop from fertilised egg, males develop from unfertilised eggs
battle of the sexes - cloning instead of sex
electric ant exploits haploidploidy
workers are produced as normal, likely because sex has major advantages
but queens clone themselves to make the colony’s vigin queens and kings clone themselves to make the colony’s virigin kings
so gene pools never meet in reproductive caste
2 fold cost of sex
cost of having to have males
cost of only passing half of ones genes to ones offspring
2 fold cost of sex and telescoping generations
asexuality may bring potential to telescope generations
sex, asex and telescoping generations
many aphids spend spring and summer breeding asexually and only start reeding sons in autumn
population then has 1 sexually reproduced generation before winter is spent as dormant eggs
why a 1:1 ratio
evolutionarily stable strategy - ratio of investment in offspring thats important
local mate competition
if males find it easy to find mates, their mother should have more daughters than sons
the easier it is to find mates, more extreme sex ration can be
local resource competition
may occur when relatives compete for resources in some way
local resource competition - honey bee
ratio of sexual is a few thousand males per potential queen
resource is the colony - only 1 daughter queen can inherit the colony so its wasteful for the mother queen to produce more than a few daughter queens
