Adélie Penguins Flashcards
Sperm Competition
The competition between the sperm of two
or more males inside the female’s reproductive tract
Male mallards mate guard to prevent their female copulating with an extra-pair male
If males can’t mate guard, timing and frequency of copulation will determine who gains paternity
American Kestrel
Up to 690 copulations per clutch
But do all behaviourally successful copulations result in sperm transfer?
Zebra Finches:
36% of copulations fail
Chickens:
50% of copulations fail
Why would a male not transfer sperm when he had the chance?
So he can reserve sperm for extra pair copulations
Fiona went to Antarctica New Zealand at Cape Bird.
300 thousand pairs of penguins. Long-lived, socially monogamous.
Adélie penguin’s main predator are arctic skuas.
They reclaim their last seasons mating site, do an ecstatic dance. Both species defend the nest. Female lays 2 eggs (+1 if an egg is lost). 10-12 days shift finding food. 35 days incubation. Then 1 day shift hunting krill.
The chicks gather in creches. Adults run the gauntlet at the ice edge where there are leopard seals.
Fiona put flipper bands on the birds at pre-laying season. Males head-bow courtship.
If successful the cloacas come into contact.
Recorded success and whether the male ejaculates. Can see the sperm on females cloaca.
Female will stay in laying down position, contracts her cloaca and draws the sperm inside. Possible Outcomes: An ejaculate enters the female’s cloaca An ejaculate misses No ejaculate is seen
Fiona examined cloacal smears (inverted the cloaca to get the samples) then stained sperm to see if there is sperm transfer
If males are monogamous then they don’t compete for paternity. However, there are two sources of sperm competition: EPCs (9.8% females do it) and mate switching (14.9% females do it).
Either sex initiates EPCs.
But the female has most control over copulation, as she can dislodge male or keep tail over cloaca
Prostitution in Adélie penguins
Nesting sites are made of stones piled up. Will initiate EPC and then take a stone from his nest
Possible Benefits of Prostitution Behaviour
Male benefits - extra offspring
potential mate
Female benefits - a source of stones
fertility assurance
good genes
Sperm Competition is a real risk for pair males……so do they ensure insemination at every opportunity? Outcome of cloacal contact
57 attempts
42 cloacal contacts
25 inseminations
Outcome of cloacal contact
Ejaculate enters cloaca 59%
Ejaculate misses 18%
No ejaculate seen 23%
Inter-ejaculate Interval
Should decrease with time:
Predicted pattern if responding to Sperm Competition
Inter-ejaculate Interval
Should increase with time:
Predicted pattern if sperm is limited
What might males do if sperm is limiting?
- carry on copulating regardless
2. conserve sperm and allocate ejaculates strategically
Zebra finches and house sparrows have limited sperm supplies
Sparrow resupplies sperm during night
Prediction: If males allocate sperm strategically they will
prioritise EPCs over Pair Copulations
By what mechanism could strategic allocation be achieved?
- males attempt EPCs only when they have sperm available
2. males withhold ejaculates from their partners to conserve sperm
Do pair males father the chicks they raise?
Extra-pair broods = 2.2% (n=46)Extra-pair chicks = 3.0% (n=67)
Male Adélies have limited semen supplies
Males withhold ejaculates from their partners and strategically allocate them to extra-pair females
Pair males gain the most copulations and father the offspring they raise
Males ter,inate pair mountings more than EPC mountings
But females disrupt EPCs more than pair copulations
Males withhold sperm and allocate it to EPCs
But they could lose pair paternity, therefore only engage in EPCs after eggs have been laid
