Adelie penguin Case Study

Question 1

Sperm competition theory suggests that monogamous males should…

Answer 1

guard their mates and prevent them from copulating with extra-pair males (E.g. mallards do this)

Question 2

In some species, males may be unable to mate guard because of … or … constraints, or because his female is…

Answer 2

social, environmental, intent on gaining an extra copulation

Question 3

If males can’t mate guard, … and … of copulation (number of sperm inseminated) will determine who gains paternity (in birds)

Answer 3

timing, frequency1

Question 4

Frequencies of behaviourally successful copulations (cloacas touch) are high in…

Answer 4

non-guarding species (e.g. American kestrels)

Question 5

In American kestrels, males are unable to guard their mates at all times as they have to hunt to provide food for his female, who stays at the nest prior to laying. To compensate for this lack of mate guarding, male American kestrels copulate up to … times per clutch of offspring.

Answer 5

690

Question 6

When paternity is at stake, behaviourally successful copulations are only valid if…

Answer 6

sperm are transferred

Question 7

In captive zebra finches, … of behaviourally successful copulations fail (i.e. no sperm transfer). In chickens, … fail. If it is in a male’s interest to inseminate his partner frequently, why do males fail to transfer sperm after courting, mounting and copulating? well well well

Answer 7

36%, 50%

Question 8

Male Adelie penguins engage in a mean of … copulation attempts per breeding season. However, less than … of these attempts result in successful insemination of sperm. Why would a male not transfer sperm when he had the chance? This seems an evolutionary paradox

Answer 8

57, half

Question 9

The study took place at … … in …

Answer 9

cape bird, Antarctica

Question 10

About … pairs of Adelie penguins breed at the northern rookery at cape bird

Answer 10

300,000

Question 11

Adelie penguins are relatively long-lived, socially … seabirds. … arrive at the breeding grounds first and set up a nest site, usually reclaiming the one they sed the previous year by doing what is known as an … display. … arrive a few days later and tend to pair up with their partner from the previous year, if they are present.

Answer 11

monogamous, males, ecstatic, Females (if not, she pairs up with the nearest available male, but switches mates to rejoin previous partner if he returns late)

Question 12

Both sexes defend the nest against intruders. the female lays … eggs and a … if one is lost

Answer 12

two, third

Question 13

The male takes the first long … shift, while to female goes off to …. She comes back after 10-12 days and takes over while he goes out to sea (for another 10-12 days).

Answer 13

incubation, feed

Question 14

They must guard the eggs from attacks by predators such as … … (main predators of eggs and young chicks)

Answer 14

antarctic skua

Question 15

After around … days of incubation, the eggs hatch. The parents swap over …, bringing … into the nest for the chicks to feed on. After the 2-3 week guard stage where the parents stay with their offspring, the parents have to do more feeding and both get food for the chicks, which gather in …

Answer 15

35, daily, krill, creches

Question 16

When the adults leave on foraging trips they have to avoid predators such as…

Answer 16

leopard seals and orcas

Question 17

At the centre of the northern rookery there is a group of breeding pairs which were banded with flipper bands with … …, readable with …, to tell the individuals apart.

Answer 17

unique numbers, binoculars

Question 18

Data set of around … copulation attempts. The male initiates the copulation by doing a head bowing courtship display. If the female accepts his advances, she lays down and he … her. He then treads slowly down her back and curls his tail round and their … come together.

Answer 18

10,000, mounts, cloacas

Question 19

For each copulation attempt, the … of the male and female and the … of the attempt (e.g. cloacal contact, reason for why not achieved e.g. male fell off) were recorded. Also whether male ….

Answer 19

identity, outcome, ejaculated (as can see ejaculate in female’s cloaca afterwards)

Question 20

The female rhythmically … her cloaca to draw sperm in.

Answer 20

contracts

• shows whether sperm transfer was successful

Question 21

What are the 3 possible outcomes after cloacal contact?

Answer 21

1. An ejaculate enters (is drawn into) the female’s cloaca
2. An ejaculate misses (may be due to female or male)
3. No ejaculate is seen

Question 22

… … were examined to be sure that no insemination was occurring when it looked that way: found to be the case

Answer 22

cloacal smears (stained sperm on under microscope)

Question 23

This shows that observations of cloacal contact alone are…

Answer 23

not a reliable indicator of sperm transfer

Question 24

There are two potential sources of sperm competition in socially monogamous species: … and … …. In Adelies, 15% of sample of 47 females showed… and 10% were involved in successful…

Answer 24

EPCs, mate switching (female has 2 or more partners and copulates a number of times with each male), mate switching behaviour, extra-pair copulations (could be imitated by either sex)

Question 25

If a female does not want to mate with a paired or extra-pair male, she can…

Answer 25

simply stand up and dislodge him or keep her tail pressed to the ground - males never successfully force matings - so females are in control of who mates with them

Question 26

Adelies are the first bird species to display … behaviour

Answer 26

prostitution

Question 27

They exchange extra copulations for … …

Answer 27

nest material

Question 28

Adelies use small stones to build … on which the female lays her eggs - the benefit of collecting and defending a large pile of stones is realised in the springtime when … can inundate the colony. Pairs with inadequate stone platforms are likely to lose their eggs and chicks. Stones are collected by both males and females and even stolen from other birds (met with aggressive response). Females engage in prostitution with …-… males for a source of stones to improve their nest and increase their offspring’s chances of survival (+ good genes? single stones actually don’t give much benefit themselves), while the EP male gets the fitness benefit of potential fertilisation of the female’s egg, without even having to look after the young.

Answer 28

platforms, meltwater, extra-pair

Question 29

average male: 57 attempts, 42 cloacal contacts, 25 inseminations (under half)
Sperm competition is a real risk for pair males in this species - so why do they not ensure insemination at every opportunity (especially as they will be looking after the young)?

Answer 29

Nearly a quarter of cases of cloacal contact don’t even end in ejaculation for the male.

• maybe because sperm and seminal fluids are limited and take time to regenerate
• or because the birds allocate ejaculates strategically to maximise paternity

+ look at graph at 28:00 lecture 8)

Question 30

If sperm/seminal fluids are limited, we would predict that…

Answer 30

the average time between two successful ejaculations would be longer than the average between a successful followed by a failed ejaculation.
- There was significant difference (about 30 mins difference) - supports the idea that semen is limited - males must replenish sperm stores before they can ejaculate again

We’d also predict that the intervals between ejaculations would increase towards the female’s fertilisation period
- data supported this

Question 31

What might males do if sperm is limiting?

1. carry on copulating regardless until they become sperm-depleted
2. conserve sperm and allocate ejaculates strategically to maximise paternity

Answer 31

yes.

Question 32

Found no evidence that males produce more sperm when…

Answer 32

the time since the last ejaculate had been longer

- so sperm depletion does not occur in these penguins

Question 33

If males allocate sperm strategically then we’d predict that they’d be more likely to transfer sperm in…

Answer 33

EPCs than in pair copulations

Question 34

This is because males are not…

Answer 34

guaranteed to have another opportunity to inseminate that EP female

Question 35

If males are unable to allocate ejaculates strategically then they should have the same…

Answer 35

ejaculatory success, regardless of who they copulate with

Question 36

Found that behaviourally successful EPCs were significantly…

Answer 36

less likely to result in failed ejaculation than pair copulations (males almost never failed to produce an ejaculate in EPCs)

Question 37

Males were significantly more likely to terminate … copulations than … copulations, whereas the reverse was true for females

Answer 37

pair, extra-pair

Question 38

So males do indeed…

Answer 38

strategically allocate ejaculates to extra-pair females.

Question 39

By what mechanisms could strategic allocation be achieved?

1. Males attempt EPCs only when…
2. Males … ejaculates from their partners to … sperm for use in EPCs

Answer 39

they have sperm available, withhold, conserve

Question 40

If males withhold ejaculates from their partners, we’d predict that males that engage in EPC attempts will ejaculate … often when achieving cloacal contact with their partner than males that don’t engage in any EPC attempt.

Answer 40

less

• found this to be the case
• appears that males withhold sperm from their pair female in order to have ejaculates available for extra-pair copulations
• however would find the same result if, by engaging in EPCs, males couldn’t produce ejaculates in pairs due to running out of sperm - found not to be the case as those who ejaculated during EPCs were not found to ejaculate less during PCs than those that didn’t ejaculate during EPCs - so withhold rather than running out

Question 41

There is a conflict between allocating sperm to … and protecting pair … - a male that withholds sperm from his partner may risk losing paternity of her offspring. Adelies are … breeders so all females will be simultaneously fertile over a limited period (for … effect). So if a male wants to engage in EPCs he must do so during his own female’s … period. As paternity is determined by … copulation, the important question is who gains the most copulations: the pair male or a rival male?

Answer 41

EPCs, paternity, synchronous, dilution, fertile, frequent

Question 42

If we look at the relative frequencies of copulations involving females that have extra-pair partners, we find that pair males gained significantly more … … than their rivals: despite having limited sperm reserves and allocating some ejaculates to EP females, males appear to do well in achieving frequent copulations with their pair female. Is this enough to ensure paternity? Do pair males father the chicks that they raise?

Answer 42

successful inseminations

Question 43

Blood samples collected from … parents (pair males and females) and their … and carried out a … analysis. of the 46 families analysed, only … contained an EP chick (2.2%). Neither of the two chicks in this family were fathered by the male that … them - means 3% of chicks overall were fathered by a male that did not raise them.

Answer 43

putative, offspring, paternity, one, raised

Question 44

Despite being under constraints of sperm availability, male Adelie penguins appear to be able to … EPCs and copulations that involve initial males, simply by copulating ….

Answer 44

outcompete, frequently

Question 45

So why do males bother to allocate sperm to EP females when they are so unlikely to be successful in fathering their offspring?

Answer 45

The potential benefits of fathering EP offspring are so high that even if there is even only a slight chance of winning, males are likely to attempt it. 2% of extra pair fathers show there is a slight chance of success. if we assume that out of the 300,000 pairs at cape bird, 120,000 males are producing offspring, that means there are 2400 extra-pair males that achieve extra pair offspring - considerable potential benefit.