Case study - Accentor mating systems

Question 1

Focusing on two species of the same genus:

• …
• … accentor

Answer 1

dunnock, alpine

Question 2

Dunnock study started by Nick Davies in the Cambridge university botanical gardens in the 1980s.

Answer 2

Represent

Question 3

Alpine accentor study in the central pyrenees stemmed from the dunnock study, and was also led by Nick Davies

Answer 3

.

Question 4

Dunnock mating systems are extraordinary in their ….

In a single population of dunnocks, you will likely see …, …, …. and ….

Answer 4

variability,

polygyny, polyandry, polygynandry

See graphs and listen to slide 7 lecture 13

Question 5

Resources are expected to determine … dispersion, as the rate at which females can turn resources into offspring defines her reproductive rate. In turn, male dispersion is determined by…

The combination on female and male dispersion is what determines the … … in any given species

Answer 5

females, female dispersion

mating system

Question 6

The hypothesis in dunnocks is that the mating system depends on female … size and hence the ability of males to … them.

Answer 6

territory, defend

Question 7

If we look at the average female territory size in the main 3 mating systems (monogamy, polygyny, polyandry), on average, monogamous and polygynous females have relatively … territories (… ha) and polyandrous females have relatively … territories (…ha). This correlational test supports the hypothesis.

Answer 7

small, 0.25, large, 0.55 (over double the size)

Question 8

To confirm the hypothesis, an experiment must be conducted:

Some females provided with a feeder (supplementary food), meaning their home range would reduce in size as they would not need to travel as far for food. Other females had no food supplementation (control group). What was the effect of changing the female territory size on male territory and the emergent mating system?

Answer 8

Female territories were, as expected, smaller when supplementary food was provided. Male territories, on the other hand, were unaffected by the distribution of resources (as predicted by general mating system model). The contraction in female territory size meant that a single male was better able to monopolise a female territory and therefore the likelihood of polyandry was lower. The number of males per female was significantly reduced. This supports the hypothesis of the general mating system model.

Question 9

Alpine accentors do not have the variability in mating systems seen in dunnocks. In fact, all alpine accentors are …. There is typically … between female ranges. On average, there are … females and … males in one territory with a dominance ….

Answer 9

polygynandrous

overlap

3, 3, hierarchy

Question 10

Why do we see such differences in the dunnock ad alpine accentor mating systems?

(see table on phone for data on differences)

Answer 10

Dunnocks in the Cambridge botanical gardens have a very predictable habitat (varies through year) and can always rely on being able to find enough food on their small ranges. In contrast, high altitude alpine environments are very unpredictable (in terms of weather conditions and therefore food(insects)/resource availability and distribution)

There are fewer invertebrates, for most of the year, in high altitude environments, therefore accentors must explore larger territories in order to forage enough food.

There is also much higher variablity in resources at high altitudes

Question 11

There is clearly a strong … … for mating system variation.

Answer 11

ecological basis

Question 12

The basic breeding biology of dunnocks and alpine accentors is very similar:

• female … nest
• she lays 3-5 blue eggs
• she … them
• both sexes feed the chicks and …
• the pair often have … broods per year

Answer 12

builds, incubates, fledglings, two

Question 13

Paternity and parental care in monogamous dunnocks:

Once a female becomes fertile and has made a nest, she is fertile for around a week before egg laying. During that time, males closely … their females, staying very close to them (usually ~10m) and driving off other males. During this period, females solicit copulations from the male at a very high rate (~every 15 minutes). The males peck at the female’s cloaca for up to a minute before copulation, waiting for the female to eject a small droplet containing … from earlier matings. Copulation itself is very brief. Guarding males … matings with the female.

Answer 13

guard, sperm, monopolise

Question 14

Monogamous male dunnocks typically gain … paternity of the brood that they are raising (measured using DNA fingerprinting). Males share chick feeding equally with the female.

Answer 14

100%

Question 15

Polygynous male dunnocks (male defends territory of two different females, each living on exclusive territories) … and copulate with two females. This can be difficult, especially if both females are fertile synchronously. When his broods hatch, the male will either … in the brood of one female but … the other, or…

Answer 15

guard, invest, not, divide their investment between the two.

Question 16

Polyandrous dunnocks (single female territory, 2 males living in it):
... intensely compete to copulate. There is a ... ... where alpha males secure the most copulations but females may sneak copulations with beta males.

Male parental care varies:

• alpha males always care
• beta males sometimes … …, but may work as hard as the alpha males

Answer 16

males, dominance hierarchy

do nothing

Question 17

Why does male investment vary so much?

Answer 17

In polyandry, paternity is often shared between males, and paternity varies between broods. Beta males with more of their own chicks (higher paternity) in a brood are significantly more likely to provision food for that brood.

Question 18

How do males know they have paternity?

Answer 18

They assess their probability of paternity according to their share of the matings (as the higher the proportion of copulations they secured, the higher the average percentage of the brood sired by them will be).

We find that the proportion of feeds provided to the brood by the beta male is positively correlated with the proportion of matings by the beta male. (remember this is just correlation)

Question 19

This correlation could also potentially be due to quality of beta males - those of higher quality are able to secure more matings and have more energy for foraging and food provisioning. An experiment is required to dismiss this notion.

When alpha males are temporarily removed from their polyandrous groups, and therefore beta males are allowed to mate with the female unhindered. Found that…

Answer 19

the proportion of male feeds provided by the beta male was indeed closely correlated with the proportion of matings by the beta male (which, importantly, was manipulated by the experimenters).

Therefore in dunnocks, the amount of paternal care is dependent on their relative mating success (a good cue of their paternity)

Question 20

In Alpine accentors, parental investment is, again, positively related to their relative … ….

Answer 20

mating success

Question 21

There is also conflict among ….

Answer 21

females

Question 22

In any territorial bird, territorial interactions are very likely, often become escalated …. In the majority of species, most of these fights are between … …. However, they are also very common in …, in the case of the dunnock. They are particularly common in … mating systems. These occur either at the territory …, or occasionally if one female approaches the other’s nest and tries to disturb her incubation behaviour. Sometimes these contests cause … to the females, which occasionally results in ….

Answer 22

fights, neighbouring males, females, polygynous (single male, two females), boundary, damage, desertion

Question 23

The desertion rates of females are highest in … mating systems in dunnocks, followed by … then … mating systems

Answer 23

polygynous (39%), monogamous (20%), polyandrous (8%)

Question 24

This territorial behaviour may benefit females if…

Answer 24

it allows them to monopolise the male territory and therefore the paternal care of the male (no longer has to share with another female)

Question 25

Why should a polyandrous female attempt to copulate with both males in her group?

Answer 25

to gain their parental investment (if they don’t mate, they won’t invest)

• she should aim for a 50:50 share of matings with the alpha and beta males, as this maximises the total male contribution to her brood
• this appears to be what they do

Question 26

Female alpine accentors attempt to gain as much male investment into their broods as possible by…

This is because there are 3, or sometimes 4, females competing for the investment of and copulation with the male(s) in their polygynandrous systems.

Answer 26

copulating up to 1000 times per clutch (to convince males they have some paternity). To cope with such a high copulation rate, males have the largest testes relative to their body mass of pretty much any bird species (8% of body weight) and a large cloacal protuberance.
Females solicit copulations from their male guards with a bright red cloaca every few minutes during their fertile period.

Question 27

Fertile female alpine accentors also … to attract males to copulate.

Answer 27

sing (complex)

Question 28

There is a lot of variation in paternal effort invested in broods in dunnocks. Some females have no male help at all (when males in polygynous systems are helping another female only). Some females in polygynous systems have part time male help (split between their brood and another female’s). Monogamous and sometimes polygynous or polyandrous females get full-time male help. In polyandrous systems, if a female has successfully mated with both males, she may get both helping full time to raise her brood. This difference in the amount of ale help has knock on effects for the brood itself:

Answer 28

• starvation is highest with no male help (81%) and decreases as males help more and more males help.
• same goes for number of fledglings produced from a nest
• see photo on phone for stats

Question 29

We see a similar effect in alpine accentors: as the proportion of feeds by males increases…

Answer 29

the average mass of nestlings increases, which is likely to increase their chance of survival

Question 30

We can use this information to judge what male and female reproductive success (per season) looks like in the different mating systems. We see that, for females, polyandry (both males feeding) is the most successful strategy, followed by monogamy, then polygyny. For males, the reverse is true. The most successful strategy is polygyny, followed by monogamy then polyandry (both males feeding). Therefore there is a … between the sexes in the ideal mating system strategy. For both, … is a sort of compromised solution that doesn’t maximise their own reproductive success.

(see photo on phone again)

Answer 30

conflict, monogamy

• Females, when the opportunity arises, should opt for polyandry. Males, when the opportunity arises, should opt for polygyny