Lecture 6 - evolutionary history

Question 1

what is cooperative breeding?

Answer 1

systems where more than 2 individuals in a group care for young

Question 2

cooperative breeding evolved by a 2 stage process - the ecological constraints hypothesis (Elmen 1982) - what are the stages ?

Answer 2

STAGE 1 :Ecological factors (no territories), demographic factors (no partners ), or low chances of successful reproduction constrain independent breeding, causing grown young to delay dispersal and ‘stay at home’ on their natal territory

STAGE 2: Fitness benefits of helping exceed those of not helping, so helpers provide care for a brood. Helpers may gain inclusive fitness benefits either directly (by increasing their own current or future personal reproduction) or indirectly (by increasing the fitness of non-descendant kin; i.e. kin selection)

Question 3

what is intraspecific evidence for the ecological constraints hypothesis?

Answer 3

• there is strong observational and experimental support for the ECH showing that when constraints are relaxed, cooperation decreases

Question 4

what is the issue with the ECH?

Answer 4

most species have constraints on breeding but are not cooperative so what is the difference between cooperative and non-cooperative breeders

Question 5

what have analyses identified as the critical differences between cooperatively breeding species and non-cooperative breeders and which group is good to analyse?

Answer 5

strong phylogenetic signal in cooperative breeding, and the multiple evolutionary transitions to and from cooperative breeding in the avian phylogeny, in particular, makes them very well suited to comparative analyses helps us to see if we can identify a trait which correlates with each of these evolutionary transitions and why they occurred -

couldn’t do the same with mammals because there isn’t as many independent evolutionary events - only seen within a few lineages

Question 6

what are the 4 hypothesis to explain cooperative breeding?

Answer 6

1) ecology constrains breeding 2)Benefits of philopatry select for delayed dispersal
3) Life history traits predispose some lineages to cooperate
4) Cooperative breeding is associated with brood parasitism

Question 7

give examples of the hypothesis ‘ecology constrains breeding’

Answer 7

African starlings - 45 spp in Africa - some are cooperative and some are not - looked at the habitat these species lived and looked for an association with cooperation - found that all cooperative species were savannah living and non-savannah living = non cooperative
thought that cooperative breeding evolves in unpredictable environments
- looked on a global scale and found cooperative breeding associated with greater variation in rainfall i.e. unpredictable environments

Question 8

what is the issue with the evidence for the ecology constrains breeding hypothesis

Answer 8

there is a huge amount of variation - it is a weak hypothesis - little predictive power

Question 9

describe the western blue bird example as evidence for benefits of philopatry selecting for delayed dispersal

Answer 9

Sons usually spend the winter on their natal territory, and may help in following year - mistletoe is key resource they feed on

• In some territories they would manipulate the amount of mistletoe available - less sons would stay when the mistletoe was reduced - less benefits = individual more likely to leave
• Not to do with constraints just to do with benefits at home

Question 10

describe the green woodhoopoe examples evidence for benefits of philopatry selecting for delayed dispersal

Answer 10

• Both sexes may stay at home for several years before dispersing to breed
• Females (but not males) who
• stay for a while have higher Lifetime reproductive success
• suggested there is the benefits to the female staying at home for longer and learning how to be a food mother etc

Question 11

how do the ecological constraints hypothesis and benefits of philopatry hypothesis differ ?

Answer 11

only in the emphasis placed on the pros and cons of staying/leaving
Constraint on dispersal = Benefit of staying

Question 12

describe the life history traits hypothesis?

Answer 12

proposes that certain lineages are predisposed to be cooperative because they have ‘slow’ life histories (i.e. long-lived, small clutches) so the turnover in breeding vacancies is low. Lineages with ‘fast’ life histories (short-lived, large clutches) have high turnover and tend not to be cooperative

Question 13

what are the 3 key life history traits looked at when understanding the hypothesis?

Answer 13

• Longevity (long life span) - if it is short there is a constant turnover of breeding vacancies opposite for long
• clutch size - slow life history = small clutches - opposite for long
• migratory - if they leave the reproductive area every winter there is a lot of opportunity for young breeders

Question 14

what is a problem with the life history traits hypothesis?

Answer 14

when you look at distributions you find there is a strong biogeographic bias of cooperative breeding in tropical areas- might just be in tropical regions life history is longer
-It’s hard to distinguish life history from phylogeny and biogeography

Question 15

what is an example of the hypothesis that cooperative breeding is associated with brood parasitism?

Answer 15

• superb fairy wren parasitized by horsfields bronze cuckoo
• For cuckoos if they live in a group there will be more food = advantage
• For suberb fairy wrens it is better to be in a group because there is more protection against this happening
• parasites prefer cooperative breeders because the chicks are heavier and more likely to feldge
• on the other hand more time is spent mobbing cuckoos in large groups that cooperative breed

Question 16

what did they find on a global scale for brood parasitism and cooperative breeders?

Answer 16

found that global distributions of cooperative breeding and obligate brood parasitism match
-Hosts of brood parasites are more likely to be cooperative breeders…but direction of association is uncertain - hard to demonstrate causation e.g. does parasitism select for cooperative breeders etc

Question 17

3 reasons why predicting sociality is so difficult?

Answer 17

1) diverse social systems - is hard to define cooperative systems
e. g. you can find; monogamy + non-breeding helpers, polygamy + non-breeding helpers and cooperative polygamy
2) diverse constraints - when you look at species level analyses the ecological constraints vary massively e.g. could be food, nest cavities , mates etc- so any broad level analysis will run into this problem
3) phylogeny, biogeography and life history traits - There is a strong phylogenetic component to cooperative breeding in birds and mammals. Some families are composed entirely of cooperative breeders, some have none, and in some lineages cooperative breeding has evolved and then been lost. Phylogenetic analyses are fraught with difficulty because some taxa are found only in particular environments, and because life history traits are highly conserved within families, so these traits will be confounded with phylogeny