Kin selection and co-op breeding Flashcards
Evolution of cooperative breeding
ECH Hypothesis (Emlen 1982) Independent breeding is constrained - Grown offspring delay dispersal and “stay at home” - Grown offspring help to rear later broods
Direct fitness - fitness component resulting from personal reproduction.
(i) Current reproduction (ii) Increased future reproduction - acquisition of skills/mate/territory - group augmentation
Indirect fitness – kin-selected fitness component from increased production of non-descendant kin.
(i) Increased fitness of relatives - increased productivity of related broods - increased survival of relatives through reduced reproductive costs
The relative importance of indirect or direct fitness benefits in the evolution of helping behaviour is still debated.
Major evolutionary transitions The evolution of life on earth can be viewed as a series of major transitions in complexity, for example: origin of chromosomes origin of eukaryotes origin of sex origin of multicellularity origin of social groups origin of human society/language
Each transition involves cooperation, so modern social evolution theory aims to understand each transition using the logic of inclusive fitness theory
See: Bourke (2011) Principles of Social Evolution, OUP
Eusociality ‘true sociality’, with
non-reproductive castes
Predictions:
(i) All eusocial spp. passed through a ‘monogamy window’
(ii) Multiple mating may evolve later, following specialisation
Why should individuals join together to become mutually dependent?
Hypothesis: High relatedness between individuals played key role in transition to sociality
Monogamy hypothesis:
Strict lifetime monogamy results in individuals who are equally related to offspring and siblings (both r = 0.5). Any small net benefit from raising siblings rather than offspring will favour cooperation and potentially eusociality.
In eusocial insects
… all eusocial lineages have passed through an ancestral ‘monogamy window’
Hypothesis: Cooperative breeding in birds has evolved in kin groups
Cooperative taxa
(84 families, 852 species)
55 families, 644 species
Cooperation in
non-kin groups
18% of families
8% of species
Cooperation in
kin groups
82% of families
92% of species
Riehl (2013) – 213 well-studied cooperatively breeding spp.
55% helped in nuclear family groups
30% helped in groups with mix of kin and non-kin
15% lived primarily with non-kin
85% total
Kin groups predominate among cooperative breeders
- the exceptions are generally cooperative polygamists where all individuals attempt to breed
Why is kinship so important?
Inbreeding avoidance reduces conflict within groups
And kin-selected helping is often assumed to be important
A sceptic’s view of evidence for kin selection
(i) Confounding effects of territory/individual quality?
Laughing kookaburra
(Legge 2000)
Productivity increases
with group size
But, compare productivity of same territories with different number of helpers in different years
Female helpers hindered!
(ii) Direct benefits of helping under-estimated?
Paternity in fairy wrens Superb fairy wren 72% EPP Splendid fairy wren 73% EPP
(ii) Direct fitness benefits are routinely underestimated
DNA technology has allowed a clearer resolution of relatedness in social groups, often with surprising results (e.g. fairy wrens).
The Seychelles warbler illustrates the effect of such information on assessment of the role of kin selection. Early studies on this species assumed close relatedness and an important role for kin selection (Komdeur 1994), but recent studies show low kinship and direct rather than indirect fitness benefits dominating (Richardson et al. 2002).
(iii) Costs of kin competition ignored
There may be negative as well as positive consequences of interacting with kin.
An individual’s inclusive fitness may be reduced by competition with kin (Griffin & West 2002). Such conflicts will be discussed in two later lectures.
In many species, some helpers are unrelated to recipients and it has been argued that in such cases, kin selection can’t operate. Helpers may make two kinds of decision: whether to help or not, and, if they do help, how hard to help. There is now good evidence from several species for kin discrimination in both decisions (e.g. Wright et al. 2010; and see next lecture).
A meta-analysis of kin discrimination studies (meta-analyses ask whether there is a consensus that can be drawn across studies on the effect of one variable on another, taking sample size into account) shows that on average, studies show significant kin discrimination (Griffin & West 2003). In addition, inter-specific variation in the effort that helpers expend in feeding broods is predicted by their mean relatedness to those broods (Green et al. 2016); i.e. in those species where helpers are close relatives of the recipient brood they generally work just as hard as parents do, but when they’re distantly related to the brood they work less hard, as Hamilton’s rule would predict.
Conclusions
There is some validity to the first two criticisms
(Confounding effects of territory/individual quality?- control for statistically or experimentally
(ii) Direct benefits of helping under-estimated? - need genetic analyses of relatedness )
, but both effects can be accommodated.
The latter two criticisms
((iv) Evidence for active kin discrimination? - good evidence
Costs of kin competition ignored? – see lectures 11 & 12 - many studies of intra-familial conflict )
have less validity because the conflicts in social groups are widely recognized, and there is now extensive evidence for kin discrimination.
Therefore, we can summarise the circumstantial evidence for kin selection as being strong (ubiquity of family structures) and the evidence from single species studies as being strong. However, we are still a long way from answering the question of how relatively important are direct and indirect benefits across cooperative species. Quite a few studies have calculated short-term measures of fitness (e.g. Emlen 1991; Richardson et al. 2002; Cockburn et al. 2008), and in most of these there is some role for kin selection, albeit sometimes minor. But, there are undoubtedly quite a large number of species where kin selection cannot explain cooperative breeding because groups do not contain relatives, especially in cooperatively polygamous species (e.g. dunnocks), and also in some joint-nesting species such as anis (Riehl 2010), yuhinas (Yuan et al. 2004) and guira cuckoos (Macedo et al. 2004). More studies are needed to fully understand the role of kin selection.
