L3- Kinship + Sociality

Recap:

Constraints Hypothesis for the evolution of cooperation:

• constraint on independent reproduction→ drives grown offspring to stay at home

• offspring become helpers

• similar idea in eusocial insects

  

Benefits received from helping behaviour:

• direct fitness benefits:

  • current reproduction

  • increased future survival and reproduction (skills to be being a better parent)

• indirect fitness benefits:

  • increased fitness of relatives

    • better productivity (increase survival of brood)

    • better survival of breeders (reduce cost on parents)

• kin selection→ selection on traits due to their beneficial effects on the fitness of relatives

Applying IFT to the origin of social groups:

• IFT hypothesis→ high relatedness played a key role in the transition to eusociality

• eusociality→ true sociality, have non-reproductive casts that are sterile e.g. wasps, termites, bees, ants, shrimps

• Q→ how has kinship played a role in the evolution of eusociality?

  • monogamy hypothesis→ strict lifetime monogamy results in individuals with equal relation to their offspring and their siblings (r = 0.5)

    • eusociality will only occur when there is strict monogamy

    • the more females a male mates with, the lower the relatedness between the siblings

      

  • predict→

    • all eusocial species passed through a monogamy window in their evolutionary history

    • multiple mating evolved later after specialisation

  • results:

    • all eusocial lineages of the hymenoptera have passed through an ancestral monogamy window

    • polyandry occurs mostly on the right hand side- recent evolution and when the workers were already specialised for helping- hard to flip back to non-social

      

→ transition to eusociality was driven by high relatedness determined by strict lifetime monogamy:

• mammals-

  • predict- cooperative groups are monopolised by 1 male and female, same degree of reproduction in non-cooperative groups

  • in cooperative groups, there is nearly 100% reproductive skew, where reproduction is monopolised by 1 male and1 female, high relatedness in these groups

    

    → monogamy hypothesis works well for mammals

• birds-

  • significantly less promiscuity in cooperative species

  • the higher the level of promiscuity, the lower the proportion of cooperative nests

    

  → the frequency of promiscuity affects cooperative breeding evolving (but not as strong evidence)

→ the monogamy hypothesis applies to eusociality and may apply to cooperative birds and mammals

How important is kin selection?

• Question→ do species that have helpers live in groups made mostly of kin?

• Hypothesis- cooperative breeding has evolved in kin groups

• Methods→ phylogenetic tree of 18 cooperatively breeding mammal species

• Results→

  • ½ live in groups of same-sex kin

  • ½ live in groups of mixed same-sex kin and non-kin

    

  → kin ship has importance in cooperative mammal species but there are only a few species to study

• Birds-

  • have lots of families of cooperative taxa→ lots of independent evolutions of cooperation

  • mainly cooperative groups are made up of kin

    

  • another study found 85% of cooperatively breeding bird species are in kin groups:

    

→ kin groups predominate among cooperative breeders in mammals and birds but is not universal like eusociality in the hymenoptera

Is cooperation kin selected?

• early studies show a general association between productivity and group size (increasing in helpers) but this shows correlation, not causation

  

• need to account for:

  • confounding effects of territory/individual quality:

    • compared productivity of pairs with less helpers and the same pairs with more helpers

    • found no benefit of increasing male helpers and less benefits of increasing female helpers

      

  • direct benefits of helping under-estimated?

    • need to know about parentage- helpers could be reproducing themselves

    • calculated indirect fitness in wrens and found high levels of extra pair paternities→ males and helpers have low relatedness to the offspring

      

    • in seychelles warblers 44% of subordinates reproduce and 40% of young are due to extra-group paternity→ average helpers-brood r = 0.13, have low indirect fitness

      

  → need to reassess the role of kin selection

  • evidence for active kin discrimination

    • helpers work harder when they are more related to the brood, doesn’t show causal relationship though

      

    • there are more species that show positive kin discrimination but it is quite variable

      

    • positive correlation of helper effort and relatedness across 37 species of bird

      

  → good comparative and meta-analysis evidence for active kin discrimination

Kin selection has variable importance in the evolution of cooperation across species e.g. birds:

Summary:

• Transitions to sociality are associated with monogamy (Hymenoptera) or low promiscuity (mammals and birds), both of which cause high intragroup relatedness

• Kin selection is critical in the origin of eusociality (obligate social species)

• Among birds, groups in most social species are composed primarily (but not exclusively) of kin

• Kin selection not always important in facultative cooperative breeders, especially when there are no non-breeding helpers

Reflection:

• Define kin selection → traits are selected due to relatedness

• What is cooperative breeding? → breeding with helpers