I) Comparing and contrasting kin selection with reciprocal altrusim

Reciprocal altruism and Kin Selection are not mutually exclusive hypothesis and both may influence whether animals within a group cooperate with one another.

This can confuse studies that attempt to define whether one or the other is reponsible for

Consider the conditions that promote reciprocity:

B >> C

Individuals exposed to many altruistic opportunities

Cheaters can be recognized and selectively unaided

Now consider the conditions that promote kin selection

High levels of relatedness

Kin recognition

B > C

Notice the similarities:

Both require high B/C ratios

Both require some form of recognition (of kin or cheaters)

Also, many of the factors that may promote high levels of relatedness and kin recognition (limited dispersal, high levels of association, etc) also fufill the conditions for reciprocity (many opportunities to interact)

Thus, in many groups, it may be that both kin selection and reciprocal altruism are positive feedback mechanisms to promote group cohesion and stability, this in turn creates conditions that enhance the effects of kin selection and reciprocity

II) A look at cooperation at its most apparent: Helpers at the nest and Eusociality  

Cooperation can be expressed at various levels. We can define increasing levels of cooperation, but this is a continuum, not a set of clear categories

Solitary: no cooperation (the rule rather than the exception... even when you include parental care)

Subsocial: minimal cooperation, often associated with advantages of group formation (like Striped Parrotfish or Pied-Wagtails)

Social: clearly evolved social behaviors including cooperative care of young, territory maintenance (like Groove-billed Anis or Lions)

Eusocial: extreme levels of cooperation, division of labor, etc (like social insects, Naked-Mole Rats, Florida Scrub Jays)

Two forms of cooperation with care not directed at one's own offspring

Helpers at the nest

Plural breeders

For these types of care, with dominance (breeders) and subordinates (helpers) we must still answer two questions (as with group territoriality):

A. Why do dominant individuals tolerate subordinates?

B. Why do subordinates accept low social rank rather than dispersing elsewhere (why help care for siblings rather than offspring)?

Answer to A is often easy: subordinates actually do help (benefits of tolerating outweigh costs)

Answer to B is ultimately related to limited opportunities for successful breeding elsewhere (best of a bad situation)

Ecological constraints model:

Habitat saturation limits opportunities for younger individuals (either lack of food or lack of mates)

This important cost can be mediated by:

Kin benefits (caring for sibs does help copies of genes)

Inheritance of good areas

Some helpers are not kin, so gene arguments are not necessary

In species like Groove-billed Anis, helpers produce some offspring, but not as many.

Three criterial define eusocial systems

Cooperative brood care

Overlap of generations

Reproductive division of labor

There are two routes to eusociality in Hymenoptera. These are identified from studies of different, but related species.

Familial route: vespoid wasps (also ants and termites)

Solitary: no parental care. Eggs are placed near larval food and abandoned (parasitoids).

Subsocial: overlap of generations.

Parental care develops, female builds a nest, mass-provisions it with food and may guard nest.

If female remains with larvae, progressively feeding them and guarding until they emerge....

then overlap of generations achieved.

Social: cooperative brood care. Daughters and mother all lay eggs and care for them in the same nest (rare).

Eusocial: reproductive division of labor. Daughters become workers.

Low levels of eusociality, with small colonies, dominance maintained behaviorally, daughters may leave to form their own nest.

Advanced eusociality, with large colonies, workers permanently sterile, queen dominates chemically.

Communal route: bees

Solitary: each female makes a nest, mass-provisions it with pollen and honey, seals it up, then leaves.

Communal: passive group formation with unrelated individuals

Quasisocial: cooperative brood care. Unrelated females cooperate mutualistically.

Semisocial: reproductive division of labor. Some females dominate others, form queen and worker roles.

Eusocial: overlap of generations. Some females live long enough to coexist in same nest with daughters.

Spiders

Orb-web spiders: communal route

Solitary orbs

Communal: aggregation of several orbs into large structure, each individual feeds and breeds in own web

Quasisocial: communal roost and egg sac.

Sheet-web spiders: familial route

Solitary: most spiders lay egg sac and abandon or at most guard eggs, disperse young when they hatch.

Subsocial: spiderlings remain in maternal web, mother offers prey, regurgitates, or sacrifices herself.

Social: young remain longer in maternal web, cooperate in webbuilding, prey capture, and in most social species cooperate in brood care.

Eusociality never reached by spiders as far as known.

Birds

Familial route: helpers at the nest in jays via retention of sons.

Communal route: multiple nests per territory and joint nesting in Crotophaginae (anis); no eusociality but evidence of conflict within groups.

Mammals

Familial route:

Solitary:	a very typical strategy, young disperse after weaning
Subsocial:	female young retained in parental group, cooperative foraging, common (monkeys)
Social:	cooperative brood care among related females, occasional (lions, elephants, banded mongoose).
Eusocial:	division of labor, Rare (dwarf mongoose, mole rats).

Communal route

Aggregation, cooperative foraging, and cooperative defense among non-relatives occurs in many species, but cooperative care of young is rare.

General patterns: Ecological constraints are critical in the degree to which they promote the retention of subordinates.

In the communal route to sociality, the initial step is group formation. Ecological factors must favor grouping such as predator defense, cooperative foraging, etc.

In the familial route, initial step is long retention of young. Ecological factors favoring retention are shortage of territories, nest sites, mates, or high cost of nest construction.

Eusociality is most commonly reached by the familial route, but division of labor can evolve among unrelated individuals.

In animal societies with evidence of evolved cooperation, eusociality is most common in Hymenoptera. In other groups is either rare (mammals), controversial (birds) or absent (spiders).

Why is eusociality more likely to evolve in some groups and not others?

Overlap of generations: many solitary Hymenoptera and spiders may be excluded from sociality via familial route due to lack of parental care and no overlap of generations but all birds and mammals meet this requirement.

Parental care: must be considerable effort expended in parental care, otherwise no need for helpers or cooperation.

All eusocial species forage at a distance from nest and make many trips with food (excludes spiders).

Non-reproductives must be capable of performing parental care.

Fecundity: must be high for true eusociality. The dominant breeder (queen) must be able to produce the same number of eggs that the helpers would have produced. Dominant breeders can or must be ablt to also afford to sacrifice some young to raise others - tradeoffs between fitness of different individuals).

Differences in eusociality between invertebrates (permanent sterility) and vertebrates (temporary, reciprocated) related to life expectancy and reproductive biology

Differences in sex of helpers/cooperators in birds versus mammals: territorial sex is retained, non-territorial sex disperses. Male territoriality more common in birds, female territoriality in mammals.

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