Cooperative breeding
[4] Cooperative breeding occurs across taxonomic groups including birds,[5] mammals,[6] fish,[7] and insects.
Kin selection is the evolutionary strategy of aiding the reproductive success of related organisms, even at a cost to the own individual's direct fitness.
[12] Additional species such as Neolamprologus pulcher have shown that kin selection is a dominant driving force for cooperative breeding.
Additionally, an increase in members reduces each helper's duration as a sentinel (standing upon a high surface to survey for predators) or babysitting (guarding the offspring and den).
The model is based on the evolution of larger litters forcing the need for helpers to maintain the high reproductive costs, thus leading to cooperative breeding.
[1] Today, there is growing support for the theory that cooperative breeding evolved by means of some form of mutualism or reciprocity.
[16] The greatest amount of research has been invested in reciprocal exchanges of beneficial behavior through the iterated prisoner's dilemma.
Sexual dispersal is the movement of one sex, male or female, from the natal territory to establish new breeding grounds.
Carrion crow (Corvus corone) were found to produce more female offspring in favorable environmental conditions.
Female Corvus corone have been found to establish successful breeding territories at a higher rate than males.
If environmental conditions are unfavorable females may produce the philopatric sex, therefore generating more helpers and increasing the occurrence of cooperative breeding.
[22] Guarding behaviors, such as babysitting, can cause individuals to experience weight loss on an exponential scale depending upon the duration of the activity.
Other activities, such as sentinel behavior and bipedal surveillance, cause helpers to have reduced foraging intervals inhibiting their weight gains.
Helpers aid the breeding females with provisioning, lactation stress, guarding of offspring and prenatal investment.
[18][19] Helper food provisioning reduces the need for the dominant breeding pair to return to the den, thus allowing them to forage for longer periods.
The dominant female and male will adjust their care input, or food provisioning, depending on the degree of activity of the helpers.
[11] This type of kinship may lead to inheritance of quality foraging and breeding territories, which will increase the future fitness of helpers.
[31] For example, by preventing their mothers from engaging in extra-pair matings, they can help their biological fathers protect their paternity and so increase their relatedness to future members of the cooperatively breeding group.
[31] Approximately eight percent of bird species are known to regularly engage in cooperative breeding, mainly among the Coraciiformes, Piciformes, basal Passeri and Sylvioidea.
[32] Only a small fraction of these, for instance the Australian mudnesters, Australo-Papuan babblers and ground hornbills, are however absolutely obligately cooperative and cannot fledge young without helpers.
One example is the azure-winged magpie (Cyanopica cyanus), in which studies found that the offspring's cell-mediated immune response was positively correlated with increase in the number of helpers at the nest.
However, many observers today believe cooperative breeding arose because of the need for helpers to rear young in the extremely infertile and unpredictable environments[36] of Australia and sub-Saharan Africa under the rare favourable conditions.
[37] Phylogenetic analysis shows evidence of fourteen discrete evolutionary transitions to cooperative breeding within the class Mammalia.
[37] These two factors, social monogamy and polytocy, are not evolutionary associated, suggesting that they are independent mechanisms leading to the evolution of cooperative breeding in mammals.
[45] Cooperative breeding requires "repression" of helpers' reproduction, by pheromones emitted by a breeder, by coercion, or by self-restraint.
Sarah Blaffer Hrdy believes that cooperative breeding is an ancestral trait in humans, a controversial proposition.
[citation needed] In most non-human primates, the reproductive success and survival of offspring is highly dependent to the mother's ability to produce food resources.
[50] Therefore, human offspring are highly dependent on caregiver investment, a necessity that serves as the precursor for theories on the development of pair-bonding, alloparenting, and cooperative breeding.
[51] Additionally, pro-social behaviors in cooperative breeding in humans had a by-product effect of enhancing cognitive capabilities, especially in social tasks involving coordination.
[46] This intergenerational flow of resources supports the theory of mutualism as an evolutionary pathway to cooperative breeding in humans.
