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(New page: {{CompPsy}} '''Cooperative breeding''' is a social system in which individuals help care for young that are not their own. The non-parental care givers ([[alloparenting|alloparents...)
 
 
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{{CompPsy}}
'''Cooperative breeding''' is a [[social system]] in which individuals help [[care]] for young that are not their own. The non-parental care givers ([[alloparenting|alloparents]]) may be other reproducing adults, as in the case of lionesses who litter at the same time nursing and caring for their cubs communally; reproductively mature but non-reproducing adults, as in subordinate wolves helping to feed and protect the pups of the alpha female; sub-fertile or infertile adults, such as the worker castes in social insects species; post-reproductive adults, as in human [[grandmother hypothesis|grandmothers]] caring for their grandchildren; or sub-adults, as in young Florida scrub jays who stay with their parents a year or two as [[helpers at the nest]] before leaving to mate. [[Bi-parental care]], in which a male forgoes pursuit of additional mating opportunities to serve as an [[allomother]] and help care for youngsters that are likely his offspring, shares many characteristics with cooperative breeding and could be considered a subset of it.
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'''Cooperative breeding''' is a [[social system]] in which individuals contribute care to [[offspring]] that are not their own at the expense of their own [[reproduction]].<ref>{{cite book | first=Edward O. | last=Wilson | authorlink=E.O. Wilson | year=1975 | title=Sociobiology: The New Synthesis}}</ref> When reproduction is monopolized by one or few of the adult group members and most adults do not reproduce, but help rear the breeder’s offspring, the majority of these cooperative breeding species exhibit high reproductive skew. However, there are plural breeding species with low reproductive skew, in which the subordinates commonly breed. This kind of cooperative breeding systems is particularly rare and includes [[communal breeding]], in which more than one female lays eggs or gives birth to young.<ref>5. Gilchrist, Jason. 2006. Cooperative behaviour in cooperative breeders: costs, benefits, and communal breeding. Behavioural Processes 76: 100-105.</ref>
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Cooperative breeding is different from [[alloparenting]], which is simply the act of caring completely for another conspecific's offspring but not at their own expense.
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==Evolution==
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Generally the helpers in cooperatively breeding [[birds]] and [[mammals]] are relatives of the dominant breeders who still remain in the group or are individuals whose own breeding attempts have been unsuccessful and have come back to their original group to help with [[Kinship|kin]].
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[[Kin selection]] was previously thought to be one of the major contributing factors to the evolution of cooperative breeding. Kin selection is when individuals increase their fitness through indirect benefits by helping relatives.<ref name="Clutton-Brock Science">{{cite journal|last=Clutton-Brock|first=Tim|title=Breeding Together: Kin Selection and Mutualism in Cooperative Vertebrates|journal=Science|year=2002|volume=296|issue=5565|pages=69–72|doi=10.1126/science.296.5565.69|pmid=11935014}}</ref> Today, kin selection is not a compelling explanation for the [[evolution]] of cooperative animal [[societies]] for a number of reasons. Most permanent groups of [[social animals]] are composed of relatives, and it is unclear if the degree of relatedness is consistently higher in cooperative breeders than in other species that simply live in stable groups that don’t breed cooperatively.<ref name="Clutton-Brock Science" /> There are many studies of cooperative birds and mammals that have shown that [[unrelated]] helpers can invest just as much as close relatives. Another reason why kin selection doesn’t fully explain the evolution of cooperative breeding is that the relative importance of indirect
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[[Fitness (biology)|fitness]] benefits of helpers has probably been overestimated. Many times, the benefits received by the helpers and those they confer on kin have both been included, leading to a double accounting of kin-selected benefits.<ref name="Clutton-Brock Science" />
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Today, there is growing support for the theory that cooperative breeding evolved by means of some form of [[Mutualism (biology)|mutualism]] or [[Reciprocity (evolution)|reciprocity]]. Mutualism is a form of symbiosis that is beneficial to both involved organisms. Mutualism has many forms and can occur when the benefits are immediate or deferred, when individuals exchange beneficial behaviors in turn, or when a group of individuals contribute to a common good, where it may be advantageous for all group members to help raise young. When a group raises young together, it may be advantageous because it maintains or increases the size of the group.<ref name="Clutton-Brock Science" /> The greatest amount of research has been invested in reciprocal exchanges of beneficial behavior through the [[iterated prisoner's dilemma]]. In this model, two partners can either cooperate and exchange beneficial behavior or they can defect and refuse to help the other individual.<ref name="Clutton-Brock Science" />
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Research has found that there is not one theory that can explain the evolution of all cooperative breeding species. In addition to mutualism and reciprocity, [[group augmentation]] has been suggested as one way cooperative breeding could have evolved in some species. Group augmentation occurs when animals living in a group behave in a way that increases the group's size. This type of behavior would be selected for if larger groups increased the individual's chances of survival. This ultimately would select for individuals that help raise other animals' offspring.<ref>3. Clutton-Brock, T.H., Brotherton, P.N.M., O’Riain, M.J., Griffin, A.S., Gaynor, D., Kansky, R., Sharpe, L., and McIlrath, G.M. 2000. Contributions to cooperative rearing in meerkats. Animal Behaviour. 61: 705-710.</ref>
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==Benefits of Cooperative Breeding==
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There are many other possible explanations for cooperative breeding other than kin selection. Helping is not restricted to groups of closely related members, and it could also be a form of gaining parental experience, acquiring social status, “rent payment” for a shared habitat, or a gateway for future mating opportunities.<ref name="Kokko2001">{{cite journal | last1 = Kokko | first1 = H. | last2 = Johnstone | first2 = R.A. | last3 = Clutton-Brock | first3 = T.H. | year = 2001 | title = The evolution of cooperative breeding through group augmentation | url = | journal = Biological Sciences | volume = 268 | issue = 1463| pages = 187–196 | pmid = 11209890 | pmc = 1088590 | doi=10.1098/rspb.2000.1349}}</ref> Another primary explanation for cooperative breeding is group augmentation. In many species, survival is greater in large groups due to the benefits of large group numbers. Some species may experience passive benefits (actions that indirectly increase the fitness of an animal) due to the presence of other group members, such as the [[Mobbing (animal behavior)|dilution effect]], while others may experience active benefits (actions that are directed specifically to increase an animal’s fitness) that depend on the help that new members might offer.<ref name="Kokko2001" /> These benefits of cooperative breeding will occur in a population only if it is better to stay and help other individuals than to move somewhere else and attempt breeding.<ref>{{cite journal | last1 = Griffin | first1 = A.S. | last2 = West | first2 = S.A. | year = 2003 | title = Kin Discrimination and the Benefit of Helping in Cooperative Breeding Vertebrates | url = | journal = Science | volume = 302 | issue = 5645| pages = 634–636 | doi = 10.1126/science.1089402 | pmid = 14576431 }}</ref> In this way, helping could evolve through group augmentation if the larger group sizes result in automatic passive benefits to all group members. However without passive benefits, larger groups could still receive active benefits in the form of delayed [[Reciprocity (cultural anthropology)|reciprocity]]. Therefore it might be advantageous for a subordinate to provide aid to a dominant individual even if it is completely unrelated.
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==Costs of Cooperative Breeding==
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The primary disadvantage of cooperative breeding is the cost of expending energy towards raising the offspring of another individual. A study conducted by Cornwallis et al. showed a strong negative correlation between the evolution of promiscuity and the evolution of cooperative breeding, suggesting that cooperative breeding is more likely to evolve in populations where females mate with fewer males.<ref>{{cite journal|last=Cornwallis|first=Charlie K.|coauthors=Stuart A. West, Katie E. Davis, Ashleigh S. Griffin|title=Promiscuity and the evolutionary transition to complex societies|journal=Nature|date=19 August 2010|volume=466|pages=969–972|doi=10.1038/nature09335|pmid=20725039|issue=7309}}</ref> For species with multiple-mating systems, the time and energy spent raising another’s offspring would prove too costly for cooperative breeding to be selected for.
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==Biological Examples==
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===Birds===
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Approximately eight percent of bird species are known to regularly engage in cooperative breeding, mainly among the [[Coraciiformes]], [[Piciformes]], basal [[songbirds|Passeri]] and [[Sylvioidea]].<ref name="uncertainty">{{cite journal | last1 = Jetz | first1 = Walter | last2 = Rubinstein | first2 = Dustin R. | year = 2011 | title = Environmental Uncertainty and the Global Biogeography of Cooperative Breeding in Birds | url = http://www.columbia.edu/~dr2497/PUBLICATIONS_files/Jetz%26RubensteinCB.pdf | format = PDF | journal = Current Biology | volume = 21 | issue = | pages = 1–7 }}</ref> Only a small fraction of these, for instance the [[Australian mudnester]]s, [[Australo-Papuan babbler]]s and [[ground hornbill]]s, are however absolutely ''obligately'' cooperative and cannot fledge young without helpers.<ref>See Cockburn, Andrew; [http://rspb.royalsocietypublishing.org/content/273/1592/1375.full “Prevalence of different modes of parental care in birds”]</ref>
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The benefits of cooperative breeding in birds have been well-documented. 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.<ref>{{cite journal|last=Valencia|first=Juliana|coauthors=Elena Solis, Gabrielle Sorci, and Carlos de la Cruz|title=Positive correlation between [[Helpers at the nest|helpers at nest]] and nestling [[immune response]] in cooperative breeding bird|journal=Behavioral Ecology and Sociobiology|year=2006|volume=60|issue=3|pages=399–404}}</ref> Studies on cooperative breeding in birds have also shown that high levels of cooperative breeding are strongly associated with low annual adult mortality and small clutch sizes, though it remains unclear whether cooperative breeding is a cause or consequence.<ref>{{cite journal|last=Arnold|first=Kathryn E.|coauthors=Ian P. F. Owens|title=Cooperative breeding in birds: a comparative test of the life history hypothesis|journal=Proceedings: Biological Sciences|date=7 May 1998|volume=265|issue=1398|pages=739–745|url=http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1689041/pdf/YR16ANRGCE6F70VL_265_739.pdf|pmc=1689041}}</ref> It was originally suggested that cooperative breeding developed among bird species with low mortality rates as a consequence of “overcrowding” and thus fewer opportunities to claim territory and breed. However, many observers today believe cooperative breeding arose because of the need for helpers to rear young in the extremely infertile and unpredictable environments<ref>See McMahon T.A. and Finlayson, B.; ''Global Runoff: Continental Comparisons of Annual Flows and Peak Discharges''. ISBN 3-923381-27-1</ref> of [[Australia]] and [[sub-Saharan Africa]] under the rare favourable conditions.<ref name="uncertainty"/>
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[[File:Suricata.suricatta.with.young.2.jpg|thumb|An older female watches over pups while alpha female is away.]]
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===Meerkats===
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[[Meerkat]]s become reproductively active at one year of age and can have up to four litters per year. However, usually it is the [[alpha]] pair that reserves the right to mate and will usually kill any young that is not their own. While the alpha female is away from the group, females that have never reproduced lactate and hunt in order to feed the pups, as well as watch, protect, and defend them from predators. Although it was previously thought that a meerkat’s contribution to a pup’s diet depended on the degree of relatedness, it has been found that helpers vary in the number of food items they give to pups. This variation in food offering is due to variation in foraging success, sex, and age. Research has additionally found that the level of help is not correlated to the kinship of the litters they are rearing.<ref>3. Clutton-Brock, T.H., Brotherton, P.N.M., O’Riain, M.J., Griffin, A.S., Gaynor, D., Kansky, R., Sharpe, L., and McIlrath, G.M. 2000. “Contributions to cooperative rearing in meerkats”. ''[[Animal Behaviour (journal)|Animal Behaviour]]''. 61: 705-710.</ref>
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===Primates===
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In many non-human primate species, cooperatively breeding social structures are the major form of social living. Usually, the effort put into caring for the dominant breeder’s offspring is shared by a group's members. Parents, siblings, and immigrant adults will share [[child rearing]] duties for the group's young. These duties may include carrying, protecting, feeding, comforting, and even engaging in play behavior with collective offspring. The [[Cotton-top tamarin]] (''Saguinus oedipus'') is a [[New world monkey]] that arranges into cooperatively breeding groups. Males of the species display high levels of [[paternal investment]] during infant care. In this species, males, particularly those that are paternal, show a greater involvement in caregiving than do females.<ref name="CB2">Cleveland and Snowdon. Social development during the first twenty weeks in the cotton-top tamarin ('' Saguinus o. oedipus''). [[Animal Behaviour]] (1984) vol. 32 (2) pp. 432-444</ref> It is hypothesized that males invest additional support in rearing offspring as a form of [[courtship]] to win favor of the group’s dominant female.<ref name="CB13">Tardif and Bales. Is infant-carrying a courtship strategy in [[callitrichid]] primates?. [[Animal Behaviour]] (1997) vol. 53 (5) pp. 1001-1007</ref> However, this may not be the whole reason for male investment in cooperative breeding since evidence indicates that time spent carrying infants does not strongly correlate with a male's overall [[copulation]] frequency.<ref name="CB13"/>
   
 
==See also==
 
==See also==
*[[Reproduction]]
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*[[Alloparenting]]
*[[Mating system]]
 
 
*[[Breeding season]]
 
*[[Breeding season]]
 
*[[Communal breeding]]
 
*[[Communal breeding]]
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*[[Helpers at the nest]]
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*[[Mating system]]
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*[[Reproduction]]
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== Sources ==
 
== Sources ==

Latest revision as of 20:03, December 24, 2012

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Cooperative breeding is a social system in which individuals contribute care to offspring that are not their own at the expense of their own reproduction.[1] When reproduction is monopolized by one or few of the adult group members and most adults do not reproduce, but help rear the breeder’s offspring, the majority of these cooperative breeding species exhibit high reproductive skew. However, there are plural breeding species with low reproductive skew, in which the subordinates commonly breed. This kind of cooperative breeding systems is particularly rare and includes communal breeding, in which more than one female lays eggs or gives birth to young.[2] Cooperative breeding is different from alloparenting, which is simply the act of caring completely for another conspecific's offspring but not at their own expense.

EvolutionEdit

Generally the helpers in cooperatively breeding birds and mammals are relatives of the dominant breeders who still remain in the group or are individuals whose own breeding attempts have been unsuccessful and have come back to their original group to help with kin.

Kin selection was previously thought to be one of the major contributing factors to the evolution of cooperative breeding. Kin selection is when individuals increase their fitness through indirect benefits by helping relatives.[3] Today, kin selection is not a compelling explanation for the evolution of cooperative animal societies for a number of reasons. Most permanent groups of social animals are composed of relatives, and it is unclear if the degree of relatedness is consistently higher in cooperative breeders than in other species that simply live in stable groups that don’t breed cooperatively.[3] There are many studies of cooperative birds and mammals that have shown that unrelated helpers can invest just as much as close relatives. Another reason why kin selection doesn’t fully explain the evolution of cooperative breeding is that the relative importance of indirect fitness benefits of helpers has probably been overestimated. Many times, the benefits received by the helpers and those they confer on kin have both been included, leading to a double accounting of kin-selected benefits.[3]

Today, there is growing support for the theory that cooperative breeding evolved by means of some form of mutualism or reciprocity. Mutualism is a form of symbiosis that is beneficial to both involved organisms. Mutualism has many forms and can occur when the benefits are immediate or deferred, when individuals exchange beneficial behaviors in turn, or when a group of individuals contribute to a common good, where it may be advantageous for all group members to help raise young. When a group raises young together, it may be advantageous because it maintains or increases the size of the group.[3] The greatest amount of research has been invested in reciprocal exchanges of beneficial behavior through the iterated prisoner's dilemma. In this model, two partners can either cooperate and exchange beneficial behavior or they can defect and refuse to help the other individual.[3]

Research has found that there is not one theory that can explain the evolution of all cooperative breeding species. In addition to mutualism and reciprocity, group augmentation has been suggested as one way cooperative breeding could have evolved in some species. Group augmentation occurs when animals living in a group behave in a way that increases the group's size. This type of behavior would be selected for if larger groups increased the individual's chances of survival. This ultimately would select for individuals that help raise other animals' offspring.[4]

Benefits of Cooperative BreedingEdit

There are many other possible explanations for cooperative breeding other than kin selection. Helping is not restricted to groups of closely related members, and it could also be a form of gaining parental experience, acquiring social status, “rent payment” for a shared habitat, or a gateway for future mating opportunities.[5] Another primary explanation for cooperative breeding is group augmentation. In many species, survival is greater in large groups due to the benefits of large group numbers. Some species may experience passive benefits (actions that indirectly increase the fitness of an animal) due to the presence of other group members, such as the dilution effect, while others may experience active benefits (actions that are directed specifically to increase an animal’s fitness) that depend on the help that new members might offer.[5] These benefits of cooperative breeding will occur in a population only if it is better to stay and help other individuals than to move somewhere else and attempt breeding.[6] In this way, helping could evolve through group augmentation if the larger group sizes result in automatic passive benefits to all group members. However without passive benefits, larger groups could still receive active benefits in the form of delayed reciprocity. Therefore it might be advantageous for a subordinate to provide aid to a dominant individual even if it is completely unrelated.

Costs of Cooperative BreedingEdit

The primary disadvantage of cooperative breeding is the cost of expending energy towards raising the offspring of another individual. A study conducted by Cornwallis et al. showed a strong negative correlation between the evolution of promiscuity and the evolution of cooperative breeding, suggesting that cooperative breeding is more likely to evolve in populations where females mate with fewer males.[7] For species with multiple-mating systems, the time and energy spent raising another’s offspring would prove too costly for cooperative breeding to be selected for.

Biological ExamplesEdit

BirdsEdit

Approximately eight percent of bird species are known to regularly engage in cooperative breeding, mainly among the Coraciiformes, Piciformes, basal Passeri and Sylvioidea.[8] 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.[9]

The benefits of cooperative breeding in birds have been well-documented. 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.[10] Studies on cooperative breeding in birds have also shown that high levels of cooperative breeding are strongly associated with low annual adult mortality and small clutch sizes, though it remains unclear whether cooperative breeding is a cause or consequence.[11] It was originally suggested that cooperative breeding developed among bird species with low mortality rates as a consequence of “overcrowding” and thus fewer opportunities to claim territory and breed. However, many observers today believe cooperative breeding arose because of the need for helpers to rear young in the extremely infertile and unpredictable environments[12] of Australia and sub-Saharan Africa under the rare favourable conditions.[8]

File:Suricata.suricatta.with.young.2.jpg
An older female watches over pups while alpha female is away.

MeerkatsEdit

Meerkats become reproductively active at one year of age and can have up to four litters per year. However, usually it is the alpha pair that reserves the right to mate and will usually kill any young that is not their own. While the alpha female is away from the group, females that have never reproduced lactate and hunt in order to feed the pups, as well as watch, protect, and defend them from predators. Although it was previously thought that a meerkat’s contribution to a pup’s diet depended on the degree of relatedness, it has been found that helpers vary in the number of food items they give to pups. This variation in food offering is due to variation in foraging success, sex, and age. Research has additionally found that the level of help is not correlated to the kinship of the litters they are rearing.[13]

PrimatesEdit

In many non-human primate species, cooperatively breeding social structures are the major form of social living. Usually, the effort put into caring for the dominant breeder’s offspring is shared by a group's members. Parents, siblings, and immigrant adults will share child rearing duties for the group's young. These duties may include carrying, protecting, feeding, comforting, and even engaging in play behavior with collective offspring. The Cotton-top tamarin (Saguinus oedipus) is a New world monkey that arranges into cooperatively breeding groups. Males of the species display high levels of paternal investment during infant care. In this species, males, particularly those that are paternal, show a greater involvement in caregiving than do females.[14] It is hypothesized that males invest additional support in rearing offspring as a form of courtship to win favor of the group’s dominant female.[15] However, this may not be the whole reason for male investment in cooperative breeding since evidence indicates that time spent carrying infants does not strongly correlate with a male's overall copulation frequency.[15]

See alsoEdit


Sources Edit

  • The Past, Present, and Future of the Human Family, by Sarah Blaffer Hrdy, one of The Tanner Lectures on Human Values, Delivered at University of Utah February 27 and 28, 2001 [1]
  • BIO 555/755 Behavioral Ecology, Instructor: Gary Ritchison
    • Lecture Notes 8: Cooperation & Helping - Cooperative Breeding in Vertebrates [2]
    • Lecture Notes 8b: Insect Sociality [3]
  • Cooperative Breeding in Mammals, by Nancy G. Solomon (Editor), Jeffrey A. French (Editor) Cambridge University Press (November 28, 1996), ISBN 0-521-45491-3

Further readingEdit

  • Mace, R. and Sear, R. (2005) Are humans cooperative breeders? In: Grandmotherhood: the Evolutionary Significance of the Second Half of Female Life. Edited by E. Voland, A. Chasiotis & W. Schiefenhoevel. Rutgers University Press, Piscataway. pp 143-159. Full text
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