Group augmentation

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In animal behaviour, the hypothesis of group augmentation is where animals living in a group behave so as to increase the group's size, namely through the recruitment of new members. [1] Such behaviour could be selected for if larger group size increases the chance of survival of the individuals in the group. Supported hypothesis of selection mechanisms towards increasing group size currently exist, in helping raise other animals' offspring (alloparental care) and performing other cooperative breeding acts including kin selection. It is currently proposed that group augmentation may be another mechanism (closely related/connected to cooperative breeding) which occurs through the recruiting of new group members and helping of unrelated individuals within a group. [1]

Contents

Group Augmentation Mechanisms

Group augmentation can occur via two separate mechanisms. Passive group augmentation is described as the mere presence of other individuals in a group providing a benefit to a group member. [1] Where as active group augmentation is described as the presence of other individuals causing no benefit or a detrimental effect to a group member; but where the presence of the other individuals later increases the overall level of reproductiveness of the group, also known as delayed reciprocity. [1] [2] An example of the phenomenon of delayed reciprocity (or "returning the favour") is where an organism will help raise an un-related individual at a cost, and once the individual is an adult it helps the organism which raised it; either by its presence increasing group size, or by assisting in breeding activity. [1] [2] [3] [4] [5] Research suggests that both types of group augmentation can be used to explain the expensive helping behaviour of non-reproducing subordinate individuals as evolutionary stable. [1] It is also important to note that both forms of group augmentation are thought to act in tandem with kin selection to further explain increased levels of helping behaviour. Aside from helping to raise offspring, another way by which helping behaviour leads to group augmentation is through lowering group mortality (through actions such as vigilance behaviour). [1] [2] [6] Group augmentation is proposed to help explain the evolution of helping behaviour, such as cooperative breeding. [1] [7] Group augmentation may be used in cooperative breeding groups, in particular, to explain helping behaviour between individuals which have low relatedness. [1] Certain species show that costly helping behaviour which can not be explained solely by kin selection, may be explained by the underestimated value a large group to an individual. [2] [3] [8]

Species Specific Examples

Meerkat (Suricata suricatta)

The meerkat is one species where group augmentation is suspected to be an important driver of cooperative behaviour. [9] It is believed that relatedness degree, or kin selection, is not the only driver of helping behaviour in meerkats, as research has demonstrated that weight, age and sex of the subordinates may better correlate with helping babysitting behaviour. [2] [3] [8] As meerkats have been noted to help un-related individuals, one potential explanation is the benefit of increasing group size (as group size is correlated with survival); this non-related altruistic behaviour is thus thought to be a cooperative behaviour driven by group augmentation. [2] [3] [8] [9]

White Winged Choughs (Corcorax melanorhamphos)

The White Winged Choughs display a unique behaviour, according to some research, of kidnapping and raising unrelated young. [10] In one experiment spanning four years a total 14 young birds were regarded to be "stolen" from one group of Choughs to another, here it is evident that kin selection is likely not the driving force as stolen individuals were captured from seemingly un-related groups. [10] Associated research has concluded that helpers (which can include young birds) are necessary for successful reproduction, and no instance of successful breeding has been noted to occur without helpers. [11] Here group augmentation theory is largely supported as it was also demonstrated that reproductive success linearly increased with group size, and the choughs are actively recruiting new unrelated members. [10] [11]

Chimpanzees (Pan troglodytes)

Chimpanzees are a nonhuman primate which exhibits an interesting cooperative behaviour of territorial boundary patrolling. As with most cooperative behaviours some aspects are strongly attributed to kin selection; including an increased incidence of patrol behaviour when offspring were present in the group. [12] Other aspects of this behaviour however were better attributed to the group augmentation theory, in that, the chimpanzees had individuals which routinely patrolled at high cost although the immediate gain was minimal, but led to a larger group size and future potential for reproductive success. Evidence of this cooperative behaviour being related to group augmentation was based on the fact that some males were notice to patrol, even when there were no offspring or maternal relatives in the group. Further observations included that increase in group size did not impact the totally patrolling effort of the group, so helping behaviour was continuously attempting to increase group size. [12]

Criticism of Group Augmentation Hypothesis

The group augmentation hypothesis is not universally accepted by all ethologists, as other well studied explanations for cooperative behaviour exist. Kin selection has been largely proven to be the main driver of the cooperative breeding strategy, through the application of Hamilton's rule across a large variety of studies. [13] Kin selection is the theory that animals act altruistically towards members of their own species in a ratio which is dependent on how genetically related those individuals are to one another. [14] A further criticism of group augmentation predictions replacing or occurring in tandem with kinship, is that the augmentation theory lacks clear empirical data. [13] It is also argued that animals live in groups only for the purpose of an immediate net benefit towards reproductive success. [13] [15] One study of a bird obligate cooperative breeder in particular showed that, while breeding success was dependent on cooperative behaviour, linkage to kinship was ultimately able to explain the behaviour of those species. [13] Overall, literature suggests more empirical data is required for group augmentation theory to be generally accepted.

See also

Related Research Articles

<span class="mw-page-title-main">Meerkat</span> Species of mongoose from Southern Africa

The meerkat or suricate is a small mongoose found in southern Africa. It is characterised by a broad head, large eyes, a pointed snout, long legs, a thin tapering tail, and a brindled coat pattern. The head-and-body length is around 24–35 cm (9.4–13.8 in), and the weight is typically between 0.62 and 0.97 kg. The coat is light grey to yellowish-brown with alternate, poorly-defined light and dark bands on the back. Meerkats have foreclaws adapted for digging and have the ability to thermoregulate to survive in their harsh, dry habitat. Three subspecies are recognised.

<span class="mw-page-title-main">Lek mating</span> Type of animal mating behaviour

A lek is an aggregation of male animals gathered to engage in competitive displays and courtship rituals, known as lekking, to entice visiting females which are surveying prospective partners with which to mate. A lek can also indicate an available plot of space able to be utilized by displaying males to defend their own share of territory for the breeding season. A lekking species is characterised by male displays, strong female mate choice, and the conferring of indirect benefits to males and reduced costs to females. Although most prevalent among birds such as black grouse, lekking is also found in a wide range of vertebrates including some bony fish, amphibians, reptiles, and mammals, and arthropods including crustaceans and insects.

<span class="mw-page-title-main">Long-tailed tit</span> Species of bird in Europe and Asia

The long-tailed tit, also named long-tailed bushtit, is a common bird found throughout Europe and the Palearctic. The genus name Aegithalos was a term used by Aristotle for some European tits, including the long-tailed tit.

<span class="mw-page-title-main">Cooperation</span> Groups working or acting together

Cooperation is the process of groups of organisms working or acting together for common, mutual, or some underlying benefit, as opposed to working in competition for selfish benefit. Many animal and plant species cooperate both with other members of their own species and with members of other species.

<span class="mw-page-title-main">Helpers at the nest</span>

Helpers at the nest is a term used in behavioural ecology and evolutionary biology to describe a social structure in which juveniles and sexually mature adolescents of either one or both sexes remain in association with their parents and help them raise subsequent broods or litters, instead of dispersing and beginning to reproduce themselves. This phenomenon was first studied in birds where it occurs most frequently, but it is also known in animals from many different groups including mammals and insects. It is a simple form of co-operative breeding. The effects of helpers usually amount to a net benefit, however, benefits are not uniformly distributed by all helpers nor across all species that exhibit this behaviour. There are multiple proposed explanations for the behaviour, but its variability and broad taxonomic occurrences result in simultaneously plausible theories.

<span class="mw-page-title-main">Reproductive success</span> Passing of genes on to the next generation in a way that they too can pass on those genes

Reproductive success is an individual's production of offspring per breeding event or lifetime. This is not limited by the number of offspring produced by one individual, but also the reproductive success of these offspring themselves.

<span class="mw-page-title-main">Alloparenting</span> Parenting not done by the birth parents

Alloparenting is a term used to classify any form of parental care provided by an individual towards young that are not its own direct offspring. These are often referred to as "non-descendant" young, even though grandchildren can be among them. Among humans, alloparenting is often performed by a child's grandparents and older siblings. Individuals providing this care are referred to using the neutral term of alloparent.

In biology, altruism refers to behaviour by an individual that increases the fitness of another individual while decreasing the fitness of themselves. Altruism in this sense is different from the philosophical concept of altruism, in which an action would only be called "altruistic" if it was done with the conscious intention of helping another. In the behavioural sense, there is no such requirement. As such, it is not evaluated in moral terms—it is the consequences of an action for reproductive fitness that determine whether the action is considered altruistic, not the intentions, if any, with which the action is performed.

<span class="mw-page-title-main">Siberian jay</span> Species of bird

The Siberian jay is a small jay with a widespread distribution within the coniferous forests in North Eurasia. It has grey-brown plumage with a darker brown crown and a paler throat. It is rusty-red in a panel near the wing-bend, on the undertail coverts and on the sides of the tail. The sexes are similar. Although its habitat is being fragmented, it is a common bird with a very wide range so the International Union for Conservation of Nature has assessed its conservation status as being of "least concern".

Philopatry is the tendency of an organism to stay in or habitually return to a particular area. The causes of philopatry are numerous, but natal philopatry, where animals return to their birthplace to breed, may be the most common. The term derives from the Greek roots philo, "liking, loving" and patra, "fatherland", although in recent years the term has been applied to more than just the animal's birthplace. Recent usage refers to animals returning to the same area to breed despite not being born there, and migratory species that demonstrate site fidelity: reusing stopovers, staging points, and wintering grounds.

In evolution, cooperation is the process where groups of organisms work or act together for common or mutual benefits. It is commonly defined as any adaptation that has evolved, at least in part, to increase the reproductive success of the actor's social partners. For example, territorial choruses by male lions discourage intruders and are likely to benefit all contributors.

Cooperative breeding is a social system characterized by alloparental care: offspring receive care not only from their parents, but also from additional group members, often called helpers. Cooperative breeding encompasses a wide variety of group structures, from a breeding pair with helpers that are offspring from a previous season, to groups with multiple breeding males and females (polygynandry) and helpers that are the adult offspring of some but not all of the breeders in the group, to groups in which helpers sometimes achieve co-breeding status by producing their own offspring as part of the group's brood. Cooperative breeding occurs across taxonomic groups including birds, mammals, fish, and insects.

Extra-pair copulation (EPC) is a mating behaviour in monogamous species. Monogamy is the practice of having only one sexual partner at any one time, forming a long-term bond and combining efforts to raise offspring together; mating outside this pairing is extra-pair copulation. Across the animal kingdom, extra-pair copulation is common in monogamous species, and only a very few pair-bonded species are thought to be exclusively sexually monogamous. EPC in the animal kingdom has mostly been studied in birds and mammals. Possible benefits of EPC can be investigated within non-human species, such as birds.

<span class="mw-page-title-main">Reproductive suppression</span>

Reproductive suppression is the prevention or inhibition of reproduction in otherwise healthy adult individuals. It includes delayed sexual maturation (puberty) or inhibition of sexual receptivity, facultatively increased interbirth interval through delayed or inhibited ovulation or spontaneous or induced abortion, abandonment of immature and dependent offspring, mate guarding, selective destruction and worker policing of eggs in some eusocial insects or cooperatively breeding birds, and infanticide, and infanticide in carnivores of the offspring of subordinate females either by directly killing by dominant females or males in mammals or indirectly through the withholding of assistance with infant care in marmosets and some carnivores. The Reproductive Suppression Model argues that "females can optimize their lifetime reproductive success by suppressing reproduction when future conditions for the survival of offspring are likely to be greatly improved over present ones”. When intragroup competition is high it may be beneficial to suppress the reproduction of others, and for subordinate females to suppress their own reproduction until a later time when social competition is reduced. This leads to reproductive skew within a social group, with some individuals having more offspring than others. The cost of reproductive suppression to the individual is lowest at the earliest stages of a reproductive event and reproductive suppression is often easiest to induce at the pre-ovulatory or earliest stages of pregnancy in mammals, and greatest after a birth. Therefore, neuroendocrine cues for assessing reproductive success should evolve to be reliable at early stages in the ovulatory cycle. Reproductive suppression occurs in its most extreme form in eusocial insects such as termites, hornets and bees and the mammalian naked mole rat which depend on a complex division of labor within the group for survival and in which specific genes, epigenetics and other factors are known to determine whether individuals will permanently be unable to breed or able to reach reproductive maturity under particular social conditions, and cooperatively breeding fish, birds and mammals in which a breeding pair depends on helpers whose reproduction is suppressed for the survival of their own offspring. In eusocial and cooperatively breeding animals most non-reproducing helpers engage in kin selection, enhancing their own inclusive fitness by ensuring the survival of offspring they are closely related to. Wolf packs suppress subordinate breeding.

Timothy Hugh Clutton-Brock is a British zoologist known for his comparative studies of the behavioural ecology of mammals, particularly red deer and meerkats.

<span class="mw-page-title-main">Eusociality</span> Highest level of animal sociality a species can attain

Eusociality, the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care, overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups. The division of labor creates specialized behavioral groups within an animal society which are sometimes referred to as 'castes'. Eusociality is distinguished from all other social systems because individuals of at least one caste usually lose the ability to perform at least one behavior characteristic of individuals in another caste. Eusocial colonies can be viewed as superorganisms.

<span class="mw-page-title-main">Evolution of eusociality</span> Origins of cooperative brood care

Eusociality evolved repeatedly in different orders of animals, particularly the Hymenoptera. This 'true sociality' in animals, in which sterile individuals work to further the reproductive success of others, is found in termites, ambrosia beetles, gall-dwelling aphids, thrips, marine sponge-dwelling shrimp, naked mole-rats, and the insect order Hymenoptera. The fact that eusociality has evolved so often in the Hymenoptera, but remains rare throughout the rest of the animal kingdom, has made its evolution a topic of debate among evolutionary biologists. Eusocial organisms at first appear to behave in stark contrast with simple interpretations of Darwinian evolution: passing on one's genes to the next generation, or fitness, is a central idea in evolutionary biology.

Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. Animals only rarely exhibit inbreeding avoidance. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating and natural and sexual selection, in order to prevent breeding among related individuals. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of such mechanisms.

Evolutionary biologists have developed various theoretical models to explain the evolution of food-sharing behavior—"[d]efined as the unresisted transfer of food" from one food-motivated individual to another—among humans and other animals.

Allomothering, or allomaternal care, is parental care provided by group members other than the genetic mother. This is a common feature of many cooperative breeding species, including some mammal, bird and insect species. Allomothering in humans is universal, but the members who participate in allomothering vary from culture to culture. Common allomothers are grandmothers, older siblings, extended family members, members of religious communities and ritual kin.

References

  1. 1 2 3 4 5 6 7 8 9 Kokko H, Johnstone RA, Clutton-Brock TH (January 2001). "The evolution of cooperative breeding through group augmentation". Proceedings. Biological Sciences. 268 (1463): 187–96. doi:10.1098/rspb.2000.1349. PMC   1088590 . PMID   11209890.
  2. 1 2 3 4 5 6 Griffin, Ashleigh S.; West, Stuart A. (2002-01-01). "Kin selection: fact and fiction". Trends in Ecology & Evolution. 17 (1): 15–21. doi:10.1016/S0169-5347(01)02355-2. ISSN   0169-5347.
  3. 1 2 3 4 Clutton-Brock TH, Brotherton PN, O'Riain MJ, Griffin AS, Gaynor D, Sharpe L, Kansky R, Manser MB, McIlrath GM (February 2000). "Individual contributions to babysitting in a cooperative mongoose, Suricata suricatta". Proceedings. Biological Sciences. 267 (1440): 301–5. doi:10.1098/rspb.2000.1000. PMC   1690529 . PMID   10714885.
  4. ↑ Creel, Scott R.; Rabenold, Kerry N. (1994). "Inclusive fitness and reproductive strategies in dwarf mongooses". Behavioral Ecology. 5 (3): 339–348. doi:10.1093/beheco/5.3.339. ISSN   1045-2249.
  5. ↑ "14. Direct Fitness, Mutualism, and Reciprocity", Helping Communal Breeding in Birds, Princeton University Press, 1987, pp. 224–249, doi:10.1515/9781400858569.224, ISBN   9781400858569
  6. ↑ Wiley, R. Haven; Rabenold, Kerry N. (May 1984). "The Evolution of Cooperative Breeding by Delayed Reciprocity and Queuing for Favorable Social Positions". Evolution. 38 (3): 609–621. doi:10.2307/2408710. ISSN   0014-3820. JSTOR   2408710. PMID   28555990.
  7. ↑ Kingma SA, Santema P, Taborsky M, Komdeur J (August 2014). "Group augmentation and the evolution of cooperation". Trends in Ecology & Evolution. 29 (8): 476–84. doi:10.1016/j.tree.2014.05.013. PMID   24996259.
  8. 1 2 3 English S, Nakagawa S, Clutton-Brock TH (August 2010). "Consistent individual differences in cooperative behaviour in meerkats (Suricata suricatta)". Journal of Evolutionary Biology. 23 (8): 1597–604. doi: 10.1111/j.1420-9101.2010.02025.x . PMID   20492087. S2CID   205432855.
  9. 1 2 Clutton-Brock T (April 2002). "Breeding together: kin selection and mutualism in cooperative vertebrates". Science. 296 (5565): 69–72. Bibcode:2002Sci...296...69C. doi:10.1126/science.296.5565.69. PMID   11935014.
  10. 1 2 3 Heinsohn, Robert G. (June 1991). "Kidnapping and reciprocity in cooperatively breeding white-winged choughs". Animal Behaviour. 41 (6): 1097–1100. doi:10.1016/s0003-3472(05)80652-9. ISSN   0003-3472. S2CID   53182362.
  11. 1 2 Heinsohn, Robert; Cockburn, Andrew (1994-06-22). "Helping is costly to young birds in cooperatively breeding white-winged choughs". Proceedings of the Royal Society of London. Series B, Biological Sciences. 256 (1347): 293–298. Bibcode:1994RSPSB.256..293H. doi:10.1098/rspb.1994.0083. ISSN   0962-8452. S2CID   129443595.
  12. 1 2 Langergraber KE, Watts DP, Vigilant L, Mitani JC (July 2017). "Group augmentation, collective action, and territorial boundary patrols by male chimpanzees". Proceedings of the National Academy of Sciences of the United States of America. 114 (28): 7337–7342. doi: 10.1073/pnas.1701582114 . PMC   5514721 . PMID   28630310.
  13. 1 2 3 4 Browning LE, Patrick SC, Rollins LA, Griffith SC, Russell AF (September 2012). "Kin selection, not group augmentation, predicts helping in an obligate cooperatively breeding bird". Proceedings. Biological Sciences. 279 (1743): 3861–9. doi:10.1098/rspb.2012.1080. PMC   3415917 . PMID   22787025.
  14. ↑ "Kin selection | behaviour". Encyclopedia Britannica. Retrieved 2018-11-19.
  15. ↑ Wright J (October 2007). "Cooperation theory meets cooperative breeding: exposing some ugly truths about social prestige, reciprocity and group augmentation". Behavioural Processes. 76 (2): 142–8. doi:10.1016/j.beproc.2007.01.017. PMID   17693040. S2CID   46701731.
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