Alloparenting (or alloparental care) is a term for any form of parental care provided by an individual towards young that are not its own direct offspring. These are often called "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 called by the neutral term "alloparent" (or "helper").
Alloparental care encapsulates a diverse range of parenting systems across a range of animal groups and social structures. The alloparent–young relationship can be mutualistic or parasitic, and between or within species. Cooperative breeding, joint brood care, reciprocal allonursing, brood parasitism and cuckoldry represent situations in which alloparenting plays a role.
This form of parenting is often seen among humans. However, it is not as popular among other species. Alloparenting is rare among classes of animals such as birds and mammals, with only about 3% of mammals exhibiting this parenting style, but this does not mean it does not occur. In species that alloparent, it has been seen that offspring grow at faster rates and are often weaned earlier.
Behavior The behavior revolving around alloparental care is more or less the same among species. The term "babysitting" is often used as a way to describe how this parental style works. In humans, alloparenting is common and mainly revolves around this term. Other parents and people watch others' young and help care for them while the biological parents are busy. This is seen in sperm whales as well. To allow the mother to dive and gather food and resources, the whales in their social group separate their dives allowing for the baby to be monitored and overseen by a whale during all times. Superb starlings also perform this behavior. Their group living situation contributes to many potential parent figures in the young's life. The mother and father may provide the heat and guarding of the nest however it is a network of other superb starlings that also watch over and take care of the offspring as well. These behaviors allow for the parents to have more freedom while knowing that the young are cared for. Alloparental care itself involves certain behaviors from the individuals partaking in this care. In humans and chimpanzees, this may involve carrying, walking with, cleaning, and physical contact with the young. In other animals such as whales, birds, and Indian free-range dogs, these behaviors may be feeding/regurgitating food, giving warmth, and guarding. In sea lions, behaviors such as allonursing may be seen. Behavior is the center of alloparenting and without parental care, many species' young would not survive.
Allonursing Allonursing falls under alloparenting. Allonursing is when a female provides nourishment for offspring that is not her own. Alloparenting is rare, but allonursing is even rarer. One reason why, is that for a female to breastfeed, she must have given birth recently. In milk, different antibodies and immune boosting nutrients can be found. Allonursing helps the offspring receive more immune compounds than those of just its mother. Allonursing not only benefits the offspring but it also benefits the nurser as well by allowing her to gain maternal experience, and therefore when her offspring is around she will be able to strengthen its survival. In a study done with cooperative breeders and non-cooperative breeding species, the researchers found that there were fewer cooperative breeding species that allonursed however it was not a significant amount. In noncooperative breeding species, 66% of litter-bearing group living species allonursed compared to 31% of monotocous species. In both cases, milk composition was not a factor.
In a case study on sea lions, allonursing can be seen as well. In this study, the researchers recorded an allonursing event when an individual was observed nursing more than one pup at a time and suckling was being performed by a pup or yearling that was confirmed as not her own by tags, brands, or natural marking. If there was any doubt in this, the event was not concluded. During this study, allonursing was seen twice during the pupping season and more commonly occurred later on. Primiparous females were seen more often allonursing a pup than multiparous females. Unless the multiparous female was sleeping, oftentimes she would not allow nonfilial pups to suckle and immediately terminate any allosuckling as soon as she noticed the nonfilial pup. This was different from the primiparous females who allowed for allonursing to continue.
Through these studies, it can be seen that allonursing is not common and for many, it is all based on the specific species and way of life. Though allonursing is beneficial to the offspring in receiving a wider variety of immune compounds, many species do not partake in this event.
Theory In biology, ethology and sociology, alloparental care is defined as any form of parental care, which is directed towards non-descendant young. It was first used by Edward O. Wilson in 1975, in his book Sociobiology in an attempt to define a neutral term which could encapsulate the gender and relation specific terms of 'aunite' and 'auncle' which had previously been coined in the literature to describe this sort of behaviour. In addition, Wilson used the term alloparent (or helper) to refer to the individuals providing the care, and proposed allomaternal and allopaternal as phrases that could be used to distinguish the sex of the helper. "Alloparent" roughly means "other-parent"; from the Greek root "allo-", meaning other.
Alloparenting encapsulates a diverse range of parenting systems and behaviours. Simply, it can be understood as a system of parenting where individuals other than a direct genetic parent act in a parental role, either for a short, or extended period of time. This definition does not exclude alloparents who are blood relatives of the offspring, such as siblings and aunts, who are often observed as 'helpers at the nest'. In such cases, the alloparent and the offspring share a degree of relatedness (r (coefficient of relatedness) > 0); so kin selection is often involved in the evolution of the behaviour. Use of the term non-descendant young, as opposed to non-related young is therefore an important distinction in the definition of alloparenting. The non-descendant young in whom the alloparent invests can be conspecific (of the same species) or heterospecific (of a different species), a phenomenon often observed in fish and a select number of bird species.
There is some debate as to whether interspecific alloparenting (caring for the young of another species) constitutes 'true' alloparental care, particularly when the relationship is parasitic for the alloparent, and the care being directed is therefore 'misdirected' or constitutes a maladaptive behaviour. Though such parasitic relationships, such as what occurs with cuckoo chicks, were not specifically addressed by Edward O. Wilson in his original discussion, adoption and slavery across species in ants was discussed; a relationship which could be described as parasitic for the heterospecific young. This article will consider interspecific and parasitic alloparental behaviours to satisfy the definition of alloparental care.
Alloparental investment In 1972, Robert Trivers defined parental investment as: "any investment by the parent in an individual offspring that increases the offspring's chance of surviving (and hence reproductive success) at the cost of the parents ability to invest in other offspring".
This concept of parental investment applies to the alloparent in the same way that it does to a genetic parent; however, any investment into the production of gametes, which Trivers included in his definition, is not relevant, and is therefore usually restricted to behavioral considerations for the alloparent. Possible forms of investment provided by an alloparent can be defined by three of the four classifications of energy expenditure proposed by Crawford and Balon (1996): Type II – Preparing for the offspring prior to zygotic development in terms of nest/den building and territory defense. Type III – Direct provisioning of food for the young. Type IV – Tending to, caring for, feeding, defending and teaching the young. Given that the alloparent is never the genetic parent, and was therefore not involved in the reproductive behavior/copulation that produced the young, the Type I classification, 'energy investment in gametes', is not relevant when we consider alloparental investment.
Classification
The forms of alloparental care which occur in nature are numerous and varied and resist classification. Relationships between the alloparent and the young, and the alloparent and the genetic parent, range from cooperative and mutualistic to exploitative and parasitic. The below outline provides one classification for the many forms of alloparenting which have been observed:
'True' (mutualistic)
This form of alloparenting is characterized by interactions/relationships which provide and overall fitness benefit to the alloparent, the young, and the genetic parent. This sort of parental care is often closely tied to social organisation and is thus very common in advanced animal societies such as primates. It can take on the forms of:
Cooperative breeding – This system of breeding is characterised by individuals (alloparents) who delay or forego their personal reproduction in order to assist in the reproduction of other individuals within the group, often a dominant breeding pair. The alloparent 'helpers' are most commonly the siblings of the new offspring, or siblings to the breeding pair. This system is common amongst birds, primates and mammals such as the blackbacked jackal, and African wild dogs who share in pup feeding and display 'babysitting' behaviour. Cooperative breeding is often provided as strong evidence in support of kin selection. Cooperative breeding, particularly in birds, is favored in marginal environments where food is limited or there are high predation rates and it is therefore tough for a breeding pair to successfully raise young on their own. Newly independent young may also find alloparenting the most successful reproduction option available to them in environments where the resources are scarce or there is habitat saturation. An extreme case of cooperative breeding is what occurs in eusocial insects such as some bee and ant species where a caste system has evolved and workers forgo their personal reproduction to aid in the reproductive success of the colony, gaining indirect fitness benefits through assisting related young.