Helping Behavior

Helping behavior is the defining feature of meerkat sociality. Pup rearing requires help in the form of baby-sitting and even allolactation. Once pups are old enough to leave the burrow, they are fed by all adult meerkats. Sentry behavior and mobbing behavior offer protection from predators. All of these behaviors are associated with costs to the meerkats performing the behavior and benefits to other meerkats. The behaviors must bring significant benefits to the meerkats who perform them, or they would disappear from the population due to natural selection. Because meerkats live in groups of high relatedness, both indirect and direct benefits are possible. For each behavior, it must be determined to what extent, if at all, the behaviors are selfish or altruistic. Do they arise from natural selection, kin selection, or some combination of both?

The tendency is to assume that a high coefficient of relatedness means that kin selection is the primary manner in which helping behavior is passed from generation to generation. However, related helpers may accrue direct fitness benefits as well as indirect benefits. These direct benefits, the result of natural selection, are often overlooked. In meerkats, helping behavior in the form of baby-sitting often depends on the characteristics of the helper, not on the degree of relatedness between the helper and the pups or the mother. This lack of correlation between helping and relatedness leads to the conclusion that the behavior has at least some selfish aspect. Indeed, apparent altruism may be selfish, even in kin groups. Competition for reproductive opportunities is high in meerkats. Because many meerkats remain in their natal burrows, competition is between relatives. Such competition reduces the benefits of the indirect fitness (Griffen and West, 2002). Meerkats benefit from reproduction by relatives, but they compete viciously with those relatives. If indirect fitness were their only benefit from helping, they wouldn’t compete because competition weakens their relative, thus reducing its mating opportunities.
Helping behavior can increase group size, which is important to species with high predation rates, like the meerkat. Helping behavior may also increase the number of animals who will mature to become helpers. If a meerkat attains the alpha position, it will benefit from this increase in helpers. If it remains subordinate, it will have to help less if there are more helpers in the group. In all three cases, helping is selfish. As behaviors that seem altruistic are encountered, it is important to avoid overlooking potential selfish aspects. While kin selection may have been necessary for the evolution of a particular helping behavior, it does not always continue to play a role as the species evolves further.
For an example of natural selection in meerkats with indirect fitness benefits that are inconsequential to the behavior’s tenure in the population, click here.

Babysitting Baby-sitters are subordinate meerkats of either sex who take care of another meerkat’s young before they are old enough to leave the burrow. This helping behavior has a direct effect on the pups, and it also affects the breeding female by reducing the time and energy that she must devote to pup care. Babysitting, especially when it includes allolactation, is very costly to the baby-sitters, who must therefore derive substantial fitness benefits from the behavior. The majority of meerkats baby-sit at least once in each breeding season, and some meerkats spend more time at the burrow with pups than others. Animals that spend the most time baby-sitting tend to be closely related to the breeding female, indicating the influence of kin altruism. These baby-sitters are just as likely to be male as female (Clutton-Brock et al., Feb 1998).
Costs of Babysitting Baby-sitters remain at the burrow with pups all day. They forfeit their foraging opportunities, fasting for more than twenty four hours at a time (Clutton-Brock et al., Feb 1998). Baby-sitters usually switch off from day to day so that they do not go for an extended period of time without food, though some meerkats baby-sit for four or more consecutive days. Helpers contribute to pup care through thermoregulation and predator protection. They also move pups if the burrow floods while the band forages (Doolan and MacDonald, 1997, Zoology). However, the most substantial way that meerkats contribute to pup raising is allolactation. Subordinate females who have lost a litter are most likely to allolactate, though meerkats may be able to lactate in response to suckling (Scantlebury et al., 2002).
	Photo courtesy of the San Diego Zoo
Costs of baby-sitting can be measured by weight decrease during the period of pup growth to which baby-sitters contribute. The breeding female and baby-sitters who don’t baby-sit regularly do not lose weight over this period (Scantlebury et al., 2002). Those who baby-sit often experience significant weight loss (Clutton-Brock et al., Feb 1998). Allolactators lose the most weight (Scantlebury et al., 2002). Clearly, the costs of baby-sitting are significant. In addition to the cost of reduced foraging time, baby-sitters also endure the risks involved in defending pups from predators and from entering flooding burrows to move pups. If non-breeding baby-sitters lose more weight than the breeding female, they must garner benefits that balance out the cost of babysitting.

Influences of Babysitting
A breeding female invests the maximum amount of energy that she can into producing offspring (Scantlebury et al., 2002). Because meerkat pups need constant care and care precludes foraging, she cannot raise her pups alone. She needs the help of baby-sitters. Pup survival increases with increasing numbers of helpers. However, the main factor influencing litter size and pup survival is pup weight (Russell et al., 2002). Pup weight at birth depends on the weight of the breeding female at conception (Russell et al., 2003). Weight at emergence depends directly on weight at birth, and reproductive success depends directly on weight at emergence (Russell et al., 2002). Thus, a meerkat’s fitness can be predicted in part by the weight of its mother at its conception.

Meerkat females often conceive soon after giving birth, so they experience significant energy drains in the form of lactation and gestation. Weight at conception depends on the amount of energy a female has had to dedicate to her previous litter. By baby-sitting pups, helpers reduce the amount of energy the breeding female must expend on her offspring and increase the amount of time she can spend foraging. As a result, they increase the number of litters that she can give birth to each year (Russell et al., 2003). By allowing her to forage more often, helpers increase her weight and thus the weight of her pups. The amount of baby-sitting per pup does not depend on helper number. Instead, helpers increase the percent of their time spent helping as their numbers decrease (Clutton-Brock et al., Feb 1998). Ultimately, helpers contribute not by increasing pup survival, but by increasing female fecundity and pup long term fitness.

Benefits to Baby-sitters Because the costs that they experience are so great, baby-sitters must derive significant benefits from increase in pup number and pup fitness. These benefits may be direct or indirect. If they are direct, natural selection is responsible for maintaining helping behavior in the population. If they are indirect, kin selection is at work.
Direct benefits are found in the increase in group size that occurs when the breeding female has more litters per season. A larger group increases predator surveillance and defense, which is crucial to meerkats, who experience such a high predation rate. Direct benefits also occur because pups that are born thanks to helping behavior may mature to become helpers. If the original baby-sitters gain breeding status, they will have more helpers and will be able to produce more litters of their own. If they don’t gain breeding status, they will have to invest less energy in helping behavior, as it will be diluted by the presence of additional helpers.
Indirect benefits occur only when the helpers are related to the pups born to the breeding female. Because they share genetic information, helpers’ genes are passed down when the breeding female produces more pups. The more closely related they are, the more of the helpers’ genes are passed on, and the more fitness they gain. In this case, helping behavior is not selected against because better helpers will have more indirect fitness.

Meerkats live in kin groups, and animals that do the highest percent of baby-sitting are related to the breeding female. This supports kin selection as the means by which helping is passed down from generation to generation. However, meerkats immigrate, and foreign animals, who share little or no genetic information with the breeding female, contribute equally to baby-sitting efforts. This can only be explained by natural selection, as the immigrant helpers get no indirect fitness benefits from babysitting. The only conclusion is that baby-sitting brings benefits that can be direct and indirect, and that both natural selection and kin selection are responsible for maintaining this behavior in the population. The extent to which each affects helping has yet to be determined (Clutton-Brock et al., Feb 1998).

Evolution of Cooperation Many different theories for the evolution of cooperative breeding in meerkats exist. One suggests that meerkats’ diet paved the way for helping behavior. The abundance and predictability of food led to group living. It is not feasible to take insects to and from the den to provision young, and ability to forage takes time to develop. Adults cannot gather food and take care of young at the same time, so eventually parents must leave the burrow to get food. Helpers evolved because pups cannot survive on their own (Doolan and MacDonald, 1996, Zoology: 239). Another theory is that cooperative breeding is derived from energetic constraints on the dominant female. She simply cannot reproduce regularly and take care of her pups because the investment would be more than she can physically bear. Her energy intake must be high, and helpers invest energy in her young so that she can forage more. As a result, she survives to reproduce again (Scantlebury et al., 2002.
A third hypothesis is that the environment was the primary influencing factor in evolution of cooperation in meerkats. Rain is unpredictable and increases resource abundance. When the rainy season contains dry spells, which are common, the breeding female would not be able to survive if she had to lactate and take care of pups while subsisting on limited resources (Doolan and MacDonald, 1997, Zoology). Another possible stimulus for cooperative breeding is predation pressure. Pups alone in the den risk predation, so they benefit when an adult stays with them. Meerkats are safer in groups, and if the breeding female spent part of the day foraging and then left the group to take care of her young, she would risk predation. There would be a higher turnover in female dominance, and subordinates would expend more energy fighting for the position. This hypothesis also explains why baby-sitters do not switch off in the middle of the day.
While it is impossible to reconstruct the evolution of cooperative breeding in meerkats, it is probably described by some combination of the above hypotheses, along with other influences that have yet to be determined.

Pup Feeding
Once pups emerge from the den, they follow alongside the adults as they forage and beg for food. They emit a call constantly that reminds foraging adults that they are present. When an adult close by catches prey, the pups emit a higher pitched noise in an effort to convince the adult to feed them the prey. The calls do not reflect the hunger of the pup. Adults feed the closest pup (Manser and Avey, 2000), and they are more likely to feed pups large prey than small prey. Thus, the time spent interacting with the pup is less, minimizing foraging time lost per mass of food. Adults are more likely to feed pups than are juveniles because juveniles spend more energy growing and are less successful foragers. Parents and helpers feed pups at equal rates according to their sex. Females feed pups more than males because they stand to benefit more from an increase in group size. If they are dominant or become dominant, their fitness will depend on helper number (Brotherton et al., 2001).

Though meerkats live in kin groups, the above information points to natural selection as the primary influence on pup feeding. All meerkats benefit from an increase in group size, though females benefit more than males. Feeding rates depend on age and sex of the feeder, size of the prey, and proximity of the pup, and not on relatedness of pup and feeder. Indirect fitness is only a slight secondary consequence of natural selection in pup feeding. The behavior is ultimately selfish.

Sentries and Mobbing Behavior
When meerkats forage, a sentry stands guard, sacrificing foraging time to watch for predators. Larger groups may have multiple sentries at a time (Bednekoff, 1997), though sentry behavior is more prominent in smaller groups because there are fewer eyes to spot predators (Brotherton et al., 2001). While they are guarding, sentries are safer than foraging animals because they have a better view of the surroundings and are focusing all of their energy on predator detection, though they face an increased risk of predation when leaving or rejoining the group. An animal can only serve as a sentinel if it can afford not to forage. Meerkats sentinels give alarm calls that warn other meerkats to retreat to the burrow. They do not preferentially warn relatives, and immigrants serve as sentinels (Bednekoff, 1997). These facts lead to the conclusion that natural selection is the means by which sentinel behavior is passed on genetically.

Mobbing behavior occurs in response to ground predators. One or more meerkats attacks a predator in an effort to prevent it from killing band members. Helpers often mob predators that attack pups. This behavior has both direct and indirect fitness benefits, though the influence of each is not clear.

Click here to see a short clip of sentry behavior.

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This web site was completed by Katie Fitzpatrick in partial fulfillment of the requirements for Dr. Verna Case’s Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2004.

Please direct all comments and questions to Katie Fitzpatrick at kafitzpatrick@davidson.edu