Sociality in the framework of Tinbergens questions

What do we know about phylogeny? It is not normally possible to find behavior in fossilized form, thus we have to take another, but also reliable approach, by comparing the phenomenon in question among as many living species as possible. When doing this with regard to social systems, the most basic one seems to be a sort of solitary or dispersed female system, foraging alone in undefended home ranges. This pat tern can be found in members of so many different taxa that we may assume it to be one that their common ancestors probably shared. Taking males into account as well, we can assume that a system of dispersed polygyny, one male overlapping the ranges of several females, probably was the basic male-female system. From the basic female system, evo-

A spotted hyena (Crocuta crocuta) feeds on a young elephant that a lion killed earlier. (Photo by Harald Schütz. Reproduced by permission.)

lutionary paths could have led either via territorial defense (then group defense and dispersed feeds) to social foraging in group territories, or without defense, via formation of ephemeral, and then later persistent groups.

What do we know about selective advantages of sociality? Behavioral ecology and sociobiology, those areas of behavioral biology that deal with this question, are among the most productive ones in about 20-30 years. Thus, only a few studies should be mentioned, to cover several aspects of this question. Anti-predator vigilance in the dwarf mongoose is, over a longer period of time, only guaranteed in groups of at least six adults; smaller groups sooner or later fell prey to raptors. Jackal pairs with one or more helpers had more success in rearing young—the energetic demand on parents for hunting and producing milk was significantly lower, and juvenile survival higher. Adult male sugar gliders that share dominance with an adult son have a higher proportion of time spent with young in the absence of the mother, which is helpful in defending as well as warning them. Pairs of klipspringer take turns in anti-predator vigilance, one feeding while the other watches out. Eastern gray kangaroos form larger groups in open areas and also during those times of the day when their main predator, the dingo, is likely to hunt. Lastly, survival of alpine marmots is higher when more young of the previous year hibernate together with their parents.

Physiological mechanisms that regulate mammalian social behavior are also currently subjects of intense studies. We already heard about the influence of oxytocin on development of social bonding, studies which have predominantly been conducted on the monogamous vole Microtus ochrogaster. Pro-lactin has been identified as the hormone of parental care, and, excitingly enough, is not only maternal but also elevated in helpers, such as subordinate individuals in canid packs that help to rear the alpha pair's young. Testosterone in both sexes is connected with status/dominance position. Remarkably enough, testosterone levels often follow, not precede, an increase in status such as after winning a fight. Cortisole, one of the stress-related glucocorticoids, actively lowers status-related behavior and makes an individual more submissive, particularly in contest-related aggressive situations. Stressful reactions to potentially harmful or frightening situations are lower, or absent, if the situation is encountered in the presence of one's bonding mate.

Finally, some data related to the fourth Tinbergen question, ontogeny. The importance of complete socialization has been demonstrated in countless studies. Guinea pig males that had been reared in an all-female group were unable to integrate themselves peacefully into new colonies at sexual maturity due to a lack of two important behaviors: they did not behave submissively towards adult males, and they courted any female (even firmly bonded ones) that they might meet. However, young males reared in the presence of an adult male performed "correctly" immediately after introduction, and thus were integrated without any stress or aggression. Feral cats reared in the presence of other cats (or people) apart from their mothers and litter-mates, and coyote pups raised in presence of adult helpers at the den, became more gregarious than those without these influences. Monkeys reared in isolation were unable to perform socio-sexual behavior correctly, if they did not get at least regular play sessions with other juveniles. Female monkeys without experience in baby care (prior to giving birth themselves) were less competent in handling their own infants.

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