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Male bonding works for dolphins too

By Dave Armstrong - 28 Mar 2012 0:1:1 GMT
Male bonding works for dolphins too

Bottlenose dolphins image via Shutterstock

As a successful, 'catholic feeder', the bottlenose dolphin occurs worldwide as different sub-species, now often becoming species. Genetics can really help with rare organisms where we need to conserve and maintain species integrity. Here however, the Indo-pacific bottlenose (Tursiops sp!), is being studied in all its behavioural glory as a near match for advanced human and other sociability. Srdan Randic, Richard Connor, William Sherwin from the University of Massachusetts and the University of New South Wales and Michael Krutzen from the University of Zurich have collaborated on a paper that should really challenge us to comprehend what some animals understand about each other. Proceedings of the Royal Society B: Biological Sciences publish it today.

While elephants have matrilineal groups and chimpanzee use male bonding to a high degree, the dolphin lives in an environment where sociability can be more freely practised. The travel cost of moving around for some animals is so great that social aspects of behaviour are reduced. Elephants have the lowest recorded cost of locomotion for a terrestrial mammal. Dolphins themselves require little effort to greet, meet and even breed, possibly without being noticed, at least by human experimenters. Even humans have developed at least partly because they evolved a lean mean bipedal locomotion method. Dolphin social relationships however require semi-closed groups, even in Shark Bay, Western Australia. Male alliances are "nested," meaning that they cooperate in groups of two or three (first-order alliances) to consort with female individuals and, in larger groups, to attack and defend other alliances.

Boundaries between groups are variable, leaving a kind of social network available to young, aspirational male dolphins who want to get on. Females behave much as in chimpanzee society (and some human), with less same-sex bonding than the male. The larger male alliance (second-order) of up to 14 individuals has been seen to last for > 15 years. It can extend to a third type of alliance in which a relationship establishes with other alliances, in order to resolve conflicts over females.

Shark bay is the first and only population in which three types of alliance between males have been established. Petting, rubbing and synchrony of behaviour, as seen here, are the hallmarks of affiliation.

A pod of bottlenose dolphins

A pod of bottlenose dolphins form second-order alliance groups that can interact; Credit: The Dolphin Alliance Project

Females in the Shark Bay Tursiops population have variable relationships, but seem to form no alliances against other females. In the last 25 years, only once have female coalition banded together to temporarily to fight off aggressive young males. It seems the classic female defence force found in many other mammals is absent, at least from the females of Shark bay. The sex-specific bonding in the dolphins here is termed fission-fusion group formation. Although much closer than the same formation in chimpanzees or other terrestrials, there is no community territory.

Individuals in such groups must learn the rank and kin relationships of group members. This may have contributed to brain evolution, but more directly, prevents individuals from performing certain behaviours. How does an individual assess the risk of any procedure, whether in mating or taking food from a smaller animal? In particular, what happens when a new alliance changes the risk? Dolphins' "fluid" social system might allow deviations from the terrestrials' more limited social structure.

The data was collected over five months, including the breeding season, for five years. "Groups" were defined as those within a 10m limit of each other.

These two males are exhibiting

These two males are exhibiting "synchrony," swimming in unison to demonstrate their pair bond; Credit: The Dolphin Alliance Project

The third-order alliances with other groups seemed to be involved with exclusive access to females. Total home range for each second-order alliance was plotted, including a core range of 50% of the complete recorded area. As expected no group extended over the whole study area, the largest estimated alliance area being 229km2. Some alliances had no overlaps, but mating season overlap was extensive, even when they didn't have a third-order alliance with other groups. The females were consorted by first-order alliances of up to three males. Sixty five females travelled in three or more consorting groups, with only one popular girl seen with a second-order alliance group and in three consortships. Many third-order alliances seemed to be involved in 31 female consortships out of 32. These ladies also chose to be in at least two consortships with males from more than one second-order alliance.

All of this documentation provides evidence that the novel social system employed is open, with mosaics of overlapping female and male ranges. A much larger network is suggested by the data as at least 100 other males appeared during the survey. Apparently, their alliances overlapped those of the survey groups. As second-order alliances begin in the males' teen years, kinship alliances are less likely, and were completely absent in one large second-order alliance studied.

two bottlenose dolphins in Shark Bay

These two bottlenose dolphins in Shark Bay have performed a "fission" from the main group and show typical dolphin synchrony again, but can be regarded as "fusing" once more when they rejoin their second-order alliance group; Credit: The Dolphin Alliance Project

The authors finally compared the dolphins with other fission-fusion societies in mammals, cetaceans and birds. Unlike the chimpanzee society, these dolphins don't have semi-closed, male defended communities, despite superficial resemblance. Bonobos are close to chimpanzees, but can provide a very basic interactive third-order alliance for group members. The dolphins complex nested alliance has no equal in these primates, but matrilineal elephant groups seem to ally in some ways with other groups.

If we could study sperm whales, their society could be as Dr. Doolittle suggested, but, alarmingly, we have to seek out a small parrotlet called Forpus to discover great similarities with the dolphins of Shark Bay. These birds belie their relatively-unknown status by using strong fission-fusion patterns and communicating with individually-distinctive contact calls.

It remains to be seen if any such parrot has an alliance structure outside of pair bonding and an open social network, but I wouldn't put it past my wise old African Grey! As Dr Richard Connor, puts it, "the possibility is really interesting because both the parrotlets and dolphins have individual-specific contact calls and both live in a big fission-fusion society. At the moment, we do not know if the parrotlets have alliances beyond the pair-bond or if their society is open or closed."

Forpus passerinus

Forpus passerinus, the alarmingly-sociable green-rumped parrotlet - Green-rumped Parrotlet image via Shutterstock

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Topics: Dolphins