Marsupials might have better social lives than previously believed.
Pooched animals are considered lonely, and they have been There are many types of social relationshipsA new analysis, published October 26, in recognition of the fact that these issues have been overlooked, was published by The New York Times. Proceedings of the Royal Society B suggests. These findings could impact how scientists view the lives of early mammals.
“These findings are helpful to move us away from a linear thinking that used to exist in some parts of evolutionary theory, that species develop from supposedly simple into more complex forms,” says Dieter Lukas, an evolutionary ecologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who was not involved with the study.
Mammals have a wide range of social organization systems. These include loose, temporary interactions like Jaguar aggregationsFrom the South American wetlands, to the antlike underground societies of Naked mole-rats (SN: 10/13/21; SN: 10/20/20).
But marsupials — a subgroup of mammals that give birth to relatively underdeveloped young reared in pouches — have traditionally been considered largely solitary. Some species of kangaroos were known to form temporary or permanent groups with dozens of members. However, marsupials are known to form long-lasting bonds between males or females. There is no evidence of members working together to raise young. Previous workBased on patterns of mammalian socio evolution, approximately 90 percent of all examined marsupial species were considered to be solitary.
“If you look at other [studies]You will find information about a specific species. [the researchers] tend to assume that the marsupials are solitary,” says Jingyu Qiu, a behavioral ecologist at CNRS in Strasbourg, France.
Sorting out social lives
Qiu and her coworkers developed a database of field research that illuminated marsupial sociology. They took into account the variation in populations within a species, and looked into the evolutionary history and marsupial society. The researchers compiled data from 120 studies on 149 populations of 65 marsupial species, categorizing each population as solitary, living in pairs — such as one male and one female — or falling into four kinds of group living, including one male and multiple females (or vice versa), multiple males and females, or single sex groups.
19 species, which is 31 percent, seem to be living alone. However, close to half of all species live in pairs or group situations. The team also found lots of variation within species; 27 of the 65 species — more than 40 percent — fell into multiple social organization classifications.
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The researchers compared this social variation to Australia’s climate conditions and found that social variation was more prevalent in dry environments that have less predictable rainfall. It’s possible that being able to switch between solitary and group living acts as a buffer against resource unpredictability.
The researchers’ focus on social flexibility “highlights that there is nothing simple even about a supposedly solitary species,” Lukas says.
Implications of the earliest mammals
Qiu, along with her colleagues, also conducted computer analyses that compared the evolutionary relationships of marsupials to how they form social relationships. This allowed the team to predict the social organization and evolution of the earliest marsupials. They split off from placental mammals around 160 million year ago. Because modern marsupials have been considered solitary, the marsupial ancestors — and the earliest mammals on the whole — have generally been assumed to be solitary as well.
The study found that the ancestral marsupials were most likely to be single, with a 35% probability. Qiu, however, points out that 65 percent of the remaining population can be found in combinations of group and pair living. So “it is more likely that the ancestor was also non-solitary,” she says. She also says the findings offer insight into the various lifestyles that early mammals could have experienced.
But Robert Voss, a mammalogist at the American Museum of Natural History in New York City, questions the analyses’ insights about a potentially social ancestral marsupial. The uncertainty about the solitary alternative, he says, is largely due to the researchers’ benchmarks for what does and what doesn’t constitute social behavior — thresholds that Voss views as too permissive. For example, Voss disagrees with the team’s characterization of opossum social organization.
“Anecdotal observations of [members of the same species] occasionally denning together is not compelling evidence for social behavior,” says Voss. “None of the cited studies suggest that opossums are anything other than solitary.”
Qiu says that future work will include collecting data on a larger number of mammals than marsupials in order to gain a better understanding of how social traits have evolved among mammals.
