behavioral ecology – It's Interesting

mice

It is a cruel world out there, particularly for young animals born into social groups where infanticide occurs. This dark side of evolution is revealed when adults – often males – kill offspring to promote their own genes being passed on, by reducing competition for resources or making females become sexually receptive more quickly.

This behaviour proves expensive for females, who have evolved strategies to avoid this fate. One strategy is to join forces with other females to physically ward off killer males. A more interesting strategy is to mate with several males, known as “polyandry”, so fathers can’t distinguish their young from others’, which means they avoid killing pups so that they don’t accidently kill their own.

Now, researchers at the University of Zurich have found a new type of infanticide counter-strategy: mothers can achieve paternity confusion even if they don’t mate with multiple males, through nesting with other females, which they call “socially mediated polyandry”. And such a strategy might be happening close to home, in the unassuming house mouse.

Yannick Auclair and his colleagues put their theory to the test on a wild population of mice living in an old agricultural building outside Zurich. They measured the genetic relationships within litters and found a complex picture of female social relationships and mating patterns. These allowed them to identify mothers nesting alone or with others and those who mated with one or more males. To examine the risk of infanticide for pups born into these different types of litters, they assessed survival until just before weaning, which is about two weeks after birth.

Direct observations of infanticide are extremely rare in natural systems. But studying an enclosed population without the presence of a predator meant that infanticide becomes the most likely cause of death for young pups. And indeed, from the corpses of pups that were recovered, most gave direct evidence – missing limbs or holes in the skull – of this harsh fate.

The results of the study were published in the journal Behavioral Ecology. The researchers found that pups born to females nesting alone and who had only one mate had the lowest survival rate (50% surviving, the rest presumably killed by males who were confident they were not the father). Meanwhile, those born to females nesting together were better off (80% surviving).

Key evidence supporting their theory was that some of these communal litters were composed of pups whose mothers had actually only mated once, but the different females had different mates. These litters had similar survival to those where paternity was mixed for individual mothers, suggesting that mothers can achieve the same survival benefits of communal nesting without mating with multiple males.

There were also a few communal litters (nine of the 90 studied) where the different females had mated with the same male and, as such, featured multiple mothers but no paternity confusion. These litters had worse survival rate (40% surviving) suggesting that – as predicted by the theory – paternity confusion is a more important driving factor of communal nesting than the physical warding off of males.

According to Elise Huchard of CNRS Montpelier: “This study presents an interesting idea, and an interesting system to test it.” Yet the data raise more questions than they answer – and additional experiments or comparative work would be insightful.

For example, it is not clear whether higher survival in litters with multiple fathers might actually reflect variation among females if, as in the case of mouse lemurs, higher-quality females have more mates. Dieter Lukas of Cambridge University concurs that the theory is interesting, but believes it is too early to assess its generality.

Infanticide occurs across diverse mammal systems – from meerkats and rabbits, to lions and gorillas – and comparative analyses could help assess how this theory fares among the many hypotheses about the evolution of infanticide.

Communal nesting may have evolved as an alternative to mating with multiple mates (which is costly when males harass females during mating or transmit disease) as a strategy to avoid infanticide through paternity confusion. “We don’t know whether other social behaviours may have evolved through similar ways,” said Auclair.

Comparative analyses will lead to new insights and future research on the nest-box population will also address such interesting questions as how females choose their nesting partners – and why some still nest alone even if this comes at a cost to offspring survival.

http://theconversation.com/whos-your-daddy-mice-nest-together-to-confuse-paternity-and-reduce-infanticide-31796

When an elephant killed a Maasai woman collecting firewood near Kenya’s Amboseli National Park in 2007, a group of young Maasai men retaliated by spearing one of the animals.

“It wasn’t the one that had killed the woman, says Graeme Shannon, a behavioral ecologist at Colorado State University, in Fort Collins. “It was just the first elephant they encountered—a young bull on the edge of a swamp.”

The Maasai spiked him with spears and, their anger spent, returned home. Later, the animal died from his wounds.

Elephants experience those kinds of killings sporadically. Yet the attacks happen often enough that the tuskers have learned that the Maasai—and Maasai men in particular—are dangerous.

The elephants in the Amboseli region are so aware of this that they can even distinguish between Ma, the language of the Maasai, and other languages, says a team of researchers, who report their findings today in the Proceedings of the National Academy of Sciences.

The results add to “our growing knowledge of the discriminatory abilities of the elephant mind, and how elephants make decisions and see their world,” says Joyce Poole, an elephant expert with ElephantVoices in Masai Mara, Kenya.

Indeed, previous studies have shown that the Amboseli elephants can tell the cattle-herding, red-robed Maasai apart from their agricultural and more blandly dressed neighbors, the Kamba people, simply by scent and the color of their dress.

The elephants know too that walking through villages on weekends is dangerous, as is crop raiding during the full moon.

They’re equally aware of their other key predator, lions, and from their roars, know how many lions are in a pride and if a male lion (the bigger threat because he can bring down an elephant calf) is present.

And they know exactly how to respond to lions roaring nearby: run them off with a charge.

Intriguingly, when the Amboseli elephants encounter a red cloth, such as those worn by the Maasai, they also react aggressively. But they employ a different tactic when they catch the scent of a Maasai man: They run away. Smelling the scent of a Kamba man, however, troubles them far less.

“They have very clear behavioral responses in all of these situations,” says Karen McComb, a behavioral ecologist at the University of Sussex, in the United Kingdom. “We wondered if they would react differently to different human voices.”

To find out, she and her colleagues played recordings to elephant families of Maasai and Kamba men, as well as Maasai women and boys, speaking a simple phrase in their language: “Look, look over there, a group of elephants is coming.”

Over a two-year period, they carried out 142 such playbacks with 47 elephant families, each time playing a different human voice through a concealed speaker placed 50 meters (164 feet) from the animals. They video-recorded the elephants’ reactions to the various human voices, including a Maasai man’s voice they altered to sound like a woman’s.

As soon as an elephant family heard an adult Maasai man speak, the matriarch didn’t hesitate, the researchers say. “She instantly retreats,” Shannon says. “But it’s a silent retreat. They sometimes make a low rumble, and may smell for him, too, but they’re already leaving, and bunching up into a defensive formation. It’s a very different response to when they hear lions.”

In contrast, the voices of Kamba men didn’t cause nearly as strong a defensive reaction: The elephants didn’t consider the Kamba a serious threat.

“That subtle discrimination is easy for us to do, but then we speak human language,” says Richard Byrne, a cognitive biologist at the University of St. Andrews, in Scotland. “It’s interesting that elephants can also detect the characteristic differences between the languages.”

The Amboseli elephants were also sufficiently tuned in to the Maasai language that they could tell women’s and boys’ voices from men’s, seldom turning tail in response. “Maasai women and boys don’t kill elephants,” Shannon points out. Nor were the elephants tricked by the man’s altered voice; when they heard it, they left at once.

“The elephants’ decision-making is very precise,” McComb says, “and it illustrates how they’ve adapted where they can to coexist with us. They’d rather run away than tangle with a human predator.”

Why, one wonders, don’t elephants retreat when poachers descend on them?

“Unfortunately, there are going to be things they cannot adapt to, things such as humans’ ability to come after them with automatic weapons or mass poisonings,” McComb says. “And in those situations, we have to protect them—or we will lose them, ultimately.”

http://news.nationalgeographic.com/news/2014/03/140310-elephants-amboseli-national-park-kenya-maasai-kamba-lions-science/?google_editors_picks=true

Thanks to Da Brayn for bringing this to the It’s Interesting community.

It's Interesting

Category: behavioral ecology

Scientists learn that mice nest together to confuse paternity and reduce infanticide

New research shows that elephants know how dangerous people are from how they speak