December 4, 2012
Lemur Love: How Daughters Avoid Mating With Dad

Tiny nocturnal lemurs recognize their dad’s cries amid the other sounds of the nighttime Madagascar forests, a new study finds. The research is the first to show that solitary animals may avoid inbreeding by keeping an ear out for familiar voices.

Previous studies have found that animals living in complex social groups have no trouble recognizing their own kin’s calls, particularly the sounds of maternal relatives. Even goat mamas keep a long-term memory for their baby’s calls, according to a study published earlier this year.

But less is known about how animals recognize their father’s calls, and the cries of the relatives on dad’s side of the family. Likewise, researchers know very little about how solitary-living animals avoid inbreeding with dad’s side of the family.

That’s where the gray mouse lemur (Microcebus murinus) comes in. These cartoonishly cute lemurs are raised by their mothers without help from dad. When they grow up, they head out of the nest to forage on their own. But male lemurs’ ranges are large, and they often overlap with that of their daughters’, suggesting the primitive primates have evolved some way to avoid accidentally mating with a relative.

To find out how, researchers led by Arizona State University’s Sharon Kessler played male mating calls and alarm cries for 10 adult female gray mouse lemurs housed at the University of Veterinary Medicine in Hannover, Germany. Each lemur heard her father’s cries as well as an unrelated male’s. The researchers recorded how attentive the lemurs were to each call. For example, an interested lemur might stare at or run over to the speaker playing the call.

The female lemurs paid equal attention to alarm calls from fathers and unrelated males, the researchers report in an upcoming issue of the journal BMC Ecology. But when it came to mating calls, lady lemurs perked up much more at unrelated male’s calls. Compared to when they heard a father’s cry, the lemurs approached the non-kin speakers faster, sooner and stayed longer looking for the source of the sound.

The take-away, Kessler and her colleagues wrote, is that recognizing dad’s voice requires neither a big brain nor a complex social life. In fact, ability to recognize kin may have preceded complex social structures in evolutionary history.

From livescience.com

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Filed under: Lemur Mouse Lemur Primate Prosimian Mating Call Communication Animal Science 
August 6, 2012
How Cooperation Can Trump Competition in Monkeys

Being the top dog — or, in this case, the top gelada monkey — is even better if the alpha male is willing to concede at times to subordinates, according to a study by researchers from the University of Pennsylvania, the University of Michigan and Duke University.

Alpha male geladas who allowed subordinate competitors into their group had a longer tenure as leader, resulting in an average of three more offspring each during their lifetimes.

The findings, collected from data during a five-year period ending in January 2011 through the University of Michigan Gelada Research Project, were published in theProceedings of The Royal Society.

The research was conducted by Noah Snyder-Mackler, then a graduate student in the Department of Psychology in Penn’s School of Arts and Sciences. He collaborated with Thore Bergman, assistant professor of psychology at Michigan, and Susan Alberts, professor of biology at Duke.

Cooperation is surprisingly common among wild animals, the researchers said. While it makes evolutionary sense for animals to help their kin, it is harder to explain cases where competitors — especially unrelated adult males — join forces. This conundrum is particularly hard to explain because mating is generally a zero-sum game in which males can only reproduce by stealing mating opportunities from each other.

Why would an alpha male allow other males to be a part of his unit, if they will inevitably decrease the probability that he will pass on his own genes? The researchers felt there must be a reason since this kind of behavior is observed in many species.

“For example, in some species unrelated males will sometimes tolerate the presence of one another and, in rare cases, form bonds and even appear to cooperate,” Snyder-Mackler said.

To understand why potential rivals might team up, researchers compared the fitness consequences for dominant male gelada monkeys living in single- or multi-male groups. They found that, although subordinate males father some of the offspring in multi-male groups, dominant males gain a lifetime fitness benefit because the subordinate aids in defense of the group from other males, thus extending the dominant male’s reproductive career.

Even more tantalizing is evidence that the subordinate males that are allowed to mate stay around in the group for much longer.

“This suggests,” Bergman said, “that the alpha males may allow the subordinate to reproduce as a ‘staying incentive’ for defending the group, a payment for their services.”

While it is not yet clear that a willing exchange is occurring — subordinate males may simply steal some chances at reproduction — the evidence is strong that subordinates confer some benefit to the leader.

“These findings demonstrate a benefit of forming multi-male groups in a predominantly single-male system, an important step in the evolution of sociality among unrelated competitors,” Bergman said.

Read More at sciencedaily.com

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Filed under: Gelada Hierarchy Mating Monkey Primate Social Social Structure Baboon Gelada Baboon 
May 4, 2012
taxonomynow: Bigger Gorillas Better at Attracting Mates and Raising Young ScienceDaily (May 1, 2012) — Beauty may be in the eye of the beholder, but even for gorillas, some traits stand out. A new study conducted in the rainforests of the Republic or Congo shows that female western lowland gorillas seek out bigger mates to father their offspring. Continue Reading

taxonomynow:

Bigger Gorillas Better at Attracting Mates and Raising Young

ScienceDaily (May 1, 2012) — Beauty may be in the eye of the beholder, but even for gorillas, some traits stand out. A new study conducted in the rainforests of the Republic or Congo shows that female western lowland gorillas seek out bigger mates to father their offspring.

Continue Reading

(via fyeahgreatapes)

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Filed under: Gorilla Ape Primate Breeding Mating Sex Selection Mate Selection 
February 29, 2012
Pregnant Monkeys Miscarry To Avoid Infanticide By New Males

When a new male gelada monkey takes control of a reproductive group, he will typically kill off the babies of his predecessor. Now, new research shows that pregnant females have an adaptive strategy to minimize their losses: They spontaneously miscarry.

In 1959, biologist Hilda Bruce first demonstrated the so-called Bruce effect in mice, where recently pregnant females miscarry after being exposed to novel males. Since then, researchers have documented the phenomena in other rodent species. However, until now, the Bruce effect seemed to be something restricted to the laboratory, as nobody had conclusively shown that it exists in wild animal populations. Moreover, studies have not shown that there is any evolutionary advantage to miscarrying when confronted with new males.

To see if the Bruce effect exists in gelada monkeys (Theropithecus gelada), Jacinta Beehner, an anthropologist at the University of Michigan, and her colleagues tracked 110 females across 21 groups of wild geladas living in the Simien Mountains National Park in Ethiopia.

“We saw that as soon as a new male came into a group, there were no births for the next six months,” Beehner told LiveScience. In fact, the researchers documented only two births in these replacement groups in the five years of the study. “We get this big gap, screaming out that something is going on — it’s statistically almost impossible to get this by chance.”

To be sure what they were seeing was indeed the Bruce effect, the researchers also took hormonal data from the fecal samples of females before and after a new male arrived. Out of the 10 cases of pregnancies the researchers looked at, eight of the females miscarried within two weeks of a new male coming on to the scene. Most surprising to the researchers, the miscarriages happened the same day the male took over.

Of the two females that didn’t miscarry, one quickly showed signs of fertility swelling and eventually mated with the new male while still pregnant. The other didn’t, and probably as a result, the male killed her infant, but didn’t kill the infant of the female with whom he mated. This behavior suggests that the males figure out which babies are theirs simply by knowing which females they mated with, Beehner said.

Females that miscarried as soon as new males arrived also became pregnant again, and the researchers saw a twofold increase in births during the seven to 12 months after new males took over. They also found that females that experienced such primate infanticide took longer to become pregnant again, suggesting these miscarriages are evolutionarily advantageous to the mama monkeys.

Peter Brennan, a physiologist at the University of Bristol in the United Kingdom who was not involved in the research, said that the study was quite convincing. “It’s a great example of pregnancy block being demonstrated quite convincingly in the wild,” said Brennan, who has studied the Bruce effect in lab mice. “And there’s good evidence that it’s adaptive in evolutionary terms.”

Brennan is curious as to exactly how the females miscarry. In lab mice, he notes, females miscarry after picking up on chemical signals put off by the new males. “The actual physiological mechanism (in geladas) may be different,” he said, adding that the miscarriages might be a response to social stress.

Beehner said that the next step is to pinpoint this mechanism, though this research cannot be conducted on a threatened wild primate like the gelada. Domestic horses may be good candidates for further research, as scientists have seen the Bruce effect in the species before, she said.

From msnbc.com

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Filed under: Monkey Primate Mating Social Society Reproduction Sex Miscarriage Infanticide 
October 20, 2011
Female Monkeys Indulge In Synchronised Sex

Supposedly, if women live together their hormonal cycles start to synchronise, thanks to a pheromone. If that were true it would mean that they all have their period simultaneously. Just think about it.

This “menstrual synchrony” argument was first reported in 1971 by psychologist Martha McClintock, who noticed signs of it in her own college dorm. But it may not really exist. Studies have had mixed results, often reporting no synchrony at all.

Assamese macaques, however, have evolved an unmistakable kind of synchrony: they all have sex at the same time.

Assamese macaques live in troupes of a few dozen, including about a dozen adults of each sex, plus offspring. Although there are strong social bonds within the troupes, they are dominated by the males, who compete vigorously to mate with the females.

The mating season runs from October to January, and the males become increasingly aggressive as it goes on. The males do show some solidarity. If a female attacks a male, other males will rally to his defence. But it is the females who form close friendships with each other, while males are only loosely allied with their fellows.

The females also have ways of resisting the males’ control of the troupes, says Ines Fürtbauer of the University of Göttingen in Germany. For one thing, like human females, they do not show external signs of fertility, so males have no way of knowing whether the female they are mating with is actually able to conceive. The females mate throughout their cycles, further confusing the issue. As a result, the dominant males can’t monopolise fertile females. Instead each female mostly mates with her preferred male, regardless of how high-ranking he is – although she will mate with every male at some point.

This suggests that the females are trying to keep all the males friendly. Not knowing who fathered which baby, the males ought to refrain from killing young. In fact, Fürtbauer says, the young spend most of their time being cared for by the males.

It’s easier for a female to keep the males onside if she mates with all of them, but the dominant males will try to monopolise her. To find out how the females get around this problem, Fürtbauer and colleagues monitored a troupe of wild Assamese macaques in Thailand over two mating seasons. As well as monitoring their behaviour, they took samples of their dung: the hormone levels in it told the researchers where each female was in her cycle.

There was no sign of the females synchronising their hormonal cycles, but they did synchronise their sexual receptiveness. On a given day, each female was more likely to mate if other females were mating. Spoilt for choice, the alpha male could only mate with some of them, ensuring that the other females could mate with someone else.

Fürtbauer thinks the females are working together to thwart the dominant males, ensuring that each female can sleep around without getting punished for it.

From NewScientist.com

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Filed under: Monkey Macaques Primate Sex Oestrus Mating Reproduction 
October 5, 2011
Female Lemurs Benefit From Having Multiple Mates

While it may not be as socially acceptable among humans, a female choosing to take multiple mates is a common phenomenon in the animal kingdom. But why the practice of polyandry (a female having more than one male mate at a time) is so prominent is still a mystery in most species.

Most theories predict that taking multiple mates would be risky for a female without adding benefits. However, new research finds that in gray mouse lemurs, a type of small primate from Madagascar, healthy females seek out multiple mates in the few hours of one night they are receptive to mating every year. These multiple mates must confer some kind of benefit to the females, though exactly how they benefit is unknown.

“Males get benefits from mating with multiple females, because they can impregnate multiple partners,” study researcher Elise Huchard, of the German Primate Center in Göttingen, told LiveScience. “In most species, females only have a few oocytes [eggs], so mating with multiple males will not increase the number of offspring they will have.”

During the intense few hours female lemurs mate annually, two things can happen — either different males chase one female up to 100 times an hour, with some chases ending successfully in mating, or one male monopolizes her the whole night.

The females have a choice to make: Either let these males exhaust them while hunting for food, or choose to hide from the males and miss a night of feeding. During their normal breeding season, females are typically smaller than males. To see if size guided the choice and larger females could fight off the males better, the researchers fed the females either a normal food or a reduced-calorie chow.

They then watched the females on their mating nights, in a cage with three male lemurs. They expected to see the larger females push off the unwanted, harassing suitors. Instead, the researchers saw the heavy females scurrying around their cages mating with multiple males. The skinny females were more likely to be monopolized by one male lemur, and had fewer mates overall.

“Polyandry might not respond only to sexual conflicts [harassment], but also provide benefits to females,” Huchard said. “That’s probably quite general in animal societies; it’s been found in multiple studies in invertebrates.”

There is some evidence that a type of cryptic choice between different sperm donors occurs in these gray mouse lemurs. Previous studies have found that female lemurs in the wild preferentially use the sperm from mates with certain genes that are different from hers. Researchers don’t know how, but after mating with multiple males, the females are able to choose which male fathers her baby lemurs. It’s possible she can distinguish between each mate’s sperm, and uses only that from the most compatible mates.

In other species, it seems a female’s ability to make a cryptic choice can offer benefits to her offspringl. The female can choose males that are better genetic matches, for example those that aren’t her close relatives, which would make for healthier offspring.

And so this cryptic choice in mouse lemurs could be one way that taking multiple mates can benefit females in the long run, allowing them to choose the best genetic match, the researchers said.

The study was published Tuesday (Oct. 4) in the journal Proceedings of the Royal Society B: Biological Sciences.

From LiveScience

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Filed under: Lemur Lemurs Mouse Lemur Mating Reproduction Sex Breeding Oestrus Polyandry 
September 28, 2011
Promiscuous Apes Make More Sperm

Chimpanzees produce 200 times more sperm than gorillas, the world’s largest primates, and 14 times more than orangutans, scientists based in Japan reveal.

Promiscuous ape species have bigger testicles, and the latest discovery finally provides evidence that they also produce more sperm.

Scientists previously proposed that chimps have large testicles because several males mate with a single female, and so have to produce more sperm in order to compete.

For their research, published in the American Journal of Primatology, scientists studied chimpanzees, orangutans and gorillas from zoos in Japan and Indonesia.

Analysing samples of testicular tissues at a microscopic level, researchers found remarkable variation between the apes.

They found that the sperm-producing tissue lining gorillas’ testes was much thinner than that of orangutans and chimpanzees.

Chimpanzees were found to produce 14 times more sperm than orangutans and even more than the world’s largest primates.

“Our data indicated that a chimpanzee usually produces about two hundred times more sperm than a gorilla,” explained researcher Hideko Fujii-Hanamoto.

For these three species of ape, the scientists have now proven that testes size is proportionate to sperm production.

The researchers claim that these findings also support theories that sperm production relates directly to reproductive competition and mating behaviour.

Previous studies proposed that testes are smaller in polygynous species such as gorillas where one alpha male monopolises mating with multiple females.

In promiscuous species such as chimps however, there is greater competition between males as several copulate with one female.

This competition is thought to be the driving factor for sperm production and larger testes are thought to produce more sperm.

However, practical limitations meant sperm production in apes was difficult to accurately measure.

“It is generally difficult to get semen from the animals even if they [are] kept in zoological gardens,” said Ms Fujii-Hanamoto.

“Therefore, the testis weight or the ratio of testis weight [to] body weight was used to estimate the ability of sperm production.”

Visual observations confirmed that chimpanzees have larger testes compared to their body size than gorillas but it was not clear whether they actually produced more sperm.

From BBC Earth News

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Filed under: Ape Chimpanzee Chimp Gorilla Orangutan Primate Sex Mating Competition Reproduction 
September 25, 2011
Bonobos Make Most Noise When Mating With High Ranking Partners

The new study by researchers at the University of St Andrews suggests that females produce copulation calls as a way of showing off high powered relationships during sexual interactions. The psychologists set out to study vocal communication in apes, in particular investigating the social use of copulation calls in female bonobos.

Bonobos, the sister species of chimpanzees and closest living primate relative to humans, are known for their extensive use of non-reproductive sex for social purposes, such as making friends within groups.

Researcher Zanna Clay commented, “During mating events, females of many primate species produce loud and distinct vocalisations known as ‘copulation calls’, which are considered to promote the caller’s reproductive success. “Female bonobos are unusual amongst the non-human apes in terms of their heightened socio-sexuality. We found that female bonobos engaged in frequent sexual interactions with both males and other females, while producing copulation calls in both contexts.

“However, during same-sex mating, calls were always given by the lower-ranking partner, while the likelihood of calling increased with the partner’s rank, regardless of the partner’s gender.” The study, published in the latest edition of science journal Biology Letters, suggests that the increase in calls is a sign of signifying powerful friendships as well as pleasure.

The researcher concluded, “Our results highlight the social significance of sex in this species and suggest that copulation calls in bonobos have undergone an evolutionary transition from a purely reproductive function to a more general social function. “Like humans, sex among bonobos is not only used for reproduction, but it is also important in friendships and bonding, and keeping close to those in power.”

Source Physorg.com

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Filed under: Bonobo Chimpanzee Sex Mating Reproduction Ape Primate Social