Wednesday, December 16, 2020

Whole genomes map pathways of chimpanzee and bonobo divergence

A bonobo in the wild. "Understanding the physiological mechanisms underlying the differences in chimpanzee and bonobo behaviors may also give us information about the genes underlying our own behaviors," says Emory anthropologist John Lindo. (Photo by Sarah Kovalaskas)

By Carol Clark

Chimpanzees and bonobos are sister species that diverged around 1.8 million years ago as the Congo River formed a geographic boundary and they evolved in separate environments. Now, a whole-genome comparison of bonobos and chimpanzees reveals the gene pathways associated with the striking differences between the two species’ diets, sociality and sexual behaviors. 

The journal Genes, Brain and Behavior published the comparative analysis, conducted by anthropologists at Emory University.

 

“Our paper is the first whole-genome positive selection scan between chimpanzees and bonobos,” says John Lindo, Emory assistant professor of anthropology and senior author of the study. “We contrasted the genomes of both species to understand how natural selection has shaped differences between the two closely related primates.”  

 

Lindo is a geneticist specialized in ancient DNA and natural selection. “Chimpanzees and bonobos are fascinating because they are very, very closely linked genetically but they have huge behavioral differences,” he says.

 

The two species also share around 99 percent of human DNA, making them our closest living relatives in the animal kingdom. “Understanding the physiological mechanisms underlying the differences in chimpanzee and bonobo behaviors — particularly the much stronger propensity of bonobos toward conflict resolution instead of fighting — may also give us information about the genes underlying our own behaviors,” Lindo says.

 

Sarah Kovalaskas, an Emory graduate student of anthropology, is first author of the paper. Before joining Emory she spent nine months in the field, studying the social development of juvenile bonobos in the Democratic Republic of Congo (DRC). Wild bonobos, an endangered species, are only found in forests south of the Congo River in the DRC.

 

“Bonobos are well-known for being playful, even as adults,” Kovalaskas says. “It was fun to observe the juveniles twirling around in the trees, chasing one another and trying to pull each other down. When the mothers tried to wean them, they would sometimes throw tantrums and scream and run around. You can’t help but recognize the similarity in behaviors to humans.” 


Emory graduate student Sarah Kovalaskas in the field in the Democratic Republic of the Congo.
 

Populations of chimpanzees, also an endangered species, are found in a forested belt north of the Congo River and scattered in a few other areas of west and central Africa. 

 

Bonobos and chimpanzees closely resemble one another physically and they were not recognized as separate species until the 1930s. Their behavioral differences are much more distinct. While bonobos organize into female-led societies, chimpanzees are patriarchal. When bonobos encounter other bonobo groups they generally interact peacefully. Bonobos are also known for using sexual behaviors to defuse tension — including same-sex behaviors among females. Chimpanzees, however, tend to act more aggressively when encountering other chimpanzee groups and may even have violent exchanges that include fatalities. 

 

A leading hypothesis suggests that different feeding ecologies were key to the behavioral divergence between the two species. This theory posits that the abundant ground vegetation in the bonobo territory provided easy access to year-round food without competition from other individuals. Larger groups could feed together instead of foraging in isolation, allowing females to develop strong bonds to counter male domination, and to mate with less aggressive males, leading to a kind of “self-domestication.”

 

The whole genome comparison showed selection in bonobos for genes related to the production of pancreatic amylase — an enzyme that breaks down starch. Previous research has shown that human populations that began consuming more grains with the rise of agriculture show an increase in copies of a closely related gene that codes for amylase.

 

“Our results add to the evidence that diet and the available resources had a definite impact on bonobo evolution,” Kovalaskas says. “We can see it in the genome.”

 

Compared to chimpanzees, bonobos also showed differences in genetic pathways well-known to be related to social behaviors of animals — as well as humans. Bonobos had strong selection for genes in the oxytocin receptor pathway, which plays a role in promoting social bonds; serotonin, involved in modulating aggression; and gonadotropin, known to affect sexual behavior.

 

“The strong female bonds among bonobos, in part, may be mediated by their same-sex sexual behaviors,” says co-author James Rilling, professor and chair of Emory’s Department of Anthropology. “Our data suggest that something interesting is going on in the bonobo pathways for oxytocin, serotonin and gonadotropin and that future research into the physiological mechanisms underlying behavioral differences between bonobos and chimpanzees may want to target those specific systems.”


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Thursday, December 10, 2020

First-known iguana burrow fossil discovered

An illustration of how the trace fossil of the iguana burrow (shown in cross-section) and the surrounding landscape may have looked during the Late Pleistocene Epoch. (Illustration by Anthony Martin)

The discovery of the first known fossil iguana nesting burrow, on an outer island of the Bahamas, fills in a gap of scientific knowledge for a prehistoric behavior of an iconic lizard. PLOS ONE published the finding by scientists from Emory University, which also uncovers new clues to the geologic and natural history of the Bahamas. 

The fossilized burrow dates back to the Late Pleistocene Epoch, about 115,000 years ago, and is located on the island of San Salvador — best known as the likely spot where Christopher Columbus made his first landfall in his 1492 voyage. 

“San Salvador is one of the outer-most islands in the Bahamas chain and really isolated,” says Anthony Martin, a professor in Emory’s Department of Environmental Sciences and senior author of the PLOS ONE paper. “It’s a mystery how and when the modern-day San Salvadoran rock iguanas arrived there. Today, they are among the rarest lizards in the world, with only a few hundred of them left.”

Martin’s specialty is ichnology — the study of traces of life, such as tracks, nests and burrows. He documents modern-day traces to help him identify trace fossils from the deep past to learn about prehistoric animal behaviors. 


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Thursday, December 3, 2020

A new view of how the brain decides to make an effort

"The willingness to expend effort is something crucial to our survival that we use every day," says Emory psychologist Michael Treadway, senior author of the study.

Neuroscientists have provided clear visual evidence that a region of the human brain known as the ventral striatum kicks in during decision-making to weigh the costs versus the benefits of making a physical effort. 

Nature Human Behavior published the research by scientists at Emory University. It gives the first detailed view of ventral striatum activity during three phases of effort-based decision-making — the anticipation of initiating an effort, the actual execution of the effort and the reward, or outcome, of the effort. 

“It’s important to understand the neural mechanisms underlying motivation,” says Shosuke Suzuki, first author of the study and an Emory graduate student of psychology. “Our work has wide implications for treatment of disorders related to reduced motivation, such as depression, schizophrenia and PTSD. It may also help enhance motivational programs for everything from education to athletics and public health.”


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