University of Michigan
Department of Ecology and Evolutionary Biology

Monkey business: what howler monkeys can tell us about the role of interbreeding in human evolution

Did different species of early humans interbreed and produce offspring of mixed ancestry? Recent genetic studies suggest that Neanderthals may have bred with anatomically modern humans tens of thousands of years ago in the Middle East, contributing to the modern human gene pool. But the findings are not universally accepted, and the fossil record has not helped to clarify the role of interbreeding, which is also known as hybridization.

Now a University of Michigan-led study of interbreeding between two species of modern-day howler monkeys in Mexico is shedding light on why it's so difficult to confirm instances of hybridization among primates – including early humans – by relying on fossil remains.

One of the authors of the study, published online Dec. 7, 2012 in the American Journal of Physical Anthropology, is Dr. Liliana Cortés-Ortiz, an evolutionary biologist and primatologist and an EEB assistant research scientist at the Museum of Zoology. The study is based on analyses of genetic and morphological data collected from live-captured monkeys over the past decade. Morphology is the branch of biology that deals with the form and structure of animals and plants.

The two primate species in the study, mantled howler monkeys and black howler monkeys, diverged about 3 million years ago and differ in many respects, including behavior, appearance and the number of chromosomes they possess. Each occupies a unique geographical distribution except for the state of Tabasco in southeastern Mexico, where they coexist and interbreed in what's known as a hybrid zone.

The researchers found that individuals of mixed ancestry who share most of their genome with one of the two species are physically indistinguishable from the pure individuals of that species.

"The implications of these results are that physical features are not always reliable for identifying individuals of hybrid ancestry. Therefore, it is possible that hybridization has been underestimated in the human fossil record," said Cortés-Ortiz.

The paper was widely covered in the media, including the Spanish language news outlets. Previously on the U-M Gateway. 

U-M News Service press release and slide show

From humble beginnings: refreshed Animal Diversity Web reaches millions worldwide

University of Michigan biologist Philip Myers was preparing to teach a new animal diversity course for nonmajors, but he couldn't find a textbook that contained the right mix: detailed information about individual species, lots of photos, and material about ecology and conservation.

So Myers and a few U-M colleagues created a new learning tool called the Animal Diversity Web, a searchable database and multimedia encyclopedia of animal natural history that was launched on the fledgling World Wide Web in 1995.

From modest beginnings, ADW has steadily grown to become one of the world's largest and most widely used natural history websites. During busy months, more than 5 million pages of content are provided to more than half a million users worldwide, said Myers, who added that the popularity and global reach of his brainchild was "totally unexpected."

"I would attribute our success to the fact that we filled a niche, and we filled it early," said Myers, an ecologist and evolutionary biologist and a curator of mammals at the U-M Museum of Zoology. "This was the early days of the World Wide Web. At the time, we were one of the only animal diversity websites out there. And once we began seeing the potential impact that we could have on the field of animal diversity, we ran with it."

And now, thanks to the first top-to-bottom site redesign in more than a decade, ADW has a fresh new look, with more graphics, new navigation tools that provide quicker access to information, and added features such as daily "animal headlines." Check out the revamped ADW, which was redesigned by U-M's Michigan Creative, at http://animaldiversity.ummz.umich.edu.

"The original and continuing goal has been to use this for educating students," said Myers, a professor in the Department of Ecology and Evolutionary Biology. "We had no way of knowing, at the start, what the real potential of this project was. I could see that it had a great deal of potential for my personal use here at the University of Michigan, but the fact that somebody in Argentina would be using it in 2012 just never occurred to me."

U-M News Service press release

Climate warming unlikely to cause near-term extinction of ancient Amazon trees

A new genetic analysis has revealed that many Amazon tree species are likely to survive human-caused climate warming in the coming century, contrary to previous findings that temperature increases would cause them to die out.

However, the authors of the new study warn that extreme drought and forest fires will impact Amazonia as temperatures rise, and the over-exploitation of the region's resources continues to be a major threat to its future. Conservation policy for the Amazon should remain focused on reducing global greenhouse-gas emissions and preventing deforestation, they said.

The study by University of Michigan evolutionary biologist Christopher Dick and his colleagues demonstrates the surprising age of some Amazonian tree species – more than 8 million years – and thereby shows that they have survived previous periods as warm as many of the global warming scenarios forecast for the year 2100.

The paper was published online Dec. 13, 2012 in the journal Ecology and Evolution. The new study is at odds with earlier papers, based on ecological niche-modeling scenarios, which predicted tree species extinctions in response to relatively small increases in global average air temperatures.

"Our paper provides evidence that common Amazon tree species endured climates warmer than the present, implying that – in the absence of other major environmental changes – they could tolerate near-term future warming under climate change," said Dick, an associate professor of ecology and evolutionary biology and acting director of the U-M Herbarium.

U-M News Service press release

Saber-toothed cats and bear dogs: How they made cohabitation work

The fossilized fangs of saber-toothed cats hold clues to how the extinct mammals shared space and food with other large predators nine million years ago.

Led by the University of Michigan and the Museo Nacional de Ciencias Naturales in Madrid, a team of paleontologists has analyzed the tooth enamel of two species of saber-toothed cats and a bear dog unearthed in geological pits near Madrid. Bear dogs, also extinct, had dog-like teeth and a bear-like body and gait.

Soledad Domingo, a postdoctoral fellow at the U-M Museum of Paleontology, is the first author of a paper on the findings published in the Nov. 7, 2012 edition of Proceedings of the Royal Society B. Professor Catherine Badgley is co-author of the new study.

The researchers found that the cat species—a leopard-sized Promegantereon ogygia and a much larger, lion-sized Machairodus aphanistus—lived together in a woodland area. They likely hunted the same prey—horses and wild boar. In this habitat, the small saber-toothed cats could have used tree cover to avoid encountering the larger ones. The bear dog hunted antelope in a more open area that overlapped the cats' territory, but was slightly separated.

To arrive at their findings, the researchers conducted what's called a stable carbon isotope analysis on the animals' teeth. Using a dentist's drill with a diamond bit, they sampled teeth from 69 specimens, including 27 saber-toothed cats and bear dogs. The rest were plant-eaters.

U-M News Service press release

Genetic tradeoff: harmful genes are widespread in yeast but hold hidden benefits

The genes responsible for inherited diseases are clearly bad for us, so why hasn't evolution, over time, weeded them out and eliminated them from the human genome altogether? Part of the reason seems to be that genes that can harm us at one stage of our lives are necessary and beneficial to us at other points in our development.

The idea that the same gene can be both beneficial and harmful, depending on the situation, is called antagonistic pleiotropy. The theory has been around since the 1950s and has been used to explain aging, cancer and genetic diseases.

But until now, no one has been able to determine just how common antagonistic pleiotropy is -- on a genome-wide scale -- in any organism. In a paper published online Oct. 25, 2012 in the journal Cell Reports, Professor Jianzhi Zhang and his coworkers report that antagonistic pleiotropy is very common in yeast, a single-celled organism used by scientists to provide insights about genetics and cell biology.

Zhang and his colleagues say the findings have broad biomedical and evolutionary implications. "From our yeast data we can predict that humans should have even more antagonistic pleiotropy than yeast," he said. "This suggests that special cautions are needed when treating inherited diseases, because a treatment that removes a disease-causing genetic effect may lead to adverse effects in other aspects of life."

Lead author of the Cell Reports paper is recent U-M EEB graduate, Dr. Wenfeng Qian. Another recent graduate, Zhi Wang was a coauthor.

U-M News Service press release