Happy World Orangutan Day- A Brief Review of Recent Research and News

Happy World Orangutan Day. Orangutans, both Bornean (Pongo pygmaeus) and Sumatran (Pongo abelli), are some of my favorite primates. These orange, solitary creatures live a primary arboreal life in the country of Indonesia on the islands of Borneo and Sumatra. They are highly intelligent and one of our closest living relatives. In honor of International Orangutan Day, I thought I'd celebrate with a post on some of the latest orangutan research.

Starting off with some good news: there are more Sumatran orangutans than was previously thought. There are possibly 8,000 more, bringing the total up to approximately 14, 600 individuals. Better methods and techniques are the main reasons behind the increase in numbers with areas previously not surveyed visited and orangutans found at elevations higher than researchers previously thought it was likely they inhabited.

Sumatran orangutans have been classified as critically endangered since they were first listed on the IUCN Redlist. However, Bornean orangutans were previously listed as endangered, until it was announced earlier this year that they have slipped to critically endangered as well. Habitat loss due to palm oil and rubber plantations threaten this species as well as hunting.

Rocky, an orangutan at the Indianapolis Zoo, can reproduce grunting sounds made by humans. He is able to mimic the pitch and tone of sounds made by humans and started mimicking at age eight. When compared to a database filled with the sounds of other orangutans, Rocky is unique. This new finding raises more questions about the development and origin of language in humans and what our last common ancestor with orangutans looked (and sounded?) like.

Another zoo-based study has shown that orangutans have the ability to use past experiences to create new images in their mind about new experiences. This ability is referred to as affective forecasting. Naong, an orangutan housed at a Swedish zoo, is able to guess whether he likes a new juice flavor based on the past juices he's tasted.  Originally given four flavors of juice, once Naong was familiar with these flavors, the juices were mixed together. Naong, if he observed the mixing, was able to guess whether or not he liked the mixed flavors based on his past preferences. This is yet another way humans are not as unique and different from our primate ancestors than perhaps we thought. Although anyone who has spent a significant amount of time observing these animals at a zoo or reading up on them probably won't be too surprised.

An unsettling study shows how just aggressive female orangutans can be. For the first time, researchers have observed the death of a female orangutan due to the aggressive actions of other orangutans. A young, female, Bornean orangutan attacked an older female with the help of a male orangutan for over thirty minutes. The two attackers traded off, with one attacking and the other preventing the victim from escaping. The older female later died as a result of her injuries. While aggressive behavior on this scale is known in chimpanzees, this is the first time such extreme behavior has been observed in wild female orangutans.

To end on a lighter note, a Sumatran orangutan has released his first music single. Playing on the drums and piano while a zookeeper recorded, Kluet is on his way to international fame perhaps. You can purchase the single here. Proceeds are going towards conservation efforts.

To conserve these animals and show your support for them, consider buying sustainable palm oil, being mindful of your overall consumption and energy expenditure, and donating your time or funds to charities that support these magnificent apes, such as Orangutan Foundation International, Bornean Orangutan Survival Foundation, or the Center for Great Apes.

Lemur habitat was changing before humans even arrived

New research from the DNA of mouse lemurs (of the genus Microcebus) has lead to a surprising discovery about Malagasy forests and their ancient past. Madagascar, a large island off the west coast of Africa, is made up of many forests that are presently not connected and haven't been since around the time humans reached the island. The eastern rainforests (green in the image below) are separated from the western, deciduous forests (blue in the image below) by an expanse of grasslands (in yellow). There are multiple theories concerning what the landscape looked liked in the past and why the eastern and western forests are separated, and research from Yoder and colleagues (2016) uses the genetic history of lemurs to tell us more.

Habitats of Madagascar and species locations. 

From Yoder et al., 2016

Some believe that, rather than this disconnect we now see between western and eastern forests, Madagascar was covered in closed-canopy forests prior to the arrival of humans, with humans acting as the primary agents of change. This so-called forest hypothesis maintains that the large expanse of grasslands that experience frequent burning were once forests and their reduction was not natural.Others believe that the grasslands we see today are similar to ancient grasslands found in Madagascar. Thus, the landscape was not so radically different from the present. This is referred to as the grassland hypothesis by Yoder and colleagues (2016). Finally, another idea termed the mosaic hypothesis by Yoder and colleagues (2016) suggests that the central part of the country was covered with a mix of wooded savanna and closed-canopy forests.


Some of the world's top lemur experts have provided us with new information on the history of Madagascar's forests. Yoder and colleagues (2016) looked at the DNA of five different species of mouse lemurs, a genus dependent on the forest, to understand how the forests across this island nation changed. One of their research questions asks if the divide between the two forest habitats is natural or what remains of a transitional cline?

Results suggest that the five species studied started diverging from one another roughly five hundred and forty thousand years ago with the last node of divergence around fifty-five thousand years ago. The timing of mouse lemur evolution and divergence coincides with evidence suggesting great variation in climate.

M. murinus. Photo: Joachim S. Muller

Genetic analysis of M. myoxinus, a subspecies of mouse lemur that lives in continuous forests, and M. lehilahytsara, another subspecies that lives in a mosaic of forests, show significantly different patterns in regards to geographic patterns of divergence. Results suggest that M. lehilahytsara, the mouse lemur in a mosaic of forests, has lived in this type of habitat for a very long period of time, since before the arrival of humans. Thus, genetic evidence from mouse lemurs does not support the forest hypothesis.

Yoder and colleagues (2016) also discovered that  M. berthae and M. rufus are more closely related than would be expected, given their geographic differences. One species lives lives in the southeast in humid forests and the other in dry forests of the west. This close genetic relationship points towards the mosaic hypothesis of Madagascar's ancient geography. We see a genetic divergence that is tens of thousands of years old and not uniform across all Microcebus species.

Thus, using the genes of mouse lemurs, Yoder and colleagues (2016) were able to conclude that the central part of Madagascar was composed of a mosaic habitat composed of forests and grasslands. The arrival of humans does not appear to have caused a tremendous change from an entirely forested landscape to grasslands similar to what we see today.


Links of possible interest:

Ecosystems in Madagascar
Read the paper here
They may be cute, but you shouldn't have a primate as a pet


Works cited: 

Blome, M. W., Cohen, A. S., Tryon, C. A., Brooks, A. S., & Russell, J. (2012). The environmental context for the origins of modern human diversity: a synthesis of regional variability in African climate 150,000–30,000 years ago. Journal of Human Evolution, 62(5), 563-592.
Cannon, C. H., Morley, R. J., & Bush, A. B. (2009). The current refugial rainforests of Sundaland are unrepresentative of their biogeographic past and highly vulnerable to disturbance. Proceedings of the National Academy of Sciences, 106(27), 11188-11193.
Scholz, C. A., Cohen, A. S., Johnson, T. C., King, J., Talbot, M. R., & Brown, E. T. (2011). Scientific drilling in the Great Rift Valley: the 2005 Lake Malawi Scientific Drilling Project—an overview of the past 145,000 years of climate variability in Southern Hemisphere East Africa. Palaeogeography, Palaeoclimatology, Palaeoecology, 303(1), 3-19.
Yoder, A. D., Campbell, C. R., Blanco, M. B., dos Reis, M., Ganzhorn, J. U., Goodman, S. M., ... & Ralison, J. M. (2016). Geogenetic patterns in mouse lemurs (genus Microcebus) reveal the ghosts of Madagascar's forests past. Proceedings of the National Academy of Sciences, 201601081.

Viruses detected on plants chewed by primates

New research has discovered a noninvasive way to test primates for viruses. Collaboration between UC Davis and Gorilla Doctors has shown that the plants mountain gorillas (Gorilla beringei beringei) and golden monkeys (Cercopithecus mitis kandti) consume and discard can be collected and analyzed to determine what viruses the animals have. Blood samples and oral and rectal swabs all require the researcher to anesthetize the animal, something that is not done with critically endangered mountain gorillas unless absolutely necessary.

Thus, this new noninvasive method will allow researchers to detect viruses simply by following the animals at a distance and collecting any bits of chewed bark, leaves, or fruit the individual discards. For this study, Smiley Evans and colleagues (2016) spent almost a year collecting these vegetation discards from 294 gorillas from 26 different family groups across the Volcanoes National Park, Bwindi Impenetrable Forest, and Mgahinga Gorilla Park.

The authors also looked at golden monkeys, collecting plant samples on three different dates in order to determine if their methods could be used on other primate species. Samples were collected from 18 individuals. For both species, researchers observed the animals, collected disregarded plant parts, and sampled from plants with visible bite marks and saliva.

It was possible to collect samples from nearly every individual in a family, including infants who may not consume the plants but still bite and chew them. DNA and RNA viruses were both successfully detected using this method with minimal disruption. Compared to other methods, Smiley Evans and colleagues were able to sample more individuals with less risk and little behavioral disruption. Using this method, the researcher easily knows the age of the sample because close behavioral observation is required.

Golden monkeys proved more challenging than mountain gorillas because they are arboreal and handle food less with their mouths when compared to mountain gorillas. However, it is still possible to collect samples, but researchers should prepare to collect fewer samples per visit.

This research is especially important for mountain gorillas because infectious diseases are one of the greatest threats to this species, and as wildlife increasingly comes into contact with humans, breakthroughs in disease ecology have the potential to positively impact these gentle giants. Roughly 60% of the remaining 880 mountain gorillas are habituated to humans (Gray et al., 2011; Robbins et al., 2011), meaning they encounter humans, whether tourists, researchers, or others, on a regular basis and are accustomed their presence.

Links of possible interest: 

IUCN mountain gorilla page

Gorilla Doctors

Mountain gorilla genome sequenced

Works cited:
Gray, M., Fawcett, K., Basabose, A., et al., (2011). Virunga Massif Mountain Gorilla Census 2010 Summary Report. International Gorilla Conservation Programme.

Robbins, M. M., Roy, J., Kato, R., Kabano, P., Basabose, A., Tibenda, E., ... & Gray, G. (2011). Bwindi Mountain Gorilla Census 2011-Summary of Results. Uganda Wildlife Authority, 28.

Smiley Evans, T., Gilardi, K. V., Barry, P. A., Dsebide, B. J., Kinani, J. F., Nizeyimana, F., ... & Mazet J. A. (2016). Detection of Viruses Using Disregarded Plants from Wild Mountain Gorillas and Golden Monkeys. American Journal of Primatology.

Adapted for adaptability-evidence suggests primate brains use reservoir computing

Photo: Christopher Walsh, Harvard Medical School

Primate brains are incredibly adaptive, responding to new situations and stimuli as needed. Think of all of the various skills we learn from computer programming to making pottery to neuroscience. Our brains learn new content and do so relatively efficiently, but how? How are humans and other primates so good at adapting to new information and scenarios?

Enel and colleagues (2016) wanted to better understand how our primate brains adapt to situations and stimuli that evolution could not have directly anticipated. They took advantage of developments from Rigotti and colleagues (2010) in reservoir computing, a branch of recurrent neural networks in which randomly connected neurons form a network of recurrent loops. Recurrent connections are fixed but connections from to output neurons can change. Rigotti and colleagues (2010) propose that recurrent neural networks with multiple, different neuronal responses are significant in the ability to complete complex cognitive tasks.

Enel and colleagues (2016) developed a recurrent neural network model that would perform a specific cognitive task and then compared predictions from the model to data from rhesus monkeys. Of four potential targets on a touch screen, only one would reward the monkeys with fruit juice. The monkeys needed to discover the fruit juice target by trial and error. The target corresponding to fruit juice changed after every trial.

Model Architecture, Figure from Enel and colleagues 2016 paper, Reservoir Computing Properties of Neural Dynamics in Prefrontal Cortex

Results show that the model was able to shift when it did not receive a reward and repeat when it did, a new extension of the functions of reservoir computing. The model was able to perform the task almost perfectly using a circular search and an ordered search and when trained on a schedule that was derived from the performance of one of the monkeys. Enel and colleagues (2016) compared the neural coding behavior of the model with the primate cortex. They found that variance in the presence of reservoir neurons in 1) target choice and 2) phase of the problem (either continue searching to find the reward or repeat because the reward has been discovered) show significant effects for both choice and phase. Choice and phase could not be directly derived from current inputs, but instead needed the history of previous inputs and their responses. This has also been observed for the primate brain (Barone and Joseph, 1989). See the published paper for the full results and more details about their findings.

This new research helps to explain how primates face and then handle a diverse and endless range of situations. It will be interesting to see if the same mechanism for behavioral adaptability is found in non-primate species or if it is unique to primates.

Works cited:

Barone, P., & Joseph, J. P. (1989). Prefrontal cortex and spatial sequencing in macaque monkey. Experimental brain research, 78(3), 447-464.

Enel, P., Procyk, E., Quilodran, R., & Domineer, P., F. (2016) Reservoir Computing Properties of Neural Dynamics in Prefrontal Cortex. PLoS Comput Biol, 12(6): e1004967. DOI: 10.1371/journal.pcbi.1004967 

Rigotti, M., Ben Dayan Rubin, D. D., Wang, X. J., & Fusi, S. (2010). Internal representation of task rules by recurrent dynamics: the importance of the diversity of neural responses. Frontiers in Computational Neuroscience, 4, 24.

Cercopithecus monkeys opportunistically prey on bats

C. mitis, photo Diana Robinson

Two species of Cercopithecus monkeys in Kenya have been observed and documented feeding on bats when the opportunity presents itself. Tapanes and colleagues (2016) photographed and filmed this behavior in Blue monkeys, Cercopithecus mitis, and in one monkey which was a hybrid species of C. mitis and C. ascanius, the Red-tailed monkey. They report on thirteen observations of bat predation attempts over six and a half years at two sites, Gombe in Tanzania and the Kakamega Forest in Kenya). Of these thirteen attempts, eleven were successful. Surveying researchers of blue and red-tailed monkeys at other sites did not identify further instances of bat predation.

Although identifying the bats was challenging, Tapanes and colleagues determined that multiple species of bats were consumed. Researchers observed two instances where an individual grabbed a lone roosting bat and consumed it. In the other observations, the researchers did not witness the individual capturing the bat.

Unsurprisingly, the evidence suggests that bats are a preferred food item for Cercopithecus monkeys. In two of a successful predation event, other monkeys gathered around and observed the monkey feeding on the bat. Three instances were observed where some sort of aggressive display or behavior to either obtain or retain the bat, implying this food item is worth fighting over.

All observed instances of this behavior occurred in either forest edges or human-modified habitat, raising the question as to whether or not this behavior occurs naturally or is a product of habitat destruction and alteration due to human activities. It is possible that anthropogenic changes to the landscape have resulted in blue and red-tailed monkeys altering their feeding patterns and behaviors accordingly, with increased consumption of bats as a potential modification. Thirty-six years of data collection at Kakamega forest show that bat predation coincides with increased use of plantation forests that has occurred due to forest fragmentation and loss. Tapanes and colleagues (2016) also suggest that bat predation could be more widespread, but it is simply easier for researchers to observe this rare behavior within altered habitats. They do not think this reason is likely, stating that observation conditions were similar in both plantation forest and forest that is more natural.

Blue monkey feeding, photo Christoph Strässler

These findings have important implications for the transmission of zoonotic diseases, or diseases that can be transmitted from animals to humans. It has previously been hypothesized that primates contract diseases from bats when they consume fruit with an infected bat's saliva or feces (Dobson, 2005; Alexander et al., 2015; Rodhain, 2015). This latest study forces us to consider the fact that directly handling the bats themselves may be a method for disease transfer. As monkeys can transmit many diseases to humans, it is worth studying this phenomenon more, if possible.

Links of potential interest:
IUCN Redlist page for C. mitis
Primate zoonotic diseases
Which primate is likely the source of the next pandemic?
Ebola, primates, and bushmeat

Works cited:
Alexander, K. A., Sanderson, C. E., Marathe, M., Lewis, B. L., Rivers, C. M., Shaman, J., ... & Eubank, S. (2015). What factors might have led to the emergence of Ebola in West Africa?. PLoS Negl Trop Dis, 9(6), e0003652.
Dobson, A. P. (2005). What links bats to emerging infectious diseases?. Science, 310(5748), 628-629.
Rodhain, F. (2015). Chauves-souris et virus: des relations complexes. Bulletin de la Société de pathologie exotique, 108(4), 272-289.
Tapanes, E., Detwiler, K. M., & Cords, M. (2016). Bat Predation by Cercopithecus Monkeys: Implications for Zoonotic Disease Transmission. EcoHealth, 1-5.

What do geladas and humans have in common? Apparently, vocal patterns.

T. gelada. Photo: Ron Waddington

They live in very large groups called herds, they primarily graze on terrestrial vegetation, and they roam on large open plains. In more than a few ways, geladas (Theropithecus gelada) are similar to cows. Geladas are more vocal than cows though. They have a diverse range of vocalizations for various behaviors and situations, such as contact, showing submission, aggression, and others (Kawai, 1979; Aich et al., 1990).  The diversity and complex communication exhibited by geladas is one of the reasons this is a very interesting primate species to study.

A new study on their vocal sequences shows that this species of Old World Monkey follows patterns that are similar to humans. As far back as the late eighties, Richman (1987) suggested the geladas use melody and rhythm in ways similar to humans. Now, Gustison and colleagues have shown that the longer the sequence of sounds is that a gelada makes, the shorter the sounds within that long sequence. This is the same pattern observed in humans and is called Menzerath's law. The longer our sentences, the shorter the words tend to be in those sentences.

The authors studied fifty-seven male geladas in the wild and recorded and analyzed over 1000 vocal sequences. In addition to discovering that longer sequences are made up of shorter calls, Gustison and colleagues report that long sequences start with short calls and short sequences start with long calls. Thus, the start of the sequence is an indicator of its overall length. Longer sequences also have faster tempos. Gustison and colleagues state this might be to reduce the possibility of one gelada being "talked over" by another. You can understand how this might be a problem in a chatty species that lives on open plains. If you have a lot to say, you better say it quickly.

Geladas grazing. Photo Alastair Rae

Interestingly, there was no negative relationship between the position of a call and its duration (calls later in the sequence were not shorter). Yet, the proportion of grunts where the gelada was exhaling decreased in longer sequences and the proportion of grunts where the individual inhaled increased. The authors believe this pattern is due to the fact that individuals make grunts with both inhalations and exhalations on the same breath as the sequence lengthens. Once geladas have more than 15 calls per sequence, the majority of their calls have both inhale and exhale grunts and the proportion of inhale and exhale grunts hardly varies.  Thus, respiration and energy demands may constrain gelada vocalizations, and be partially the reason for conforming with Menzerath's law.

This is the first time Menzerath's law has been studied in non-humans. Thus, other animals with expansive vocal repertories, such as songbirds, may also exhibit this law. It is hard to draw conclusions about the evolution of communication in non-human primates and our human ancestors without knowing if Menzerath's law holds true for species that are further separated from humans. For now, we know humans are not unique in adhering to Menzerath's law.  It is possible that this pattern existed before meaningful combinations of vocalizations had evolved. Tests in other species will only serve to improve our understanding of sequences, vocal patterns, and the evolution of language and communication in general.



Links of potential interest:
Menzerath's Law
IUCN page on geladas
YouTube video on gelada chatter

Works cited:

Aich, H., Moos-Heilen, R., & Zimmermann, E. (1990). Vocalizations of adult gelada baboons (Theropithecus gelada): acoustic structure and behavioural context. Folia primatologica, 55(3-4), 109-132.
Kawai, M. (1979). Auditory communication and social relations. Ecological and Sociological Studies of Gelada Baboons, 219-241.
Gustison, M., Semple, S., Ferrer-I-Rancho, R, Bergmann, T. (in press). Gelada vocal sequences follow Menzerath’s linguistic law. PNAS. www.pnas.org/cgi/doi/10.1073/pnas.1522072113 
Richman, B. (1987). Rhythm and melody in gelada vocal exchanges. Primates, 28(2), 199-223.

What you may not have read about the scary decline in Grauer's Gorilla numbers

Cover of the WCS and FFI Report

Over a week ago, a report from Wildlife Conservation Society and Fauna and Flora International hit the press about Grauer's gorillas (Gorilla beringei graueri).  Grauer's gorillas, previously known as eastern lowland gorillas, are one of four subspecies of gorillas. Consuming fruits and vegetation, Grauer's gorillas are the largest subspecies. They are listed as endangered and are found only in the Democratic Republic of Congo (DRC).

They made the headlines, and not just on the science news sources, because the latest data shows their numbers have declined dramatically. Over the past twenty years, Grauer's gorilla numbers have declined by an astonishing 77%, with only 2, 585 animals estimated alive today. Their range has been reduced by 84-93%. If you saw this on the news, you probably also saw that civil unrest and other human pressures are the reasons behind the sudden decline. This is hardly surprising.

What you may have missed are some of the more nuanced details behind these numbers, details that can be found in the report itself, which also covers chimpanzees in the same area. In their report titled, "Status of Grauer's Gorilla and Chimpanzees in Eastern Democratic Republic of Congo: Historical and Current Distribution and Abundance," we learn that increases in agriculture and the availability and use of shot guns caused habitat loss and extinctions of local populations in the 60s and 70s. Surveys done in the 90s also suggested species decline due to expanding human populations and hunting. The late 90s and early 2000s saw these threats exacerbated when refugees from civil war in Rwanda, internally displaced people, and armed groups in the DRC put further pressure on DRC forests and wildlife. This influx of people needed fuel for firewood, land for agriculture, timber, and also hunted wildlife and mined.

The main threats to Grauer's gorillas are hunting for bushmeat and habitat loss due to the spread of agriculture. Hunting practices are related to artisanal mining though. These mines are found adjacent to or even in protected areas, are illegal, and are controlled by armed militias (Kirkby et al., 2015). They allow people an economic opportunity to earn an income quickly and attract people from multiple social classes(Kirkby et al., 2015). Once working at these remote mines, miners rely on bushmeat for food and consume primates and other large mammals(Kirkby et al., 2015). The miners aren't evil people though, as many said they wouldn't hunt bushmeat if alternatives were available and also said they wanted to leave the mining industry.

SMART patrols, reconnaissance surveys, transects, and occupancy surveys were used to determine gorilla decline and show that one of the areas with the highest number of animals, Kahuzi-Biega National Park saw a decline of 87% in gorilla density, and this is with a portion of the Park protected reasonably well. Seven of the eleven sites surveyed through encounter rates show an average decline of 94%. These findings are enough to support raising the IUCN status of Grauer's gorillas to critically endangered.

Occupancy probability model from report. Blue areas
mean high likelihood and red very low likelihood of gorillas

Behind these alarming numbers, a story emerges of people pushed beyond their limits and forced to use the forests available in order to survive. Civil war, changes in government, and general civil unrest gives the DRC its tumultuous historic timeline, the effects of which not only impact people but also the flora and fauna of the region. Some may find it easy to forget, but humans and nature are intricately linked.

You may think you have no connection to this story other than one as an innocent bystander, but the resources mined from the DRC are part of an industry many of us play into. Most of the mines are for cassiterite, gold, coltan, and wolframite. The first is an important source of tin, the second you may be wearing now, coltan is used in electronics such as our cell phones, and the last is an important source of tungsten. Given that mining is one of the main reasons Grauer's gorillas are threatened, chances are many of us are connected to this problem, as uncomfortable as that may make us feel.

Links of potential interest
IUCN Page for Grauer's Gorillas
IUCN Categories and Their Criteria
BBC's Country Profile of the DRC

Works cited:

Kirkby, A., Spira, C., Bahati, B., Twendilonge, A., Kujirakwinja, D., Plumptre, A., ... & Nishuli, R. (2015). Investigating artisanal mining and bushmeat around protected areas. Unpublished report to USAID and Arcus Foundation.

Plumptre, A.J., Nixon, S., Critchlow, R., Vieilledent, G., Nishuli, R., Kirkby, A., Williamson, E.A., Hall, J.S. & Kujirakwinja, D. (2015). Status of Grauer’s gorilla and chimpanzees in eastern Democratic Republic of Congo: Historical and current distribution and abundance. Unpublished report to Arcus Foundation, USAID and US Fish and Wildlife Service.

Bonobos focus on the positives: humans focus on the negatives

Photo: Mark Dumont

A recent study done on captive bonobos (Pan paniscus) reports that these apes focus on images that are of a more positive nature (compared to images of danger or aggression). Using a test designed to understand attentional bias in humans, researchers from various institutions in The Netherlands studied attentional bias in bonobos, our close relatives.

Four female bonobos each completed either twenty-five or twenty-six trials in total over thirteen separate testing sessions. They were briefly shown two images and then a dot appeared on the screen which remained there until the individual tapped the dot. Upon tapping the dot, the individual is rewarded with a food item. In half of the trials, the images briefly shown were of a bonobo in some sort of emotional state, such as pant hooting, playing, or in distress. In the other half, the images were of a bonobo in a neutral state.

By looking at the reaction time, Kret and colleagues (2016) were able to determine that bonobos are more captivated by images of other bonobos that are affiliative or protective rather than images with bonobos in distress or aggression, which has found to be the case most often for humans (Vuilleumier and Schwartz, 2001; Williams et al., 2004; Tamietto et al., 2005; Flaisch et al., 2009).

Images of yawning, grooming, and sexual behavior caught the bonobo's attention the most. Reaction time was longest for yawning, followed by grooming and then sexual behaviors. Yawning is a contagious behavior in humans and also for bonobos (Palagi et al., 2014). Grooming and sexual behavior are both types of behavior that reduce tension (Manson et al., 1997; De Waal, 1997; Crockford et al., 2013).

The increased attention devoted to these social behaviors suggest that they are of greater importance to bonobos than aggressive behaviors or actions associated with a threat. Given that this isn't the case with humans and what captures our attention, this study highlights another intriguing difference between the two species.

Links of potential interest:
Paper in PNAS 
Are bonobos more peaceful than chimpanzees?
IUCN page on bonobos


Works cited:
Crockford, C., Wittig, R. M., Langergraber, K., Ziegler, T. E., Zuberbühler, K., & Deschner, T. (2013). Urinary oxytocin and social bonding in related and unrelated wild chimpanzees. Proceedings of the Royal Society of London B: Biological Sciences, 280(1755), 20122765.

De Waal, F. B. (1997). The chimpanzee's service economy: food for grooming. Evolution and Human Behavior, 18(6), 375-386.

Flaisch, T., Schupp, H. T., Renner, B., & Junghöfer, M. (2009). Neural systems of visual attention responding to emotional gestures. Neuroimage, 45(4), 1339-1346.

Kret, M. E., Jaasma, L., Bionda, T., & Wijnen, J. G. (2016). Bonobos (Pan paniscus) show an attentional bias toward conspecifics’ emotions. Proceedings of the National Academy of Sciences, 201522060.

Manson, J. H., Perry, S., & Parish, A. R. (1997). Nonconceptive sexual behavior in bonobos and capuchins. International Journal of Primatology, 18(5), 767-786.

Palagi, E., Norscia, I., & Demuru, E. (2014). Yawn contagion in humans and bonobos: emotional affinity matters more than species. PeerJ, 2, e519.

Tamietto, M., Latini Corazzini, L., Pia, L., Zettin, M., Gionco, M., & Geminiani, G. (2005). Effects of emotional face cueing on line bisection in neglect: a single case study. Neurocase, 11(6), 399-404.

Vuilleumier, P., & Schwartz, S. (2001). Emotional facial expressions capture attention. Neurology, 56(2), 153-158.

Williams, M. A., & Mattingley, J. B. (2004). Unconscious perception of non-threatening facial emotion in parietal extinction. Experimental Brain Research, 154(4), 403-406.

The latest puzzling chimpanzee behavior

Young chimpanzee. Photo credit Sabine Bresse

Of the animal kingdom, chimpanzees, Pan troglodytes, are one of the well-known tool users. All populations of wild chimpanzees studied have been observed using leaves to obtain food and some populations have been observed modifying branches to forage for termites and even fashioning spears to hunt bushbabies (Shumaker et al, 2011; Boesch, 2012).

As is the case with studying many primates, our knowledge of tool use and how it is passed from generation to generation is limited by the number of field sites where long-term research occurs. Chimpanzees must first become used to human presence (or habituated) before their natural behavior can be studied, and this can take a great deal of time.

Theorizing that the repertoire of chimpanzee behavior is much wider than what is currently known, Kühl and colleagues used camera traps to study multiple populations of chimpanzees in West Africa that are not habituated. This is when they noticed some very interesting behavior. Researchers first noted unusual piles of rocks in trees and used camera traps to determine what was behind this puzzle. They observed chimpanzees picking up rocks from piles around or in trees and then throwing them at the tree.

Through the camera trap footage, researchers were able to determine that chimpanzees would throw the stones at the trees and vocalize a long-distance pant-hoot at the same time. The stones are mainly thrown by adult males and they seem to be independent of any sort of foraging behavior. The same chimpanzee was often observed returning to the tree and engaging in the behavior. This strange accumulative stone-throwing has only observed in West Africa and was seen in four populations of chimpanzees.

Stone throwing may be a type of male display, during which the individual attempts to draw attention to one's strength and impress other chimps. Kühl and colleagues theorize that using the stones in this manner may produce a loud sound resulting in a greater display. Another theory the authors present is that this may be a symbolic behavior. In either case, obviously more data is needed. Stone-throwing chimpanzees raises more questions than it does answers in terms of behavior and possibly cognition in the case of the latter theory.
 
This work goes to show that you can still learn a great deal about a comparatively well-studied primate species even if you're not Jane Goodall and haven't been working at the same research site for decades. Kühl and colleagues have captured some truly fascinating behavior that raise a series of new questions using technology to their benefit.

Links of potential interest:
Video of behavior
Pan African Programme: The Cultured Chimpanzee
How human are chimps?
Females more likely to use tools when hunting



Works cited:

Boesch, C. Wild Cultures: A Comparison between Chimpanzee and Human Cultures. (Cambridge University Press, 2012).

Kühl, H. S. et al. Chimpanzee accumulative stone throwing. Sci. Rep. 6, 22219; doi: 10.1038/srep22219 (2016).

Shumaker, R. W., Walkup, K. R. & Beck, B. B. Animal Tool Behavior: The Use and Manufacture of Tools by Animals. (JHU Press, 2011).

What effect temporally and spatially complex fruits may have on chimp cognition

Photo credit Sergio Morchon

A recent study by Janmaat and colleagues (2016) details how fruits in chimpanzee habitat are spatially and temporally complex (see that post here). As Janmaat and colleagues stated, this complexity in diet has implications for chimpanzee intelligence.

Fruits are a preferred food. It's worth hunting down these high-energy food items. That said, fruits aren't always easy to find. It's a waste of energy to travel to a specific fruiting tree with the thought of consuming a high-energy meal if that tree isn't producing. Wasting energy wandering around a forest looking for fruits that don't exist definitely isn't adaptive, and it's not something we would expect to see in chimpanzees or in any other species. It's in a chimpanzee's best interest to know where a fruit tree is and whether or not it will be fruiting. This type of processing  takes a certain amount of knowledge and brain power. 

The ecological intelligence hypothesis suggests that primates consuming foods that are fleeting in their availability and scattered geographically would require larger ranges and the cognitive capability to forage optimally for those ephemeral and scattered foods (Milton and May, 1976; Milton, 1980; Milton, 1981; Milton, 1988). Being able to remember where these scattered foods are and when they are available would be advantageous for the primate.

Janmaat and colleagues (2016) found substantial variation between fruiting species in regards to the timing of fruit production, and the authors suggest that chimps would benefit from learning species-specific fruiting patterns to locate these foods. There was also significant variation within a species in the monthly percentage of fruiting trees across years and between forests. Rather than this knowledge being genetic or something all chimpanzees are born with, it is more likely that chimpanzees learn about synchronicity of fruiting.

In regards to remembering trees that produce large amounts of fruit, the authors used existing literature and their own observations of great variation in fruit tree production histories to hypothesize that chimpanzees use their ranging patterns to monitor trees that are likely to produce large crops of fruit. Chimps would need to store information on fruit production histories over many years, particularly for species that fruit every few years rather than every few months, providing further evidence of how chimpanzees use their brains and intelligence to survive in their environment.

The forests chimpanzees inhabit clearly provide challenges for our closest relatives in terms of finding their preferred foods, ripe fruits. However, these intelligent animals have the brain power needed to master this environment and the challenges forests present. Their intelligence not only helps them navigate living in a social group and managing complex relationships but it also allows them to navigate the complex ecology surrounding them.

Links of possible interest:
Chimpanzees and long term memory
NOVA's Ape Genius


Works cited:

Milton, K., & May, M. L. (1976). Body weight, diet and home range area in primates. Nature, 259(5543), 459-462.

Milton, K. (1980). The foraging strategy of howler monkeys: a study in primate economics. Columbia University Press.

Milton, K. (1981). Distribution patterns of tropical plant foods as an evolutionary stimulus to primate mental development. American Anthropologist, 83(3), 534-548.

Milton K. 1988. Foraging behaviour and the evolution of primate intelligence. In: Byrne RW, Whiten A, editors. Machiavellian intelligence: social expertise and the evolution of intellect in monkeys, apes and humans. Oxford: Clarendon Press. p 285–305.

Gorillas and humans diverged from one another earlier than thought

Studying ancient humans and primates tells us more about our owns selves and what it means to be human, what it means to be of the species modern Homo sapiens. While we can look at our closest living relatives, apes and other primates, to theorize a great deal about how our ancestors acted  5 million years ago (mya), we also rely on fossil evidence and genetic studies. Studying human ancestors presents one very large problem: lack of fossil evidence. The fossilization process requires just the right conditions at time of death and the right conditions afterwards.  Thus, there are many gaps in our knowledge because the data simply isn't available. The fossils haven't been found.

Juvenile mountain gorillas, Photo credit: Philip Milne

Scientists are particularly interested in fossils from 12-7 mya because this is around the time when African apes (gorillas, chimpanzees, and bonobos) and humans split. Yet, few fossils from this time have been discovered.

Katoh and colleagues (2016) studied fossilized teeth found in Ethiopia's Afar Rift from an ancestral gorilla, called Choroapithecus abyssinicus, and the surrounding layers of earth these fossils were found in. Their results that suggest C. abyssinicus is older than previously believed. The teeth have been dated to 8 mya, which would mean that these ancestral gorillas and ancestral humans had to have diverged earlier in time than previously thought.

Previous estimates of the split between African apes and humans suggested the two lines diverged more recently. Data from genetics suggests that humans and gorillas split somewhere between seven to eight million years ago.  When C. abyssinicus was first discovered, it was found in deposits that are older than 8mya. The geology previously suggested that this species lived 10-10.5 mya (Suwa et al., 2007). Thus, this study provides some needed clarity on the age of these fossils.

With these new results, we can place the age of these fossils at 8 mya, meaning this ancestral ape and humans likely split around 10 mya rather than 8 mya and suggesting the mutation rate between the two was slower than previously thought. We can also confirm that ancestral great apes evolved in Africa, as opposed to Europe or Asia.

It's always impressive how a few extra teeth and a lot of hard work can transform what we know about our own origins.

Works cited:

Katoh, S., Beyene, Y., Itaya, T., Hyodo, H., Hyodo, M., Yagi, K., ... & Nakaya, H. (2016). New geological and palaeontological age constraint for the gorilla–human lineage split. Nature, 530(7589), 215-218.

Suwa, G., Kono, R. T., Katoh, S., Asfaw, B., & Beyene, Y. (2007). A new species of great ape from the late Miocene epoch in Ethiopia. Nature, 448(7156), 921-924.

The spatial and temporal complexity of fruit species consumed by chimps

Chimpanzees live in a variety of environments, thus the types of food they consume vary accordingly. We wouldn't expect a chimpanzee troop living in Fongoli (a savanna) to consume the same foods as chimpanzees living in Gombe (a tropical forest).

That caveat aside, chimpanzees across habitats prefer fruits to other food types. We know this because fruits make up a greater proportion of their diet than would be expected given fruit availability (Hladik, 1977; Tutin et al., 1997; Conklin-Brittain et al., 1998; Wrangham et al., 1998; Doran-Sheehy et al., 2006). Fruits are high in energy and low in secondary compounds, or digestive inhibitors or toxins, such as tannins or lignin. (Remember that the fruits we see in a grocery store or at a food stand have been selectively bred to look and taste considerably different than most wild fruits). Interestingly, chimpanzees in Guinea-Bissau consume mainly wild fruits and flowers even when they are in close proximity to agricultural areas (Carvalho et al., 2015). Thus, it seems safe to conclude that fruits are high up on the desired menu.

Feeding on Ficus sur fruits, Photo credit: Alain Houle

A recent study by Janmaat and colleagues (2016) looked at three populations of chimpanzees in tropical lowland rainforest, lowland tropical moist forest, and a moist evergreen tropical forest to better understand how chimpanzees access energy-rich foods. They considered multiple food types that are high-energy: young leaves, unripe fruit, and ripe fruit. The authors also had a particular interest in large crops of ripe fruit. They described the probability of finding trees for each of the aforementioned, three food types and how predictable ripe fruit production is in each focal tree in regards to timing, frequency, and quantity of ripe fruit produced. 

 The authors found that individuals were more likely to encounter young leaves or unripe fruit than ripe fruit, confirming that fruits present more of a challenge than other food types. However, over half of all of the trees chimpanzees encountered over the course of this study were species of fruiting trees consumed by chimps. Thus, finding a tree species known to produce an edible fruit isn't a monumental challenge for these populations. The challenge lies in timing.  

There was considerable variation in the timing of fruit production within a population of a tree species. Within the same species, the length of fruit production varied: one individual may produce fruit for a few months over multiple years whereas another individual may fruit for many more months within the same period. There was also monthly variation in the size of fruit crops produced. Further variation within a species complicates matters for chimps even more, as they can't count on large crops of fruits in certain months, even within individual species.

Look for an upcoming post on the implications of finding ripe fruits in a complex environment. How might the ecology of chimpanzee habitat and their dietary choices affect their intelligence?

Links of potential interest:
Chimps understand and choose to cook
Female chimpanzees more likely to use tools when hunting than males
 

Works cited:

Carvalho, J. S., Vicente, L., & Marques, T. A. (2015). Chimpanzee (Pan troglodytes verus) Diet Composition and Food Availability in a Human-Modified Landscape at Lagoas de Cufada Natural Park, Guinea-Bissau. International Journal of Primatology, 36(4), 802-822. 

Conklin-Brittain, N. L., Wrangham, R. W., & Hunt, K. D. (1998). Dietary response of chimpanzees and cercopithecines to seasonal variation in fruit abundance. II. Macronutrients. International Journal of Primatology, 19(6), 971-998.

Doran-Sheehy, D. M., Shah, N. F., & Heimbauer, L. A. (2006). Sympatric western gorilla and mangabey diet: re-examination of ape and monkey foraging strategies. Cambridge Studies in Biological and Evolutionary Anthropology, 48, 49.

Hladik, C. M. (1977). Chimpanzees of Gabon and chimpanzees of Gombe: some comparative data on the diet. Primate Ecology: Studies of Feeding and Ranging behaviour in Lemurs, Monkeys, and Apes, 81-501.

Janmaat, K. R., Boesch, C., Byrne, R., Chapman, C. A., Bi, G., Zoro, B., ... & Polansky, L. (2016). Spatio‐temporal complexity of chimpanzee food: How cognitive adaptations can counteract the ephemeral nature of ripe fruit. American Journal of Primatology.

Tutin, C. E., Ham, R. M., White, L. J., & Harrison, M. J. (1997). The primate community of the Lopé Reserve, Gabon: diets, responses to fruit scarcity, and effects on biomass. American Journal of Primatology, 42(1), 1-24.

Wrangham, R. W., Conklin-Brittain, N. L., & Hunt, K. D. (1998). Dietary response of chimpanzees and cercopithecines to seasonal variation in fruit abundance. I. Antifeedants. International Journal of Primatology, 19(6), 949-970.

Find yourself being spiteful? Blame these primate relatives.

It looks like humans aren't the only ones who make an effort to punish or act negatively towards those we believe are undeserving. Leimgruber and colleagues (2015) recently published a new study on inequality and fairness in the journal Evolution and Human Behavior. They looked at whether capuchins (Cebus apella) would punish individuals who stole food or who benefited from an unequal distribution of food. The results and how they compare to other research might surprise you.

Capuchins are a New World Monkey that are closely related to us. Humans and capuchins last shared a common ancestor roughly 30 million years ago (Fragaszy et al., 2004). These social primates live in large groups with dominance hierarchies. To learn more about this species, including their behavior, click here.

C. apella Photo: John Mittermeier

As you can probably guess, capuchins were tested in captivity to determine how they responded when a reward was not equally given and when a resource was stolen from them. Six individuals were tested. All individuals were tested against a low-ranking member of their social unit. Monkeys were tested in different enclosures but with a shared table that spanned both enclosures. Multiple conditions were tests: one where the test individual had access to the food, one where the test individual briefly had access to the food and then a researcher moved it to the low-ranking individual, and one where the low-ranking individual could steal the food outright. When the low-ranking individual gains control over a food source (due to the researcher moving the food source towards the individual), capuchins will pull on a rope that collapses the table holding the food. They will also do this when the low-ranking individual is given the ability to steal the food.

Intentions don't seem to matter if you're a scorned capuchin. Capuchins punish the low-ranking individual even when that individual was not to blame for the unequal distribution of food. As Leimgruber stated when interviewed for Phys.org, capuchin monkeys appear to have a sort of "If I can't have it, no one can"attitude.

Similar inequality studies have been conducted with chimpanzees, our closest living relatives. When we think of chimpanzees in comparison to capuchins, chimpanzees may seem more ruthless. They will kill one another and they've been observed going to "war" with other troops of chimpanzees. Yet, chimpanzees will only make an effort to punish if the other individual is responsible for the inequality (Riedl et al., 2012). Perhaps capuchins are the anomaly or maybe this spiteful behavior does have its evolutionary origins 30 million years ago, making chimpanzees the anomaly. Similar studies will need to be done in other primate species to better understand the evolutionary history of this trait in primates.

Of course, we can't actually blame capuchins for our spiteful actions (nor should we: let's not forget the power of human agency), but this study adds to our knowledge of human behavior while, perhaps, raising more questions.

Links of potential interest:

Phy.org article
Video of capuchin fairness test
Frans de Waal Ted Talk on Moral Behavior

Works cited:

Fragaszy, D. M., Visalberghi, E., & Fedigan, L. M. (2004). The complete capuchin: the biology of the genus Cebus. Cambridge University Press.

Leimgruber, K. L., Rosati, A. G., & Santos, L. R. (2015). Capuchin monkeys punish those who have more. Evolution and Human Behavior.


Riedl, K., Jensen, K., Call, J., & Tomasello, M. (2012). No third-party punishment in chimpanzees. Proceedings of the National Academy of Sciences, 109(37), 14824-14829.