Joel Bray was awarded a Leakey Foundation Research Grant during our spring 2017 cycle for his project entitled “Social relationships in male chimpanzees: Form, function, and development.” Click here to read a summary of his project.
Joel Bray, a graduate student at Arizona State University, is studying the development of male-male social relationships in chimpanzees at Gombe National Park, Tanzania. Using a combination of original fieldwork and long-term data collection, he is interested in how early social experiences predict variation in the strength and diversity of adult male social bonds.
A calm and relaxing day in the forest, just meters from the beach. In the background, adult males socialize while my focal, Google, grooms with his mother in the branches above.
Hearing chimpanzee vocalizations in the distance, a juvenile male wraps his arm around an adult male for comfort. Will the nearest adult male do or are young males more likely to approach and make contact with specific adult males rather than others?
Finished feeding, a juvenile male takes a moment to groom an adult. These types of grooming bouts tend not to last long (young kids have short attention spans), but I’m interested in whether the frequency and duration varies according to the identity of the adult partner.
Two young males take a keen interest in the activity of an adult; this type of close observation often occurs while an adult male is feeding, self-grooming, or inspecting a wound.
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Physical contact is not required to nurture a relationship: here, an adolescent male is content to rest in close proximity to an adult. Immature males spend less time in close proximity to adult males than I would expect, but there is substantial variation across individuals. What effect does socialization during infancy and juvenility have on the ability to form social relationships later in life?
Carrie Miller trying to follow one of many playful juveniles. (photo credit: Jacob Kraus)
Now halfway through my dissertation field season, I’m at a total of 26 months with the Guassa gelada monkeys split over a handful of years, and these geladas continue to surprise me. Since my first year with the Guassa Gelada Research Project (GGRP) as a field manager in 2012, I have seen many changes: Geladas have come and gone (some of them my favorites), the ranging has shifted and expanded to new regions of Guassa, and relations between the geladas and local farmers bordering Guassa have grown ever tenser. Despite these changes, Guassa continues to be the home of several hundred gelada monkeys and the researchers who study them.
The entire L-unit (six adult females, ten juveniles, four infants, and their fearless leader-male) huddling to stay warm in the fog and rain.
My current research at Guassa investigates how adult males interact with immatures in their units and how the stresses of living in a multi-level social system with high infanticide risk and frequent encounters with rival males seeking to acquire their own harem effect these interactions. Do males provide any parental care, or are they strictly investing in mating effort? Are these investment decisions based on features of their current status and environment? What, if any, are the benefits to offspring of having a father who sticks around? With The Leakey Foundation Research Grant, I am spending this year collecting data which will answer these questions.
Ayesha and Arya playing together
Geladas, like humans in certain respects, live in multi-level societies, which have core social units nested within one or more larger units of organization. In humans, the core unit consists of a family group. Families live within larger societies with multiple males and females and multiple overlapping sets of identities (e.g. band, tribe, nation). For geladas, the core unit is the one-male unit (OMU), consisting of a dominant leader-male, a number of related adult females and their offspring, and occasionally one or two subordinate follower-males. OMUs exist within larger units known as bands and herds. The multi-level society of geladas raises an interesting set of challenges. The OMU system suggests there should be high paternity certainty for leader-males. Yet, the multi-level structure potentially provides opportunities to acquire paternities outside of the OMU. Furthermore, this system provides opportunities for frequent encounters with rival males in bachelor groups who potentially pose a significant threat to the leader-males and their offspring.
The Guassa gelada study population consists of approximately 220 individuals divided among 13 OMUs. Individuals are identified using natural features, such as scars, cuts, parasitic swellings, and fur color. For adults, keeping track of individuals is a fairly simple task. For juveniles, who have not yet acquired many significant injuries and whose lively, playful activities are more difficult to follow, keeping track of individuals can be a bit more challenging. For example, the L-unit (one of the larger OMUs studied) currently contains six juvenile females that are all about the same age and size. As you can imagine, sometimes it is quite hard to tell them apart. Yet, despite these struggles, the subtle differences in physical features and personalities become obvious as you spend more time with them. Of course, as soon as you get used to the groups, something happens…
The farms below one of the gelada sleeping cliffs. Farmers plant barley and other crops which the geladas occasionally attempt to raid, making relations between the two a bit tense.
Since beginning my year of fieldwork to collect data for my dissertation, we have had a number of strange and unexpected disappearances and take-overs. During take-over events, a new male becomes the leader, which is very stressful for the OMU. In the relatively short space of six months, six take-over events have occurred in five OMUs (one unit was taken over twice). For five of these six take-over events, the previous leader-male appeared in perfect health, in the prime of life, and had easy to identify features. Usually, we should expect to see at least some of these males present as a follower male or as a member of a bachelor unit, but they are nowhere to be found. In one particularly strange case, the D-unit was unexpectedly leaderless for an entire morning after their leader-male went missing on the previous day. Of course, bachelor males could not ask for a better opportunity to acquire a harem of their own. Several bachelor males quickly took advantage of the abandoned and defenseless unit, fighting amongst themselves until one male won, becoming the new leader-male. As interesting as these take-over events are, the disappearances remain a puzzle. It is possible that these disappearances are the result of unobserved conflict with local farmers or predators (a recently observed leopard may be very successful at hunting).
While we may not be certain of the cause, these strange and mysterious events have provided abundant opportunities to explore how the absence of a father affects the OMU and offspring he left behind. How many more offspring are lost to infanticide? Do immatures receive more aggression from the new male? How long does it take for the OMU to settle back into a sense of calm following the take-over? In the R-unit, Radagast and Reginald, the two youngest infants in the OMU, disappeared shortly after their unit was taken over by a new male. Radagast was last seen struggling to heal from two puncture wounds on his right side, which probably resulted from an attempted infanticidal attack from the new leader-male. Many of the older juveniles in the group frequently submit to their new leader-male while nearly all the adult females resumed cycling and began presenting to the leader. While primate research does not always go as planned, even the unexpected can provide a wealth of data for my own research while providing intriguing questions worth exploring in the future. Never a dull day with the Guassa geladas.
Sam Patterson processing a fecal sample in Laikipia, Kenya
Sam Patterson, PhD candidate from Arizona State University, was awarded a Leakey Foundation Research Grant for the project entitled “Maternal predictors of infant developmental trajectories in olive baboons.”
Early life experiences can have substantial influence on development and adult outcomes. The mother is a crucial component of the early life environment for humans and other primates. Recently, researchers have begun to examine the complexities of maternal signals, how infants use these signals to navigate developmental trade-offs, and the impact of trade-off decisions. For my dissertation research, I am taking a maternal signaling lens to examine how infants navigate development in response to the maternal environment in an ecologically diverse population of olive baboons (Papio anubis). Specifically, I will address three questions: What predicts variation in maternal signals? How do infants respond to maternal signals? How do infants navigate developmental tradeoffs?
Infant olive baboon chewing a stick
I am currently collecting data on mother and infant baboon pairs in Laikipia, Kenya. The study site provides the opportunity to compare animals that rely heavily on invasive Opuntia stricta fruits and animals that have limited access to these fruits. For groups that range in areas where O. stricta is common, its fruit has become an important component of the baboons diet, and reduced seasonal variability in food availability.
This study will capitalize on long-term ecological and demographic data and provide detailed behavioral, physiological, and growth data. I am using photogrammetry to measure body size and growth trajectories, fecal samples to measure glucocorticoid levels in mothers and infants, and focal samples to obtain detailed information about nursing behavior, infant activity levels, and maternal responsiveness.
Mother and infant olive baboon
By considering the maternal environment and multiple dimensions of development simultaneously in an ecologically varying population, I hope that this project will provide an integrated understanding of how the maternal environment shapes maternal signals and guides infant development and provide insights into the evolution of human health, development, growth, behavior, and physiology. In the future, I hope to expand on this project by investigating consequences of tradeoff decisions. One future research goal is to monitor weaning patterns and age of reproductive maturity for the infants sampled in this study.
Over a 16-year period, about half of the orangutans living on the island of Borneo were lost as a result of changes in land cover. That’s according to estimates reported in Current Biology on February 15 showing that more than 100,000 of the island’s orangutans disappeared between 1999 and 2015.
Many of those losses were apparently driven by the demand for logging, oil palm, mining, paper, and associated deforestation. However, many orangutans have also disappeared from more intact forested areas, the researchers say. These findings suggest that hunting and other direct conflicts between orangutans and people remain a major threat to the species.
“The decline in population density was most severe in areas that were deforested or transformed for industrial agriculture, as orangutans struggle to live outside forest areas,” says Maria Voigt of the Max Planck Institute for Evolutionary Anthropology in Germany. “Worryingly, however, the largest number of orangutans were lost from areas that remained forested during the study period. This implies a large role of killing.”
To estimate changes in the size of the orangutan population over time, Voigt, along with Serge Wich from Liverpool John Moores University in the UK and their colleagues representing 38 international institutions, compiled field surveys conducted from 1999 to 2015. They extrapolated the overall size of the island’s population from the number of orangutan nests observed throughout the species’ range in Borneo.
All told, the team observed 36,555 nests. They estimated a loss of 148,500 Bornean orangutans between 1999 and 2015.The data also suggest that only 38 of the 64 identified spatially separated groups of orangutans (known as metapopulations) now include more than 100 individuals, which is the accepted lower limit to be considered viable.
In order to identify the likely causes of those losses, the researchers relied on maps of estimated land-cover change over the same period that have been made possible by advances in remote sensing technology. The comparison of orangutan and habitat losses suggests that land clearance caused the most dramatic rates of decline. However, a much larger number of orangutans were lost in selectively logged and primary forests. That’s because while the rates of decline were less precipitous in those areas, that’s also where far more orangutans are found, the researchers explain.
This photograph shows where Bornean forest was cleared for a factory. Photo: Marc Ancrenaz
By 2015, they report, about half of the orangutans estimated to live on Borneo in 1999 were found in areas in which resource use has since caused significant changes to the environment. Based on predicted future losses of forest cover and the assumption that orangutans ultimately cannot survive outside forest areas, the researchers predict that over 45,000 more orangutans will be lost over the next 35 years.
They say that effective partnerships with logging companies and other industries are now essential to the Bornean orangutan’s survival. Public education and awareness will also be key.
“Orangutans are flexible and can survive to some extent in a mosaic of forests, plantations, and logged forest, but only when they are not killed,” Wich says. “So, in addition to protection of forests, we need to focus on addressing the underlying causes of orangutan killing. The latter requires public awareness and education, more effective law enforcement, and also more studies as to why people kill orangutans in the first place.”
They note that Indonesia and Malaysia are both currently developing long-term action plans for orangutan conservation. By taking into account past failures, the hope is that new strategies to protect orangutans can be developed and implemented.
This work was funded by The Leakey Foundation, the Max Planck Society, Robert Bosch Foundation, and many other funding organizations.
Most mammals rely on scent rather than sight. Look at a dog’s eyes, for example: they’re usually on the sides of its face, not close together and forward-facing like ours. Having eyes on the side is good for creating a broad field of vision, but bad for depth perception and accurately judging distances in front. Instead of having good vision, dogs, horses, mice, antelope – in fact, most mammals generally – have long damp snouts that they use to sniff things with. It is we humans, and apes and monkeys, who are different. And, as we will see, there is something particularly unusual about our vision that requires an explanation.
Over time, perhaps as primates came to occupy more diurnal niches with lots of light to see, we somehow evolved to be less reliant on smell and more reliant on vision. We lost our wet noses and snouts, our eyes moved to the front of our faces, and closer together, which improved our ability to judge distances (developing improved stereoscopy, or binocular vision). In addition, Old World monkeys and apes (called catarrhines) evolved trichromacy: red-, green- and blue-colour vision. Most other mammals have two different types of colour photoreceptors (cones) in their eyes, but the catarrhine ancestor experienced a gene duplication, which created three different genes for colour vision. Each of these now codes for a photoreceptor that can detect different wavelengths of light: one at short wavelengths (blue), one at medium wavelengths (green), and one at long wavelengths (red). And so the story goes our ancestors evolved forward-facing eyes and trichromatic colour vision – and we’ve never looked back.
Colour vision works by capturing light at multiple different wavelengths, and then comparing between them to determine the wavelengths being reflected from an object (its colour). A blue colour will strongly stimulate a receptor at short wavelengths, and weakly stimulate a receptor at long wavelengths, while a red colour would do the opposite. By comparing between the relative stimulation of those shortwave (blue) and longwave (red) receptors, we are able to distinguish those colours.
In order to best capture different wavelengths of light, cones should be evenly spaced across the spectrum of light visible to humans, which is about 400-700nm. When we look at the cone spacing of the honeybee (fig. 1), which is also trichromatic, we can see that even spacing is indeed the case. Similarly, digital cameras’ sensors (fig. 2) need to be nicely spaced out to capture colours. This even cone/sensor spacing gives a good spectral coverage of the available wavelengths of light, and excellent chromatic coverage. But this isn’t exactly how our own vision works.
Our own vision does not have this even spectral spacing (fig. 3). In humans and other catarrhines, the red and green cones largely overlap. This means that we prioritise distinguishing a few types of colours really well – specifically, red and green – at the expense of being able to see as many colours as we possibly might. This is peculiar. Why do we prioritise differentiating red from green?
Several explanations have been proposed. Perhaps the simplest is that this is an example of what biologists call evolutionary constraint. The gene that encodes for our green receptor, and the gene that encodes for our red receptor, evolved via a gene duplication. It’s likely that they would have originally been almost identical in their sensitivities, and perhaps there has just not been enough time, or enough evolutionary selection, for them to become different.
Another explanation emphasises the evolutionary advantages of a close red-green cone arrangement. Since it makes us particularly good at distinguishing between greenish to reddish colours – and between different shades of pinks and reds – then we might be better at identifying ripening fruits, which typically change from green to red and orange colours as they ripen. There is an abundance of evidence that this effect is real, and marked. Trichromatic humans are much better at picking out ripening fruit from green foliage than dichromatic humans (usually so-called red-green colourblind individuals). More importantly, normal trichromatic humans are much better at this task than individuals experimentally given simulated even-spaced trichromacy. In New World monkeys, where some individuals are trichromatic and some dichromatic, trichromats detect ripening fruit much quicker than dichromats, and without sniffing it to the same extent. As fruit is a critical part of the diet of many primates, fruit-detection is a plausible selection pressure, not just for the evolution of trichromacy generally, but also for our specific, unusual form of trichromacy.
A final explanation relates to social signalling. Many primate species use reddish colours, such as the bright red nose of the mandrill and the red chest patch of the gelada, in social communication. Similarly, humans indicate emotions through colour changes to our faces that relate to blood flow, being paler when we feel sick or worried, blushing when we are embarrassed, and so on. Perhaps detection of such cues and signals might be involved in the evolution of our unusual cone spacing?
Recently, my colleagues and I tested this hypothesis experimentally. We took images of the faces of rhesus monkey females, which redden when females are interested in mating. We prepared experiments in which human observers saw pairs of images of the same female, one when she was interested in mating, and one when she was not. Participants were asked to choose the mating face, but we altered how faces appeared to those participants. In some trials, human observers saw the original images, but in other trials they saw the images with a colour transformation, which mimicked what an observer would see with a different visual system.
By comparing multiple types of trichromacy and dichromacy in this way, we found that human observers performed best at this task when they saw with normal human trichromatic vision – and they performed much better with their regular vision than with trichromacy with even cone spacing (that is, without red-green cone overlap). Our results were consistent with the social signalling hypothesis: the human visual system is the best of those tested at detecting social information from the faces of other primates.
However, we tested only a necessary condition of the hypothesis, that our colour vision is better at this task than other possible vision types we might design. It might be that it is the signals themselves that evolved to exploit the wavelengths that our eyes were already sensitive to, rather than the other way round. It is also possible that multiple explanations are involved. One or more factors might be related to the origin of our cone spacing (for example, fruit-eating), while other factors might be related to the evolutionary maintenance of that spacing once it had evolved (for example, social signalling).
It is still not known exactly why humans have such strange colour vision. It could be due to foraging, social signalling, evolutionary constraint – or some other explanation. However, there are many tools to investigate the question, such as genetic sequencing of an individual’s colour vision, experimental simulation of different colour vision types combined with behavioural performance testing, and observations of wild primates that see different colours. There’s something strange about the way we see colours. We have prioritised distinguishing a few types of colours really well, at the expense of being able to see as many colours as we possibly might. One day, we hope to know why.
James P Higham is associate professor of anthropology at New York University, and a Leakey Foundation grantee.
This article was originally published at Aeon and has been republished under Creative Commons.