Another primate "sleeps" away hard times

Hibernation allows an organism to lower its metabolism, heart rate, body temperature, and breathing in order to expend less energy during what may be a difficult time, such as a cold winter.  Hibernation is a tactic commonly associated with rodents and polar bears but primates do it too. The fat-tailed dwarf lemur (Cheirogaleus medius) on the island of Madagascar hibernates during the dry season, using the fat in its tail to survive the winter. The Crossley's dwarf lemur (Cheirogaleus crossleyi) and the Sibree's dwarf lemur (Cheirogaleus sibreei) also hibernate. Some primates (Microcebus murinus, Allocebus trichotis, Galago moholi, and others) will enter what is called torpor, during which body temperature and metabolism is lowered but for a period less than 24 hours. Lemurs were thought to be the only primate that hibernated, until a close cousin changed the game.

Pygmy slow loris. Photo: David Haring at Duke Lemur Center

It has recently been reported that the pygmy slow loris (Nycticebus pygmaeus), a nocturnal primate living in Cambodia, China, Laos, and Vietnam does in fact hibernate (Ruf et al., 2015). The authors behind this study set out to find a hibernating primate outside of Madagascar and they succeeded.

Ruf and colleagues found it hard to believe that hibernation in primates would be restricted to only Madagascar, so they started thinking about what environmental conditions and physical characteristics would make an animal likely to hibernate. They hypothesized that a hibernating primate would be small, as most hibernating animals are (Ruf and Geiser, 2015), that the animal would live in an environment that is distinctly seasonal in temperatures and/or precipitation, and in an environment with seasonal changes in food availability. Given the primates known to use torpor, primates falling into the suborder Strepsirrhines seemed like their best bet.

The pygmy slow loris fit their criteria. It was logical that a small primate facing cold temperatures in winter and low food availability would adapt using hibernation. Thus lowering energy requirements during a period of limited resources. While previous descriptions of the pygmy slow loris were in accord with hibernation (Ratajszczak, 1998; Streicher, 2005), no measurements had been taken. Thus, Ruf and colleagues decided to take some.

After measuring temperature (but not metabolic rate) in five adults over 769 days total, animals hibernated for several days during midwinter interspersed with periods of activity and or torpor. On average, animals hibernated for 43 hours (± 3 hours with a range of 25.9-62.6 hours).

Thus, evolutionary mechanisms have not limited hibernation in primates to Madagascar. As more research is done, it is possible that hibernation will be found in other primate species inhabiting seasonal environments.

Links of possible interest:
Discovery of hibernation in fat-tailed dwarf lemur
Primate hibernation more common than previously thought
The costs and benefits of hibernation

Sources:

Ratajszczak, R. (1998). Taxonomy, distribution and status of the lesser slow loris Nycticebus pygmaeus and their implications for captive management. Folia Primatologica, 69(Suppl. 1), 171-174.

Ruf, T., Streicher, U., Stalder, G. L., Nadler, T., & Walzer, C. (2015). Hibernation in the pygmy slow loris (Nycticebus pygmaeus): multiday torpor in primates is not restricted to Madagascar. Scientific reports, 5.

Ruf, T. & Geiser, F. Daily torpor and hibernation in birds and mammals. Biol. Rev. 90, 891–926, doi: 10.1111/brv.12137 (2015).

Streicher, U. (2005). Seasonal body weight changes in pygmy lorises Nycticebus pygmaeus. Verhandlungsber. Zootierkrk, 42, 144-145.

Male squirrel monkeys made to see in living color

Squirrel monkey in Bolivia. Photo: author

Squirrel monkeys, like many New World Monkeys, are a bit unusual when it comes to their vision. Males are dichromatic, meaning that they do not have the ability to see red wavelengths but can see blue and green wavelengths. Females on the other hand, may be dichromatic or they may be trichromatic like us, able to see blues, greens, and reds. Males are dichromatic because trichromatic vision requires two copies of a certain opsin gene, a gene that is found on the X chromosome. Thus, females, who have two Xs, likely (but not always) carry two copies of the gene. The majority of female squirrel monkey can see shades of green and shades of red. Male monkeys have the gene that codes for seeing green colors but not the gene that allows them to see red.

When we refer to color blindness in humans, often what we really mean is that the person has dichromatic color vision. True color blindness in humans, where the person can only see in black and white, is very rare, although something similar does occur in another New World Monkey. Night monkeys have very poor color vision. As their name suggests, these monkeys are active only at night. Thus, seeing reds, greens, and blues isn't very advantageous given their environment. Over time, owl monkeys have evolved so that they have fewer cones, which allow the eye to see colors, and more rods, which allow the eye to distinguish blacks and whites. To further adapt for their mainly nocturnal lifestyle, the size of their eyes has also expanded. Again, being monochromatic is rare in humans, yet dichromatic color vision does occur in one out of twelve men.

Visible Wavelengths Dichromats lack red cones

Now, there may be hope for those who have dichromatic color vision and it's thanks to research done in squirrel monkeys. Two male squirrel monkeys have been made to see all three wavelengths.

Mancuso and colleagues injected the gene that would allow two male squirrel monkeys to see red into a virus, and then they injected that virus behind the retina. (Review your eye anatomy here.) Two years later, the monkeys have had no side effects and are able to see all three wavelengths. Squirrel monkey brains, like our own, are quite plastic, meaning they can change. These two animals can now distinguish reds from greens and their brains have apparently rewired themselves so that seeing and processing information about the red wavelength can be done.

Why do humans see in all three colors? There isn't a certain answer. Multiple hypotheses have been proposed. Peter Lucas, my former professor, believes our ability to see reds was advantageous in helping our ancestors see young red leaves, which are especially nutritious, against a background that is mostly made up of shades of green (Lucas et al., 1998). Our closest living relatives, chimpanzees and gorillas, consume a diet mainly composed of leaves. Or perhaps we see reds because red fruit is often ripe and therefore we can distinguish ripe  fruit against a green background (Allen, 1879; Mollon, 1989; Fleagle, 1999). Yet, if this were the complete answer, wouldn't we expect New World Monkeys, who consume fruit, to see red wavelengths? Another hypothesis suggests that our ability to see shades of red occurred so that male Old World Monkeys could more easily discern the sexual swellings of females that were in estrous (Liman and Innan, 2003).

Regardless of why trichromatic vision evolved in our ancestors, it seems that those humans unable to see all three wavelengths may one day be able to enjoy the Christmas colors following gene therapy. Trials in humans are underway and we have two male squirrel monkeys to thank for that.


Links of interest:
Color vision in primates
Color vision in humans 
Night monkeys and their morphology
A molecular view of how human color vision evolved


Works cited:
 Allen, G. 1879.  The colour-sense: its origins and development. Trubner, London.
Fleagle, J. G. 1999. Primate adaptation and evolution. 2nd ed. Academic Press, San Diego, CA. 

Liman, E. R., & Innan, H. (2003). Relaxed selective pressure on an essential component of pheromone transduction in primate evolution. Proceedings of the National Academy of Sciences, 100(6), 3328-3332

Lucas, P. W., Darvell, B. W., Lee, P. K. D., Yuen, T. D. B., & Choong, M. F. 1998. Colour cues for leaf food selection by long-tailed macaques (Macaca fascicularis) with a new suggestion for the evolution of trichromatic colour vision. Folia Primatologica, 69(3), 139-154.

Mancuso, K. et al. Nature advanced online publication, doi:10.1038/nature08401 (2009). 

Mollon, J. D. 1989. “Tho'she kneel'd in that place where they grew…” The uses and origins of primate colour vision. Journal of Experimental Biology, 146(1), 21-38.

No, humans did not evolve from monkeys

Frequently used image depicting evolution

I often hear, "humans evolved from monkeys" or substitute monkeys for apes or chimps. Unfortunately, this is a common misconception. It's simply inaccurate and a result of poor understanding of how evolution works. Humans did not in any circumstances evolve from monkeys or chimps or lemurs. For the sake of clarity, let me repeat, humans did not evolve from monkeys or chimps or lemurs. I'm not about to go on a creationist rant but I am about to explain hopefully dispel some common misconceptions about evolution. To understand why saying humans evolved from monkeys is so wrong, we first need to take a closer look at how evolution work and we're going to start with phylogenetic trees. A phylogenetic tree is a visual representation of the evolutionary relationships between species. They're often just called trees for short and they're very useful. If we look at the one below, we see multiple species (named "A" and "B" and so forth). The nodes or areas where multiple lines come together represent common ancestors.

For example, if we trace species A back through time we see it eventually connects at a spot I've labeled X. The same is true for species B and C: we can trace their lines back to species X.

Example of a phylogenetic tree

 Species A, B, and C are all descendants of species X, which no longer exists. Species X is the last common ancestor species A, B, and C shared. A common ancestor is simply an ancestor that two or more species have in common, and the last common ancestor is the most recent common ancestor of two or more species. If we keep traveling down the line of A (and back in time), we see that species Z is also a common ancestor of A and B, but the last common ancestor of A and B is species X. There's a slight difference in meaning between common ancestor and last common ancestor. All of the species on this tree originally evolved from species Z, but this was a very long time ago. Usually, trees represent millions of years. Over time, species change. Species Z was one species at the start of this tree, but something happened (either gradually or suddenly) to make this species split into two different species, X and Y. Maybe one population was separated by another due to an earthquake, as time progressed, those two populations became so different from each other, they formed new species (X and Y).  Species X may have been separated from a critical food source, and thus gradually began foraging only at dusk and dawn for insects, whereas the other population started interbreeding with another population made up of only white-colored individuals. Over time, the two become distinct populations and eventually distinct species.

Close-up of some of the phylogenetic tree

Let's take a closer look at another side of the tree and pretend that these alphabetically named species are species of monkeys. D, E, and F separated or diverged from species Y. If I look the tree over from the top to the bottom, I see that species D, E, and F are relatively young (their lines separating them from Y are relatively short), and that species Y spent a great deal of time successfully as species Y before it split into multiple species. Let's say one of the main reasons why species Y split into multiple species was because a new predator was introduced into the habitat. One population of Y changes its behavior and activity patterns to become nocturnal, thus avoiding the diurnal predator entirely. That population becomes E. Enough time passes and E can no longer breed with close relatives, D or F. Another population E finds success in foraging lower in the canopy, thus avoiding the predator, which let's say is some sort of predatory bird. E forages lower in the canopy but has to make behavioral changes to do so, feeding on different items and relying on its tail less to balance on thicker tree branches. Over time, E becomes a distinct species and cannot breed with F or D. It retains some success for a while but eventually it begins to lose numbers due to feeding competition from other animals occupying this part of the canopy, and E goes extinct. This is why species E's line does not extend all the way to the top of the tree, or the present time. It did not survive. The same is true for species D, which managed to adopt certain vigilance behaviors to avoid the predator, but was sadly wiped out from a disease that destroyed the population.

If you follow the lines, you can see that species F eventually splits again into separate species, making species F an ancestral species. It is the last common ancestor to H and I, both of which still survive to this day. Species H is more closely related to species I than it is to species C, which it last shared a common ancestor with a long time ago. That means that H and I will share more characteristics than species I and C.

Tree showing relationship of great apes and humans

Now, all you have to do is apply this to primates. Chimpanzees, lemurs, and so forth are all living species. Replace A with lemurs and I with humans and you can see immediately that we did not evolve from lemurs. A does not come from I. That's obviously wrong. However, A and I do share a common ancestor, Z. Now, these A and I have been evolving, over time, separately for a while. They've taken different paths, but they do share a common ancestor, a common ancestor, Z, which is no longer alive. It may seem like a small difference, but the number of people who actually believe that we did evolve from monkeys is perhaps greater than we'd all like to believe. By saying, we shared a common ancestor with monkeys or we evolved from an ape-like ancestor as did chimpanzees, some of the confusion might be avoided. Or someone may ask you to clarify, and you can explain that humans did not, in fact, evolve from chimpanzees. Looking back to the first image depicting evolution of humans, if you said that first animal was a gorilla, that would be inaccurate. If you said it was an ancestor of both gorillas and humans, you'd be okay.

It's important to remember that while it looks like species H and I separated from each other at a very distinct point according to this tree, that's not always the case. Populations are always evolving, and it may take a few generations or a hundred generations for a species to gradually become a separate one. It is humans who define when exactly a species arises or diverges, but the reality is that it is a process, and the exact time when one species became two is debatable. There usually isn't a right answer. Scientists are forever learning about species, finding new ones, and reassembling these trees using the best information available. The end of the tree, in our case A, B, and so forth, don't need to represent species. You could do a phylogenetic tree and go as far as genera if you'd like or go all the way to subspecies even. It depends on what your purpose is.

True or false: humans are more closely related to orangutans than gorillas.
Answer: false
True or false: humans are more closely related to chimpanzees than bonobos.
Answer: false. If you switch bonobos and chimpanzees in the tree above, you'd be within your right to do so. The same amount of time has passed since we split from the last common ancestor we shared with both species.


Further reading:
Reading trees: a quick review
Chimpanzees and humans may have split much earlier than thought
Phylogenetic tree of primates
Large phylogenetic tree based on genetics

Finding new species in 2015-how it happens

Articles like this one from Mother Nature Network, titled 9 newly discovered species, pop up from time to time about new organisms that have been found by scientists. Just recently a previously unknown species of fish was discovered no less than five miles below the ocean's surface. New primate species are even discovered, although finding such large species is very rare.

Newly identified Rana kauffeldi Photo credit: Brian Curry

Wait, how is that we're still discovering completely new animals?  Scientists estimate that there are millions, yes millions, of species we still don't know about. While some of these unknown species are reptiles or rodents, most of them are less charismatic. Many species of insect have yet to be identified and many bacteria and plants are unknown too.

New species are often discovered when scientists look at the genome of one species only to find out that one species is really two or more separate species. For example, Bornean and Sumatran orangutans were once thought to be one species. No attention was given to breeding Bornean orangutans only with Bornean orangutans, and many zoos now have hybrid orangs because of this. It was through genetic analysis that we discovered that each island held its own, distinct species.

Some of the time scientists do discover completely new species that are unheard of to science. This usually happens in far-away and poorly studied areas of the globe. Scientists talk to locals in remote areas and hear about a species that doesn't match descriptions of known species. Behavior, anatomy, reproduction, and even vocalizations are all examined when determining if something is a new species. Scientists hunt around in the jungle, struggle to obtain a photograph or grab a sample specimen, and ideally consult with as many other experts as possible to make sure that this is in fact a new, distinct species. It's important to compare a possible new species with existing species to ensure that there are enough differences to satisfy calling something an entirely new species.

Classification of Saimiri oerstedii

A species is a group of organisms that are similar and capable of interbreeding. (To learn more about what the term species means in biology, check out this great page and this one from Berkley.) A species is given a Latin binomial name. Examples of Latin binomial names you might be familiar with include Homo sapiens for humans, Pan troglodytes for chimpanzees, and Drosophila melanogaster for the common fruit fly. When we discover new organisms, it is the taxonomists who study those organisms and decide how they should be named. Taxonomy is the branch of science that includes the classification, identification, and description of organisms. You can see the classification for a species of squirrel monkey to the right. Taxonomy may sound a little boring, but classifying animals isn't always black and white. There's currently a debate about the classification of capuchin monkeys that you can read more about in this article.

So the next time you click on a link about the ten most interesting species discovered in 2014, you understand how it is species are found, how it's determined that those species are distinct, and how they are named.

Food for thought: What do you think is the best way to determine if a species is separate or distinct from another? Would you rely on genetics? Or look at the behaviors of the animal? Is whether or not the two populations coexist in the wild important? There are many things to consider!


News stories about recently discovered species:

Head to LiveScience to read about a species of monkey first spotted in 2007.
Read about a coughing frog species that was recently discovered or
five new bird species discovered in 2014.

Mean male chimps produce more offspring-implications for humans?

A study came out about chimpanzees recently that has received a lot of attention. You may have seen a headline on sites such as ScienceDaily, Smithsonian, and other websites stating that male chimps that bully females are more likely to reproduce. Specifically, researchers looked at 16 years worth of data from Gombe National Park in Tanzania (Gombe is where Jane Goodall first studied chimps). They found that males that were sexually coercive, or those or threatened or used force against females,  fathered more young than males that were less violent towards females. Male chimpanzees that acted violently towards females year-round (as opposed to just when females were receptive, or ready to mate,) were more successful. Those males that increased aggressive behavior towards females only when females were receptive did not have any advantage in fathering offspring.

Our closest genetic relative, the chimpanzee

Now, this study is a great example of how results and interpretations differ. It also presents the perfect opportunity to talk about how science reporters for the general public often misunderstand or sensationalize scientific research. News sites will get more people to click on their site if they use certain words and only report some facts to create a more interesting (although probably misleading) story.

The fact is, there are many ways to interpret this study, and the close genetic relationship between chimpanzees and humans means that of course we're all going to ask, what does this mean for humans?

Well, with sixteen years of data, there's certainly enough evidence to say that bullying females provides an advantage for chimpanzees at Gombe. However, how do we not know that these bullying males are aggressive with all chimpanzees, males and females and that aggression in general is the trait increasing their sexual advantage? Maybe this is the case or maybe not. My point here is simply that chimpanzees and complex and their reproduction and mating rituals are also complex.

Chimpanzee and offspring Photo credit: Neil McIntosh

It's not as simple as saying, "Oh, well if chimps that are mean towards females are more successful reproductively, the same must be true for humans." Many factors go into chimpanzee reproduction and many factors go into human reproduction. As similar as we are, we are not the same. Study author Joseph Feldman even states on ScienceDaily, "The glaring difference between chimpanzee and human mating behavior is that in chimpanzees females mate promiscuously with most male group mates during most cycles, while human females do not. Thus, the system that favors male coercion in chimpanzees is not present in humans to favor this behavior." The authors also point out a fact that all of the articles I've read so far seem to overlook: studies of chimpanzees at other sites have not found a link between sexually coercive males and the number of offspring they father. Thus, we need to remember that these results are specific to the chimpanzees studied at this site and not all chimpanzees in Africa.

The take home messages are; 1) be careful when reading about science from sources other than the original scientists and 2) with animals and biology especially, remember that simple studies are needed for us to ask answerable questions, but that the reality may be very complex.

Female Chimps and Male Attention

Everything is connected. More time spent resting means less time spent grooming. Less time spent grooming may mean greater chance of parasites and thus a greater chance of illness. Illness means greater chance of mortality. This is just one example of how everything is connected and one aspect of life affects another. The same is true whether one is a chimpanzee or a human. If you spend more time playing soccer with your friends, you will need to spend less time doing your homework. Or maybe you will compensate for that time lost doing your homework by working late into the night and sleeping less.

Chimps grooming, Photo credit flickr user Tambako the Tiger

One would think that receiving male attention would be a good thing, if one is a female chimpanzee. The more males seeking your attention, the more choice you have, right? The more opportunities to mate, and since an individual's fitness is a measure of the number of offspring one produces that survive to maturity, mating is an important part of life. So it's straightforward then. The more male attention, the better. Right? Not so fast...

A recent study led by Melissa Emery Thompson of the University of New Mexico found that male attention comes with costs. In the world of chimpanzees, males do indeed compete to mate with females. (Chimpanzees live in groups of multiple males and females and males are dominant over females.) A female will give birth to an offspring and then raise that offspring for five to seven years, which is a pretty long time in the animal kingdom. In part because female chimps raise their young for so long, males compete seriously for access to females. It's not as though the guys always have a chance with that type of reproductive schedule. Females will mate with multiple males, some of whom will then guard her to prevent other males from mating with her, so she can receive quite a bit of attention, whether she wants it or not.

For eleven years, researchers observed chimpanzee behavior and collected their urine to analyze or study hormones (naturally occurring substances that affect or regulate the activity of other cells or organs), such as estrogen and progesterone, which are two female sex hormones important for female sex characteristics and for reproduction. Emery Thompson and colleagues also collected urine to look for C-peptides, a byproduct of insulin. Declining levels of C-peptides indicate a female is spending more energy than she is currently consuming, which is not good.

Chimpanzees with offspring, Photo credit: flickr user Valerie

What they found was that females with more males surrounding them had lower levels of C-peptides and lower levels of those reproductive hormones. Thus, females with all of this attention are not consuming enough energy and are producing fewer hormones than needed. It appears that all of this male attention could very well stress out the females. Perhaps all of that attention from males means that females are less efficient at foraging and obtaining the food they need. Or perhaps they feel a need to keep an eye on those males, as males are dominant, and this extra vigilance is taxing or stressing. Whatever the exact connection is, it appears there are costs to having a lot of males around when cycling or lactating.


Food for thought: Why might female chimpanzees mate with multiple males? Hint: do some research into infanticide and think about how this might protect against it.

Island living

Madagascar is the world’s fourth largest island. It is thought to have reached its present day location in relation to the African continent about 130 million years ago. Today, 400km separate Madagascar from the rest of Africa. Lemuriformes are though to have colonized Madagascar roughly around 65 million years ago, so how did the ancestors of sifakas, ring-tailed lemurs, and others arrive on the island? Are lemurs great endurance swimmers? Not exactly.

Madagascar's hissing cockroaches

What determines whether a species colonizes an island? Is colonization of an island something scientists can predict? The principles of island biogeography lend us a hand in determining whether or not an island will be successfully colonized by new species.

For starters, the closer the island is to the mainland or another large land mass, the more likely that island is to be colonized. The older the island is the more likely the island is to be colonized. The larger the island is the more species are likely to colonize it. All of these fancy rules are pretty simple once you think about them. The older the island is, the more time has passed, allowing species to reach the island. The larger the island is, the more space there is for all of those new species. And the closer the island is to other landmasses, the less distance between the two landmasses makes for an easier crossing for new species.

In terms of the genetics behind island biogeography, the following rules apply. As time passes and the island has been settled by those species that were able to the island and been successfully live there, genes are less likely to be exchanged between the original population from the mainland and the population on the island. As even more time passes, the two populations become genetically different.

Ancestral lemurs likely reached Madagascar by a series of rafts. This would have occurred not over a summer holiday but over an extended period of time in a series of events. As time passed, ancestral lemurs diverged from their original population and became genetically distinct. They thrived on the island of Madagascar and became the species we know today.

Survival of the fittest

Baobab tree

“Survival of the fittest” is a phrase most people have heard of. Some people may even attribute it to Charles Darwin, although he actually adopted it from someone else. Many people don’t understand what the fittest means in terms of biology. An individual’s fitness is their ability to successfully produce offspring that survive to adulthood. I have a fitness of zero because I have no children. My sister has a fitness of two because she has two children. A primate mother who gives birth to twins, but only one infant survives to adulthood would have a fitness of one. An individual’s fitness is related to its adaptations, or traits that make an individual or a species better suited to the environment.

Introduced Brown Lemur on Trail

I am attempting to adapt by changing my project. I originally proposed to study four troops of sifakas. I wanted two troops in the spiny forest and two groups in the gallery forest. However, upon my arrival, I learned from my Malagasy assistant that there are only three groups total in the spiny forest, and each had one lactating female. We were able to locate two groups in our first few days but only one still had a lactating female. Given the scarcity of lactating females in the spiny forest, I have adapted to my environment and am only studying three troops in the gallery forest. I have five lactating mothers total, which is less than I wanted but this is the reality of the situation. We all have to adapt to our surroundings. A species may be perfectly well-adapted to it’s environment, but if a large change comes about, say humans start hunting that species, well then that species better adapt. Those most able to adapt to change are usually the ones most able to survive. Humans aren't exempt from change. 

Brown lemurs were introduced to Berenty, meaning they are not native to this area. The only diurnal primates at Berenty should be ring-tailed lemurs (Lemur catta) and Verreaux's sifakas. However, brown lemurs were introduced in 1975 and I have seen far more of them than sifakas. Clearly they have adapted to their new environment. They seem to be thriving as far as I can tell! The species of brown lemur at Berenty is actually a hybrid of two, genetically distinct species that bred together. They range wherever there is food, although they are a bit more timid than ring-tailed lemurs, the species of lemur Berenty is well-known for. The ring-tailed lemurs often steal food from the tourists and show up to breakfast for any table scraps left behind. Certain troops of ring-tailed lemurs have creatively adapted to the tourists here.

Critical thinking: Can you think of other examples of animals adapting due to their close relationship with humans?