Wednesday, February 24, 2016

When The Early Bird Is Also The Night Owl

Biology concepts – cathemerality, circadian rhythm, adaptation, predator/prey relations

One carnivorous and three vegetarian friends
stranded on a island – what could go wrong?
The 2005 movie ”Madagascar” had some animals that we recognize from zoos; a lion, a zebra, a hippopotamus, a giraffe. But who were the bad guys? They were called the “Foosa” but what kind of animal was the foosa?  And who were those little primates they were trying to eat?

Being an island, Madagascar has developed ecosystems all its own. There are plants and animals that live there and nowhere else on Earth. This can lead to some interesting and exceptional behaviors and activities.

Tenrecs are a weird group. Different species can
be a few grams to over a kilogram, may have between
30 and 45 teeth, are related to elephants, and a have
a common anal and urogenital opening like birds. With
all that going on, being blue and yellow doesn’t seem
that weird.
Madagascar has its share of diurnal activity (daytime) and even more activity under the cover of dark (nocturnal). The streaked tenrec (Hemicentetes semispinosus, one of about 30 species) is crepuscular (active at dusk and dawn), so that activity pattern is covered as well. This black and yellow-striped cross between a hedgehog and a shrew (just by the looks of it, not by parentage) feeds on worms and other invertebrates. A study from early 2011 described a unique behavior from the tenrec, one that may cause us to include the cricket in the tenrec’s ancestry.

The quills on the tenrec come in two sizes, the long ones are for protection, but the shorter ones can be rubbed together to make high pitched (ultrasonic in many cases) sounds that can be used for communication or navigation. In the low light conditions of sunrise and sunset, scientists are considering the idea that tenrecs use stridulation (making sound by rubbing body parts against each other) to echolocate in their surroundings, similar to bats. They can also keep tabs on one another, communicating constantly with other tenrecs, even with a mouthful of worm.

The short spines on tenrecs are controlled by individual
muscles, so that one spine can be rubbed against another
to make noise.
Crickets, beetles, and some vipers stridulate, but the tenrec is a stridulating exception in two regards. One, it is the only mammal known to do so; and two, it is the only animal of any kind known to communicate both vocally and by stridulation. Madagascar would be a cool place to visit – weirdness like this is around every corner.

Even though the tenrec is a Madagascar native, I didn’t see him anywhere in the movie. Some animals are too weird even to be believable in a cartoon about talking animals.

The movie did feature a primate group from Madagascar, one that had a penchant for dance. Lemurs (from Roman mythology, lemurs = ghosts) are playful and energetic, and some are even said to dance, but I don’t think they crave house music like in the movie. The Sifaka verreauxi is called the dancing lemur, as it is the exception to four legged motility among the lemurs. S. verreauxi walks on two legs, but the outward turn of their hips make them sway back and forth, like they are dancing.

Lemurs of the genus Sifaka bounce around on two
legs to cover ground quickly. This looks like dancing, and
probably gave the movie makers the idea to turn the
lemurs into a group of party animals.
In the movie, I saw no less than seven different types of lemurs, but in truth there are about 100 lemur species and subspecies live on Madagascar and the nearby Comoro Islands (and nowhere else). Together, they are a microcosm of Madagascar activity patterns. Some lemurs species, like the large Sifaka verreauxi, are diurnal, while the smaller species, like the aye-aye, are generally nocturnal. Some are even crepuscular, active at both dusk and dawn (so they are not vespertinal or matutidnal).  But the weirdest types of lemurs are those that don’t show any of these patterns; in fact, they show no pattern at all! If that isn’t an exception, I don’t know what is.

The lack of an activity pattern does have a name, cathemerality (from the Greek, cat = complete and hemera = day). Cathemeral animals are active for periods of the day and/or periods of the night. In some cases, the periods of activity are driven by competition, when competitors are resting or prey is active. In other cases, periods of activity might be influenced by the seasonal temperatures or even the phase of the moon.

Whatever the stimulus, cathemeral (sometimes called metaturnal) animals can sleep day or night and hunt day or night, with no period of adjustment needed. African lions are cathemeral, driven by hunger and the success rates of their hunts, or by a need to conserve water.

In Madagascar, the red-fronted lemur (Eulemur fulvus rufus) is cathemeral in activity, as is the blue-eyed black lemur (Eulemur macaco flavifrons). Among primates, only humans and this species of lemur have blue eyes. However, the males have black hair while the females are reddish, so there is no chance of little blonde-haired, blue-eyed lemurs.

It is called the blue-eyed black lemur, so why is it
reddish-brown? This species is sexual dichromatic;
picture above is of a female, only the males are black.
The blue-eyed black lemur sees in color and is generally adapted to diurnal living; this is witnessed by the increase of its nocturnal activity when there is a full moon and with the nocturnal light level in general. However, the blue-eyed lemur has at least some activity spread across the 24-hour day all year round. This is one of three cathemeral patterns of lemurs in Madagascar lemurs.

A second cathemeral pattern is seasonally driven. In summer, when the daylight hours are greatest, it is enough for some cathemeral animals to limit themselves to daylight activity, but expand their active hours a bit during winter, so they are active in both day and night. This is driven by a need to find sufficient food.

The third cathemeral pattern is one in which there is mostly diurnal activity in one season and mostly nocturnal activity in another season. This may be driven by changes in temperature or perhaps resource availability. In Madagascar, the tropical climate ensures that food is always available, and the lack of a winter means that the temperature ranges between 60˚F and 80˚F all year round.

Many scientists believe that cathemerality may be an transient evolutionary middle ground, that all the species that display cathemeral activity are merely moving from diurnal to nocturnal, or the opposite direction. This is also known as an evolutionary disequilibrium hypothesis, as opposed to the idea that cathemerality is a stable evolutionary strategy.  A recent study using genetic markers across time (phylogenetics) indicate that there was a common ancestor lemur that was cathemeral as far back as 9-13 million years. This would indicate that cathemerality is VERY stable. These results therefore suggest that the three cathemeral patterns are related to stable patterns predation risk or food gathering.

However, the diets of the red-fronted lemurs and the blue-eyed black lemurs are very different considering that they are closely related species, called true lemurs (eulemurs, eu = true). Red-fronted lemurs eat only leaves, while blue-eyed black lemurs eat fruits. But they are both herbivores, and are both potential meals for a predator. This would be a good reason for being cathemeral; the lemurs can just choose to be active when the predator isn’t. Great idea, huh? Well, Madagascar’s biggest predator apparently read the lemurs’ playbook.

The fossa is not a cat, it is not a mongoose, it is not a monkey.
It is a predator and it is found only in Madagascar. It has
retractable claws, the same as all cats except the cheetah.
The fossa (pronounced foosa - get the connection to the movie?) is really Madagascar’s only big predator. It looks like a cat as it walks, and has retractable claws like most cat species, but its tail is as long as its body, like a monkey or a lemur. The fossa’s snout is more mongoose-like, as is the length of its body compared to the length of its legs. The film version of Madagascar didn’t do justice to the physical nature of the fossa; the bad guys in the movie pass for large cats.

The fossa spends much of its time up in the trees (it is arboreal) and chases the lemurs from tree to tree. Its long tail and sleek body design help it to move and maintain its balance as it moves through the branches. Most interesting, and an exception to mammal body design, the fossa’s outside digits on its rear paws are its biggest, this helps it to grasp the surfaces of the trees.

The long tail of the fossa helps it chase down
lemurs in the trees by improving its balance.
It also helps that the fossa hunts lemurs in
groups, using cooperative strategies.
Up in the trees we have the lemurs; some diurnal, some nocturnal, some crepuscular, and some cathemeral. What a buffet for the fossa! No matter what time he (or she) wishes to dine, there could be lemur on the menu, so the fossa has adopted cathemerality as well.

The movie was accurate in showing the fossas and lemurs active in both day and night now, but did the lemurs become cathemeral to get away from fossas? Maybe. The lemurs evolved before the fossa; were they cathemeral because they didn’t have to worry about predation, and a few species have stayed that way? Could be. Did the fossa become cathemeral to take advantage of the lemur smorgasbord? Nobody knows –yet. You can be sure that there are scientists who support each possibility.

Whichever way it happened, it points out a wrinkle that few people consider. Some animals can actually change their activity pattern. The shift is often in response to some ecological or physiologic pressure. Skunks are crepuscular - except for males in the mating season - they become diurnal.

Another example is the short-eared owl of the Galapagos Islands. The owls are crepuscular on islands that have a predatory buzzard species, but on islands without buzzards, the owls are diurnal. Finally, some anole species change their activity pattern from diurnal to nocturnal as the temperature rises. Even their color can change from green to brown as the temperature changes.

These shifts in activity patterns occur often enough that they can’t be called exceptions, but the majority of animals do hold a single pattern throughout the year. As such, nocturnal animals interact with other nocturnal animals and the same with diurnal animals. This isn’t a tough concept to grasp, even the movie got it right. Unfortunately, some folks in 1880’s Hawaii just didn’t seem to understand, and they are still dealing with the problems it caused.

Griffin, R., Matthews, L., & Nunn, C. (2012). Evolutionary disequilibrium and activity period in primates: A bayesian phylogenetic approach American Journal of Physical Anthropology, 147 (3), 409-416 DOI: 10.1002/ajpa.22008

For more information and classroom activities on cathemerality, lemurs, or fossa, see:

Cathemerality –

Lemurs –

fossa –

Wednesday, February 17, 2016

Sunrise, Sunset – Life In the Twilight

Biology concepts – activity patterns, crepuscular, co-evolution, active pollination

Nocturnal and diurnal activity patterns are like vanilla and chocolate cupcakes. But what if you like rose hip or green tea flavors – are there cupcakes out there for you?

Who knew lizards like cupcakes. I bet they just lick
off the icing.
In a word – yes. In fact, there are so many organisms that are neither nocturnal nor diurnal that I hesitate to call them exceptions – like how everyone has mocha cupcakes now. And I bet you know some of animals with extraordinary activity…… ever heard of sweat bees or deer or infants?

Diurnal animals have developed color vision and ways to deal with the heat and the sun. Nocturnal animals have sensitive vision and other adaptations to make use of the dark. But there are some animals that are active on the edges of both situations; dawn and dusk. What adaptations would help an animal succeed in this niche?

In general, crepuscular (latin for twilight) animals have vision most like nocturnal animals. A tapetum lucidum (Form Follows Function) is present behind the retinas of many crepuscular mammals. Your cat is crepuscular, although she will adapt to a diurnal pattern as a pet…..if she feels like it, you know how cats are.

Those great light shows put on by nature in the evenings
have a name – crepuscular rays. Impressive trivia
for your next party. Photo by van049.
There are advantages to crepuscularness (I just now invented that word). By curtailing activity during the heat of the day, less energy is spent conserving water. Not surprisingly, many desert species are crepuscular. Heat, on the other hand, doesn’t seem to be as much of an issue, since there are endothermic as well as ectothermic species that are active in these time frames, for instance desert lizards like the gila monster.

The dim light available at dawn and dusk is also an advantage for crepuscular animals. There may be enough light to see, but not enough to make these animals stick out like a sore thumb. This works for deer; along with their coloring, the dim light helps them blend into the background. Deer caught out during the day become very stressed and confused. They may end up playing in traffic; just a case of clouded judgment due to sunshine.

The aim of the crepuscular pattern is often to reduce the chance of being eaten. Most terrestrial predators are diurnal or nocturnal (except for several cat species), so crepuscular animals are active after diurnal predators have had their warm milk, and before nocturnal animals drink their coffee.

Chimney swifts perch on vertical surfaces and
have saliva that dries like glue and is practically
insoluble. They use it to build nests on chimney
walls. They have weak claws and can’t perch on
branches, they can perch on vertical surfaces
using their stiff tail feathers, but mostly they just
fly 16-18 hours each day.
Slightly more common are the crepuscular birds, including the American woodcock, which is a ground bird that eats worms and nests in brushy young forests. The chimney swift is also crepuscular, but it nests in chimneys and other vertical surfaces, eats insects out of the air, and can maintain flight for an entire year. These are birds with very different behaviors, diets, and ranges, but are both crepuscular. As is the rule in nature - maybe the only rule without an exception - it is impossible to predict the behavior of one species based on characteristics similar to other species.

In the plant/pollinator part of the community, some crepuscular pollinators have developed special relationships with plants that flower in the evening only. This represents a special form of crepuscularness (there’s that new word again, I think it will catch on) called vespertinal (vesper = evening in latin) activity. These plants and insects are active only in the evening, and often co-evolve mutualistic relationships.

In the desert where the Joshua tree lives, water is at a premium, and the heat doesn’t help the water situation.  Remember in our discussion of nastic movements (Plants that Don’t Sleep) we saw that turgor pressure of water is responsible for the opening of the flowers. But open flowers promote water evaporation! Therefore, the best strategy for the Joshua tree is to have its flowers open outside the heat of the day. Et voila - it is vespertinal.

Joshua trees are native to the Mojave desert. They
were named by the Mormon settlers who were
reminded of Joshua raising his arms in prayer.
Predictions are that 90% of the trees could be wiped
out by global warming by the year 2100.
The price of water also has also driven the Joshua tree to produce no nectar – it must have some other way to attract the yucca moth. It is the yucca moth who really taken this upon its (her) shoulders. She has found a way to make pollinating the Joshua tree flowers pay off for her species. But only the yucca moth has made this connection, and this makes their relationship an exception to a biological rule.

Since they are available to one another in the same part of the day (evening) it is more likely that vespertine plants might have a single pollinator, which we learned a few weeks ago (The Perils Of Plant Monogamy) is the exception to the rule of multiple pollinators.

The female yucca moth is not drawn to the flowers by nectar, but by the need to propagate her species. At one flower, the female moth gathers pollen and balls it up into a large mass. Palps (appendages like arms but located near the mouth) hold the pollen ball as she travels to another Joshua tree; almost always to another tree. We know that cross-pollination is better than self-pollination (Is It Hot In Here), but the question remains, how does the moth know that?

At a second tree, the yucca moth lays an egg inside the carpal (which houses the ovule and is where the seeds will form once the flower is pollinated), but only in one or two of the many caprals. Then the moth swipes the pollen ball over the stigma (the top of the carpals), ensuring that the seeds will develop.

Most pollinators are passive, they transfer pollen as a result being drawn by some attractor (nectar, odor, color, etc.). Pollen transfer is not the reason for their visits. But yucca moths are an exception to this rule; they are active pollinators. They visit the flowers with the express intent of collecting and transferring pollen. But why spend energy to purposefully pollinate?

In the left image, you can see the palps that the yucca moth uses to gather up a pollen ball. These are modified mouth parts, and mouth parts are modified ancient legs. The middle image shows the yucca moth actively pollinating the flower after it laid its egg inside the carpal. The right image shows the larvae growing inside one ovule tube (the top-left cavity), eating the seeds as food.
The seeds are the payoff. The moth larva eats the seeds of that one carpal while developing. This is symbiotic mutualism, both species benefit from their relationship – food for the moth larva, and sure pollination for the Joshua tree.

But certain precautions must be taken. Production of seeds (and fruit) takes energy. If the flower won’t produce enough seeds to make it worth the energy expenditure, the tree will abort the flower.  So, if moths deposit eggs in too many carpals of the same flower, the larvae will eat too many seeds, and the flower will commit suicide. This will kill the larvae as well. To prevent this, the moths emit a chemical scent to indicate that a flower has been visited and pollinated; other moths will move on to flowers that have not been marked as occupied.

The yucca plants and yucca moth are an example of the vespertine lifestyle, but are there organisms that live exclusively on the other edge of the night? Yep.

Several types of bees are active only in the early morning hours, just after sunrise. This type of activity pattern is called matutinal (Matuta, the Roman goddess of dawn). Some flowers open up very early in the morning, and these are the targets of matutinal bees. The morning glory is a good example, although the flowers remain open long after the early bird bees have gone to bed.

This is the false dandelion. Sweat bees and
schinia moths appreciate for giving them
food and helping in reproduction. I appreciate
it for not being a true dandelion– the lawn
care expert’s mortal enemy!
Other matutinal flowers include the plants of the pyrrhopappus family. These are perennial herbs of the American southwest, south central, and southeast grass lands, and include the carolinus species that is called a false dandelion. They flower for two-four days a year, opening at sunrise and closing by 10:00 am on a hot, sunny day.

The matutinal flower moth (schinia mitis) and the sweat bee (Hemihalictus lustrans) have relationships with the pyrrhopappus plants. The bees use them as their exclusive source of pollen, although they must visit other flowers, like the morning glory, for nectar.

The Schinia mitis moth is more dependent on pyrrhopappus than are the sweat bees. Food, shelter, mating, and a place to lay eggs are all supplied by these specific herbs, as well as shelter and a food source for the larvae. The moths mate on the open flowers between 7:00 am and 9:45 am (rain or shine), and the female then lays the eggs deep within flower.

The mitis moth egg is laid deep within
the false dandelion flower for protection.
Its going to cramped quarters for the larva.
The reason for flowers developing a matutinal lifestyle might be similar to those for vespertine or fully crepuscular species, ie, water and energy savings. But the pollinators, especially the bees, seem to have followed suit for other reasons. True sweat bees (many people misidentify them) take advantage of the early morning hours to avoid the lines at the flowers; it is a simple matter of reduced competition. On the other hand, the mitis moth has co-evolved with the flower and become completely dependent upon it. If the flower is open only in the morning, the moth better be ready on time.

Who knew that so many plants and animals had thrown off the yoke that tethered them to either day or night activity, and now work at the edges of both? Next time we will take it even further; some organisms have stopped working on any schedule at all.

Chen Y, & Seybold SJ (2014). Crepuscular flight activity of an invasive insect governed by interacting abiotic factors. PloS one, 9 (8) PMID: 25157977

Rockhill, A., DePerno, C., & Powell, R. (2013). The Effect of Illumination and Time of Day on Movements of Bobcats (Lynx rufus) PLoS ONE, 8 (7) DOI: 10.1371/journal.pone.0069213

For more information, classroom activities, or laboratories on crepuscular activity, yucca moth reproduction, or Schinia mitis moth reproduction, see:

Crepuscular activity –

Yucca and yucca moths –

False dandelions and moths –

Wednesday, February 10, 2016

Form Follows Function - It’s About Time

Biology concepts – circadian rhythm, vision sense, adaptation, parasitism, form follows function

The sun and the moon are symbols of different
activity cycles. As with everything else, we have to give
them human characteristics (anthropomorphism).
Many animals are active in the day or the night, but not both. So what are humans, diurnal (active in the daytime), nocturnal (active in the nighttime), or something else?

Maybe humans are two species, because I know folks who can’t accomplish anything before noon, and do their best work after 11:00 pm, whereas I get up around 5:00 am and am pretty much useless after 8:00 pm.

Whether diurnal or nocturnal, organisms are physically and behaviorally adapted to their activity pattern. This includes the way they sense their environments. Diurnal animals are more likely to have color vision, while nocturnal animals may only see in black and white. The upside for nocturnal animals is greater visual sensitivity, so they can see better than diurnal animals in low light conditions.

The reasons for these different visual talents lies in the types of light receptors on the retina. Rods sense light, but only its presence or absence (white/black). Different receptors, called cones, detect various wavelengths of light (colors). Diurnal animals have about 5-10 times more cones than nocturnal animals (3 types, one for yellow, one for green to violet, and one for red to orange), but they only function in higher levels of light. Therefore, the greater number of rods in nocturnal animals allow for more sensitive night vision, a good thing to have if you are active after sundown.

Rods (yellowish) and cones (blue) are different light receptors located on the retina. Rods are more numerous and detect low levels of light. Cones are less numerous and sense colors of light, but require more light. As shown in the middle image, the tapetum is located beneath the retina in some animals, and can bounce light back to the retina. This bouncing around is responsible for animals glowing eyes at night.
Many nocturnal species have an additional adaptation to improve their night vision. Their retina has an iridescent layer called the tapetum lucidum that bounces the available light around so it may hit more rods. This improves sensitivity, but at a cost to acuity (the image gets a little fuzzier). When you shine a flashlight in the woods at night, the little pairs of reflections you see are the tapetum lucida of the animals looking back at you. The light bounces around inside the eye and some escapes back out through their pupils and that is what you see. Some look at your flashlight to see if you are a predator, others look to see if you are worth eating.

But not every animal with a tapetum lucidem is necessarily nocturnal. An interesting new study has looked at the visual system of the Peter’s elephant nose fish (Gnathonemus petersii). This weakly electric fish has a long nose-like appendage that was thought to mediate location and communication through electrical pulses. But scientists at the University of Cambridge have found that this fish has surprisingly good vision to go along with electrical impulse usage.

The elephant nose fish lives in the dark, murky waters of Central Africa. For this low light environment, it has evolved a unique retinal arrangement for its rods and cones. The cones are arranged in discrete packets, each housed in a cup lined with a tapetum lucidem. Behind these cones are the rods that work in lower level light. In this way, the visual field can respond with cones and rods at the same time. It is believed that this gives the elephant nose fish the ability to pick out predators moving quickly through its visual field.
Humans don’t have a tapetum lucidum, so when reflected light bounces off our retinas and back out the pupils, they appear red like the retinal blood vessels and tissues. This is the eerie red eye effect on some flash photography. I always thought it was a sign of vampirism!

Other nocturnal animals, like many owls, rely on hearing and smell more than vision. They are adapted to maximize these senses. We have discussed previously the changes in owl anatomy (Do You Have To Be Ugly To Hear Well) as examples of form following function to improve hearing. Other animals, like raccoons, have a heightened sense of touch. Their paws have elongated sensor pads, and thousands of touch receptors. With these, raccoons can differentiate textures well enough to tell if a fruit is ripe or not, even in the darkest night.

Raccoons have a strong sense of touch for moving around in the dark.
Their elongated paws have thousands of touch receptors to increase the
sensitivity of this sense. On the dorsal (back) side of the raccoon’s paw,
whiskers (vibrissae) on the ends of their digits heighten the sense of touch.
Raccoons don’t even have to touch something to sense it; they have vibrissae (whiskers) on the ends of their digits, above their claws. Whiskers in general are a potent aid to nocturnal animals, whether located on faces, paws, or bodies (remember the naked mole rat’s whiskers on its torso in Take Off Your Coat And Stay A While).

Even plants can be adapted for nocturnal activity. Moonflowers, night-blooming philodendrons, and other flowers that rely on nocturnal pollinators tend to be white (since their pollinators most likely can’t sense color), and strong smelling. Indeed, the increased temperature of the P. selloum spadix (Is It Hot In Here Or Is It Just My Philodendron) is an adaptation to nocturnality.

So why be nocturnal? Anyone who has tried to negotiate an unfamiliar room in the dark knows that being active in the dark brings certain obstacles that must be overcome. There must be distinct advantages to it or needs for it, or else nature wouldn’t go to the trouble of adapting. Some scientists believe that nocturnality arose from originally diurnal organisms taking advantage of an underused ecological niche. Being active at night can be a form of crypsis (hiding), either to make them better hunters, or to avoid being hunted.

Nocturnality can also reduce the amount of water lost to the environment, and can lower the thermal stress on certain species of animals. For example, many frogs lose water through their skin, so daylight and higher temperatures can dehydrate them quickly.

That doesn’t mean that certain species won’t be exceptions. Moths are all nocturnal, except for the polka-dotted wasp moth, that is. There are four species of wasp moths, all diurnal, but the polka-dot is the prettiest, so we will fall into that old trap and give the pretty one all the attention. Diurnally active, this moth has abandoned many of the nocturnal adaptations of its brethren.

The polka dot moth has color and patterns that might be useful
for mating or for warding off other animals, but they would
be wasted if the animal was nocturnal.
For instance, it is beautifully colorful - usually a no-no for nocturnal moths. Since color doesn’t show up at night, moths are generally white, tan, or grey. Second, the coloration, especially the bright rump, mimics a wasp (hence the name) and warns of a toxic mouthful if consumed. This defense is called aposematism (apo = away from, and soma = body, basically, keep away from me). Many brightly colored insects will make predators sick, purely a diurnal method of survival, as the warning colors would be of no use at night.

Just as this moth species is diurnal when its close relatives are nocturnal, there is a single genus of primate that has chosen to be nocturnal when all others, including humans, are diurnal. Owl monkeys (8 species) live in Central and South America, and leave their sleeping sites about 15 minutes after sunset each day. They forage for fruits and the odd flower or insect until just before sunrise, then retreat to a hollow tree or within dense foliage to sleep away the day.

Owl monkeys adopted a nocturnal pattern after millions of years being diurnal, so it must have afforded them some advantage or was an answer to some overwhelming stressor. They have adapted by developing larger eyes, with more rods and fewer cones. They still see color, but less so than other monkeys.

The owl monkey is nocturnal, so it needs to have more sensitive vision.
For this reason, it eyes (and eye sockets) are huge! Compare the eye
size and skull morphology in the diurnal capuchian monkey. Form of
the skull follows the functional capacity of the eye.
Owl monkeys are interesting to science for being the source of another exception, as they are the only primates susceptible to the human form of malaria. In The Perils of Plant Monogamy, we used malaria in chimps and humans as an example of divergent evolution; malaria developed into species-specific forms. But the owl monkey is susceptible to both the primate and human species, so they can substitute for humans in malaria research.

Malaria is caused by a parasite, and as such, depends on its host organism for nutrition. The rule is that parasites are active when their host is active (feeding). A good example is the intestinal parasite of the surgeonfish, E. fishelsoni (Of Fish Guts And Cancer).

As I am sure you have committed to memory and made a part of your life, E. fishelsoni grows to an amazing size and replicates its DNA thousands of times before it divides into two or three progeny organisms. It takes tremendous energy for a bacterium to grow 80 fold and produce 85,000 copies of its DNA in one day, so it must occur when nutrients and carbohydrates are plentiful - during the day when the fish is feeding. Although it is a stretch, I guess you could call E. fishelsoni a diurnal parasite.

The malaria parasite, Plasmodium falciparum, has chosen a different path. P. falciparum’s host is man, and man is diurnal (teenagers and third shift workers excepted), but the parasite works to produce many progeny (gametophytes) and have them mature in the nighttime. The reason is simple; malaria has two hosts.

Plasmodium falciparum needs two hosts to complete its life
cycle. One immature form (sporozoite from oocyst) grows
only in the mosquito, while another (gametocyte) forms only
from mature sporozoites in the human red blood cells.
While one stage of the organism grows in the human, another needs to be inside a mosquito in order to complete its life cycle. After finishing its development, it is ready to be injected into another human when the mosquito feeds again. The key is that the mosquito is nocturnal and the gametophyte is short-lived. The gametophyte must be produced and mature just in time to be sucked and deposited into the mosquito gut. P. falciparum has been pressured to conform to the activity of one host while it is inside a host with the opposite activity pattern.

It is common that most species within a group will have similar activity patterns, since they are derived from common ancestors and therefore many characteristics are similar, including those that determine fitness for day life or nightlife. But there are exceptions. For instance, most rodents are nocturnal, but we see squirrels all day long - they are diurnal. Also, we mentioned above that most primates are diurnal, but the owl monkeys are nocturnal.

But there are bigger exceptions, organisms that aren’t diurnal or nocturnal. Ants, primates, and cats have species that are all over the place; some are nocturnal, some are diurnal and some are neither. It is the in-betweeners and the neithers that we will talk about next time.

Kreysing, M., Pusch, R., Haverkate, D., Landsberger, M., Engelmann, J., Ruiter, J., Mora-Ferrer, C., Ulbricht, E., Grosche, J., Franze, K., Streif, S., Schumacher, S., Makarov, F., Kacza, J., Guck, J., Wolburg, H., Bowmaker, J., von der Emde, G., Schuster, S., Wagner, H., Reichenbach, A., & Francke, M. (2012). Photonic Crystal Light Collectors in Fish Retina Improve Vision in Turbid Water Science, 336 (6089), 1700-1703 DOI: 10.1126/science.1218072

For more information or classroom activities on activity cycles, night vision or adaptation, see:

diurnal/nocturnal –

night vision –

adaptation –

Wednesday, February 3, 2016

Plants That Don’t Sleep Will Take The Dirt Nap

Biology concepts – nastic movements, turgor pressure, evolutionary pressure, tropism, osmosis

If you don’t let a Mimosa pudica (sensitive plant) plant rest at night, it will wilt away to nothing. A plant that needs a good night’s sleep? Really? We have talked about how sleep revitalizes different brain functions, especially within the hypothalamus (The Best Cure For Insomnia Is To Get A Lot Of Sleep), but plants don’t have a hypothalamus or any brain for that matter. So why does it die if it can't rest; is it out of its mind?

The prayer plant on the left is how it looks during the day, but
on the right, the leaves have folded or curled up. They also stand
straight up, as if at attention. A tough way to spend the night, but
it must serve some purpose.
The prayer plant (Maranta leukoneura) folds up its leaves at night and tilts them upward. When morning comes, the leaves tilt back into their day position and unfold to catch as much sunlight as possible. The folded leaves might look like they are praying (hence the name), and it may appear that they are sleeping, but this is just anthropomorphism.

Humans have a need to feel connected to the rest of Earth’s life, and in the process, we tend to see the behaviors of other organisms in human terms, trying to assign some human motivation to them. So, is the plant sleeping? Does it need to rest? No. Sleep in animals implies inactivity and neural rearrangement, and these don’t occur in plants.

Charles Darwin performed crucial experiments
in plant movement in his later life, including the
identification that chemical signals moving in the
plant are responsible for growth toward the light
(heliotropism). Notice that his son got pretty good
billing as an assistant.
However, the fact that the plant carries out this activity every night suggests that it has evolved in response to some pressure, some need. Surprisingly little is known about why plants move their leaves at night, but there are a few hypotheses. Some scientists believe that changing the angle of the leaves helps funnel dewdrops and overnight rain down the trunk or stem to the roots. Charles Darwin published two books on these plant movements, his theory being that the behavior reduced the chance of chill or freezing.

Another hypothesis suggests that leaves fold up to keep the rain from pooling on them and promoting bacterial or fungal growth. Or perhaps, apposing one leaf closely to the opposite leaf reduces the amount of water lost overnight. However, aquatic plants don’t have to worry about loss of water, but some immersed plants, like Myriophyllum Mattogrossense, still fold up at night. It may be a holdover from their terrestrial days, as most of today’s aquatic plants evolved from terrestrial plants.

My personal favorite proposes that by folding up their leaves, the plants give nocturnal predators a better shot at seeing, hearing, and smelling nocturnal prey. By helping the predators, plants are indirectly protecting themselves from animals that would eat them- plants are sly little devils (more anthropomorphism). It is probable that different plants move for different reasons, so one hypothesis almost certainly won’t cut it for all organisms.

Plants have night moves other than folding leaves. Morning glories (Ipomoea violacea) close their flowers overnight. The reasons for this movement may be a little plainer. Dry pollen sticks to pollinators better than wet pollen, so closing off the stigma to rain or dew keeps the pollen dry. It also takes energy to maintain an open flower; this energy would be best spent when pollinators are around. If the plant’s pollinators are diurnal, they why leave the buffet open all night?

Just as animals have an internal clock, plants gauge
their movements according to the circadian period.
Often plants match their rhythms to pollinator animals
they depend on or to avoid the active periods of
predators. Anyway, I like the picture.
There are also flowers that have the exact opposite behavior, opening their flowers as the sun sets. Philodendron selloum (Is It Hot In Here Or Is It Just My Philodendron) is a classic example, with its spathe closing down in the early morning hours.

Moonflowers (Ipomoea alba) are another example.  At about 8:00 pm, the moonflower opens. A single flower can go from completely closed to fully open in less than a minute ( The morning glories and the moonflowers are both of genus Ipomoea, but they have opposite behaviors – different pressures lead to different adaptations, even in closely related species.

These movements of plant structures are independent of the direction of the stimulus, ie. they are not following the sun or being blown by a particularly wind, so they are called nastic movements. Nyctinasty (nyc = night or darkness, nastic = firm or pressed close) is the specific movement of leaves or flowers in a daily pattern, open during the day and closed at night. If directed by the position of a stimulus, the movements are called tropisms (heliotropism, thigmotropism, gravitropism).

The left picture shows that changes in the pulvinus shape could affect the direction of the entire petiole and all the leaves, or individual leaves (like on the sensitive plant). The middle cartoon indicates that filling the central vacuole with water can change the shape of the cell, pushing in one or more directions. The right image shows just how the extensor cells on the bottom must be inflated to lift the petiole, while turgidity in the flexor cells makes the leaf drop.
Nyctinastic movements are accomplished by the flow of water in and out of specific cells in the pulvini (swellings, singular is pulvinus) at the base of the petioles (the stalk that attaches the leaf blade to the stem). It is not unlike our muscle movements in that there is an extensor and a flexor pair. When K+ and Cl- are pumped into the extensor cells on the bottom of the pulvini, they become hypertonic and water follows the ions through osmosis. This causes the extensor cells to swell due to increased turgor pressure.

Turgor pressure refers to the pressure of the cell contents against the cell wall. This increased turgor pressure at the bottom of the petiole pushes the leaf up. In an opposite fashion, night causes a movement of ions to the flexor cells on the top of the petiole. Water flows out of the extensors and into the flexors by osmosis, causing the stem to droop. Flowers and leaves open and close by the same movements, with the extensor and flexor cells located at their bases.

Turgor pressure is the same mechanism which causes the venus flytrap (Dionaea muscipula) to snap closed its jaws of death when an insect disturbs its trigger hairs. These hairs are located on the nectar laden, red lobes of the trap. Touching just one trigger hair doesn’t spring the trap, two must be displaced within 20 seconds of each other. This saves energy and unnecessary trap closings; each trap snaps shut only four or five times, then dies. If you thought the moonflower moved fast, check out the venus flytrap ( I’m just surprised we can’t hear the water shooting into the flexor cells!

The venus flytrap supplements its diet of water and carbon
dioxide with proteins from the insects it catches and digests.
The bright surface with nectar draws them in, where they trigger the
mechanosensor hairs. The magnified image on the right shows a
trigger hair with its hinge that transmits a signal to the pulvini to
swell quickly and snap the trap shut.
The trigger hairs are mechanosensors. The stimulus that trips the trigger and causes the flow of ions and water in the extensor and flexor cells of the hinge region is directionally irrelevant; therefore, the snapping shut of the trap can be considered a nastic movement. In this case, as with the sensitive plant (Mimosa pudica), the movement is called haptonasty (hapto = touch).

A small percentage of plants have nyctinastic movements, so they are an exception to the rule that plants don’t move actively, but even a small percentage means that thousands of species do have these movements. This many exceptions underscores the point that nyctinasty must perform an important function.

Just as humans with fatal familial insomnia die from a lack of sleep (An Infectious, Genetic Disease), the sensitive plant has a much shorter lifespan when nyctinasty is prevented. A plant hormone that stimulates leaf opening was identified in 2006. When given to plants continuously, it caused the leaves to remain open. When nyctinasty was prevented in this way, the leaves were noticeably damaged within a few days, and the plant was dead in less than two weeks. It may not be sleep, but whatever it is, it is just as important.

Some plants are open during the day and some are open at night, just as some animals are active during the day and some during the night. And just as plants adapt to a time schedule to promote survival, animal adaptations are crucial to life in the light or the dark. But that doesn’t mean that some organisms won’t throw us a curve, as we will discover next time.

Ueda, M., & Nakamura, Y. (2006). Metabolites involved in plant movement and ?memory?: nyctinasty of legumes and trap movement in the Venus flytrap Natural Product Reports, 23 (4) DOI: 10.1039/b515708k

For more information, classroom activities or laboratories on nastic movements or turgor pressure, see:

nastic movements –

turgor pressure –