Showing posts with label co-evolution. Show all posts

Wednesday, July 13, 2016

The Perils of Plant Monogamy

Biology concepts – pollination, single pollinator, co-evolution, co-divergence

What’s bugging her, it’s supposed to be a party!

Imagine the best party of the year – it’s cold outside, but hot inside. The food is great, all your friends are there, everyone is receptive to flirtations by the opposite sex, it lasts for two nights in a row where it is, and then picks up in a new location again and again. Where is it and how do I get invited?

Last week we learned that the Philodendron selloum flower becomes endothermic for a 2 day period each year in order to facilitate its pollination. In this state, it attracts a single species of beetle, which parties down inside the flower and then takes the pollen to the next party - sort of BYOP.

The heating of the P. selloum spadix evaporates and spreads a pheromone that attracts male Cyclocephala beetles. Pollination by beetles (cantharophily) is not one of the most common mechanisms for the spread of pollen to ovules; pollination by bees (melittophily), butterflies (psychophily), or even the wind (anemophily) is more common. In most cases of cantharophily, the flowers are big, white, strong-smelling, and the male flowers are usually eaten but the ovaries are protected. This is exactly the scenario in P. selloum.

When the male beetles enter the flower, the angle of the spadix makes the male flowers available to be eaten, while the covering of the spathe discourages the beetles from leaving the pit. The nectar, pheromone, and flowers help draw the beetles in, but it is really the atmosphere and the company that keep them there.

Female beetles are drawn to the warm temperatures as well, as this affords the beetles the ability to feed and mate through the night, when the ambient temperature outside the flower would require them to slow down their activity (being ectotherms).

The Cyclocephala beetles, but there are other examples.

Orchids are famous for finicky polli beetles follow the

pheromone back to the flower, and after partying, the

flower closes down and kicks them out.

As the party winds down in this first P. selloum, the temperature is reduced and the spathe starts to close down on the spadix, forcing the beetles out – it’s closing time, you don’t have to go home, but you can’t stay here (lyrics by Third Eye Blind). As the beetles leave the flower two things happen, first they pass the viscidium, which coats the beetles with a sticky substance, and then they pass by the pollinia, which covers them with pollen grains.

The next night, a new P. selloum is ready to open its doors for the party. When the previous night’s revelers show up with their coating of pollen, they head directly to the nectar bar at the bottom of the pit, right where the female flowers are located. While getting their first drink of the night, they deposit the pollen on female flowers that reside there and pollinate the plant. The beetles do the work, but their rewards (increased mating time, increased food) are as important to them as the pollen is to P. selloum.

Pollinators can various animals.Non-animal

pollinators work in some cases too,

such as wind and water.

This is one type of pollination party, but not the only one. Most plants invite a variety of different pollinators, or a plant might self-pollinate. In some orchids of colder regions where pollinators are particularly rare, self-pollination can be a last resort. If the flower is not visited by any pollinator, the caudicle (the stalk on which the pollen resides) will shrivel up in a particular shape, dropping the pollen directly on the stigma (containing the eggs).

Most plants invite pollinators of different species. One bee may be a particularly effective pollinator of a particular plant, but that plant is probably also visited by a fly, a butterfly, a bird, a beetle, etc. Few plants have a single pollinator, but P. selloum is one exception. While Cyclocephala beetle may pollinate other plants as well, it is the only species that pollinates P. selloum.

Single pollinators provide advantages to the plant. The need to attract only one species reduces the energy a plant must expend to attract multiple pollinators. Some pollinators are attracted to color, some to different scents, some to different UV patterns, some to different nectars. To draw different pollinators the plant will have to have many attractants, and this costs energy.

The more pollinators a flower depends on, the more energy the plant must spend on attractants. For instance, some flowers use color and UV patterns, as on the left. Some flowers use nectar and visible light patterns, as with the pitcher plant. The red flower is rafflesia, the largest flower in the world. It smells like rotting flesh to attract flies. Some flowers use mimicry, like the bee orchid on the right, it looks like a female bee and attracts males that will try to mate with it.

Another advantage is seen after the pollen is gathered on the pollinator. In order for a pollination to be successful, the pollen must be delivered to the female organs of a plant of the same species. If a pollinator species has developed a relationship with a certain plant (attracted by a specific odor or color, etc.) then the chances are higher that it will visit another plant of the same species after gathering pollen. This increases the chances of cross-pollination.

The dependence of a plant on a specific pollinator amplifies the plant’s vulnerability if there is a decrease in the pollinator numbers. It has no second option for pollination. This is one reason why cross-pollination is preferred to self-pollination. Evolution does not anticipate the future; it proceeds as if the pollinators are present in good numbers. The plant needs the greatest diversity of gene mutations and rearrangements in order to adapt to unanticipated changes in pollinator number, behavior, or preference. This diversity is provided by cross-pollination with another plant, not by reiteration of existing gene patterns by pollination with the plant’s own genome.

The disadvantage of employing a single pollinator is becoming more obvious. Recent years have seen large decreases in wild pollinator populations. Honeybees have experienced colony collapse disorder, and 2011 figures indicate that 10% of American bumblebee species are near extinction. More than 40 species of pollinating insects in the US are endangered, and even more shocking, 1200 vertebrate species of pollinators are termed “at risk.” If this many pollinator species are in decline, even plants pollinated by multiple species might feel the pinch. Can you imagine how many plants that rely on a single species of pollinator might be in danger of extinction?

Many orchids use a single pollinator. Orchids are the most

diverse flower group, as show by the Dracula orchid,

the spectacle orchid, and the small tongue orchid, left to right.

P. selloum is an interesting exception to the rule of multiple pollinators, but there are other examples. For instance, orchids are famous for finicky pollination. There are >25,000 species of orchids, the largest group of plants (in contrast, all birds represent only ~10,000 species), and single pollinators are responsible for the propagation of thousands of them. In South America and South Africa, the number of single pollinator species is quite high, including many orchid species. (Why? I have no idea.)

The specific interactions between the single pollinator and the plant it pollinates are often a result of co-evolution. In technical terms, this means describes the reciprocal natural selection and evolutionary change that occurs between two species by exertion of selective pressure on each other. The two species could be trying to outfox one another, like a parasite and its host, or could be working together, like the pollinator and pollinated.

As the two interacting species interact, they may evolve so that they rely solely on each other for that particular interaction. This could also lead to each species diverging from its closest relatives. This particular type of co-evolution is called co-divergence.

Co-divergent speciation can be seen in the host parasite relationship between the malaria parasite, Plasmodium falciparum, and humans. When humans and chimps diverged (about 4-7 million years ago), some P. falciparum evolved to infect only chimps, while others followed human evolution and became specific for humans.

The Darwin hawk moth wasn’t known when the star orchid

was first described. Charles Darwin just predicted it must exist.

Predicting the existence of a moth with 35 cm tongue didn’t win
Darwin many fans, but he was right.

In similar fashion, there are numerous plants that have co-evolved with a pollinator. The Angraecum sesquipedale orchid (star orchid) is a classic example. Charles Darwin was sent several examples of this flower and described them in an 1862 publication. Darwin noted that the nectar of this flower was located deep within a hollow spur. To reach the nectar, a pollinator would bump into the pollen and it would stick.

However, the tube was so narrow, that no known insect could have been considered a pollinator of this plant. Darwin predicted that an insect with a 30-35 cm proboscis (tongue-like appendage) would be found pollinating A. sesquipedale. He was ridiculed for such a bold proposition, but 40 years later, just such an insect was discovered, the Xanthopan morganii praedicta moth (named for Darwin’s prediction).

Nature is full of exceptions to the rule of multiple pollinators, including snapdragons that need a bee of specific weight to trip the opening mechanism of the flower. Several orchids that use the same single pollinator place the pollen on different parts of the pollinator’s body, so that female flowers of the same species will come into contact with the correct pollen. These are still exceptions, as the vast majority of plants use multiple pollinators – they just aren’t as interesting.

We have seen a plant that can become endothermic in order to pollinate. Next time we will look at a mammal that has gone the other direction, but for the same reason - survival.

Chupp AD, Battaglia LL, Schauber EM, & Sipes SD (2015). Orchid-pollinator interactions and potential vulnerability to biological invasion. AoB PLANTS, 7 PMID: 26286221 Whitehead MR, & Peakall R (2014).

Pollinator specificity drives strong prepollination reproductive isolation in sympatric sexually deceptive orchids. Evolution; international journal of organic evolution, 68 (6), 1561-75 PMID: 24527666

For more information, classroom activities and laboratories on P. selloum, pollinators and co-evolution, see:

P. selloum –

http://www.floridata.com/ref/p/phil_bip.cfm

http://faculty.ucc.edu/biology-ombrello/pow/Philodendron.htm

http://www.exoticrainforest.com/Philodendron%20bipinnatifidum%20pc.html

http://www.pburch.net/plants/C3397731/E20060506081651/

pollinators –

http://www.pbs.org/wgbh/nova/nature/pollination-game.html

http://pollinatorlive.pwnet.org/teacher/lessons.php

http://www.smithsonianeducation.org/educators/lesson_plans/partners_in_pollination/lesson1_main.html

http://www.nebraskawildlife.org/ww08-PollinatorCurriculum.htm

www.mbgnet.net/bioplants/downloads/pollination.pdf

www.nybg.org/files/pollination.pdf

www.ableweb.org/volumes/vol-22/12-puterbaugh.pdf

www.ppdl.purdue.edu/ppdl/expert/Pollinate_Tomato_Pumpkin.html

www.infocusmagazine.org/6.3/env_pollinators.htm

www.pollinator.org/Resources/facts.Gardeners.pdf

co-evolution –

www.pbs.org/americanfieldguide/teachers/insects/insects.pdf

http://www.teachersdomain.org/resource/tdc02.sci.life.evo.lp_speciation/

www.stanford.edu/group/stanfordbirds/text/essays/Coevolution.html

http://www.ucl.ac.uk/~ucbhdjm/courses/b242/Coevol/Coevol.html

http://evolution.berkeley.edu/evosite/evo101/IIIFCoevolution.shtml

http://bioweb.cs.earlham.edu/9-12/evolution/HTML/converge.html

http://www.universityofcalifornia.edu/news/article/4463

http://www.teachersdomain.org/resource/tdc02.sci.life.evo.lp_speciation/

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 –

www.emnrd.state.nm.us/prd/.../5thGradeAnimalAdaptations.ppt

http://www.bio.davidson.edu/people/midorcas/animalphysiology/websites/2010/Pacious/DiurnalNocturnalCrep.htm

http://www.circadian.org/dictionary.html

http://www.enotes.com/topic/Vespertine_%28biology%29

http://www.gleaming.org/crepuscular/

http://yomi.mobi/egate/Crepuscular/a

Yucca and yucca moths –

http://waynesword.palomar.edu/ww0902a.htm

http://indianapublicmedia.org/amomentofscience/yucca-flowers-and-yucca-moths/

http://www.emporia.edu/ksn/v41n2-june1995/KSNVOL41-2.htm

http://www.insectman.us/articles/butterflies-and-moths/yucca/yucca--plant.htm

http://www.desertusa.com/animals/yucca-moth.html

http://www.fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/yucca_moths.shtml

http://bss.sfsu.edu/holzman/courses/Fall99Projects/yucca.htm

http://www.blueplanetbiomes.org/joshua_tree.htm

http://www.willamette.edu/~csmith/SCRP.htm

False dandelions and moths –

http://www.eattheweeds.com/pyrrhopappus-hypochoeris-dandelion-impostors-2/

http://www.cas.vanderbilt.edu/bioimages/species/pyca2.htm

http://www.worldfieldguide.com/wfg-species-detail.php?taxno=18360

http://www.butterfliesandmoths.org/species/Schinia-mitis

http://www.jstor.org/pss/25084173

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 –

http://zoogirl-zootopia.blogspot.com/2010/08/nocturnal-diurnal-and-crepuscular.html

http://www.desertmuseum.org/kids/oz/long-fact-sheets/Title%20Page.php

http://www.bigfoothunting.com/info/bigfoot_nocturnal.shtml

http://www.mesacc.edu/dept/d10/asb/origins/primates/day_night.html

http://www.bbc.co.uk/learningzone/clips/different-adaptations-between-nocturnal-and-diurnal-animals/12644.html

http://www.brighthub.com/education/k-12/articles/58019.aspx

www.cal.org/siop/pdfs/nocturnal-vs-diurnal-animals-lesson.pdf

http://library.thinkquest.org/25553/english/interact/lessons/noctlp.shtml

www.seaworld.org/just-for-teachers/lsa/i-014/pdf/9-12.pdf

night vision –