Showing posts with label pollination. Show all posts

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.

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

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.

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/

Is It Hot In Here Or Is It Just My Philodendron?

Biology concepts – thermoregulation, pollination, tropisms, flower structure, plant communication

In many ways, plants are “smarter” than people (forgive the anthropomorphism). We can change our environment to suit our needs or move to a better environment. But plants can’t flip the light switch, can’t buy a bottle of water to quench their thirst, can’t turn on the air conditioner, and can’t hire a truck and move all their stuff to a better place.

Plants can react to many physical signals. We can sense gravity, but they can

differentiate parts of themselves with gravity – roots grow towards gravity

(positive geotropism) and stems grow away from gravity (negative geotropism).

So what can plants do given these limitations? They can make their own food (photosynthesis) – they’ve got us beat right there. They can turn to face the light (phototropism) or the sun (heliotropism). These abilities were explained by none other than Charles Darwin and his son in an elegant series of experiments in 1880.

Plant stems can grow away from gravity (negative geotropism or gravitism), while their roots grow toward gravity (positive geotropism) or water (hydrotropism). Finally, plants can twist around a wire and hold on (thigmotropism). Pretty talented, wouldn't you say?

But wait, there's more. Plants can also communicate with one another. They alter their biochemistry to become less appealing to predatory insects or microorganisms, and their responses become better with each attack. After they develop a good defense for a particular predator, they will warn nearby members of the same species via dispersed chemicals. The warned plants then generate the best defense the first time they are attacked.

Plants can also recognize kin – and be nice to them. Research shows that plants grow less aggressively when surrounded by seedlings from the same mother plant compared to when surrounded by non-kin competitors. I wish I could get my kids to act that nicely towards one another.

Plants also commune with animals. The acacia tree has an arrangement with the ants that live on it. The tree produces hollow thorns for the ants to live in, and produces food for them to eat. In exchange, the ants protect the plant from predators such as caterpillars by attacking them. The ants will also prune away dead leaves and destroy nearby plants that might compete with their tree for light.

The acacia tree provides hollow thorns for ants to live in; the tree’s wood is so hard

that the ants can’t hollow it out on their own. The acacia wood was once used as nails.

The acacia is related to the mimosa (sensitive plant) we discussed previously.

This is a great arrangement for both ant and tree (symbiotic mutualism), but becomes tricky during pollination. The ants will attack any insect that touches their tree; even potential pollinators. So the acacia produces a chemical at the flower when an insect lands to feed on the nectar; it says, “this guy is O.K., don’t kill him.” Amazing - I can’t get the cats to come when I call them - and I feed them! Maybe saying someone is as dumb as a potted plant isn’t much of an insult.

Plants may be “smart” about temperature as well. They don’t regulate their own heat, and are usually the same temperature as the surrounding environment. Remember from the last post that it takes lots of energy to be an endotherm, so ectothermic plants enjoy great energy savings by adopting room temperature as their own.

A few plants can spike their temperature for a short time, usually to attract pollinators, but they can’t regulate the temperature. It is like setting a fire; it burns at as high a temperature as the fuel will allow, and then goes out.

P. selloum grows in tropical environments, but can

be found as a landscape planting in Georgia, the

Carolinas, and the gulf coast. It can grow 8 meters

(26 ft) tall and the leaves can be 1 meter (3 ft) in width.

Our exception to the rule of plant ectothermy is the philodendron. Many species of this genus can raise their temperature during the period when they produce pollen, and can regulate that temperature over a short period of time (2 days). The species Philodendron selloum (P. selloum, also called Philodendron bipinnatifidum, split leaf philodendron, tree philodendron) has been the most studied and will serve as our model.

P. selloum flowers in a structure called an inflorescence. This consists of a covering spathe and a spadix in the center. The flowers are located on the spadix, with a specific arrangement of male and female flowers, making the philodendron a monoecious plant (male and female on same plant). However, the flowers are incomplete, since each individual flower has only the male (pollen producing stamen) or female (ovule containing pistil) organs.

The flower of P. selloum is about 25 cm (10 in)

tall and the flowers are plain white, as it does

not use color to attract pollinators.

The male flowers are located on the top half of the spadix, while the middle region contains sterile male flowers, and the female flowers are located at the base. This arrangement, with the sterile gap in the middle, decreases the chances that the pollinators will pollinate a female flower on the same plant (self-pollination).

Self-pollination reduces genetic diversity as the offspring are clones of the parent (we will talk more about this next time). Also to help prevent self-pollination, the male flowers produce pollen in the first evening of the anthesis; the time period when the flower is open and fully functional. The female flowers can receive pollen on the second evening.

The spadix can reach and hold temperatures of 45 ˚C (113˚F)

and is most concentrated in the sterile male flowers. The female

flowers don’t produce heat, as this would damage the ovules.

P. selloum raises the temperature of the spadix, specifically the male flowers. The attractant is a female beetle sex pheromone that makes male beetles of a specific species think that potential mates are on this particular flower. To maximize the effect of the pheromone, the increased temperature of the spadix volatilizes the chemical (evaporates it into the air) so it can spread a greater distance. The beetles just follow their nose back to the correct plant!

The heat comes from a special reaction within the plant. Photosynthesis is actually an endergonic (energy consuming) reaction, it eats up heat, leaving the plant cooler. But respiration (creating ATP from the carbohydrates of photosynthesis) is exorgonic (heat releasing). These two processes are basically a wash, so P. selloum needs another way to generate the heat for the spadix.

Moreover, the P. selloum heat production must correlate to the time when the pollen is mature, must be localized to the spadix, and must be regulated. To do this, the philodendron has independently evolved the same trick that human babies use to stay warm!

Babies have a big surface area compared to their volume, so they tend to lose heat rapidly. This is why parents dress babies warmer than they dress themselves. To generate more heat, babies have brown fat (brown adipose tissue or BAT). BAT has more mitochondria than regular adipose (fat) tissue, and the iron in the mitochondria make this fat appear almost brown in color. The increased mitochondrial number helps to generate more heat as the fat is metabolized.

Fat is metabolized to generate heat instead of carbohydrates because it has more energy. Fat carries almost 9 kcal/gm, while carbohydrates contain only 4 kcal/gm. This is also why fat is used to store energy, it would take more than 2.5x the volume to store the same energy if it were all in the form of carbohydrate, especially since carbohydrates are connected with water when stored, while fats are not. Being fat is actually the most compact way to store energy.

Brown adipose tissue (BAT) has a centrally located nucleus and

several small lipid droplets in order to make room for the many

mitchondria. On the right, white fat cells have an offset nucleus

and are completely filled with a single lipid droplet.

To really up the heat ante, the mitochondria have an uncoupling protein (UCP) that disconnects the burning of fat from the generation of ATP. Instead of putting some of the energy into making ATP, all the energy is put toward giving off heat. Since babies aren’t coordinated enough to exercise to increase heat, and shivering isn’t that efficient, this non-shivering thermogenesis (NST) is their way to stay warm.

It was thought that adults didn’t have BAT, but recent studies indicate that most adults have some, and some people have a lot. BAT generation can actually help keep you thin, because the BAT is more readily metabolized –regular fat is a guard against bad times and the body holds on to it tightly, but BAT it is meant to be burned. New research suggests that chronic cold can stimulate BAT development, so forget your winter coat and just freeze your way into that size two.

P. selloum has developed BAT as well, an excellent example of convergent evolution (unrelated organisms develop similar characteristics). Plants use the alternative oxidase protein to uncouple fat metabolism from ATP generation instead of UCP, but the process is nearly the same. Using non-shivering thermogenesis, P. selloum can raise the temperature of the spadix to 104-113˚F and hold it there.

More amazing, P. selloum can somehow sense the ambient temperature and keep the spadix temperature 20-30˚F above that of the environment during that first evening. During the second day, the temperature is held around 80-95˚F, but is not controlled so stringently. The second evening sees a slow, regulated decrease in temperature to ambient by the third morning. It's a complex mechanism, but the payoff is survival of the species.

The whole thing is pretty smart for a plant, or for any organism. Next time, we will investigate the relationship between the pollinator beetle and P. selloum, and how limiting pollination to one species of beetle breaks a rule.

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For more information, classroom activities, or laboratories on tropisms, pollination, plant communication, or P. selloum:

Plant tropism –

http://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/tropisms.html

http://www.discoveryeducation.com/teachers/free-lesson-plans/the-importance-of-tropisms.cfm

http://leavingbio.net/Plant%20Responses.htm

http://www.botanical-online.com/lasplantasmovimientosvegetalesangles.htm

http://virtualastronaut.tietronix.com/textonly/act25/text-plants.html

www.the-aps.org/education/k12curric/activities/pdfs/watson.pdf

www.spacegarden.net/downloads/Gravitropism.pdf

www.sas.upenn.edu/~ltlick/Pedagogy.pdf

www.pjteaches.com/PDF/LifeScience/labs/lab13f.pd