Unlikely Allies

Photo by emmapatsie licensed under CC BY-NC-ND 2.0

On the Balearic Islands of Spain, an interesting relationship has developed between a plant and an animal. What's more, this relationship seems to have developed relatively recently in the history of these two species. The players in this story are the dead horse arum (Helicodiceros muscivorus) and an unsuspecting lizard known as Lilford’s wall lizard (Podarcis lilfordi).

Podarcis lilfordi is a lot like other fence lizards. They spend their days basking in the sun’s warmth and hunting for insect prey. They also have a tendency to feed on nectar and pollen, making them important pollinators of a handful of plant species around the island. For the dead horse arum, however, its not about pollination.

Like most members of its family, the dead horse arum relies on trickery for sex. As its common name suggests, the dead horse arum both looks and smells like rotting meat. Unsuspecting flies looking for a meal and a place to lay their eggs find the dead horse arum quite attractive in this regard. The plant even steps up its game a bit by producing its own heat. This helps volatilize its smell as well as to make it a cozy place worth investigating. Studies have found that during the peak flowering period, the inflorescence can be upwards of 24 °C (50 °F) warmer than its surroundings.

Photo by Marina Sanz Biendicho licensed under CC BY 2.0

As one would expect, this has caught the attention of the cold blooded lizards. Enticed by the heat source, lizards basking on the spathe quickly realize that the plant is also a great place to hunt. Flies attracted to and trapped by the flowers make an easy meal. On the surface this would seem counterproductive for the dead horse arum. What good is an animal hanging around that eats its pollinators?

The relationship doesn't end here though. At some point in recent history, a handful of lizards figured out that the seeds of the dead horse arum also make a great meal. This behavior quickly spread through the population to the point that Podarcis lilfordi regularly break open the seed heads and consume the fleshy berries within. Here's the catch, seeds that have passed through a lizards gut are twice as likely to germinate.

Researchers have been studying this interaction since 1999. Since then, the dead horse arum has gone from being relatively rare on the island (~5,000 individuals per hectare) to a density of roughly 30,000 individuals per hectare during the 6 year span of the study! Even though the lizards eat their pollinators, the dead horse arums of Aire Island have nonetheless benefited from interactions with their cold blooded companions.

Sadly, this novel relationship may not last too long. The introduction of cats and rats to the islands has drastically reduced the population of these lizards to the point that the IUCN has listed them as an endangered species. Research will be needed to see if the dead horse arum follows in their wake.

Photo Credit: [1] [2]

Further Reading: [1] [2]

Do You Smell Skunk?

Do you smell that?

All around northeastern North America, a strange smell is starting to hang in the air. The skunky odor could easily be mistaken for an actual skunk but it isn't quite that strong. Some say garlic is a more apt description. If you are in a wet area you may notice small chimneys in the snow or what looks like a red and yellow parrot beak poking up from the ground. The smell gets stronger as you bend down to get a closer look. What you are seeing is Symplocarpus foetidus, better known as eastern skunk cabbage.

Skunk cabbage is a true spring wildflower. It is also one of those small groups of plants that can generate their own heat. This aroid can literally melt its way through the snow cover. Skunk cabbage hails from the same family of plants as the titan arum, Araceae. The inflorescence emerges in early spring, oten before the snow (if there is any) has had a chance to melt. Using heat generated via a unique form of metabolic activity, the inflorescence can reach temperatures of 15-25°C (59-77°F).

So, why the heat and smell? Well, if you like to bloom before the snow melts, you better hope you can at least melt through some of it. In deeper areas, skunk cabbage flowers create chimneys in the snow, which helps channel the scent up into the air. Though it may seem surprising, there are in fact insects out and about during the early days of spring. The smell attracts pollinators such as carrion flies and gnats. The heat also aids in volatilizing the odor, thus causing it to spread out farther. By blooming this early, skunk cabbage assures that its flowers get a majority of the attention.

After flowering is finished, the plant then throws up its large, green, elephant ear leaves. They are unmistakable. As the plant continues to grow throughout the season, its roots contract into the soil, digging the plant deeper and deeper. In effect, skunk cabbage grows down, not up. This is advantageous if you live in an area prone to flooding. The deeper you go, the harder it is to get pulled out.

I love this plant. It is wonderful to see its blooms poking up from underneath the snow. After so many months of drab colors and short days, this harbinger of spring is a breath of fresh, albeit stinky, air.

Further Reading: [1] [2] [3] [4] [5]

Sweet Nectar

Plants produce some serious chemical cocktails. Any compound that a plant produces that isn't involved in growth or reproduction is coined a secondary metabolite. These compounds often function as herbivore deterrents. We humans are well aware of this fact and have been utilizing plants as medicine for millennia. Though the human animal may appear unique in this aspect, self-medicating has nonetheless been discovered in many other animals. Everything from monkeys to birds and even elephants seek out specific plants for things like parasite control and birthing. A study published in 2015 suggests that using plants as medication may even extend to insects. 

It has been documented that for a multitude of plant lineages, secondary metabolites are not restricted to vegetative structures. Many species produce secondary metabolites in their nectar. One interesting example of this can be found in coffee trees (Coffea sp.). These plants produce caffeinated nectar that has shown to keep bees coming back for more, not unlike we humans frequent our coffee pots. Plenty of other plants are doing this as well. Everything from amino acids, alkaloids, phenolics, glycosides, terpenoids, and even microRNA have turned up in the nectar of different plant species.

Researchers wanted to know if these chemicals may be benefiting pollinators. By isolating the different compounds, researchers found that bumblebees drinking from these flowers had drastically reduced parasite loads, specifically the gut parasite Crithidia. About half of the compounds tested were implicated in reducing parasite load but one group in particular stood out - the tobacco alkaloids. 

Alkaloids such anabasine are not limited to tobacco plants. They can be found in the nectar of trees like the basswoods (Tilia sp.) and forbs like the turtle heads (Chelone sp.). Bees that drank nectar containing these alkaloids saw parasite reductions of upwards of 80%. However, like any viable medicine, there were side effects. The eggs of bees that drank these compounds took considerably longer to develop and hatch. This cost may be well worth the lower parasite transmission rates and likely do not pose considerable selective pressures.

Whether or not bees are specifically targeting these plants for their anti-parasite properties remains to be seen. More recent work has found that we must be tentative in our conclusions at this point. Tests on other nectar compounds have shown no benefit to pollinators. Either way, these findings have opened up a whole new door into the interactions between plants and their pollinators. 

Further Reading: [1]  [2]

Fly Guild

Photo by Rictor Norton & David Allen licensed under CC BY 2.0

Lapeirousia oreogena grows in the western portion of South Africa. Though it may be difficult to tell by looking at it, this little plant is a member of the iris family. Decked out in its striking shade of purple, the white spots on its petals really stand out. Shaped like arrowheads, it would almost seem as if the plant was trying to advertise the perfect place to grab a sip of nectar. Indeed, that is exactly what they are doing. Those white arrows serve as guides for a rather peculiar pollinator.

Photo by Peter Goldblatt

Prosoeca peringueyi is a pretty incredible little fly. For starters, its proboscis is 2 inches in length! It looks rather awkward buzzing around a patch of these beautiful irises. Seeing it in action may change your mind though. It is truly an ariel acrobat as it maneuvers itself above a flower and expertly dips its long proboscis down the slightly longer nectar tube of the flowers. How is the fly so adept at hitting its target every time? The answer lies in those white arrows. 

A team of researchers performed a series of experiments in which they covered up the white arrows of some flowers. As it turned out, the flies still approached the flowers but, with no arrows visible, successful insertion of the proboscis was drastically reduced. The arrows serve as a guide for the flies to tell them exactly where they are going to be able to get an energy rich drink.

How exactly does a system like this evolve? A clue to the answer lies in the fertility of these irises. Plants that aren't visited sequentially by these long-tongued flies do not set seed. As it turns out, the plants need the flies to be just out of reach of the bottom of the nectar tube for efficient transfer of pollen. Over time, an evolutionary arms race developed in which the proboscis of the flies gradually got longer to get as much nectar as possible and thus selecting for irises with longer and longer flower tubes.

This system seems to have had an effect on other plant species growing in this region too. Lapeirousia oreogena is only in bloom for a small window of time during the growing season. What happens to these long tongued flies when this window is closed? Interestingly, other plant species form what is referred to as a guild with L. oreogena. They all cater to these flies with varying lengths of elongated nectar tubes. In total, at least 28 plant species in this region have seemed to have converged on this pollination syndrome. To see more of these plants, click here.

Photo Credits: Rictor Norton, David Allen (http://bit.ly/1jzvHeK) and Peter Goldblatt

Further Reading: [1] [2] [3] [4] [5]

Stained Glass Leaves

Photo by Jardín Botánico Nacional, Viña del Mar, Chile licensed under CC BY-NC-SA 2.0

Producing flowers is a costly endeavor for plants. They require a lot of resources and give nothing back in the way of photosynthesis. The showier the flower, the greater the investment. It should be no shock then that some plants utilize more energy efficient strategies for attracting pollinators. One of the more interesting ways in which a plant has evolved to save energy on flowering comes from a rather surprising family. 

Gesneriads are known for their showy flowers. There are many variations on the theme but most are rather colorful and tubular. However, in the jungles of Central and South America grows two species of Columnea that make such generalizations a waste of time. The flowers of C. consanguinea and C. florida are small, drab affairs, especially for a Columnea. They arise from the stem at the base of the leaves and would largely go unnoticed without close inspection. It is amazing that anything could find them among the chaos of the jungle understory let alone pollinate them. That is where the leaves come in. 

Photo by alex monro licensed under CC BY-NC 2.0

Towards the tip of the long, blade-like leaves are heart shaped red spots. They are translucent and to stand below one conjures a mental image of stained glass windows. Against the background of greens, these spots really stand out. Their purpose is to attract pollinators, specifically the green-crowned brilliant hummingbird (Heliodoxa jacula), which can then locate the nectar-rich flowers, pollinating them as they feed. By producing these translucent red spots on their leaves, these plants are able to save a lot of energy. Leaves are retained for much longer than flowers are and, of course, they photosynthesize.

Photo Credit: Jardín Botánico Nacional, Viña del Mar, Chile (http://bit.ly/1CXtToh) and alex monro (http://bit.ly/1uVwf0x)

Further Reading:

http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2745.2008.01465.x/full

Cannonball!

Photo by Joel Abroad licensed under CC BY-NC-SA 2.0

There are some trees out there that you probably shouldn't hug. Couroupita guianensis is one such example. You certainly wouldn't want to risk standing at the base of one for any length of time. What looks like a vine covering the trunk of each tree is actually the reproductive structures of this species. Beautiful flowers give way to hefty seed pods, earning this tree its common name, the cannonball tree. 

A native to Central and South America as well as parts of the Caribbean, the distinctive flowers of this tree are born on long stalks that emerge right out of the trunk. This is known as "cauliflory." Trees like this can cause you to do a double take. Indeed, it is strange seeing flowers on a trunk instead of at the tips of branches. It is likely that this type of flowering has evolved as a form of resource partitioning. Instead of vying for pollinators or seed dispersers way up in the canopy, trees like C. guianensis may opt for them at lower levels in the forest where competition may be lower. 

In the case of C. guianensis, the main pollinators are carpenter bees. The peculiar flowers don't produce any nectar, however, they make up for this by offering copious amounts of pollen. The strangest aspect of this is that two different type of pollen are produced. Each flower has two sets of anthers, one set forms a ring around the center of the flower and the other set is located at the tip of the petal that is bent inward forming a hood. What's more, the pollen grains produced by each set differs in appearance with the ring pollen being white and smaller and the hood pollen being yellow and larger. As it turns out, the hood pollen is mostly sterile whereas the ring pollen is fertile. When a bee lands on the hood of the flower looking for pollen, it is attracted to the larger grains. As it harvests pollen from the hood its body is pushed up against the ring pollen, which is carried to the next flower, where the process is repeated and the flower fertilized.

Photo by Mauricio Mercadante licensed under CC BY-NC-SA 2.0

After fertilization, large capsules are produced that sort of resemble coconuts or canon balls. Being a member of the Brazil nut family, these capsules can measure upwards of 8 inches in diameter and are chock full of pulp and seeds. Each capsule eventually falls from the tree, cracking open as it smashes into the ground. The capsules can be so large and heavy that anyone unfortunate enough to be standing under one when it fell is likely to be killed by the impact. The pulp inside is said to smell quite awful, which is a attractive to various seed dispersers around the forest.  Peccaries as well as large rodents like the paca eat the seeds, which germinate quite well after passing through their gut. 

Couroupita guianensis has been planted far outside of its natural range for a variety of reasons. It is likely that anyone visiting a botanical garden in the tropics will come across one of these odd trees. Any gardener worth their weight would do well to keep this tree away from footpaths. This is a species best admired from a distance. Aside from avoiding a head crushing blow from one of those seed capsules, this is a tree that must be seen in its entirety to truly appreciate. 

Photo Credits: [1] [2]

Further Reading: [1] [2]