Deserving Fame: the Trembling Aspen

People who grow plum trees in their backyards or farms realize that these plants not only reproduce sexually by means of their fragrant flowers, but they can also establish a ramet. A ramet is a colony of clones produced by roots that surface from the ground and which then develop into full trees. Barring mutations, the new shoots, called suckers, are genetically identical to the parent plant. This also occurs in the wild. The world’s largest known organism, by mass, is a ramet of trembling aspen trees covering 43 hectares in the Wasatch Mountains in Utah. It is named Pando, Latin for “I spread”.

P1140362b
The arrows reveal three clones, encircling my larger plum tree.
Fishlake-NF_Pando_USFS
Pando, the giant ramet in Utah. Source: Fishlake National Forest

The aspen, Populus tremuloides, is one of many species of the genus, Populus. The tremuloides part of its scientific name, which designates its species, and the “quaking” or “trembling” part of two of its many common names originate from the fact that in the wind, its leaves tremble persistently. Mechanically it happens because the petiole (the long part attaching the leaf to the stem) is flatter than usual and also because the petiole’s flat part is at right angles to the plane of the leaf. When a leaf of the trembling aspen is disturbed by the wind, as the leaf turns, the flat surface of the petiole is then exposed to the same force and turns it back to its original position. Then the cycle repeats.

As to why such a feature has evolved, interesting hypotheses from ecologists and botanists have been proposed. The trembling may help the leaves absorb additional CO2, prevent excessive heat buildup and conserve water. It may also deter insects from feeding on the leaves.

Ecologically, the trembling aspen can play a key role as an intermediate tree towards the succession of more mature forests. Forest fires actually stimulate the aspen to clone itself; a ramet of 100 000 to over 200 000 suckers per hectare can prop up after a fire. They help feed a variety of wildlife including deer, sheep, elk, voles, hares and porcupines. When beavers chew aspens down, the cutting action, like fires, stimulates them to produce suckers.

Another intriguing adaptation of the trembling aspen is the way it responds to insects such as the aspen tortrix (a caterpillar) after they start to feed on its leaves. Their cells begin to synthesize salicortin and tremulacin, two glycosides that are toxic to insects.

This slideshow requires JavaScript.

These compounds are probably derived from phehylpropanoids, which are in turn made from aromatic amino acids. Since nitrogen is often a limiting factor for plants, it is one of the reasons that the protective compounds are only made when the need arises. You may also notice that, in both toxic compounds, the aromatic part attached to a pair of oxygen atoms is the basic structure of salicylic acid (aspirin’s raw material). The former is also chemically related to a pair of other natural products found in aspen, populin and salicin.

This remarkable set of adaptations of the aspen tree is why it’s the most ubiquitous tree in the world’s second largest country, Canada. It is found in all 10 provinces and two of the three territories, coping in a variety of soils and at a range of average temperatures cooler than those of the rest of the continent. Although it is difficult to predict the impact of greenhouse gas emissions on forest distributions in a pinpoint fashion, unabated climate change will move aspen forests away from lower latitudes.

aspen-current-canada_b_2000
From http://www.nrcan.gc.ca/forests/climate-change/forest-change/17778

Sources:

Terrestrial Ecosystems. Aber and Melillo. Harcourt Academic Press. 2001

US Department of Agriculture —Forest Service

http://onlinelibrary.wiley.com/doi/10.1034/j.1399-3054.2001.1120413.x/full

https://www.na.fs.fed.us/spfo/pubs/silvics_manual/Volume_2/populus/tremuloides.htm

http://www.yourleaf.org/blog/andrea-bake/2014-01-27/be-or-not-be-trembling-aspen

https://nativeplants.evergreen.ca/search/view-plant.php?ID=00528

Advertisements

Why Elephants are Special

elephant
from https://www.sheldrickwildlifetrust.org/html/raiseorphan.htm

As Kenyan conservationist Daphne Sheldrick mentions in a BBC Witness Interview, the poaching of elephants persists due to poverty in Africa and demand for tusks from eastern Asia. And although any poaching is shameful, that of elephants is especially poignant because they are highly social and intelligent mammals. And being tuned in to chemical compounds I have to point out that even their milk is special!

Savanna elephant populations declined by about 30 percent (equal to 144,000 elephants) between 2007 and 2014. A worse decimation occurred between 1979 and 1989 when the overall population of African elephants decreased from 1.3 million to 0.6 million. Now there are only about 350 000 elephants left on the continent. The latest decline is concentrated in certain countries where large carcasses are also found in protected areas.

elephantsdw
Elephant population trends in GEC landscapes over the past ten years based on GEC data and comparable previous surveys (methodology in Chase et al. 2016). Red landscapes declining >5%/year, orange declining 2-5%/year, yellow declining or increasing <2%/year, pale green increasing 2-5%/year, dark green increasing >5%/year. From http://www.greatelephantcensus.com/final-report/

Poaching leaves behind orphans, and human attempts to adopt them has been difficult due to the uniqueness of the species. Baby elephants are fully dependent on mother’s milk until the age of two years old, and they aren’t fully weaned until they’re four or five. It took conservationists many years to find a suitable substitute for mother’s milk  because it is atypical of mammals’ milk. In animals as diverse as cows, sheep, humans and lions the main fatty acid is palmitic acid, a 16-carbon molecule. For example the fat in cow’s milk consists of 52% palmitic and oleic acids.

palmitic
Palmitic acid,which leads to severe diarrhea in baby elephants. Each vertex in the structural diagram symbolizes a carbon atom. There are 15 such vertices; add the C in the methyl group shown and you have the 16 in C16H32O2

But although elephant’s milk has 2 to 3 times as much fat overall, 82% of the fat contains the smaller fatty acids capric and lauric acids ( 10 and 12 carbons per molecule, respectively). For a long time the adopted elephant babies were dying within as little as 24 hours from dehydration after they were fed milk containing fatty acids that they could not digest. After 28 years of trial and error, Sheldrick and her helpers came up with a tolerable milk-formula that was based on coconut milk, which is 50% lauric acid.

lauric
Lauric acid, a fatty acid that infant elephants can digest.

The infants need a support for their trunks while feeding and require constant attention. Due to their intelligence, they need to play in a varied and stimulating environment similar to their natural surroundings. Once off milk, they are still too young to be released into the wild. Then the challenge becomes to find them the right combination of vegetative material to provide them with the necessary trace minerals. They instinctively reject the wrong plants. And of course any time we use that term “instinctive”, we are merely revealing our ignorance as to what kind of visual cues and/or odour or taste receptors are genetically produced within them.

African and Asian elephants belong to different genera. Both Loxodonta and Elephas, respectively, along with the extinct mastodon and mammoth, belong to the order Proboscidea, whose members are characterized by the proboscis or trunk. What is special about this organ? According to the last printed edition of the Britannica, its versatility as an organ among mammals is unrivalled:

(1) The proboscis can be used to lift loads up to 250 kg.

(2) It has transverse muscles(like in a tongue) in a network that also includes radiating muscles. This provides it with fine movement and along with the fine projections at the end of the trunk, it can pick up a coin from flat surfaces (see video).

(3) It serves as a living eating utensil, delivering food to the mouth.

(4) It’s used for drinking and most of the elephant’s inhaling.

(5) It can squirt water or even sand on itself for protection from sun and insect bites.

(6) It’s  used in social “trunk-shakes”.

Ironically in the wild, the tusks, for which most elephants are slaughtered, serve to protect the precious proboscis.

 

WordPress.com.

Up ↑