Chameleon Snake, and Internal Ant Pedometers

Returning from an army training exercise in Brunei, I saw on the news, after stepping off the plane, news that a snake which can change its colours has been found in the heart of Borneo. Having been on the same island as that snake for three weeks without knowing of it made me rather disappointed that I didn't see anything quite as remarkable or vivid while I was there. According to the report on BBC News, the snake is a venomous rear-fanged water snake and was found to possess its colour-changing property when it was put into a dark bucket. When it was retrieved, its original reddish-brown colour had become almost white. What significance this chameleon-like property has is unknown, though it might be a response to a stressful situation, since to become white it would presumably retract the pigments within the chromatophores in its skin. The mechanism by which this colour-changing act works is probably similar to that in changeable lizards like the chameleon, since both lizards and snakes are in the class of Reptiles.

Also rather recently, some Saharan desert ants have been found to use a sort of internal pedometer to count the number of paces they take when they move about, to aid in navigation. Instead of simply tracing back over the trail they took to reach a certain location to return to their nest, they can return via a direct route. To do so they need to know what direction they are facing, and what distance they have covered. For direction, they've been found to use the sky to orientate themselves, but for distance, no one knew until an experiment was conducted to see if the ants counted their steps. These ants had their legs either extended with stilts or shortened by amputation, and were set free to make their journeys. Those with extended legs overshot their target while those with shortened legs fell short, showing that they probably relied on the number of steps taken, rather than some external guide to distance. And this, of course, was part of what I was doing in the forests of Brunei, counting my paces while others took bearings with a compass and still others plotted the journey on a map. Unfortunately my instinctive abilities of navigation are no where as good as the natural abilities of ants and other animals, so it was good that we had GPS to back us up. Else I'd still be in there, somewhere, see?

latest assault on whale hunting ban

Japan and other pro-whaling allies tried to overturn the moratorium on whale hunting during the recent IWC meeting.

see this TODAY article

Scientists urge evolution lessons - From BBC News

A statement from 67 national science acdemies urge the teaching of evolution in schools.

For more please read this BBC article "Scientists urge evolution lessons".

Full statement released by Inter Academy Panel on International Issues.

fruit bats prefer fragmented habitats

excerpt:
"The theory holds that the flying foxes came out of southeast Asia by hopping islands," explained conservation biologist Dr. Richard Jenkins.

"They seem to prefer small fragments of habitat. Why they don't have a foothold in mainland Africa is a mystery," said Jenkins, who heads a local green NGO called Madagasikara Voakajy, which means Madagascar Conserved.

Accepted science holds that fragmentation of natural habitats is bad -- many species have disappeared when their habitat has been diced up by human activities like farming.

Most recorded extinctions over the past few centuries have also occurred on islands, an indication of the fragility of small populations living in isolation.

"Most of the endemic animals depend on intact forest. If it becomes fragmented, they lose species," said Jenkins.

But the big bats are exceptions to the rule.

"There are some species which choose not to live in the big forest. We are not challenging the notion that fragmentation is bad, but the notion that fragments have no ecological value," said Jenkins. END/.

full article here.

The Importance of Biological Diversity to Human Health

A new essay from PLoS Medicine talks about the relationship between biodiversity and public health issues, especially the link between vector-borne diseases like malaria and the rate of human infection. Some of the ways that disease risk might be reduced are:

• Zooprophylaxis: Another host animal living in close proximity to humans absorbs the brunt of attacks by the disease vector, hence reducing the risk of disease transmission to humans.


• Poor 'reservoir species': Disease vectors usually have several hosts (e.g. ticks that feed on mice and squirrels) and these hosts have varying degrees of success in getting the vectors infected. In more biologically diverse communities, the proportion of hosts which are poorer 'reservoirs' tends to be greater, hence reducing the proportion of potential vectors which actually bear the disease.


• The dilution effect: from the article -- "the vectors that transmit the pathogen only take a limited number of bites in their lifetime; when some of these bites are taken from hosts that are not competent to amplify the pathogen, these bites are wasted. This reduces the rate at which the pathogen is transmitted." This might be compounded by non-viremic hosts (i.e. where a diseased vector must be feeding at the same time as an undiseased one to transmit the pathogen, because the host does not get infected) and reliance of the vector upon noncompetent hosts for part of its life cycle.

Not just animals and humans but plants too suffer from diseases, and it has been found that interspersing fields planted with a single variety of crop with other species tends to reduce transmission rates of diseases that specifically infect the crop of interest, because the other species act as buffers and barriers to transmission. Predators are also shown to play a role in disease reduction by removing the sickest and weakest animals and so reducing infection rates. The authors end by highlighting the possible effect that climate change might have on disease, as the temperate zones become warmer and vector-borne diseases from the tropics move into them. As they encounter a less biologically diverse landscape, the proportion which end up infecting humans and domestic plants and animals may likely increase.

However, a few questions remain which they do not discuss: why is it that when biological diversity is reduced, the species that remain tend to be more competent reservoirs of vector-borne disease than those which do not survive? Is it merely a sampling artifact of the limited number of cases of which we are aware, or does it reflect a grimmer ecological process at work? Is high diversity always a good thing? The authors point out that for zooprophylaxis against malaria using cows, mosquito bites may be diverted away from humans in the short term, but they may contribute to mosquito abundance in the long term. Because of the innate complexity of ecological cause-and-effect, it's likely that general statements linking more biodiversity with better public health are tenuous at best, and what benefits should be examined carefully case by case.

Invasive Plant Suppresses the Growth of Native Tree Seedlings by Disrupting Belowground Mutualisms

Invasive and weedy plants are one of the big ecological concerns of this new century, as primary vegetation is increasingly cleared or disturbed by agriculture, mining, and other human activities. Very few habitats can be truly considered 'pristine', as long distance travel and human migrations help spread alien species beyond the range of their natural abilities of dispersal. Even famous isolated places of legendary idyll, such as the Hawaiian islands and the Galapagos islands, have suffered from invasive aliens. Like his Alternberg estate along the banks of the Danube which Konrad Lorenz describes in the preface to King Solomon's Ring, the 'virgin wilderness' is more often than not an illusion, in Lorenz's case because of the 'number of American plants and animals which have been introduced,' emphasizing the 'strange contrast between the character of the landscape and its geographical situation.'

Most popular notions about the success of weedy invasives tend to focus on the superior traits of the plant or animal in question compared to the natives. They may grow faster, or produce more abundant seed, or are more aggressive. Conversely, native organisms, having evolved in isolation from these invasives, have not any adaptative defences against their wiles and ways. But nature can be more subtle than that. This article in PLoS Biology describes an invasive European weed, the garlic mustard, which has taken root in North American forests. Previously confined to disturbed areas and forest edges, it has lately begun spreading into closed canopy areas, suppressing the growth of understorey plants, including the seedlings of dominant tree species such as maple and ash. Garlic mustard itself does not form mycorrhizal associations with arbuscular mycorrhizal fungi (AMF); instead it may produce phytochemicals which inhibit the growth and germination of these fungi. In high growth densities, the authors of this paper have shown that it can inhibit mycorrhizal fungi to the extent that the growth native seedlings that require AMFs to thrive (much like orchids require mycorrhiza to germinate in the wild) can also be inhibited. Worryingly, this means that plants which do not rely so much on AMFs for germination and growth, which are mostly weedly plants, will be selected for in the understorey, and hence come to dominate the forest composition when the mature trees age and and fall away. As the authors put it, "In conclusion, our results reveal a novel mechanism by which an invasive plant can disrupt native communities: by virtually eliminating the activity of native AMF from the soil and drastically impairing the growth of native canopy species."

This study highlights a few things that organismal biologists always like to repeat, like some sort of mantra:

• There is so much we do not know about how organisms interact with each other in the wild. -- Although seedling dependence on mycorrhiza has been known for a long time, as well as the allelopathic properties of many phytochemicals, this is perhaps the first time that the two chains of thought have been linked in this way.


• Systematics and taxonomy are important as baseline knowledge. -- A significant clue to the mechanism of invasion was given by the taxonomic family of the garlic mustard (the Brassicaceae, or the Lettuce family), members of which are known to produce glucosinolates, "organic plant chemicals with known anti-herbivore, anti-pathogenic and allelopathic properties...." Another point which might be noticed is that the AMF is not named in this study: fungi are notoriously difficult to identify without their reproductive structures, and experts on the taxonomy of fungi are few and not growing any younger. One way to refine this study is to examine if the phytochemicals produced by the garlic mustard are specific to certain kinds of fungi or have a general effect, but this is impossible without taxonomic expertise.


• Everything is linked. -- It may not be immediately apparent how an anti-fungal agent secreted by a small weed can affect the composition of whole forests in a century's time. Because of the complexity of the webs of ecological interactions in the wild, it is nearly impossible to predict what might happen when a habitat is tampered with. It is something like twiddling with a Jenga tower: removing one block may not make much of a difference, or it may result in the whole edifice crashing down.

Although this study was carried out in the temperate New World, it might have some application to our Old World tropics as well. Weedy invasives are a problem in Singapore's small and fragmented nature reserves, notably Clidemia hirta, a prickly ground weed that originates from the Americas. Its success in invading disturbed gaps and forest fringes is probably due to its sun-loving habit and tolerance of water stress compared to native understorey plants, but are those the only reasons? As of now we can only speculate as to what lies beneath....