February 24, 2007
February 20, 2007
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Evolution and the conservation of biodiversity
A paper out in Nature 15 February, uses a novel technique devised by one of the authors, Dan Faith, called Phylogenetic Diversity (PD), to assess the biodiversity and conservation value of endangered species and regions in terms of how unique they are in evolutionary history.
February 19, 2007
So that we may do.
Its been long since we sowed,
So that we may reap.
Its been long since we planted a kid,
Whose tender leaves quiver in wind,
Who has immense faith in us,
That we will shelter it against storm.
Let's Freshen Up!
February 14, 2007
The migrating butterflies
An interesting annual phenomenon under study
The iridescent, velvety wings flutter around in swarms: the seasonal visitors are here again. For a few years now, during the period December-February, a throng of butterflies have made their appearance in pockets of Visakhapatnam district. Environmentalists and nature-lovers are monitoring the phenomenon.
"We have been observing this peculiar behaviour of the crow and tiger butterflies," says Prof. M. Rama Murty of the Dolphin Nature Club, a founder-member of the biodiversity park at the RCD Government Hospital here.
A recent study by environmental organisations showed that the "tiger" and "crow" butterflies have a tendency to migrate in large groups from the Western Ghats to the Eastern Ghats during certain periods of the year. Such arrivals have been observed also in Bangalore, Tumkur and Mysore in Karnataka; Palakkad and Kannur in Kerala; Coimbatore, Udhagamandalam, Vellore and Chennai in Tamil Nadu, and Tirupati, also in Andhra Pradesh. It has been witnessed also in some wildlife sanctuaries.
The insects migrate in clusters and for a specific period remain rooted to a spot, where they copulate. "Interestingly, migration of butterflies is different from that of birds since the ones that return are not the original butterflies," says Mr. Murty. The long-distance migration can be attributed to a combination of climatic factors, food availability and breeding habitat preferences.
"The most obvious cause for migrations is a rapid expansion of the population of one or more species in an area leading to reduced food supply," Mr. Rama Murty says.
The migration route is yet to be determined. The groups consist of over 20 species .
The migration of the North American Monarch butterfly from Canada and northern United States to Mexico in autumn and the return journey in spring is well known. In India, larger-scale migrations occur in the Western Ghats. "In southern India, butterfly migrations have been documented in the Palni Hills and places like Assam and Rajasthan. Twenty-two species are known to migrate, travelling south in October during the rainy season," says Prudhvi Raj of the Wildlife Institute of India, Dehra Dun.
But why do the butterflies flock to only certain plants? "The males, on emerging from their pupae, lack certain chemicals essential to the process of courting females. Butterflies need pyrrolizidine alkaloids for the production of these sexual pheromones and these are obtained from plants such as Crotalaria, Heliotropium and Senecio subdiscoideus," says Mr. Raj.
Some action patterns are observed, including `mud-puddling', wherein the butterflies land on wet mud and suck salt and other minerals and nutrients from the soil.
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February 01, 2007
Toads on the Japanese island of Ishima seem to be losing their evolutionary battle with snakes. Most snakes, and indeed most other animals, avoid eating toads because of the toxins in their skin. Rhabdophis tigrinus snakes, however, not only tolerate the toxins, they store the chemicals for their own defensive arsenal.
Deborah Hutchinson at Old Dominion University in Norfolk, Virginia, US, and colleagues, found that snakes on Ishima had bufadienolide compounds – toad toxins – in their neck glands, while those snakes living on the toad-free island of Kinkazan had none.
The snakes are unable to synthesise their own toxins, so they can only have derived bufadienolide compounds from their diet. Hutchinson’s team confirmed this by feeding snake hatchlings either a toad-rich or a toad-free diet. Toad-fed snakes accumulated toad-toxins in the nuchal glands on the back of the neck; snakes on a toad-free diet did not.
“Rhabdophis tigrinus is the first species known to use these dietary toxins for its own defence,” says Hutchinson.
Fight or flight
What is more, when attacked, snakes on different islands react differently. On Ishima, snakes stand their ground and rely on the toxins in their nuchal glands to repel the predator. On Kinkazan, the snakes flee.
“Snakes on Kinkazan have evolved to use their nuchal glands in defence less often than other populations of snakes, presumably due to their lack of defensive compounds,” says Hutchinson.
Moreover, baby snakes benefit too. The team showed that snake mothers with high toxin levels pass on the compounds to their offspring. Snake hatchlings thus also enjoy the toad-derived protection.
Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas0610785104)