Friday, September 24, 2010

When life is shi#

A skipper on bird dropping
People using the phrase need to watch out for they may very well be describing a life of heavenly bliss ! There are a whole lot of animals that depend entirely on the excretions of others. Scatology must be one of those subjects that universities are not advertising about but there are lots of amazing questions out there waiting to be researched. In some habitats there are very few sources of nutrition available, particularly for organisms with limited locomotion. A cave salamander has been found to be dependent on bat guano. A 2008 article discusses the antiquity of coprophagy in the beetles of the family Scarabaeidae - the dung beetles. It seems like they only took to this diet after the rise of the mammals , making it a relatively recent trend, evolutionarily speaking. The paper notes that herbivorous dinosaur dung is unlikely to have supported dung beetles due to the high nitrogen content - the result of the urinary and excretory tract merging into a cloaca. The feature is present in the birds and a study of beetle fauna in an oil bird cave found just one Scarabaeid, but that one fed on decaying plant matter. Coprophagy is however shown by many other insect groups and interestingly it is rather rare among the lepidoptera (as a primary diet)- two pyralids are known to live on mammalian droppings. Interestingly many adult butterflies will visit animal faeces, but this is related to special functions and do not appear to be part of their regular diet. The uninitiated are usually shocked when they see some of the prettiest butterflies they have ever seen perched on poop. Entomologists  however use the attraction to get closer to some of the rarer butterflies by baiting them. Skipper butterflies (Hesperiidae) have a particular fancy for bird droppings and some South American species are known to follow army ants which in turn are followed by ant-birds to get to the bird droppings !

Painting by J B Fraser with Greater Adjutants
An exhibition of old illustrations of India at the National Gallery of Modern Art caught my attention recently. An old (1819) watercolour by James Baillie Fraser showed Adjutant storks sitting over buildings in Calcutta, While researching the subject, I decided to improve the Wikipedia article on the Greater Adjutant Stork and realized in the process that this rather ugly-looking bird is essentially endangered by improved sanitation. At one time, there were thousands of this bird all over northern India, particularly in the city of Calcutta. They were busy feeding on the dead bodies disposed into the Ganges and disposing off offal, animal and human excreta with such efficiency that the Calcutta Municipal corporation of that time decided to make them their mascot, two birds facing each other became a part of the corporation logo. Their populations however rapidly declined during the Nineteenth Century and kept dropping to become the endangered bird that it is today. The best places to see them in India now are apparently garbage dumps in Assam and the only major breeding areas are in the Brahmaputra valley.

Other scavengers have declined sharply too- the most famous being the vultures - once found along the avenues of Delhi and floating in thermals in large numbers, they are almost absent today and the cause  is usually attributed to the non-steroidal anti-inflammatory drug Diclofenac. Interestingly these hit the vultures of the genus Gyps the most. There is however a smaller vulture - the Egyptian Vulture (Neophron percnopterus) which has also declined across its range and some Spanish scientists have suggested that they might have been affected by antibiotics - which apparently depress their innate immune system. Now this black-and-white vulture has a bright yellow bare facial skin and it seems that the birds derive the colour from carotenoids derived from a diet of mammal excreta. The usual ideas is that the fitter males have a brighter face and females choose them as their mates and it seems like this might have the cost of exposing their immune systems to the onslaught of bacteria. And having a weak immunity could be bad under those circumstances - so it seems like antibiotics, pain-killers and sanitation are not without ill-effects for some.

As another aside one should note that the ancient Egyptians who revered both the dung beetles and vultures  introduced some innovations in sanitation and it is comforting to see that there are scholars looking at these aspects of daily human life.

Further reading
  • Arillo, Antonio & Ortuño, Vicente M. (2008) Did dinosaurs have any relation with dung-beetles? (The origin of coprophagy). Journal of Natural History 42(19): 1405-1408
Postscript
  • Another blog post on an allied theme 
  • Campos-Arceiz, A., 2009. Shit happens (to be Useful)! Use of elephant dung as habitat by amphibians Biotropica. 41(4):406-407.

Monday, September 20, 2010

The twisted tale of the Lycaenid

Rapala in my backyard (false head raised)
The hair-like tails of butterflies in the family Lycaenidae are quite well known. Many of these butterflies move their hindwings further drawing attention to the antenna-like hairs. These are frequently white-tipped and further enhanced by an eye-like spot at the base of the tail. In some species in the genus Spindasis, the markings on the wing appear to radiate from the false-head and even the posture of the butterfly may be altered to make the hind end look like a raised-up head. For a very long time, their role has been decided as being an anti-predation mechanism, to lure potential predators towards the non-vital end and allowing them to make an escape with minor loss. Some species will even make a quick 180° turn after landing or walk backwards a few steps to further this impression. This behaviour has been termed as "anticipatory deflection" !

Lines radiating from the false head (Spindasis)
But ideas like this can be dismissed as merely "anecdotal" these days and need to be demonstrated more carefully and several researchers have attempted this. In the 1980s R K Robbins looked at the old ideas from Victorian times. Some suggested that having two heads confused predators while others suggested that an eye would alarm predators. The evidence that Robbins looked at was the extent to which symmetrical hind-wing tips with damage were found in the wild population. He first had to decide if that kind of damage could be caused only by failed predator attacks, particularly by birds. So he first kept specimens in cages and looked at the frequency with which symmetric wing damage could be produced without predators. Convinced that this did not happen in his control population, he looked at the damage levels in the wild. He also looked at the ease with which breakage of the wing occurs and found that breakage happens more easily at the tail end. Van Someren in 1922 noted that lizards invariably attacked the hind ends of Lycaenids. Robbins found that most of the symmetrical damage was at the hind end. This was however pointed out as merely an indicator of the number of butterflies that escaped and not a clear difference in the value of the "false head" to their survival. Some later researchers took butterflies without spots and used false tails and paint to artificially add eye-spots to dead Pierids and then placed them in a cage with birds and checked out what the birds do and found that they indeed tended to peck close to these spots. The tale does not end here - in 2007 someone decided that the 1922 observations needed to be looked at more carefully and they found that there was no real evidence that caged Anolis lizards attacked eyespots on butterflies (not Lycaenids, but Bicyclus). The authors further question the evidence of bird beak marks that were used in the past as well ! Turns out that there is a renewed interest in these questions and one recent paper by Ullasa Kodandaramaiah et al. suggests that large eyespots may startle small predators. One of his fellow researchers further adds that this may be particularly effective in low-light conditions. False eyes are also found on caterpillars and in these cases, they are often on the front end of the caterpillar and these may not have the same kind of survival value as in the Lycaenids. Indeed the suggestion here is that they serve to startle potential predators by appearing like the eyes of a larger predator.

Now here comes another twist - Cordero in 2001 suggested that predators preferentially attack the rear ends of butterflies and that the false head served to deflect the attacker making them come into view and increasing the likelihood of timely evasive action !

In the Sunderbans, there was an idea of using a face mask behind the head to reduce the attacks on people by tigers, which typically ambush from behind. The idea was that the tiger would try to approach from the front giving more time and a chance for the person to make an escape. Apparently tigers are now beginning to discriminate the false face. It should be interesting to look out for and observe the behaviour of lynx spiders near Lycaenids.

Credits

Vijay Barve - photograph of Spindasis vulcanus (Creative Commons /Wikimedia)

Further reading


Wednesday, September 15, 2010

Turning over a new leaf

The hoi polloi views insects as pesky fellow passengers on this crazy ball in space and science degrees hardly have an effect on most people. However insects are perhaps one of the most interesting fellow passengers around and more than make up for the annoyance of a few biters and blood-suckers. They came out of the waters a long time before the branching of life-forms with internal skeletons. Which means that they have had that much more time encountering the problems of life and solving them using "evolutionary algorithms". What interesting answers and questions might they have figured out ? (apart from perhaps finding that the answer is 42!)

Galls on Pongamia leaves
How does one find food on a planet like this ? There is so much green stuff and yet humans in a forest find so little that is edible. What has gone wrong here ? For someone who thinks about insects and plants, the real questions are not about how to keep the insects away from plants but about how plants keep them away and stay green in spite of the onslaught. Not every plant-eating insect feeds on every plant species and the few that are found in numbers on any plant has evolved such an array of tools to deal with their dinner and dining table.

Here are some Pongamia pinnata leaves I found not so long ago. One usually finds little outgrowths on the leaves. These are mostly insect galls, but galls may also be formed by fungi. If you cut an insect-gall you will likely find a central hollow, perhaps an exit hole on the base or tip and if you are lucky, a tiny larva somewhere. That could most likely belong to one of numerous wasps or flies and you will surely be hard-pressed to find anyone who can identify the species. Galls are not always shaped like this - they can be spherical, formed at the tip of a branch and botanists have been known to sometimes describe the gall as the characteristic fruit of a new found tree species. What exactly is happening is something to consider - is the plant trying to isolate the insect like a cyst forms to engulf a foreign body or is the insect manipulating the biochemistry of the plant to make it produce tasty tissue around it ? Turns out that the latter is often the case and sometimes the gall-inducer seems to be capable of inducing galls with very specific shapes, colours and structures (this article with illustrations is particularly worthy of reading).

Ficus at Hebbal with leaves eaten away
Anyone who has worked with plant-tissue culture can tell you what a complex and sensitive cocktail of auxins, cytokinins and other compounds have to be delivered to get a bunch of cells to grow into something that resembles a plant. Now, given that the structure is essentially an insect induced "fruit", there must be a few that people can eat and after some research I came upon the "Mulga apple" (apparently on Acacia aneura) of Australia but the number of cases of edible galls seems rather low. I have a rather vague recollection of seeing swellings on nettles in the Uttaranchal Himalayas and some comments on their edibility (if anyone has eaten this or knows more please do let me know). Now plants are not taking such damage lying down and they have come up with their own defences. (some years ago some of us worked on this article on Wikipedia and hopefully it is still readable) Turns out that the biggest human use of galls is in the extraction of tannins - and tannic acid - a mixture of potent chemicals used to treat leather (tanning leather), at least in the past. And printing ink was once made by treating rust with gall extracts ! Tannins are essentially anti-insect chemicals and in some plants, the tannin content goes up rapidly when the plant is physically damaged by insects this can have an effect on the insects. Now if the insects are such experts in plant biochemistry, perhaps the plants have in turn figured out the most critical insect biochemical gears into which their molecular spanners should be thrown. Given that these are potent chemicals tailored through evolutionary time-scales, there must be something in these Chinese cocktails worthy of some serious scientific attention.

Leaf mine - note widening with age of miner
The birdwatcher's of Bangalore hold regular field outings at Hebbal and Lalbagh on the first and second Sundays of each month. On one of the Hebbal outings around June and July we came across this Ficus, the leaves with holes, the ground below covered in tea-like frass and you could hear the fall of caterpillar droppings. The caterpillars were extremely pretty, moving along the trunk in large numbers, presumably the last instars looking for a place to pupate. Unfortunately we have been unable to obtain any further identification of this lepidopteran caterpillar. With the monsoon rains, the tree has now shed all its leaves. Now leaf-shedding is actually a bit of a story of its own and there are numerous theories on when a tree "ought" to shed its leaves "if its purpose" was to achieve something and one such function, teleologically speaking, is to get rid of pesky insects. But surely dropping leaves is not a good strategy to get rid of that eat leaves . At least certainly not without withdrawing all the best nutrients.

The caterpillars on the Ficus (unidentified)
Perhaps the easiest insect targets to get rid off by leaf-shedding would be things like galls and leaf miners. Life miners, usually moth or fly larvae live in the layer of the leaf and feed under the protection of the leaf surface, no rain, no drying and perhaps some protection from parasites and predators.
So, next time you have something to ponder over when you see a fallen leaf...

Turns out that some studies suggest that leaf dropping does not kill many leaf-miners and so seems unlikely while others point out that gall infestation induces early leaf shedding.

Postscript

Also discovered Huitlacoche caused by Ustilago maydis

Sunday, September 5, 2010

Why look like an ant?

Aint an ant

This morning, I found this ant-like chap on the wall. Anyone who does not look carefully might pass it off as an ant but anyone who knows a bit about the elbowed antennae of the ant family would know it was not. But what was it ?

It had a slender neck and the long rostrum suggestive of a Reduviid of which this could have been a nymph but how wrong can one be !

Turns out that this is Dulichius inflatus, a bug of the family Alydidae. And it is not a nymph, but an adult and it is (nearly) wingless!

"Some ant like forms are the most remarkable, and Mr Wroughton recently exhibited to the London Entomological Society an Indian Coreid which associates with the Ant Polyrhachis spiniger and is furnished with spines on the pronotum &c., resembling almost exactly those possessed by the Ant" - W L Distant, Rhynchota, Fauna of British India
Elbowed antennae ?

Looking up the entry in the Fauna of British India, one learns that it was described by W F Kirby. And a later specimen produced by R C Wroughton of the now largely defunct Bombay Natural History Society was described as Dulichius wroughtoni which became a junior synonym. Wroughton notes that the species is commonly found under rocks along with colonies of Polyrhachis spiniger (which seems to be synonym of P. lacteipennis) and that the spine structure varies widely across individuals !

A real Polyrhachis
What can one do after obtaining an identification from the few taxonomists left in India and researching the literature using the name? One could create a Wikipedia entry for a start and that makes one learn a little more too, sometimes it can be a bit of a consolation, especially when one finds out that W F Kirby, entomologist who described the species also thought it was a Reduviid ! A later amateur entomologist and physician from Finland, Bergroth who saw a specimen from Wroughton described the species as Dulichius wroughtoni and then came across Kirby's own description and decided that Kirby's had priority. However his note on Kirby is quite interesting, particularly as it comes from an amateur evaluating a self-professed expert at a museum of that time-period:

Mr. Kirby has had the kindness to send me a copy of his work on the Heteroptera and Homoptera of Ceylon (Journ. Linn. Soc. XXIV, pag. 72—176, with 3 plates). The author says in the introduetion, that he has thought his paper „would be rendering a real service to science". I think no serious hemipterist will be of the same opinion. As the author is assistant in the British Museum, one schould expect to find informations on the real systematic position of the many dubious Hemiptera deseribed from Ceylon by Walker, and it is therefore with great regret we find Mr. Kirby's work to be entirely in Walker's style and almost without any scientific value Mr. Kirby further says, that he will not create many new genera, 'until those already proposed have undergone a thorough and much-needed revision, which at present I have no time to "attempt".' It is to be hoped, that Mr. Kirby never will find time to a such revision, as it seems to be unknown to him, that the genera of Hemiptera have already undergone a thorough and most excellent revision by Stäl.


Postscript
Happened to visit one of the websites where photographers dump their pictures and found some rather excellent photos in the chaotic pile. Interestingly one from Bangalore seems to have been taken around the same time. Seems like the rains might be important factor for some aspect of their life cycle:

Photo 1
Photo 2

Also discovered a photograph of a Polyrhachis that I had taken - here sitting, perhaps in a defensive posture, on the spadix of a pink Anthurium - now added above.