Clever Crows

Along with "language use" the other distinguishing ability that has always been held to mark humans off as separate/superior from the rest of the animal kingdom is "tool use" - man the tool maker. An exception had to be made in the 1970's when it was observed that chimps regularly use tools to access ants nests, to crack open nuts and for weapons. Then in 1996 Gavin Hunt from Auckland University discovered that the New Caledonian crow (Corvus Moneduloides) makes stick and leaf tools to extract grubs from crevices and dead wood. This ability appears to be confined to this one particular species found only on two adjacent islands. It was not perhaps too much of a shock for us to accept that chimps might have some crude tool making ability - after all we mostly accept that we derive from related stock some 6 million years ago - however it might give us a little more pause to take in that similar abilities have evolved quite separately in birds that diverged from our ancestral stock line at least 300 million years ago.


Some of the tool-use activity appears to be innate, that is captive chicks reared only by humans and never shown any tool-use will fashion crude leaf tools from Pandanus leaf and use these to extract food (http://users.ox.ac.uk/~kgroup/tools/animal_tool.shtml). However in the wild the tools are far more sophisticated and also there are regional differences in tool design suggesting that social learning is involved.


I was fortunate to be able to spend a month on Mare Island in 2008 observing the crows in conjunction with a University of Auckland study attempting to determine the extent of social learning involved in tool-use. It was initially a slightly surreal sensation seeing lots of crows effortlessly making these leaf tools.


The following short clip from an experimental feeding table on Mare Island New Caledonia shows; stick tool use, then leaf tool making from a pandanus leaf (at 35sec.) and leaf tool use (at 56sec. till the end). You can hear young chicks calling from canopy nests not far from the feeding table:

Two pandanus leaf tools with a pandanus leaf showing where a tool was cut from:

The following clip is a scary/unbelievable/extraordinary recording made of Betty, a New Caledonian crow held in captivity at Oxford. Two crows were part of a "Choice" experiment where there were two wire "sticks", one with a bend which would allow it to be used as a hook to access a small bucket of food from inside a glass tube, the other a straight "stick". Would the crow more likely choose the useful bent stick? There were two crows in this experiment and at the start of this clip Betty's mate grabbed the hooked stick and she was left with the less useful straight stick. This is only the fifth trial in the experiment and the only exposure the crows have had with wire.

The following clip shows a crow fishing - dropping crumbs of dry bread on the surface of the pond. I think it was taken in Israel.





The following clip is of Prof Russell Gray at Auckland University discussing the probable social learning aspect to account for the regional differences in tool design.

Solar bodies - no need to eat !

The leaf shaped green sea slug Elysia chlorotica, found widely on the Eastern seaboard of the USA, has incorporated chloroplasts (the same structures responsible for photosynthesis in all plants) into its body cells which allows it to obtain its energy needs by sunbathing rather than by having to eat.

Photo by N E Curtis and R Martinez from Wired.com article 11/1/10.


Scientists have shown that after a young slugs initial feed of a particular green algae, from whence it obtains its chloroplasts, it can survive the rest of its life - about a year - without having to eat another meal. The slug, now solar-powered, no longer needs a mouth.

I first heard of this plant/animal in Frank Ryans' book Virolution in which he explores the central role of viruses in evolution and cell metabolisim. Elysia initially needs to feed on Vaucheria algae to acquire a sufficient "skin-full" of chloroplasts. The mystery though has been how the process of photosynthesis continues long after the initial chlorophyll reserves acquired from Vaucheria have been used up (photosynthesis requires continual replenishing of this light absorbing pigment).

It seems that in the evolutionary past there has been a natural transfer of genes from the algae to the slug which allows Elysia to produce the chlorophyll pigment proteins itself. These genes are found even in unhatched sea slugs which have never been exposed to algae. While bacteria and other microbes freely exchange genetic information (e.g. the fast build-up of resistance by bacteria to antibiotics), there are not many examples of genes transfering between two different kingdoms of life. Ryan writes that there is gathering evidence that the gene transfer was probably accomplished by a retrovirus that is commonly found throughout the body of the slug. Aggressive reproduction by the same virus is implicated in the quick death of the slug soon after it has laid its eggs the following spring. Ryan speculates that we are looking here at an example of "aggressive symbiosis" where the virus that had previously enabled the slugs idyllic lifestyle now switches behaviour to cull the now redundant adults after they have laid their eggs. He sees this is as a previously unnoticed evolutionary mechanisim perhaps as important as the better known mechanisims of natural selection, adaptation and genetic drift.

So, viruses help design the creatures they inhabit. Over evolutionary time they shape their own hosts. Which virus(es) designed us? Gives a new meaning to "Lord of Hosts".

A good green argument here of course for human genetic engineering. Splice chloroplast genes into our skin cells and we can all retire to the beach. Perhaps those little green Martians have already stolen a march on us here.

Youtube clip of Elysia still with a mouth :


Rumpho ME, Worful JM, Lee J, et al. "Horizontal Gene Transfer... " Nov '08 Proceed. Nat. Acad. Sciences.

Pierce SK, "Chlorophyll a manufacture in Elysia..." Jan '10 Ann. Meeting Soc. Integrative and Comparative Biology.

What are the odds?

This item comes from David Attenborough's TV series "Life in the Undergrowth" which has a wonderful segment on the unusual progeny rearing practices of the Blister beetle. What staggering coincidences stacked up to allow this chain of behaviour to evolve in the first place and what a slim chance in any individual case for Blister beetle lavae to see adulthood.

The following seven photos are all screen shots from the BBC series "Life in the Undergrowth".

The female Blister beetle lays hundreds of eggs in a hole in the Californian desert and leaves - parenting job done.

After six weeks the eggs hatch into 2mm long lavae and proceed to climb to the top of the nearest stalk of grass where they all cluster to form a bee sized lump giving off the perfume/pheromone of the female Digger bee.

If they are lucky a keen male Digger bee, mistaking the cluster for a mate, alights briefly. Those lavae who can, quickly latch onto the body of the male bee.

Male Digger bee takes off and hopefully then strikes the real thing - mating with a female Digger bee. The Blister lavae simultaneously jump ship and now cling to the Digger female.

Mrs Digger eventually heads back to her nest, the lavae make their final jump and proceed to consume the Digger bees store of pollen put aside for her own lavae then, when the pollen has all been eaten, they eat the lavae of the Digger bee as well before happily proceeding with their own lifecycle.

You can see the complete 5 minute clip (taken from Youtube) from the series here.

A little related trivia: There are over 7000 species in the family of Blister beetles. They all have the ability to secrete cantharidin - a skin blistering chemical - as a defensive measure. This substance is collected commercially by drying and crushing the beetles and is sold as a wart remover. It is also used to induce farm animals to mate by irritating the urethral passages causing a prolonged erection. The particular beetle favoured for this latter purpose is Lytta Vesicatoria otherwise known as Spanish Fly. Also known to have been used by men. Unfortunately (for men) there is a very fine line between a dose sufficient for the intended purpose and permanent damage to the genitals or fatal poisoning.

This photo of Lytta Vesicatoria appears in Wiki Blister beetle article and is attributed to Ramona - Flickr username amiinsidemyself.

One mind many bodies.

Slime Mould Fruiting Bodies - Photo hosebirdwatcher.livejournal.com

Slime Mould Slug and Fruiting Bodies - Photo Copyright, M.J. Grimson & R.L. Blanton



I first came across Dycostelium in Maturana and Varela's mind-bending book (which I hope to revisit here one day) "The Tree of Knowledge". This creature/s is fascinating due to its amazing ability to exist for much of the time as individual one celled amoebae but then, when conditions get tough, thousands of separate individuals come together and coalesce to form a large slug (all the amoebae now inside one sheath) which moves off to fresh pastures. Finding a likely site the slug stands up to form a tall fruiting body the head of which matures to disperses thousands of spore which become individual amoebae again. For the mostpart the amoebae are happy going their own separate way foraging for bacteria on the moist forest floor only assuming the slug form when food runs out or conditions get dry.


The Youtube clip is an old film by Prof. John Bonner - the grandfather of slime molds - showing the individual amoebae coalescing to form the slug then forming the fruiting body.




Some photos of the fruiting bodies of different slime moulds:
(hosebirdwatcher.livejournal.com)

Vaguely plant-like, the slime moulds used to be classified as fungi but as taxonomy is now based more on molecular RNA they have been placed further out to the right in the Kingdom Amoebozoa (There are now six Kingdoms of life: Animal, Plant, Fungi etc...). Whatever, how amazing that apparently separate individuals can just come together and form one organism!

Another example of composite creatures and far more impressive due to their size and complexity are the Siphonophora - mostly deep-sea living animals of which some have been found 40 meters in length. Although they appear to be a single organism they are in fact made up from a vast colony of thousands of zooids - free-swimming, self-supporting individuals - which have become fully integrated to operate as a single entity. The seperate organs of the siphonophore responsible for feeding or swimming or reproduction can be considered as sub colonies of specialised zooids. The siphonophora prey on crusteaca and small fish using tentacles to poison and ensnare. A surface living example is the Blue bottle or Portuguese-man-of-war.

Above photos Claire Nouvian.

The following description of Siphonophore is from Eugene Marais' wonderful book "The Soul of the White Ant" where this South African Lawyer/Poet/Natural Scientist likened the termite community to a composite animal. While looking for community analogies in other fields of biology he wrote of Siphonophore:

"The great peculiarity of these creatures is that every full-grown specimen is a composite animal composed of hundreds of individuals. The single individual is born by a budding process from the generative group of the composite animal. These newly born individuals swim around freely and are able to continue life singly and reproduce themselves. Each is a perfect marine creature with mouth, stomach, swimming apparatus and sexual organs. If by chance a group of siphonophora happens to meet, they cling to each other. In some species organic union takes place immediately, in others something less than this. But apart from this small difference the final result is the same. Immediately after the union the single individuals undergo a curious change. One group forms a complicated swimming apparatus; another group becomes the stomach and digestive system; and yet another group develops into the sexual organs of the composite animal. One group even takes on the hepatic functions and becomes the liver. Each individual of such a group loses all its separate organic functions. Those of the stomach group for instance, forget they ever sought food or had a sexual life of their own. The new organisim is a perfect whole animal. Were you to see it in its perfect stage you would not dream that it had been formed in this way from separate individuals. Yet one can break it up again ! One can tear apart each individual until the whole animal has been disorganised. One might suppose death would be the result, but not at all. Each little part begins to stir in the water. Slowly it repairs its lost organs and functions until at last it once again is a perfect individual, as different from the composite Siphonophore as the camel from the whale." 1973 Penguin p 79.


Video of Siphonophore from CreatureCast.org