Posted by: scrubmuncher | July 11, 2012

Cryptic goings on…

[This post is adapted from a book I’ve just finished, which will be published sometime next year by Thames and Hudson.]

Nematodes are typically small animals that to the naked eye look very much alike; however, these creatures are fantastically diverse – at least on a par with the arthropods in terms of species diversity. Currently, around 24,800 nematode species have been formally described, but it’s fair to say this is the tip of the veritable ice-berg. Almost 20 years ago it was suggested there could be as many as 100 million species of nematode out there. This colossal estimate was based on an extrapolation using regional data, a technique that is beset with all manner of pit-falls. 100 million has since been revised down to around 1 million, which is quite a climb down; nonetheless the nematodes are nothing other than an incredibly speciose group of animals.

At face value nematodes lack the charisma of larger animals, so there are very few biologists who have made it their life’s work to understand them. Those that do have been rewarded with glimpses of the incredible diversity of these animals, an example of which is the complex menagerie of nematode species that dwell in the guts of large, tropical millipedes. Some SEMs (false coloured) of these nematodes can be seen below:

Parasitic nematodes from the guts of tropical millipedes (clockwise from top left: Rhigonema tomentosum, Carnoya sp., Carnoya fimbriata and Heth sp.). All images are courtesy of David J. Hunt and are false coloured SEMs.

The SEMs of the four species in the composite image above go to show how morphologically diverse the nematodes can be, but it’s their ecology we are interested in here. These four species are parasitic in the gut of their millipedes hosts where they help themselves to gut secretions, intestinal cells and the host’s food.  Nothing odd about that – there are loads of nematodes species that spend their lives in the guts of larger animals. What makes this example particularly fascinating is that these nematodes are not alone. Also in the gut of the host are other, related nematodes (Zalophora spp. see SEM below) that pursue and eat the parasitic species. What I love about this example is what it says about hidden diversity and the huge variety of ecological interactions that are out of sight and out of mind. The gut of the millipede host is a microcosm – an ecosystem in its own right – inhabited not only by a huge range of microorganisms, but also an array of other animals that are found nowhere else. Beyond the basic predator-prey interactions played out between these nematodes there is so much that we have no idea about. Does each of the parasitic species depend on a different part of the host’s gut? What adaptations do the parasitic nematodes have for evading the predatory nematodes? Can the juvenile predatory nematodes maximise their chances of getting into a millepede infested with their prey?

These hidden layers of complexity are everywhere in the living world, so it is no surprise that we have so far only scratched the surface of the Earth’s biodiversity.

The mouth of Zalophora deinostoma. The three cuticularized, jawlike structures inside the mouth slice up the prey nematodes that are hunted in the gut of the millipede host (SEM courtesy of David J. Hunt).

Further reading

Posted by: scrubmuncher | July 6, 2012

Flagellation…

The intriguing little animal below is the first instar larva of the puss moth (Cerura vinula). The egg that it has very recently emerged from is to the right. These caterpillars and their close relatives have a couple of brilliant adaptations to ward off many, many potential predators.

First off they have a pair of tail-like structures known as flagella that are actually highly modified prolegs. When it feels threatened the caterpillar waves these flagella about, their bright red ends extending to coil and uncoil.

The exact function of these flagella is not known, but they may be advertising the fact this little animal is far from palatable as it is able to squirt formic acid from glands on its head. The flagella may also be used to swipe at parasitoids, the nemeses of all caterpillars, which must alight to deposit their eggs.

This individual was found on aspen (Populus tremula), the favourite host plant of this species. The small host tree was growing in a fine bit of Hertfordshire woodland.

First instar puss moth (Cerura vinula) larva and its egg. Feeding damage on the right of the leaf is the work of this young caterpillar (Ross Piper)

Posted by: scrubmuncher | June 28, 2012

Animal architecture 2

In the last post, we were introduced to an industrious, leaf-rolling weevil. This post concerns a related, albeit more glamorous species that uses aspen leaves instead of birch leaves to make food nurseries for its young:

Image

A female Byctiscus populi, the polar leaf-rolling weevil (Ross Piper).

In the UK this species is rather rare and only known from a few sites. What makes this species particularly interesting is that adults sometimes cooperate to roll leaves and the males use small spines on their pronotum (visible in the image below) to wrestle other males for access to the females.

Image

Male (top) and female Byctiscus populi. The males lock spines (visible on the pronotum) in their efforts to win mates (Ross Piper).

Posted by: scrubmuncher | June 23, 2012

Animal architecture 1

At this time of year in temperate climes insect activity should be at it peak. Often, the insects themselves may be elusive, but evidence of their feverish activity is all around. In areas of woodland and scrub the leaves of many tree species, such as birch, oak and aspen are rolled into distinctive cigar shapes. These structures are the work of many different insects that construct these rolls either to hide in or as a nursery for their offspring. One such species is this small beetle, the birch leaf-rolling weevil (Deporaus betulae):

A female birch leaf rolling weevil (Deporaus betulae) just before she starts work on another leaf roll (Ross Piper).

This species rolls birch leaves into little nurseries for its offspring. What follows is a sequence of images showing how this 4-5mm beetle goes about doing this; a process that takes at least 1.5 hrs.

First off, the female selects a suitable leaf and then uses her mandibles to munch a wavy incision toward the mid-rib  (Ross Piper).

Next, she starts making another distinctive wavy cut away from the mid-rib, pausing for a while to chew the mid-rib a little in order to weaken it. Here, the industrious female gets on with the job in hand almost oblivious to the male trying to fertilise the egg she will lay in this particular leaf roll (Ross Piper).

The last of the cutting is almost done regardless of the weight of the male (Ross Piper).

Let the rolling begin. Using brute strength the female uses her legs to roll the leaf (Ross Piper).

It’s difficult to see exactly how the female beetle rolls the leaf, but the cuts make it limp and therefore more flexible (Ross Piper).

Almost there and the male is still clinging on tenaciously (Ross Piper).

The next three images show the female tightening up the roll by getting in amongst the structure. At some point while inside the roll she lays a single egg (Ross Piper).

The tightening of the roll continues (Ross Piper).

The female puts the finishing touches to her ingenious brood chamber (Ross Piper).

The completed roll, which took about 1.5 hours to make. The egg inside will eventually hatch and the larva will be surrounded by food and protected from many of its enemies. The fully grown larva will drop from its roll to pupate in the soil. Species that make leaf rolls for their eggs invest a lot of time and energy in this endeavour and because of how long it takes to make each roll they can only lay a relatively small number of eggs in their lifetime. However, each larva provisioned for and protected in this way has a much better chance of reaching adulthood (Ross Piper).

Posted by: scrubmuncher | June 18, 2012

Bloaters 2

Although the alder leaf beetle (see last post) can swell to rather substantial proportions in an effort to produce lots of young it has quite a lot of work to do to contend with the dock leaf beetle (Gastrophysa viridula). Gravid females of this species are seriously swollen with eggs, but this doesn’t seem to deter ardent males from clambering aboard and attempting to mate (see below). This little, metallic beetle is very interesting for a number of reasons, but it is perhaps their means of limiting population growth which is most fascinating. If the population on a given dock plant is running out of control some males take it on themselves to break up other mating couples in an effort to give their own offspring a fair munch of the leaf.

Posted by: scrubmuncher | June 7, 2012

Bloaters 1

Leaf beetles (chrysomelids), the often gaudy insects you see sitting on various plants in the summer have only a few short weeks in temperate climes to make use of the succulent foliage of their host plants. To fully exploit this flush of food the females can produce prodigious numbers of eggs, accommodated by a massively bloated abdomen. The species below, Agelastica alni (the alder leaf beetle) is quite a bloater. Here, the burgeoning abdomen no longer fits snugly beneath the elytra. Through the vanishingly thin cuticle of the abdomen it is even possible to make out the individual eggs.

A gravid female alder leaf beetle (Agelastica alni). Quite a bloater (Ross Piper).

Posted by: scrubmuncher | February 13, 2012

Microscopic jaws

In the last post, we saw a compliant little rotifer getting on with the pressing activity of collecting food. In this next bit of footage, we can see the very same rotifer, but obligingly it has changed its position a little so we can see more of its body. About one-third the way along the body is what we want to look at, because it’s how these tiny animals ‘chew’ their food. You should be able to see a structure opening and closing. This, if you can see it is the rotifer’s jaws, more correctly known as the mastax. For an animal so small and with only around 1,000 cells in its entire body, this structure is amazingly complex; an assemblage of muscles, ligaments and toothed plates (trophi) all working together to macerate the food before it’s digested. Below the video there is a SEM of these trophi teased out of a rotifer and lovingly prepared by Martin Sørensen, an expert on these animals. The SEM gives an idea of the hidden complexities of this miniature world.

Rotifer feeding: Part 1 from Ross Piper on Vimeo.

The cuticular plates that give a rotifer it's bite. A SEM of the trophi from a rotifer's mastax. The two toothed plates are moved in and out to macerate the rotifer's food (Martin V Sørensen)

Posted by: scrubmuncher | February 10, 2012

Antony and the animacules…

Antony van Leeuwenhoek, a man of magnificent hair and considerable talent, was the pioneer of microscopy. Using a device he crafted himself he scrutinised all manner of unsavoury samples to see what miniature wonders they contained. Some of the first things he saw were the decidedly odd little animals known as rotifers. Even though he was the first person to see them he rightly knew they were some sort of animal; describing them as “animacules”. These animals are small all right (most are much less than 1 mm long), but if you want to see some for yourself they’re not difficult to find. In fact you can find them just about anywhere. The footage below shows the rotifer Rotaria rotatoria, lots of specimens of which were found in the detritus that had accumulated in the bottom of a rainwater-filled bucket. They’re about 0.4 mm long, so you need a microscope to see them, but they’re definitely worth having a close look at.

In the video, you can see what look like a pair of rotating wheels; the inspiration for the name ‘Rotifera’ (Latin for ‘wheel-bearer’). On its head the animal has a corona of beating cilia and it is the movement of these that deceives the eye into seeing a pair of rotating wheels. The ‘wheels’ are nothing more than an optical illusion.

You can see the vigorous vortices generated by these beating cilia funneling food (diatoms, etc) towards the mouth of the animal. In the next blog entry we’ll see how this tiny animals deals with its food.

Rotifer feeding: Part 2 from Ross Piper on Vimeo.

Posted by: scrubmuncher | October 3, 2011

I give you the mud dragon…

Marine sediments are alive with all manner of creatures, including representatives of many lineages that are found nowhere else, such as this kinorhynch, Echinoderes kristenseni. The long spines on the head (right) are known as scalids and are thought to be sensory. Poking out between the scalids are the tips of the mouth cone stylets. The gut is also visible through the translucent body wall (Ross Piper)

Well, it’s not much of a dragon, but it does live in mud. These animals, correctly known as kinorhynchs, are miniscule, usually much less than a millimetre long, but under the gaze of a microscope they are quite appealing little things.

The specimen posing in the photo below was found in a kelp holdfast taken from the rocky shore in southwest Wales. These micro-habitats are seething with animal life, but you could say this about just anywhere in the ocean where there are sediments. The animals that live on and between these sediment grains are known as meiofauna and they’re bewilderingly diverse. It is in these marine sediments where you find the most animal lineages, many of which are found nowhere else, e.g. the Kinorhyncha.

All you need to do to see the incredible diversity of animals in these habitats is to take a handful of marine mud or sand and shake it with water for a bit. Then, let the sediment settle and all the animals will be swirling around in the water. Finally, pour the water through a very fine filter and observe the miniature menagerie with a microscope.

What we know about the kinorhynchs and the other interstitial creatures could be written on their tiny undersides. For the most part they live out their lives out of sight and out of mind, but I’d quite happily wager that the finer details of what they get up to in the sediment is as fascinating as their appearance.

Below are two photographs of another kinorhynch collected by Martin V. Sørensen from sediment on the bottom of Ikka Fjord, Greenland. This is one of the larger kinorhynch species, but it is still much less than 1 mm long. The top photo is a dark-field image, while the second was taken with a normal microscope setting. The weight of the microscope slide on the body of the animal has squeezed out the introvert (right). This part of a kinorhynch’s body can be forced out under fluid pressure and retracted by muscles. It bears characteristic sensory structures (scalids – curved backwards in this image) and the stylets of the mouth cone. In the lower image the cuticular plates of the body are very obvious as are the contents of the gut that have been squeezed out of the mouth by the weight of the cover-slip.

Pycnophyes cf. greenlandicus – dark-field image  (Ross Piper and Martin V Sorensen).

Pycnophyes cf. greenlandicus (Ross Piper and Martin V Sorensen).

 

Posted by: scrubmuncher | September 10, 2011

Something nasty in the nest…

Flies are supremely successful animals, but they tend to get a lot of bad press and let’s be honest, the way they look and what they get up to doesn’t do them any favours. For me, the  most unnerving yet fascinating flies are the keds (also known as louse flies and hippoboscids). Whatever you want to call them, there’s no getting away from the fact they look a bit nightmarish.

Just take a look at the photo below. This species, Crataerina hirundinis, takes liberties with house martins. The specimen in question was found on a young house martin that had fallen from its nest. Not only do they have something of the night about them, but these flies which have forsaken flight, scuttle about in a manner and at a speed, which makes you squeal like a girl. If you’re ever in the unfortunate position of having one of these on your person you’ll see what I mean. One moment it’ll be on your hand and the next it will have scampered, quite crab-like, to your armpit to seek refuge amongst the warm tangle of hair. One of these varmints in the trousers is not worth thinking about, but I’m sure some enterprising soul back in the middle ages probably devised some sort of torture device consisting of a handful of louse flies and a pair of metal trousers.

Louse flies, like this Crataerina hirundinis, are repulsive and fascinating in equal measure. This unlucky individual was found clinging to the body of a young house martin that had tried unsuccessfully to fledge the nest (Ross Piper)

Repugnant appearance aside they’re actually beautifully honed to a parasitic way of life. The body is flattened and the wings have all but disappeared so they can crawl about with ease in the bird’s pelage. The feet are like grappling hooks,  giving the insect a tenacious grip. With all these adaptations they scuttle around the body of the host with impunity searching for a good place to suck blood from after piercing the skin with the stylet-like mouthparts.

These elaborate feet give the louse fly a fierce grip (Ross Piper)

What I find most disturbing about these flies is their size in relation to the host. I suppose it would be something like a human playing host to a parasite the size of an edible crab.

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