New Photo-Electron Challenge & Old Answers

What is my secret name and what do I want from life?

‘To-morrow, and to-morrow, and to-morrow, Creeps in this petty pace from day to day’, but at last the the tomorrow promised in the last post (in March no less) has finally arrived. I plead overwork – I’ve had two massive taxonomic projects to complete including a listing of all of the species of mites known from Alberta – before the new field season commences.  Above is one of these little monsters saying high and below are a number of them clinging to an insect collected from a rotting oyster mushroom (Pleurotus ostreatus). Any guesses to the mite, insect, spores, ecological interactions?

Mites & insect - name them both and what is happening.

ANSWER TO PHOTON CHALLENGE

I’m fairly pleased in how well everyone did in the first Photon Challenge, especially considering the quality of the pictures.  Ray even got the fly to genus and Kaitlin got pretty close to the family of the mesostigmatan – at least according to the Manual of Acarology 3rd Edition the Halolaelapidae belongs in the Rhodacaroidea and they certainly are phoretic as deutonymphs, as one would expect in that superfamily. So Kaitlin gets points for that. Bruce got the family, and, I believe, the genus correct, at least in the broad sense: Halolaelaps s.l.  Bruce has the advantage of having described the only known Australia species of the group and to have pointed out how messy the generic concepts are (see Halliday 2008 Systematic & Applied Acarology 13, 214–230). I am neutral on what superfamily Halolaelapidae belongs to – Rhodacaroidea is unlikely to be monophyletic and deutonymphal phoresy is probably a ‘primitive’ behaviour in Mesostigmata.

Deutonymph of Myianoetus - note bifurcate claws

Alas, no one guessed the genus of the histiostomatid – Myianoetus! All acarologists should know this genus if only because it contains one of the few mites to lurk among the pages (as an anoetid) of  a large circulation, general science magazine – Science itself – and the interesting concept of ‘fly factors’:

Greenberg & Carpenter (1960) Factors in Phoretic Association of a Mite and Fly. Science 132: 738-739.

“Abstract: Combined rearing of the mite Myianoetus muscarum (L.), and the fly Muscina stabulans (Fall.) has revealed adaptations of the hypopus to a series of fly factors. These adaptations favor the mite’s dispersal. Hypopi are attracted to the pupa by a volatile substance and cluster on the anterior end, from which the fly emerges.”

Read the whole thing, as they say, but, although published over 50 years ago, you will still need access to Science to do so (and to read the next paper entitled  ‘Licking Rates of Albino Rats’). Rat licking trailer aside, I think the most interesting thing about the Myianoetus paper is that I can’t remember any follow-ups that explain ‘fly factor’ or ‘beetle factor’ or ‘ant factor’. Most of the chemical clues used to induce or terminate phoretic behaviour in mites remain unknown. Only skatoles and dung beetles come to mind. If someone out there in the ether knows of other studies, please let me know – I can use the information to help a student.

Photon Challenge: Last Chance

Business end of Antennolaelaps

Well, this Photon Challenge has gone on long enough: last chance for demonstrating your acarological expertise. Tomorrow I will reveal all.

Kaitlin and Ray have done well to the family level of the histiostomatid, but I don’t think a leap to the genus is impossible. After all, just how many mite genera have made it into the pages of Science magazine?

Ray has an embarrassingly detailed grasp of the anthomyiids breeding in indelicate accumulations of organic matter. But no one seems to be willing to stick their neck out on the phoretic mesostigmatan deutonymphs with two dorsal shields that have a death grip at the base of the abdomen of the Eutrichota. Last hint: the family of the phoretic mesostigmatan is currently placed in the same superfamily as the Antennolaelaps featured above.

Photon Challenge: New Hints

A closer view of a mitey fly

Kaitlin and Ray have both demonstrated that even the smaller of the two mites hitching a ride on our fly can be identified to family from a not so great photo: heteromorphic deutonymphs (aka hypopi) of a member of the Histiostomatidae. They also correctly placed the larger mite to order: Mesostigmata. Not much luck on the fly, though, so I guess that means mites are easier to identify than flies? Anyone who has struggled with the generic key for this family in Nearctic Diptera might very well say yes. However, the family of the fly should be an easy guess for a dipterist.

Genus anyone?

Here’s a light microscope view (this is a Photon Challenge) of the venter of one of the histiostomatid hypopodes (yet another name for these deutonymphs) and a closeup of one of the pretarsal claws. The ventral shot is layered from three images in the wonderful CombineZP and the claw from two shots. The host association and characters visible in this image should give the discerning astigmatologist a good guess at the genus (I have checked with the North American authority on this one and he had no problem).

I’ll give one more hint on the mesostigmatans too – they also are deutonymphs.

Three-in-one Phoresy Photon Challenge

Name the insect and its hitch-hikers for full credit

This is the first Challenge using a light micrograph, but the usual rules apply – name the beasts as well as you can and Macromite fame may be yours. If the task proves too daunting, well then here’s a meander through the illustrated behavior to keep you entertained.

Phoresy is a behaviour, or rather a set of behaviours, exhibited by many small animals and especially by mites. The word is a bit confusing. The root, phor- is from the Greek word phoros which means to bear, to carry or refers to movement (not phor, a thief or kind of bee), but phoresy actually requires an absence of movement and it is usually not (but not always) the mite that does the carrying. Thus, the usage is a bit inverted from similarly derived jargon, e.g. the conidiophores that bear fungal spores or electrophoresis where an electrical field is used to carry charged particles through a gel or other medium. In the case of phoresy, it is the mite that is carried, usually by some lucky, larger, and more vagile arthropod.

Hypopi have no mouths but do have sucker plates

Nature is full of interesting interactions, but to study them first requires defining them. Well, perhaps not, but that is what scientists like to do – and tying them up with definitions and tagging them with a name derived from Greek or Latin (or both) is always great fun. The term phoresy was first proposed by French entomologist and bostrichid specialist Pierre Lesne in 1896 and to quote from a delightful paper (read the pdf – the web text is full of errors) by the famous myrmecophile and ant acarologist W.M. Wheeler (1919): “In 1896 Lesne called attention to a number of small insects that habitually ride on larger insects. To this phenomenon he applied the term “phoresy” and showed that it is distinguished from ectoparasitism by the fact that the portee does not feed on the porter and eventually dismounts and has no further relations with the latter.”

Lestes damselfly (male) with parasitic water mite larvae (red blobs)

As classically defined in the mid-20^th Century, phoresy required an animal to stop its normal behaviours (e.g. seeking food or members of the opposite sex), seek out a carrier, mount the carrier and refrain from doing anything other than holding on, and then after a time to dismount from the carrier and resume normal behaviours. Taking a bite out of the carrier was considered a no-no – and animals that did so were banned from phoresy and sent to parasite prison. The heteromorphic deutonymph of Astigmatina (aka hypopus) is a classic phoriont – it lacks functional mouthparts, has no foregut (and so feeding would seem to be verboten), and has a ventral sucker disk formed from modified setae for holding onto an insect or other larger arthropod (sometimes even other  mites).

So, in an evolutionary ecology sense, classical phoresy can be thought of as an ectosymbiosis in the commensal category where the mite gets a free ride and the carrier doesn’t really care. Dispersal is assumed to be at the root of the evolution of these behaviours in the mites (although phoresy may actually concentrate, rather than disperse the mites). But are things really so simple?

Again the jargon is a bit confusing: ‘commensal’ implies eating together, and the mite can’t eat while on the carrier or it wouldn’t be considered phoretic. Consider the case of water mite larvae – they use adult aquatic insects to ‘disperse’, but since they take a bite while doing so, they are considered parasites, not phorionts. Then there are the strange hypopi of Hemisarcoptes cooremani which hitch rides under the elytra of ladybird beetles in the genus Chilochorus. Since Chilochorus beetles like to eat mites, this seems like a dangerous thing to do – but hypopi of H. cooremani that do not find a beetle die. Those that do find a beetle hang on for 5-21 days and swell up before leaving the beetle. Marilyn Houck (1994), who has studied this interaction, has suggested that beetle hemolymph (reflexive bleeding is a defense of many ladybird beetles – pick them up and noxious yellow blood oozes from their leg joints) may provide critical nutrients, possibly via the anal vestibule of the mites (which connects to a hindgut).

Another point to consider is how the porter really feels about the portees. When I look at insects covered in phoretic mites, e.g. the Photon Challenge above, I find it difficult to believe the bug is having a good time. But some bees and wasps have special mite pockets (acarinaria) that appear to have evolved to encourage mites to hitch a ride. I’ll post on acarinaria some day, but for now I will just note that some of these hymenopters do much better with their mites than without them.

Lisa Hodgkin and her colleagues at the University of Melbourne published an excellent paper last year with some interesting experimental data. They studied a bark beetle (Ips grandicollis) introduced into Australia and its phoretic mites and demonstrated that ‘phoresy’ can be both dynamic and complex. Phoretic mites were associated with both negative (adults) and positive (larvae) effects on beetle reproduction and development. Heavy mite loads were not good for female beetles, but having mites in the galleries resulted in bigger and healthier offspring. Perhaps when we are considering defining complex interactions like phoresy we should remember what Hamlet pointed out to Horatio: There are more things in heaven and earth, Horatio, Than are dreamt of in your philosophy.

References:

Lisa K. Hodgkin, Mark A. Elgar and Matthew R. E. Symonds. 2010. Positive and negative effects of phoretic mites on the reproductive output of an invasive bark beetle. Australian Journal of Zoology, 2010, 58, 198–204. http://www.publish.csiro.au/paper/ZO10034

Houck, M.A.  1994.  Adaptation and transition into parasitism from commensalism: a phoretic model. In: (Houck, M.A., ed.), Mites. Ecological and evolutionary analyses of life-history patterns. Chapman and Hall, New York: 252-281.

P. Lesne. 1896. Moeurs du Limosina sacra. Phenomenes de transport mutuel chez les animaux articules, Origine du parasitisme chez les insectes Dipteres. Bull. Soc. Ent. France 45, 1896, pp. 162-165.

WM Wheeler. 1919. The phoresy of Antherophagus. Psyche Boston Volume: 26: 145-152.

http://psyche.entclub.org/26/26-145.html

The Macromite Before Christmas

Water-skating Homocaligus adorned with Roynortonella pustules

The winter solstice (adorned with a full lunar eclipse on an almost clear night here in Edmonton) is several days past and my brief Albertan ‘mid-winter’ holiday season has just commenced. In Australia the first month of summer is almost over – Australia begins its summer on the first day of December, presumably out of the usual nonconformity or some other reason that was never clearly explained to me – but their summer solstice is just past and it is also the holiday season (with snow in the mountains, but otherwise warmer than here). Celebrating the longest night of the year makes a certain sense. Although I still have 4-5 months before green returns to the landscape, I can optimistically assume that the sun will be shining longer and longer each day, even if it is on clouds that are dumping snow on me, and eventually the winter will end, at least officially. So, in the spirit of my holiday season, I wish my readers, wherever they are and whatever their holiday or not, a happy Christmas and productive, healthy, and intellectually stimulating New Year.

An undescribed, but checklist making, Annerossella from Queensland

Over the last few years I have gotten into the habit of tarting up one of my mites for a Christmas card. This year I picked an unidentified Albertan species of Homocaligus – one of the two genera of the raphignathoid family Homocaligidae. This mite is a festive bright red in life and skates over the shallow margins of lakes among emergent vegetation and aquatic mosses. Eggs are probably laid on vegetation as in Annerossella knorri Gonzalez, a homocaligid described from the leaves of water lettuce (Pistia stratiotes) near Bangkok, Thailand. I suspect it is a predator, perhaps of the springtails (Podura aquatica) that hop along in this habitat. I once kept an undescribed Australian species of Annerossella in a small aquarium, but other than watching it skate across the water, I was unable to add anything to the knowledge of its ecology (at about 0.5 mm in length, it is difficult to observe). However, I did make one of my early coloured SEMs of the mite and posted it on the Mite Image Gallery at the University of Queensland. Much to my surprise this was the first record of the family in Australia and my friend Bruce Halliday, putting aside his doubts about the validity of ephemeral web publications, cited the image in his Mites of Australia, a checklist and bibliography (1998, CSIRO Publications). Interestingly, the image at the top of a species of Homocaligus is probably the first record of the family from Alberta.

A pustule from the gymnodamaeid Joshuella agrosticula at 40,000x

Although festive enough for the holiday in itself, I thought the Homocaligus needed more adornment. The pine cone-like bulbs on the mite are cerotegumental pustules from another mysterious Albertan mite, Roynortonella gildersleeveae (Hammer, 1952). This mite used to reside in the genus Nortonella Paschoal, named after the great oribatologist Roy A. Norton. Unfortunately, in 1908 a certain Rohwer had already used Nortonella for a genus of tenthridinid sawflies; thus, the name was preoccupied. I suggested the new name as a replacement that was in keeping with the author’s original intentions. Like other members of its family (Gymnodamaeidae), the surface of the adult mite has scattered fields of strange and intriguing Bucky Ball-like pustules. The pustules arise as the cerotegument dries after the adult moult in what must be some interaction between microfibers and wax. Their elaborate form and species-to-species variants keep me, if not tied to a particular belief in the nature of the Universe, at least still amazed by how rewarding the study of even the smallest parts of Nature can be.

For more on Homocaligidae and Gymnodamaeidae see:

Fan Q-H. 1997. The Homocaligidae from China, with description of two new species (Acari: Raphignathoidea). Entomol. Sin. 4: 337-342.

Gonzalez RH. 1978. a new species of mite on water lettuce in Thailand (Acari: Homocaligidae). International Journal of Acarology 4:221-225.

Walter DE. 2009. Genera of Gymnodamaeidae (Acari: Oribatida: Plateremaeoidea) of Canada, with notes on some nomenclatorial problems. Zootaxa 2206: 23–44.

Wood TG. 1969. The Homocaligidae a new family of mites (Acari: Raphignathoidea), including a description of a new species from Malaya and the British Solomon Islands. Acarologia (Paris): 11: 711-729.

And the Answer is: Polyxenid Millipede

the presentable part of a polyxenid from Queensland

As Christopher Taylor deduced, the 3^rd Electron Challenge is none other than a member of the millipede subclass Penicillata and its only order Polyxenida. The cephalic trichobothria and disaggregated eye cups are characteristic of this group. Müller et al. (2007) consider the eyes to be secondarily reduced, miniaturized ommatidia and used their study of eye ultrastructure to argue both for the homology of all mandibulate eyes and a possible synapomorphy of the Myriapoda (millipedes, centipedes, symphylans, and pauropods).

Polyxenid in the courtyard: tiny, but not defenceless

Christopher also hypothesizes that parthenogenesis may help them to colonize extreme habitats like the Spanish Moss (the lichen-like bromeliad Tillandsia usneoides) that dangles from trees, especially live oaks, in the south eastern USA. Some populations of species of Polyxenus, at least, are parthenogenetic, so I suppose, that is a possibility under the General Purpose Genotype Hypothesis about the persistence of parthenogens. But, both bisexual and unisexual polyxenids are unusual among Diplopoda in that many inhabit xeric environments such as rock surfaces, bark, and even Spanish Moss (Whitaker & Ruckdeschel 2010). Wright & Westh (2006) recently demonstrated that Polyxenus lagurus (L.) is capable of absorbing atmospheric water vapour down to relative humidities of 85% – so far the only known millipede to have this ability. So, this ability seems more useful for climbing trees than the ability to do without males.

Our somewhat deformed specimen is from Queensland. Three families of Polyxenida have been recorded in Australia (Lophoproctidae Silvestri, 1897; Polyxenidae Lucas, 1840; Synxenidae Silvestri, 1923), but I don’t know which one this Queensland specimen represents. Unlike all other millipedes, polyxenids (this ‘common name’ could be confusing since it can be applied both to the family and order – but I’ll use it for the order) are soft-bodied and preserving them for SEM is tricky (also the setae, especially in the posterior pencil-like tuft, fall out and get stuck to everything else in the dish). Only about 160 polyxenid species are known today, but the group is very ancient with fossils in amber known from the late Cretaceous – and all have the whorls of serrate setae and the dense pencil-like tuft of fine setae on the rear.

Eisner et al. (1996) have a fascinating (and currently freely available) paper in the unfortunately acronymned PNAS that demonstrates that a North American species of Polyxenus uses the pencil tufts of modified setae on their posterior to thwart predation by ants. In fact, they use the ant’s mechanoreceptor setae and grooming behaviour as a death trap. When an ant approaches, the polyxenid swings its butt around and brushes the tuft of setae against the ant. Grappling hook-like processes on their tips (see the excellent SEMs in the paper)  snare setae on the ants mouthparts and legs and are shed as the millipede moves away. When the befouled ant attempts to clean itself the jagged-edged bristles become entangled and an elaborate snare begins to envelop the ant’s legs and mouthparts, often resulting in the eventual death of the ant (at least in the lab).

The whorls of setae on the body lack the grappling hook ends, but easily fall off and may provide a similar, last ditch defence against being grabbed by a predator and allow the polyxenid a chance to bring its death brush to bear. Polyxenid fossils are only known from the late Cretaceous and Polyxenus from the Eocene (Nguyen Duy-Jacquemin & Azar 2004), so this behaviour may have evolved in response to ants, but millipedes seem to have originated by at least the mid Ordovician and the Polydesmida are either the sister group to all other millipedes or, at the latest, originated in the Carboniferous (Wilson 2006), so this defence may be more than just a myrmicide. Also, not all ants let polyxenids entangle them.

Neotropical ants of the genus Thaumatomyrmex (they feign death when disturbed) hunt the polyxenids abundant in leaf litter (Brandão et al. 1991). A polyxenid is seized by the ant’s antennae, snapped by the wicked-looking mandibles, and then stung and carried back to the nest. In the nest the paralyzed polyxenid is turned belly up and stripped of its setae using the fore tarsi which have “small but stout setae” (perhaps too stout to be engaged by the grappling hooks) and the mandibles. This can take 20 minutes, interrupted by bouts of grooming, so it seems the polyxenid setae may still be fighting back. Brandão et al. thought the setae must have a noxious chemical – this being the normal millipede defence – but Eisner & Deyrup have shown that the morphology of the setae themselves can be fatal and no chemical defence need be invoked. The hunter then eats most of the polyxenid and feeds the remains to a larva.

Polyxenus Latreille, 1803, seems to have given its name to this strange and ancient group of millipedes, but I’m not sure where ‘Polyxenus’ (‘very or many strange’ or ‘very hospitable’ are two possible translations) comes from. Polyxena, the daughter of King Priam of Troy, who came to such a gruesome end on the pyre of Achilles, would seem to be one possible answer, but ‘Polyxenus’ is not feminine and the animal is not hospitable and anything but a willing victim. Polyxenidas was a renegade Rhodian admiral known mainly for treachery and losing naval battles to the Romans, but there is nothing marine or ship-like about these dry-adapted animals (although they may be found on beaches). I think it must be the many strange setae that inspired Latreille and that seems very fitting.

Short Bibliography

Brandão, C. R. F., Diniz, J. L. M. & Tomotake, E. M. (1991) Thaumatomyrmex strips millipedes for prey: a novel predatory behaviour in ants, and the first case of sympatry in the genus (Hymenoptera: Formicidae). Insectes Sociaux 38: 335-344.

Eisner, T., M. Eisner and M. Deyrup. 1996. Millipede defense: use of detachable bristles to entangle ants. Proceedings of the National Academy of Sciences 93: 10848–10851.

http://www.pnas.org/content/93/20/10848.full.pdf

Müller CHG, Sombke A & Rosenberg 2007. The fine structure of the eyes of some bristly millipedes (Penicillata, Diplopoda): Additional support for the homology of mandibulate ommatidia. J. Arthropod Structure & Development 36: 463-476

Nguyen Duy-Jacquemin M. & Azar D. 2004. — The oldest records of Polyxenida (Myriapoda, Diplopoda): new discoveries from the Cretaceous ambers of Lebanon and France. Geodiversitas 26 (4) : 631-641.

Nguyen Duy-Jacquemin, M., and J.-J. Geoffroy. 2003. A revised comprehensive checklist, relational database, and taxonomic system of reference for the bristly millipedes of the world (Diplopoda, Polyxenida). African Invertebrates. 44(1):89-101.

Whitaker JO Jr & Ruckdeschel C. 2010. Spanish Moss, the Unfinished Chigger Story. Southeastern Naturalist 9:85-94.

Wilson HM. 2006. Juliformian millipedes from the Lower Devonian of Euramerica: implications for the timing of millipede cladogenesis in the Paleozoic. J. Paleont. 80: 638–649

Wright JC & Westh P. 2006. Water vapour absorption in the penicillate millipede Polyxenus lagurus (Diplopoda: Penicillata: Polyxenida): microcalorimetric analysis of uptake kinetics. The Journal of Experimental Biology 209: 2486-2494.

A long and more normal millipede:

A more traditional Australian millipede

3rd Electron Raster Challenge – Hint

Here's a hint - diagnostic character is visible

Hmm, I’m surprised no one has guessed this one. I wonder if everyone is busy shoveling snow? I would be myself, except a neighbour did my driveway for me, so we can do our food shopping this morning with no hassle. Since my neighbour was so kind, I’ll pass it along as a hint: a diagnostic character for the class this animal belongs to is visible in the new image (and the orientation is more realistic).

 

Macromite’s 3rd Electron Raster Challenge

Now that I’m back in the groove, more or less, I suppose I should offer up a new Electron Raster Challenge. This is an easy one, these things are everywhere, so for full credit, how about naming three of the structures visible too. In case anyone needs a hint or two, well, they are unusual  among their close relatives for two reasons that I can think of:  (1) they have a physiological ability that allows them to live in Spanish Moss and (2) they use their morphology to confound ants. Extra credit for explaining these two feats.

Biennial Bits & Pieces: Bat Mites

A patch of soft tick cuticle

The data is in and my hypothesis that putting up bits and pieces of mites would increase my frequency of posting is falsified (sorry Kaitlin). In fact, in spite of the interesting discussion the last posting generated, and my intent to propose a General Theory of Oribatid Mite Leg Well Ornamentation (sorry Dave, could not resist the pun), I have let other duties drag me away from macromite. Now all is snow and ice and bare trees, though, and so sitting at the computer on a Sunday morning no longer seems like chore. So how about a bit of a bat mite – or tick if you prefer?

Ventral view of a soft tick nymph Carios sp.

As a general rule, mammals are an okay habitat for mites: primates, even lemurs, carnivores, even and odd toed ungulates, sloths, armadillos, shrews, hares, rabbits, rodents, and marsupials all sport specialized mite parasites. Even duck-billed platypuses and echidnas have to deal with ticks and chiggers. Whales, dolphins, and porpoises are an exception – as far as I know they seem to have left their mites behind when they moved into the ocean – but other marine mammals such as sea lions, elephant seals, fur seals, and walruses are hosts of nasal mites in the family Halarachnidae. It is the bats, however, that seem intent on outdoing all other mammals in terms of the diversity and creepiness of their acarine inhabitants with at least 18 families and over 1000 species known. Several of these families are restricted to bats and there is even a genus of soft ticks, Antricola, that are exclusively parasitic on bats (well, there was a genus, recent research submerges Antricola into Carios).

Say hi to a bat mite and be glad you are a primate

Of course, bats are ONE OF the most successful group of mammals, with about 1,100 species known (~20% of all mammals), so this is only about one species of mite per species of bat. In comparison, only about 3,000 species of bird mites are known (from ~10,000 species of birds). So, either a higher proportion of bat mite species have been found or bats are great hosts. A simple explanation for the success of mites on bats is that bats like to hang out close together in protected spots and tend to be philopatric – they like to return to the same spot. Presumably these behaviours help bats to survive, but they also make life easy for parasites: lots of bats to eat and if they get bored with one bat, it is relatively simple to move to another. One of my favourite families of bat mites is the Spinturnicidae. These mites spend their lives on the wing membranes of bats and suck their blood and, well, they are strange and rather creepy looking – all fat legs and long hairs, especially in males where the body behind the legs is highly reduced (somewhat as in sea spiders).

Venter of male spinturnicid bat mite: X-leg arrangement is a good character

Spinturnicids have been the subject of a fair amount of scientific study and some of the most interesting has been published by a Swiss researcher at the University of Lausanne, Nadia Bruyndonckx, and her colleagues (from around the world). One of their recent papers (see below) tested for co-speciation between European bats and spinturnicid mites. They found some evidence for co-speciation, but also for failure to speciate and for host switching. So, like much of evolutionary history, that of bat mites is complicated. That may be especially true in North America. Those behaviours that have favoured mites in the past probably facilitate the spread of whatever agent causes white nose syndrome: bat mites here may be facing a lonely future.

For more on bat mites see:

Bruyndonckx, N., Dubey, S., Ruedi, M., Christe, P. (2009): Molecular cophylogenetic relationships between European bats and their ectoparasitic mites (Acari, Spinturnicidae) Molecular Phylogenetics and Evolution 51: 227–237

Krantz, G.W. & Walter, D.E. (eds.). (2009): A Manual of Acarology 3^rd Edition. Texas Tech University Press, Lubbock, 807 pages

Walter, D.E. & Proctor, H.C. (1999): Mites: Ecology, Evolution and Behaviour. University of NSW Press, Sydney and CABI, Wallingford. 322 pp.

Weekly Bits & Pieces: Oribatulid Leg-well Ornaments

A Dystopian Future Earth or on what a Zygoribatula rests its leg?

Although my postings have been infrequent, I think I’ve more or less reached my original goal of filling the mitey void left by the demise of the late UQ Mite Image Gallery with a set of false-coloured mite SEMs of equal or better quality and exceeded the original gallery in terms of scientific content (not to mention navel-gazing). Some day I will figure our how to use WordPress properly and have all of the images easily available for perusal without having to backtrack through all the omphaloskepsis, but until then I think I need to pay attention to Kaitlin’s point and try to post more frequently.

Since full-mite coloured SEMs take an extraordinary amount of time to compose, and I am flat-out fulfilling all of my other commitments, I’ve decided to start posting a few interesting bits & pieces of mites. I’m not sure that I even need to or should spend any time trying to tart these up with colour, because I find them extremely interesting just as they are. Well, I will let you all judge for yourselves:

Cerotegument in leg I well of Zygoribatula sp. 2

These images were grabbed at 18,000 magnifications and represent ‘ornamentation’ of what is called the cerotegument: a secretion alleged to be composed of waxes and proteins that coats the outer cuticle of oribatid mites. I thought that this ornamentation might be a useful taxonomic character in a messy genus, Zygoribatula, but other genera (Oribatula, Dometorina) in the family (Oribatulidae) have similar ornamentation.

Oh well, it is still interesting, but what is its function? The rest of the surface of these mites is covered with a more or less smooth and thin coating of cerotegument – presumably keeping water in the mite and other things out . But why these pedestals in the grooves where legs I are retracted when the mites are annoyed? (NB – much of the surface structure of oribatid mites can be explained as protection from predators grabbing hold of limbs.)

When I first saw this pattern, it reminded me of pictures in magazines of the pulp era showing cities of the future with interconnecting anti-gravity roadways: better yet, cities on some hive-planet of insectoid aliens (I prefer to think of our future in a more low density, back to nature, gardens in the sky kind of way). However, I am open to more realistic suggestions. I assume the flattened tops (maximum diameter about one half of a millionth of a millimeter) support the withdrawn leg and form an air chamber under the leg, but why?