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.

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?