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Rock lichen mite, dorsal, slide mounted

Rock lichen mite, dorsal, slide mounted
Sandia Mountains, Bernalillo County, New Mexico, USA
March 31, 2018
Size: 0.51 mm
Download high resolution image here.

I collected the linked specimens at 35°05'56.8"N 106°28'35.7"W, 6351 ft, Tijeras 7.5’ quadrangle, on Embudo Trl (193) in the Sandia Mountains, Bernalillo Co, NM. The mites are from a population on a large granite boulder with lichens. They scurried about rapidly in full sun, making them just visible to the naked eye despite their small size. My nephew Zach Sweet spotted them while sitting on the boulder in late March. I collected several over the next few weeks with an aspirator.

Each image in the linked set is of a different specimen from the same population preserved and mounted to best show a different set of features and/or perspective. The slide mounted specimens are immersed in index matching fluid. The mite's integument and setae are transparent and apparently have a similar index of refraction to the fluid, rendering them largely invisible. The fluid preserves the shape of the (soft-bodied) mite in life, and reveals white clumps of granules at least as small as the resolution limit (~0.2 µm) and green ~1 µm diameter spheroidal inclusions within the body. Oribatid mites are often associated with lichens(1) and camouflaged with debris, so Oribatida was my first guess for ID. However, the debris is attached to the mite's exterior in that order. The rest of the specimens are HDMS(2) treated and imaged in air. This renders the integument opaque, and greatly increases the contrast of external features such as setae and plate boundaries to aid in identification. The primary purpose of this treatement is to reduce shrivel upon desiccation, but some wrinkling of the dorsal surface still occured.

This mite may be a nonconstitutive mixotroph, receiving energy from both consumed food and photosynthesis from ingested algae chloroplasts (presumably taken from the lichen). The green inclusions are too small for whole algae cells, which are generally several µm in diameter, but about the right size for the chloroplasts therein. It is possible that the white granules forming large clusters are glycogen alpha particles. Algae chloroplasts produce glucose by photosynthesis, which both fungi and animals store as glycogen. Glycogen is initially synthesized as beta particles (polymerized glucose strands held together by a central protein) in the 15-40 nm diameter range (too small to resolve here). However, such particles may congregate into larger grains (alpha particles) in the size range observed. The transparent integument and habit of running about in full sun seem well adapted for photosynthesis, too.

Reportedly, mixotrophs are everywhere and may control the fate of the planet. Nonconstitutive ones (meaning photosynthesis is not an innate ability) can maintain whole colonies of live algae symbiotically, or merely harvest their cholorplasts, as our mite presumably does. They are mostly single-celled creatures or simple animals, but incude a mollusk and even a vertebrate in their ranks. I can find no report of an arthropod mixotroph, however, making this a potentially significant discovery, if confirmed.

This specimen is slide mounted in Cargille immersion oil type OVH and 1.18-1.42 NA darkfield illuminated. The image is from a Helicon Focus processed stack of 184 images with a 0.79 µm step taken with a Nikon CFI Plan 50×/0.9 ∞/- mm oil microscope objective + Nikon 135 mm F2.8 AIS telephoto lens + Nikon D810 camera (magnification 33.75×; technique described here).

Images of this individual: tag all
Rock lichen mite, dorsal, slide mounted Rock lichen mite, ventral, slide mounted Rock lichen mite, dorsal, HMDS treated Rock lichen mite, ventral, HMDS treated Rock lichen mite, latreral, HMDS treated Rock lichen mite habitat

Moved from Mites and Ticks.

Dave Walker suggested this as one possibility. There is one other Adamystid on bugguide. Like mine, it has the appearance of particulate inclusions for camouflage collected from its environment (assuming that is what the pink background is). I downloaded Fuangarworn 2010(1) and Ueckermann 1989(2). Can you tell what sex my ventrally imaged specimens are? I have about 50 and can image a female if necessary for the keys to try to identify it further.

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