Project Snodgrass: Trichogen cells

Figure 1. CLSM volume rendered animated GIF file of the epidermis of white eyed pupa of Bombus impatiens. trichogene unbranched=trichogen cells giving rise large, posteriorly oriented, branched setae (at this point setae are fairly developed with developing, distally blunt branches); trichogen unbranched: trichogen cells give rise small, erect and unbranched setae (only present as small tubercles on the surface of the epidermis).

Figure 1. CLSM volume rendered animated GIF file of the epidermis of white eyed pupa of Bombus impatiens. Trichogen long=trichogen cells giving rise large, posteriorly oriented, branched setae (at this point setae are fairly well formed with developing, distally blunt branches); trichogen short: trichogen cells that give rise small, more erect and unbranched setae (only present as small tubercles on the surface of the epidermis in this stage). Image by István Mikó (CC BY 2.0).

A month ago I have posted a short piece about developing trichogen cells that resemble spermatozoa. It is always good to see things from different perspectives, so today I post a CLSM media file showing the developing trichogen cells (see Smart Box below) on the third metasomal sternite of the white eyed pupa of Bombus impatiens.

Box 1. The fate of the trichogen cell
The mature bristle (seta) is a hollow structure in Drosophila that corresponds to a single sensory neuron (NEURON) surrounded by a thecogen cell (SHEATH (GLIAL) CELL), a trichogen cell (producer of the hollow bristle, BRISTLE CELL) and a tormogen cell (producer of the socket membrane, a conjunctiva trough which the bristle is flexibly connected to the rest of the cuticle SOCKET CELL).

Drosophila bristle development (Figure from Hung et al. 2010. Mical links semaphorins to F-actin disassembly. Nature. doi:10.1038/nature08724)

At the early stage of the development (white eyed pupal stadium), the trichogen cell grows a finger-like projection (by reorganization of actin and microtubule cytoskeleton) and extract cuticle around this projection (chitinous surface).

Developmental stages of bristle related cells in Calliphora vicina from Keil (1978).

In later developmental stages (when the cuticle is able to support the developing bristle) the cell projection is redrawn, leaving an empty lumen surrounded by the  hardened bristle cuticle (chitinous surface).

The general morphology of the mesonotal bristle in the bow fly (Calliphora vicina, Diptera: Calliphoridae; see figure at left) is different from this scheme (Keil 1978). As in Drosophila, the calliphorid mesonotal trichogen cell gives rise a cell projection and starts to develop the surrounding cuticle (Figure 2 a). Unlike in Drosophila, the cell not only redraws the projection, but entirely disappears during later developmental stages (Figures 2b, c). The tormogen cell, on the other hand, enlarges and eventually surrounds the neuron and gives rise the receptor lymph cavities. In Calliphora the tormogen cell has taken over the “spatial” function of the trichogen cell and represents the main cell type in adult bristles.

There are two bristle types on the third sternite of the bumble bee: Long and brownish (melanized) bristle (branched, long seta; unbranched, long seta: Fig. 3) corresponding to larger trichogen cells (trichogen long: Fig. 1.) and shorter, transparent (not melanized) bristle (unbranched, short seta: Fig. 3), corresponding to smaller trichogens (trichogen short: Fig. 1). Beside the seta-producing trichogen cells, numerous other, smaller epidermal cells are visible on Fig. 1.

Bright field image of the third abdominal sternite of Bombus impatiens (Hymenoptera: Apoidea).

Figure 2. Bright field image of the third abdominal sternite of matured Bombus impatiens adult (Hymenoptera: Apoidea). Image by István Mikó (CC BY 2.0).

The long and more melanized setae are branched in the posterior half and unbranched in the anterior half of the hairy part of the sternite.

Bright field image of the third abdominal sternite of Bombus impatient (Hymenoptera: Apoidea).

Figure 3. Bright field image of the third metasomal sternite of matured Bombus impatiens adult (Hymenoptera: Apoidea). Image by István Mikó (CC BY 2.0).

We have gathered another CLSM image that reveals that the long, melanized setae in adults correspond to one large and a few smaller epidermal cells.

CLSM animated GIF of the cross section of the second sternite of Bombus impatiens.

Figure 4. CLSM animated GIF of the cross section of the second sternite of matured Bombus impatiens adult. Image by István Mikó (CC BY 2.0)

Normally I would assume that the large cell is the trichogen cell, while one of the smaller cells (perhaps the drop-like one that is connected to the setal base) is the tormogen cell, but after reading Keil 1978 (and knowing that cell fate is different even within Diptera), I would not do this generalization without a thorough examination of the developing bumble bee integument.

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Friday Night Lice – week 5 answer

Proechinophthirus zumpti Werneck, 1955 (Echinophthiriidae), a parasite of Brown Fur Seals, Arctocephalus pusillus (Otariidae). Specimen PSUC_FEM 10005347. Photo by Andy Deans (CC BY 2.0).

Last week’s louse species was Proechinophthirus zumpti Werneck, 1955 (Echinophthiriidae), a parasite of Brown Fur Seals, Arctocephalus pusillus (Schreber, 1775) (Otariidae). P. zumpti has a lot of variation in its setae (hair-like structures) on its body. The short, thick ones near the mouth look almost like hooks. I can imagine this louse is difficult to dislodge, which is good if your host is taking you on deep dives in the ocean!

These specimens were collected from A. pusillus seals (below) in the Great White Shark-infested waters off of Cape Town, South Africa. The specimens in these images are PSUC_FEM 10005362 (female), PSUC_FEM 10005347 (male), PSUC_FEM 10005368 (nymph). Here’s a photo of the host species, mid-dive:

Brown Fur Seal swimming off the coast of Cape Town, South Africa, where last week’s lice were collected. Photo by Tim Sheerman-Chase (CC BY 2.0)

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Friday Night Lice – week 5

Our collection of this week’s Friday Night Lice species includes what is probably the cutest, stubbiest louse we’ve ever seen. Behold:

Is this the cutest louse in our collection? Probably. This specimen is a nymph of this week’s Friday Night Lice species. What is its host? Probably some mammal that is also very cute. Photo by Andy Deans (CC BY 2.0).

It’s an immature specimen of undetermined sex. This slide is another example of the strength of our Anoplura collection—we have nymphal specimens for most species. And here is an adult female specimen:

Adult female louse. What is its host mammal? Photo by Andy Deans (CC BY 2.0)

Anything strike you about its anatomy? Any structures on its head or anywhere else that might clue you into the kind of environment provided by its host? I admit that it’s not an obvious one! Another hint with minimal information: the host mammal is famous, in part, for its interactions with a top—and I mean TOP— predator. Feel free to offer your guess as a comment below!

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Korean cave specimens and the mysteries of old ethanol

Like most museums, there is no shortage of curation projects at the Frost. I’ve described some of the larger ones on our list—rehouse the Beatty Odonata collection, rebuild the teaching collection, renovate the public space—but today was partially dedicated to saving some Korean insects I found in an old box.

Insects collected from cave sites in Korea, housed in substandard conditions. Photo by Andy Deans (CC BY 2.0).

The collecting event labels point to various cave sites in Korea (see PDF of the Korean cave sites at ScholarSphere), where someone collected these insects in the 1960s. Most of them are camel crickets (Orthoptera: Rhaphidophoridae), but many are flies (Diptera) and a few are diplurans (Diplura: Campodeidae and Japygidae). The latter is what grabbed my attention, as not only do we have a relatively small dipluran collection at the Frost, but these specimens were also quite large for Diplura. I think these specimens have been sitting in the same liquid for 50+ years, and judging by its color and the level of preservative it’s time to rehouse them.

Low level of preservative, which also happens to be quite yellow. Not a good environment for this japygid. Also, the stoppers are corroded and seem to have lost their integrity. Photo by Andy Deans (CC BY 2.0).

It’s also an opportunity to dream about digitization protocols for fluid-preserved specimens. This is just a quick attempt at a mock-up, but perhaps we will end up imaging all of our vials like this:

Mock-up of an approach to image fluid preserved insect specimens. Photo by Andy Deans (CC BY 2.0).

It took very little time to set up and was ultra low tech. One can also clearly read the labels and identifier and get the gist of the specimen(s). Others have found ways to industrialize the wet specimen digitization process, of course, or at least produce much higher quality images. See the presentations at iDigBio’s Fluid-preserved Invertebrate Wiki, for starters. We’ll have to find the right balance between efficiency and quality for our material, as well as a workflow that incorporates a storage upgrade. Most of our vials and jars need to be replaced or at least have their caps replaced.

Another issue regarding old preservative was raised by one of my colleagues: Just what’s in that stuff?

Waste ethanol = old preservative. Photo by Andy Deans (CC BY 2.0).

Some of these old jars, with especially rotten specimens in them, smell highly phenolic—repulsive enough to make at least one of us wonder whether extraordinary measures should be taken when handling the material. (Of course we wear gloves and other personal protective equipment when we handle fluid-preserved specimens, and we dispose of all liquids through Penn State’s Environmental Health and Safety system.) I’d love to know what really comprises the variously yellowish, orangish, brownish, and even blackish (especially for old, large millipedes!) liquids we find in these old containers. My quick sifting of the literature yielded many articles about fluid-preserved collections, but all of them limited their chemical analysis to percent ethanol, percent formalin, and/or pH. And the context of each article was specimen health, rather than curator health. Anyway, this question sits on our shelf as a potentially useful and enlightening undergraduate project. Anyone interested?

Back to the Korean caves. It looks like most of these insects came from karst caves in central Korea (ROK), though a few are from “lava caves”. Most of these are closed to the public, and insects collected there in the mid-1960s are definitely worth preserving.

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Friday Night Lice – week 4 answer

Turkish Spiny Mice (Acomys cilicus), a related species of the host for last week’s louse species. Photo by Ettore Balocchi (CC BY 2.0).

Last week we posted images of a spiny louse and asked for guesses about its mammal host. Well, the louse in the photograph, specimen PSUC_FEM 1005427-2, was collected in Mozambique, off of a Southern African Spiny Mouse (Rodentia: Muridae: Acomys spinosissimus). These mice are notorious for their autotomy abilities. That is, they’re capable of shedding body parts if they get attacked by a predator. Acomys spinosissimus can jettison its tail (see photo above, the far left individual), just like many lizards, but other species of Acomys can shed huge areas of their skin (see high profile but paywalled article by Seifert et al. 2012). Ouch! The louse, by the way, is Polyplax acomydis Kim & Emerson, 1970 (Anoplura: Polyplacidae).

Of course many insects and their relatives use this kind of defense—Tipulidae is a famous example—including close relatives of sucking lice, the non-parasitic bark lice (e.g., Psocidae). Many of them are capable of shedding their antennae. What a crazy coincidence!

Mystery louse is a mystery no longer. Meet Polyplax acomydis Kim & Emerson, 1970. Its host is the Southern African Spiny Mouse (Rodentia: Muridae: Acomys spinosissimus. Click to enlarge! Photo by Andy Deans (CC BY 2.0).

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