Monday, March 31, 2014

The Shepherd's Purse - A Tiny Harbinger of Spring



Winter in my part of Texas is usually a non-event.  We might get a couple of days below freezing here and there, and sometimes some ice or snow, but after a day or two we warm right back up.

Not this year.  It has been much colder than we are used to and seems to have lasted forever, so I was delighted to find this little, often-overlooked wildflower growing in my backyard.  It is one if the first flowers I come across each spring.  Capsella bursa-pastoris - the Shephard's Purse - so called because its triangular seed pods supposedly resemble a type of purse shepherds used to carry.  This is one time that Google failed me because I couldn't find a single image of a shepherd with a purse.



Shepherd's Purse has very tiny flowers, so it can easily be overlooked.  What catches your attention are the triangular-shaped seed pods.  It is taller than most of the weeds in my backyard right now so it is easy to find.  (Sadly, none of my grass has decided to begin growing yet so the weeds are having a field day.)

The individual flowers are so small that one of them looks like it could be pinned to President Lincoln's lapel on a penny.


























By the way, I cut several stems of Shepherd's Purse, stuck them in water and took them to the lab with me.  They look great so if you like very tiny cut flowers, you are in luck.


This image shows the flowers at the top of the stem of Shepherd's Purse.  Plants grow from the tips so the higher up you go on the plant, the younger the structures.  Notice the unopened flower buds in the center.  The opened flowers show several stages of seed development leading to the seed pods on the outside of the photo.













Here is a close-up of the flower buds at the extreme tip of the stem.  Interestingly, the petals breaking through the sepals are purple.  By the time they open, as you will see in the images below, the flower petals are white.  
The flower at the top of this image is younger than the one at the bottom.  On the bottom flower you can already see the swelling. flattened seed pod.







This is a close up of a single flower.  The stigma, part of the female reproductive structure, is in the middle.  On the upper margin of the stigma you can see individual pollen grains.  The four structures surrounding the stigma are the stamen which produce the pollen grains.

A word about flower structure.  The role of a flower is to have sex.  Of course, plants have a hard time going to single bars and getting involved in on-line dating since they are stuck in the ground, so they have to depend upon other organisms or physical forces to spread their pollen around.  To insure that their flowers will get pollinated, flowers tend to make a lot more pollen than they might need to get the job done.

Complete flowers have all of the commonly recognized flower parts - petals, sepals, stamen (the male parts), and pistils or carpels (the female parts).  Not all flowers have all of these parts, however, and are called incomplete flowers.  Lots of trees and grasses have flowers without petals. Petals, of course, attract pollinators like insects.  Insects are very, very good at going from flower to flower taking pollen with them.  The insect has no idea that it is spreading pollen - it is just looking for nectar (sugars) and pollen (protein) to eat.  Plants provide nectar and pollen to attract insects and other pollinators, but not because they love insects.  They do it to have their pollen reliably transferred.  This is not to suggest that plants are planning or thinking about attracting pollinators.  It is a simple case of natural selection - plants that can most effectively attract pollinators are the most successful reproducers, increasing their numbers in the gene pool.

If petals attract pollinators and plants like grasses and trees make flowers  that don't have petals, how do they insure pollination?  They make TONS of pollen which is spread by wind.  If, like me, you have seasonal allergies you are very much aware of grass and tree pollen this time of year.

In this image you can see a close-up of the developing fruit or seed pod.  The yellow circle in the center is the stigma and it is covered with pollen.



Once a flower is pollinated, it no longer has use for the stamen, petals, and sepals, so it cuts off their food supply and they fall off.  In the image above you can see the triangular seed pod and a single petal and stamen.

What I have been calling a seed pod is in reality a fruit.  By definition, a fruit is a structure that contains the seeds.  The fruit is the developed ovary of the plant.

This seed pod has been opened so you can see the seeds inside


A close-up of a single developing seed.  You can clearly see the cells that make up the seed.

Another dissected seed pod revealing the seeds inside.

A single flower.  [44x]


The beautiful thing about scanning electron microscopy is the remarkable depth of field it allows. Instead of having to focus on only a single structure in an image, a much larger area of the specimen can be in focus.  (Of course, we do sacrifice color, but color is overrated at times.)

[88x]
In this image you can see the pistil in the middle of the image with its stigma on top and the ovary below.  The stamen with their pollen encrusted anthers and supporting filaments surround the pistil.  You can also see the bumpy cells that make up the petals in the background. 
[184x]
Stigma to the left, stamen in the center with pollen, and petal to the right.
[131x]
Here is a stigma that is still attached to the seed pod.  The little mouth-like structures on the stigma and on the seed pod are stomata for gas exchange.

[77x]
Seeds inside of the seed pod.

[100x]
Single seed inside of a dissected seed pod.  The little boxes are cells.

[2,300x]
Here are a couple of pollen grains from the Shepherd's Purse.  
What is the difference between a weed and a wildflower?  It is in the eye of the beholder.  Plants that you don't want growing where you don't want them are generally called weeds.  But before you reach down and yank that weed out of your yard, take a second an really look at it.  You may have discovered a wildflower.

All of the images in this blog are covered by a Creative Commons License.  You may pretty much use and modify them anyway you like as long as you credit Eastfield College, Mesquite, TX and don't sell them.

Murry Gans
Microscopy Lab Coordinator
Eastfield College







Tuesday, February 25, 2014

Moth Fly in the Men's Room




We, like most of the country, have had a colder than usual winter.  Of course, I am in Texas, so compared to people repeatedly digging out from under feet of snow I can't complain, but it has been cold enough to keep me out of the field.  No problem though - insects are everywhere - including just down the hallway in the men's room.







I first spotted these little guys many months ago and thought, "Flies in the bathroom.  Maybe someday I will take a look at them."


Collecting in the bathroom is a lot warmer than collecting outside right now, so get ready to meet the moth fly.





This image was taken with my cell phone camera in the bathroom.  The fly is on the tile wall, not in the urinal.  (Even I have some limits as to where I will collect.)  Yes, the legs and shoes reflected off the tile are mine.

Note the white spots on the wing edges and on the legs.  The scientific name for this little guy is Clogmia albipunctata.  I don't know the root of clogmia, but alb is from the Latin albus, which means "white",  and punctus is from the Latin for "spotted."  White spots.
Clogmia albipunctata has lots of common names - moth fly, moth midge, or drain fly to list a few.  This is an image of a living fly inside of a Petri dish.  Note the scale bar - these insects are small.
A ventral view of the moth fly hanging on the upper lid of a Petri dish.  The wings are iridescent.













In this image Clogmia has managed to get itself stuck to the lid of the Petri dish via static electricity.  Not only are these flies small, but they are amazingly hairy which makes them hydrophobic.  According to Borror and DeLong's The Study of Insects, the larvae have hydrofuge hairs - water shedding hairs.  I also think that is the function of the hairs on the adult flies, making it possible for them to enter drains to lay eggs without being wetted and getting stuck due to surface tension and the adhesive properties of water.
In this image Clogmia is standing on the side of the Petri dish looking straight up at the dissecting scope.  Note the plume-like antennae and the white spots on the legs.
The next set of images were made with the flies in 70% isopropyl alcohol.  The alcohol preserves the insects.  Also, filling the Petri dish so that the insect is completely submerged eliminates unwanted glare.  I learned this trick from Dr. Joe Rutledge at Children's Medical Center in Dallas about 30 years ago.

Head-on view showing the plumose antennae and the halteres or vestigial wings of the fly.    
All flies have only two functional wings.  In fact, that is the easiest way to identify an insect as a fly.  It's order name is Diptera.  Di- means "two" and ptera means "wing".  The other two wings are reduced to counterweights called halteres.  Halteres also flap and are thought to help stabilize the insect during flight.  The halteres are visible in the image above as two tan blobs just above the legs and below the tufts of whitish hair on the side of the thorax.

This image is a composite of two images taken with the digital dissecting scope.  One of the most unexpected features of this insect are the plumose antennae.
Small insects can be difficult to work with.  They are easily damaged and the mounts we use for the electron microscope are disproportionately large for the insect.  Below are some images of the mounting I engineered for the moth flies.  These images will also give you some idea of the fly's actual size.

To make sure I can see most of the insect I mounted it on a regular sewing pin.  The pin is held in place with a strip of double-stick copper tape.

How do you attach an insect to a sewing pin?  Super glue.  I often use wood glue but the hydrofuge hairs on the insect repelled the glue since it is water based.  
In this image you can see the size of the moth fly in relation to a penny.

The images below were made with the Hitachi S3400-N Scanning Electron Microscope.

Head and eyes

The head of Clogmia.  [138x]
In this image you can see the ommatidia, the plumose antennae, and the scales on the legs.  Everyone is familiar with the fact that moth and butterfly wings are covered with scales, but until I began imaging insects I never realized the some flies also have scales.  (In a previous blog you can find images of a bee fly, which also has scales. http://tinyurl.com/kd8ntrk)  [95x]
[169x]
Ommatidia of the eye.  [500x]
Ommatidia - approximatley 21 microns across.  [1,390x]

Wings

Wing at 50 x magnification.  The entire wing is only about 2mm from base to tip.
This image shows the hairs on the margin of the wing.  [37x]

Wing surface [130x]

The white spots on the wings are caused by dense patches of hairs.  [160x]

The dense hairs that make up the white patches are flattened scales.  [456x]

Close up of some of the hairs on the wing.  [2,000x]

 Antennae

The structure of the moth fly antennae are complex and wonderful.  

Middle segments of an antenna.  [189x]
Terminal segment of antenna with sensory structures.  [349x]

Connection between antenna segments.  Note the sensory openings.  [901x]

Sensory openings on the terminal segment of an antenna  These opening are between 1 and 2 microns - bacteria sized.
More sensilla on the terminal antenna segment.  [4,000x]

Now for the bad news - Bacteria

The larvae of Clogmia albipunctata grow on the slime inside of bathroom and kitchen drains, at sewage disposal sites, and in garbage cans.  They can serve as mechanical vectors for human diseases. (Ahmen)

In 2012 The Journal of Hospital Infection reported that for the first time Clogmia albipunctata has been found in Germany and is becoming a problem in German hospitals. Forty-five bacterial species were found to be colonizing Clogmia. (Faulde and Spiesberger)

Bacteria on basal segment of antenna.  [750x]

Coccus bacterial and bacillus bacteria (arrows) on hairs of antennae.  [4,000x]
Coccus bacteria on serrated hairs of Clogmia.  [8,500x]

Some of these structures, which may be bacteria, seem to be attached to the serrated hairs by a stalk.  [1,710x]


The arrow indicates a tuft of hair just below the wing.  The tip of the sewing needle is the large object at the bottom of the image.  The head of the insect is to the left of the image.  [40x]

Same tuft of hair.  You can see that some of the hairs got stuck in the super glue I used to mount the insect.  Bacterial are obvious even at this magnification.  [130x]

The tuft hairs are covered in bacteria.  [600x]

At this magnification you can see what appear to be hairs with structures that seem to really hold bacteria.  [2,500x]


Knob-shaped projections are about 500 nm across.  [4,000x]

Coccus bacteria with a diameter of 2 to 3 microns attached to knob-shaped structures on hairs. [2,500x]

Observations, conjecture, and suggestions for future work.

Why would moth flies have what appear to be specialized hairs for holding bacteria?

Could the bacteria be a food source?  I did notice that even though there were lots of bacteria near the base of the antennae, there were none farther out - exactly what I would expect of a fly cleaning its antennae. 

If not a food source, could this be how the adult fly insures that the bacteria its larvae need for food are always on hand? Complex structures are expensive for an organism to make and maintain.  If the organism is going to expend the energy to make a structure it must have a benefit, otherwise that structure would be selected against by natural selection.

Though I am not set up for it in my lab, it would be a great project for someone to culture and identify the bacteria present on our moth flies.

Also, it would be a pretty neat experiment to sample the bacterial  populations present in a drain without infestation of moth flies and then introduce moth flies and repeat the survey.

When I first discovered these little flies I didn't expect to find such an interesting subject.  I ended up with ninety-two finished images that I could have used in this blog.  

A gentle reminder that all images are covered under a Creative Commons license. You MAY copy, reproduce, modify and use any of these images in any way you like just as long as you credit Eastfield College, Mesquite, TX, and don't sell them.

References:  

Ahmen, A.  Insect vectors of pathogens in selected undisposed refuse dumps in Kanduan Town,northern Nigeria.  Science World Journal [serial online]. December 2011;6(4):21-26. Available from: Academic Search Complete, Ipswich, MA. Accessed February 25, 2014.

Borror, D. J., & White, R. E. (1970). The Peterson Field Guide Series: A field guide to insects of America north of Mexico. Boston, MA: Houghton Mifflin. 

Faulde, M., & Spiesberger, M. (2013). Role of the moth fly Clogmia albipunctata (Diptera: Psychodinae) as a mechanical vector of bacterial pathogens in German hospitals. Journal of Hospital Infection83, 51-60. Retrieved from  http://www.sciencedirect.com 

Jaeger, Edmund C. A Source-Book of Biological Names and Terms. Springfield:
Thomas, 1972. Print

Triplehorn, Charles A, Norman F. Johnson, and Donald J. Borror. Borror and Delong's Introduction to the Study of Insects. Belmont, CA: Thompson Brooks/Cole, 2005. Print.