Strawberry and friend (snailcase bagworm -- Apterona helix)

[rjlittlefield]

This is, of course, a strawberry. It's fresh from my garden, and very tasty.

But what I find especially interesting here is not the strawberry, but rather the lump of dirt stuck on its stem.

Here's a closer view.



The structure is interesting, but the behavior is even more so.

Yes, I said "behavior". I know, it's a chunk of dirt, but it moves!

Here's a sequence of frames from the stack.



And here's the reason why.







This, my friends, is a Snailcase Bagworm, Apterona helix.

It grows up to be a moth, but a very strange one: no wings, and no males. The individuals are all female; they reproduce parthenogenetically, laying fertile eggs without mating.

I first encountered this beast a couple of decades ago. There's a posting from 2007 at http://www.photomacrography.net/forum/v ... php?t=3982 that has some more images and a lot of discussion and links.

In the intervening time, I have noticed them periodically but apparently I haven't thought very much about them. As evidence of that, when I photographed these I remembered my earlier posting, but I had completely forgotten the fascinating bit of detail about how they reproduce -- which I had not only known then but had commented about. Ah, memory is such a transient thing!

The images on dark plexiglas were illuminated by diffused Janso LED lamps, photographed using Canon T1i and Canon 100mm f/2.8L IS USM macro lens, focus-stepped using AF motor control using CamRanger and an Android tablet, rendered by Zerene Stacker using DMap with manual retouching to fix the ghastly motion blur caused by the subject wiggling.

The others are single shots handheld using Canon MP-E 65 and Canon 580-EX II flash with Opteka diffuser. The subject (a different individual) was crawling around the top and sides of a white glass bowl sitting on a beige countertop.

I hope you find this interesting!

--Rik

[ChrisR]

Fascinating! Great post, Rik

[Pizzazz]

Rik

Hey, you have no time for this kind of fun!!

Very interesting. Will you keep it to let it complete its
transformation?


Mike

[brentbristol]

Very interesting how the simple act of picking a strawberry can lead to a fascinating side trail, well done! In the Phoenix area we have whip tail lizards that only reproduce by parthenogenesis as well. In the case of the whip tails they have double sets of chromosomes that may figure into how they are able to reduce the onset of genetic problems from lack of genetic diversity. I wonder if the snailcase bagworm has a similar genetic feature.

http://www.scientificamerican.com/artic ... l-lizards/

[Chris S.]

Very interesting post, Rik!

I much appreciate when photomacrography is used to tell an informative story, as you've done here. Your post nudged me to search and read about parthenogenesis. My expectation was that the parthenogenetic reproduction of this species would be a recipe for short-term boom, but long-term doom, and wondered if this were the case.

While I've studied asexual reproduction in plants and fungi, and am reasonably aware of it in protists, bacteria, and other "simple" life forms, it's much more mysterious to me in complex species such as moths and lizards. My naive sense is that parthenogenesis is a very efficient short-term strategy for getting a creature's genes to spread widely, but a chancy approach for the long term, where competitors and parasites are evolving, while the parthenogenic clones are not. (After all, the benefit of sexual reproduction over asexual reproduction is that sexual reproduction is a prodigious engine of genetic variation, which gives natural selection many more variants to select among.)

It's easy to understand the benefit to an organism that can reproduce both sexually and asexually. Sexual reproduction rolls the genetic dice, giving an organism a chance to have novel and helpful attributes for natural selection to favor (and also, novel and unhelpful attributes that natural selection will cull). Asexual reproduction gives that organism--if it survives--the best chance for spreading its genes. So an organism that has both sexual and asexual modes of reproduction would seem to have the best of both worlds.

But the species documented here would appear to rely on cloning alone, with greatly curtailed benefit of natural selection. So, upon reading your post, my immediate thought was a question: "How does this species evolve to keep up with its enemies?" After a bit of reading, I surmise that it does not evolve, but is a highly successful (perhaps temporarily so), asexually-reproducing variant of a sexually reproducing species. And in the long term, likely to find itself evolutionarily unsuccessful, when its enemies evolve while it does not.

Can someone more competent than I on the evolutionary biology of parthenogenetic insects confirm or correct my thinking?

Thanks!

--Chris

[rjlittlefield]

Thanks for the feedback -- I'm glad you found this interesting.

Hey, you have no time for this kind of fun!!

I rationalize it in terms of continued development of software and technique. Only a fraction of the time goes against my entertainment budget.

Will you keep it to let it complete its transformation?

Tradeoffs, tradeoffs... On the one hand, spending time to rear out a small wingless gray moth is way down on my list of amusing and productive activities. On the other hand, the fact that I can't find anybody else's pictures of the adult creates sort of an annoying itch. But on the other other hand, the effort is probably doomed because https://pubs.wsu.edu/ItemDetail.aspx?ProductID=13611 notes that "She stays inside the protective enclosure of the bag to lay eggs. These hatch in about 2 weeks, and the newly emerged larvae remain within the case in an inactive state. Larvae stay within the protective female case throughout the winter, and emerge the following spring." Given all that, I'll probably not spend the effort.

In the case of the whip tails they have double sets of chromosomes that may figure into how they are able to reduce the onset of genetic problems from lack of genetic diversity. I wonder if the snailcase bagworm has a similar genetic feature.

I don't know for sure, but a quick scan of the literature suggests that's a distinct possibility.

"Bionomics of Bagworms (Lepidoptera: Psychidae)?", by Marc Rhainds, Donald R. Davis, and Peter W. Price, currently accessible at http://entomology.si.edu/staffpages/Dav ... chidae.pdf, says that

Although rare in Lepidoptera, parthenogenesis has evolved independently in many genera of the Psychidae (46, 61, 65, 72). Studies on the genetics of Dahlica triquetrella Hübner reveal the existence of sexual and parthenogenetic (diploid and tetraploid) races whose distributions closely match recent geological history and biotic changes (97, 98 ).

I assume that tetraploid goes with parthenogenetic, so yeah, double the usual complement.

Reference 72 in that paper might have more information, but I don't have access and would have trouble translating it anyway.

72. Narbel M. 1946. La cytologie de la parthénogénèse chez Apterona helix Sieb. Rev. Suisse Zool. 53:625–81

--Rik

[rjlittlefield]

It's easy to understand the benefit to an organism that can reproduce both sexually and asexually. Sexual reproduction rolls the genetic dice, giving an organism a chance to have novel and helpful attributes for natural selection to favor (and also, novel and unhelpful attributes that natural selection will cull). Asexual reproduction gives that organism--if it survives--the best chance for spreading its genes. So an organism that has both sexual and asexual modes of reproduction would seem to have the best of both worlds.

But the species documented here would appear to rely on cloning alone, with greatly curtailed benefit of natural selection. So, upon reading your post, my immediate thought was a question: "How does this species evolve to keep up with its enemies?" After a bit of reading, I surmise that it does not evolve, but is a highly successful (perhaps temporarily so), asexually-reproducing variant of a sexually reproducing species. And in the long term, likely to find itself evolutionarily unsuccessful, when its enemies evolve while it does not.

Can someone more competent than I on the evolutionary biology of parthenogenetic insects confirm or correct my thinking?

I probably don't have that level of competence, but my take on the situation agrees with yours.

You'll probably be interested in the "Bionomics of Bagworms" paper that I linked in my previous post. As noted in the abstract, "The unusual mating behavior of bagworms, characterized by ... a high proportion of females that do not mate as adults, challenges conventional wisdom regarding the evolution of mating systems."

The snippet that I quoted earlier is followed by one more sentence that is particularly relevant to the issue you raise. I've added it here in boldface.

Although rare in Lepidoptera, parthenogenesis has evolved independently in many genera of the Psychidae (46, 61, 65, 72). Studies on the genetics of Dahlica triquetrella Hübner reveal the existence of sexual and parthenogenetic (diploid and tetraploid) races whose distributions closely match recent geological history and biotic changes (97, 98 ). Facultative parthenogenesis has not been demonstrated for any sexual species.

One way of making some sense of this situation is that some unknown feature of the bagworm genome makes it particularly prone to falling into the trap of using parthenogenesis as the only means of reproduction. That route is very effective for a while, and then it becomes just another dead end. (In fairness, most other routes turn out to be dead ends also.)

For this particular bagworm, Apterona helix, there's another aspect of its ecology that I find quite curious and have no idea how to explain.

As background, I note that it seems this critter will eat almost anything. The list of host plants given by https://pubs.wsu.edu/ItemDetail.aspx?ProductID=13611 includes these:

alfalfa, almond, apple, baby’s breath (Gypsophila), bean, broccoli, cabbage, clover, Douglas-fir, knapweed, marigold, mustard, oat, pea, pear, plantain, ponderosa pine, quackgrass, radish, raspberry, rhubarb, rose, squash, tomato, turnip, vetch, violet

That list is obviously incomplete, since it does not include the strawberries that mine are eating. http://ento.psu.edu/extension/factsheet ... se-bagworm gives a more general summary: "It has an extensive host range, which includes most vegetables, ornamentals, legumes, fruit and other trees, and many species of annual herbs."

Further, the beast lives in an apparently impregnable bag, is parthenogenetic so that only a single individual is needed to start an infestation, and is a European import so that local parasites and disease won't be adapted to it.

You would think, taking all this together, that this thing would be the invader from Hades. But it's not. Despite having occupied my yard for around a decade that I've been noticing, the population has never gotten large enough to be a problem. Barely noticeable, really.

Obviously something is keeping the beast well controlled. I have no idea what that is.

--Rik

[rjlittlefield]

Regarding this bagworm's dietary requirements -- or lack thereof -- I just now noticed the following snippet from https://pubs.wsu.edu/ItemDetail.aspx?ProductID=13611. The list of host plants that I had copied earlier in this thread is the Table 1 that is referenced here.

Hosts
Snailcase bagworms often attach themselves to concrete foundations, presumably to feed on algae and fungi. They also will eat nearly any plant material. Table 1 shows how wide ranging their food preferences can be.

Good grief -- "nearly any plant material", ranging from algae and fungi through quackgrass and ponderosa pine!

Now I'm wondering why I have any foliage left at all.

--Rik

[banania]

Very nice set and an interesting story.

The life of this creature seems somehow devoid of any meaning as there is no evolving or change possible. Not only in the sense of physical evolution but there cannot be any social or cultural evolution either as it is always the same copy that starts from nil, grows, clones itself and dies.

Thanks for posting this strange story and the images of this creature that so challenges (my) understanding. I wonder if she has any goals in her life that she is striving to achieve...

Henri

[Pau]

Very interesting images, insect and evolutive biology discussions!

The life of this creature seems somehow devoid of any meaning as there is no evolving or change possible. Not only in the sense of physical evolution but there cannot be any social or cultural evolution either as it is always the same copy that starts from nil, grows, clones itself and dies.
Thanks for posting this strange story and the images of this creature that so challenges (my) understanding. I wonder if she has any goals in her life that she is striving to achieve...

Some more philosophical follow-up discussion,

- Nature has not any meaning nor goals by itself, the true essence of darwinism and neo darwinism is to understand the living beings just as the products of material interactions with a strong randomness in all processes. The lack of finality is what allows us to understand the evolution in a scientific form by means of processes like mutation, recombination, genetic drift and natural selection and this is why many of us regard Darwin not only as a key scientist but also one of the most important philosophers

- Sex is so important because it provides a very effective genetic recombination method. Few species of eukaryotes lack sex in one or another form. But recombination is only one of the evolutionary processes, the primary and most important source of variation is mutation, and it affects all living forms.
The more widespread and successful forms of life, bacteria and achaea, lack sex (well, often they have some other more exotic recombination processes).
At mid or long term sex devoid species are more prone to extintion but they may have an important succes in some situations and times if they have effective asexual reproduction.

banania,do you like bananas?
They are sterile (who would like a fruit full of big hard seeds?) and are succesful because their artificial asexual propagation due to the symbiotic relationship with man.

(sorry, I know that this is not a photography topic, but is one of my favourite knowledge fields)

[ChrisR]

Is this creature more "meaningless" than a species which consumes its planet's resources far too quickly, and is likely to develop to a point where it invokes its own destruction?

[Carmen]

thank you Rik!

I loved the photo's and accompanying interesting story!

[banania]

Chris, I didn't mean to evaluate the life of this beautiful creature as meaningless. I was thinking more in terms of "how would I feel about my life if I were her". There is meaning in being a part of something evolving, whether it be evolution as a species or passing knowledge to future generations or a belief in a better future.

This cloning thing seems to take all that away.

Henri

[rjlittlefield]

This cloning thing seems to take all that away.

That strikes me as rather too pessimistic. The whole ecosystem evolves simultaneously as a result of innumerable interactions between individuals. The cloned offspring contribute to that process in just the same way that a sexually reproducing population would, with the minor exception that the cloned germline is arguably more likely to terminate in a shorter time. As I said earlier, "In fairness, most other routes turn out to be dead ends also."

Even if my own germline were to come to an end soon, I like to think that somehow or other I've had some lasting effect anyway.

--Rik