// Twitter Cards // Prexisting Head The Biologist Is In: July 2016

Tuesday, July 26, 2016

Artistry of the Insect Kind

I've been posting a lot about mimicry lately, so I figured I would post about a few interesting insects I've come across that appear to take mimicry to another level. They mimic things in the way an artist would - by painting them on a canvas. Of course, the insects aren't really painting anything. Instead, they're growing the images using some complicated developmental processes.

Goniurellia tridens
Goniurellia tridens is a species of small fly which appears to have ants/spiders/somethings on its wings. The group of flies to which this species belongs have many examples with marked/patterned wings, but usually the patterns are simpler. Generally the flies use their patterned wings in courtship displays, dancing with their wings held to the side (like in this photo) while they shift and flap one wing after the other.

It is easy to imagine them using the patterns on their wings to discourage ants/spiders/etc. from attacking them, but it isn't clear if they do this behavior. It would seem to be far less risky to simply take to the air and fly away when faced with a predator. There are quite a few jumping spiders that would be able to leap and grab them out of the air. (As well, they have an impressive visual system that would let them see the images as ants/spiders/etc. in a way similar to how we do.) If such a spider were to jump at one of the high-contrast  "prey" images instead of the fly itself, the fly might gain time to escape. A jumping spider might also see the patterns as a pair of predatory ants and choose to be elsewhere. I would love to see some video footage of how this fly responds to predators as this would help clarify if any of the above hypotheticals have any basis in reality.

Siamusotima aranea
Or next mimic is the moth, Siamusotima aranea, that appears to have a bunch of spidery legs painted on its wings. This image, again, would be most useful against a predator with acute eyesight like a jumping spider. The photo at right provides some additional evidence. Moths typically rest flat to the surface, with their wings held close. In this image the moth is holding its abdomen raised from the surface and extending its wings, effectively displaying its image in a way not associated with typical moth behavior.

Other moths (like Callimorpha dominula) will actively flash their bright hind-wings to discourage predators (or photographers) who are expressing too much interest, so it is reasonable to interpret the behavior of S. aranea in this photo as being an active display to discourage predation.

Another moth, Macrocilix maia, appears to be a very good mimic of something different - bird poop and flies. The moth even has behavior to back this hypothesis up, often choosing to rest adjacent to real bird poop. Since it rests flat to a surface, like most moths, the image isn't one presented to an predator coming along the surface. Instead the image is presented continuously to the air above, where birds are using their acute color vision to hunt for insects.

It can take some experimentation to determine if an animal is really using its patterns as mimicry. We can make a hypothesis about what their wing patterns are used for and then test the hypothesis using the "natural experiment" of the moths' behavior. If their behavior is consistent with the mimicry hypothesis, then the experiment has a positive result and we can more strongly state their wing patterns are a form of mimicry. In the moth examples above, each species definitely has behavioral traits that align with the mimicry hypothesis.

In the fly example, I haven't been able to find enough information about their behavior to be able to interpret it as a natural experiment. It could be that female flies like male flies with wing-men, so to speak. (This would be consistent with the the use of wing markings in courtship displays seen generally in the group.) It could be that we humans are seeing a pattern in the image that is essentially random with respect to predation. I definitely like the anti-predation model, but without some form of experiment, we really don't have enough information to determine which hypothesis is better aligned with reality.


Tuesday, July 19, 2016

More Crop Mimics

I've previously posted about a form of mimicry in plants (called Vavilovian mimicry) where one [or several] wild species end up mimicking a crop species due to the selection pressures in crop fields. Since then, I've come across a few other species that are useful examples for the topic.

Wheat (top) vs. Darnel (bottom).
[from link]
Darnel (Lolium temulentum) is a  mimic of wheat. It looks almost identical to wheat plants right up until the seed heads form (see at right). The seeds themselves are large and are indistinguishable from those of wheat after threshing. The seeds are also highly poisonous, leading to the common name of "Poison Darnel". When wheat contaminated with sufficient Darnel is milled into flour, the resulting bitter taste reduces its value.

Darnel control efforts have limited success and the plant is found essentially everywhere wheat is grown. Even though the toxic character of this species (when infected) means it will likely never be developed into a primary crop, it is still a nice example of Vavilovian mimicry.

Another common weed in wheat fields is Small Canary Grass (Phalaris minor). It also produces large seeds that would probably get sorted with wheat seeds at the end of the season and its seedlings look very much like those of wheat.

As a general rule, any random grass species is going to be a much better mimic of the grass we call wheat than any other random type of weed would be. Of the five weed mimics of wheat that I've come across (below), all are grasses and three have become major crops in their own right.

Rice crops are often plagued by weedy forms called "Red Rice" due to the red color of their seeds. They are generally less productive than the main cultivated varieties, so farmers try to keep it out of their paddies. Red-Rice happens to be the same species as the cultivated types. It evolved from (or alongside) cultivated rice so it really isn't a case of Vavilovian mimicry, even though it is a useful example in the discussion of crop weed mimics.


Tuesday, July 12, 2016

Ant Mimicry

Ants are often unpalatable to insect-eating birds due to the formic acid present in their abdomens, so they're often avoided in favor of other prey items. Any potential prey item that happens to look like an ant will have a better chance to live another day than one that doesn't. This selective pressure seems to have led many unrelated arthropods to take on body forms (and behavior) that mimic those of ants.

There are a large number of ant mimic spiders, that often look remarkably like the ant species they're associated with. Because they look like the ants, they are free to go about their business hunting the ants without intervention by birds. The ant mimic mantis probably gains the same freedom to hunt near ant colonies, though I haven't read anything specific about its life-style.

Though I have seen ant mimics in real life (spiders and the occasional beetle), I don't have any of my own photos for illustration. Because they mimic the behavior of ants (in addition to the look), they tend not to stay still for my camera. I've never really gotten a good photo of an ant either, for the same reason.

The photos that follow here were found around the web and I have no legal claim to them, though I feel their educational use here should provide me some protection as fair-use under US copyright law.

Macroxiphus sp cricket.
Dulichus inflatus (Hemiptera)
Euderces beetle.
Asian Ant Mantis (Odontomantis planiceps)

Wednesday, July 6, 2016

"Invasive" Squirrels

Range of American Red Squirrel (Tamiasciurus hudsonicus).
Range of Eastern Grey Squirrel (Sciurus carolinensis).
There are two native tree squirrel species in Minnesota. The Eastern Grey Squirrel (Sciurus carolnensis) would be familiar to almost anyone living in the eastern half of the USA, while the American Red Squirrel (Tamiasciurus hudsonicus) would be familiar to many people living in the north-east corner of the country (as well as most of Canada).

I happen to live in the native range of both species. I see them routinely in our yard... especially around the bird-feeder. The Greys climb down from above and snack directly from the feeder, while the Reds seem content with grabbing the seed spilled to the ground by avian visitors.

The Reds are about half the size of the Greys, but are much more feisty. We've watched single Reds aggressively attack single Greys, leading to the inevitable retreat of the larger Grey. The reds are generally more feisty, including in the intensity of their scolding calls when we scare them away from the porch.

The Greys make treetop nests out of leaves and branches. The Reds make homes of old woodpecker nests, burrows, or gaps in human establishments. We had to partially deconstruct a rear porch ceiling to discourage investigations by one Red, but most are content to reside in the piles of old wood just inside the edge of our woods.

What got me thinking about squirrels was a discussion with my wife and a third party. The third party referred to the red squirrels as invasive. Both my wife and I responded that they actually were native to the area. Later I realized that the root of the disagreement likely came down to different definitions of the word "invasive". We were interpreting the word in the context of the red squirrels being native. The third party might have been thinking of the word in the context of the red squirrels invading human structures. I don't know that this was their meaning and I don't expect to bring up the subject again with them, but this realization helps reinforce the need to be clear on what are meant even by terms in common use. (I previously posted a more extended conversation about the meanings of "diversity" in biological contexts.)

If you find someone saying something that at first strikes you as absurd, it may be because they're using words differently than you are. Don't simply discount them as being incoherent. Try to determine what they mean, not just what they say. Once you've gotten through the barrier caused by sharing the same language, their experience may help expand yours.