Madagascar part XX

[pbertner]

1) Madagascar day gecko (Phelsuma lineata) with prey:



2) Praying mantis:



3) Fulgorid hopper nymph (Belbina sp.):



4) Spiny leaf beetle black and white:



5) Carpenter ant (Camponotus sp.):



6) Microhylid frog (Platypelis tuberifera):



7)


8. Stick insect portrait:



9) Froglet camouflaged as bird dung (Boophis sp.):



10) Mating big headed flies (Pipunculidae):



Thanks for looking and commenting,
Paul

[JH]

Interesting and very nice!
Regards Jörgen

[rjlittlefield]

Nicely shot, as always.

Very obvious difference in the eyes of the male and female at 10) Mating big headed flies (Pipunculidae).

Any idea what difference in behavior might explain that? The ones on the lower beast (female?) look like they're optimized for high resolution looking straight ahead, maybe better for some sort of pursuit?

--Rik

[Ichthyophthirius]

Beatiful pictures!

Very obvious difference in the eyes of the male and female at 10) Mating big headed flies (Pipunculidae).

Any idea what difference in behavior might explain that? The ones on the lower beast (female?) look like they're optimized for high resolution looking straight ahead, maybe better for some sort of pursuit?

The larger ommatids in the front of the female's eyes usually mean lower resolution and higher light-gathering ability (night-flying).

I couldn't find information about the purpose. May it's got something to do with the female's search for host to lay its eggs?

[rjlittlefield]

The larger ommatids in the front of the female's eyes usually mean lower resolution

I would be interested to see a reference on that. The ones I have on hand say exactly the opposite.

For example, R.F. Chapman, "The Insects / Structure and Function", 4th edition, page 590:

The form and arrangement of ommatidia differs in different parts of the eye in many, and perhaps all, insects. For example, in the praying mantis, Tenodera, the facet diameter is greatest in the forwardly directed part of the eye, and decreases all round (Fig 22.4). Because the radius of curvature of this same part of the eye is greater (so the surface is flatter) than elsewhere, the angle between the optical axes of adjacent ommatidia (the interommatidial angle) is less than elsewhere and the rhabdoms are longer, but thinner. This area of the eye is functionally equivalent to the vertebrate fovea (see below) and similar regions are known to be present in the eyes of other insect species with a particular need for good resolution.

Michael F. Land, in "Visual Acuity in Insects", page 159 (pdf page 13 of 31):

In general, the only realistic way that a compound eye can achieve resolution much better than a degree is to build in an "acute zone" -- a small region with larger facets and higher acuity (23,38). We shall see that this is a very common strategy.

I notice in this image that the small area with large ommatidia is also flatter, so it seems quite a good match to Chapman's and Land's descriptions.

--Rik

[pbertner]

Thanks Rik, Ichthyophthirius and Jorgen, much appreciated.

Glad you took the initiative on finding that out Rik as I didn't know. Indeed the female's pursuit for a host seems like the most logical explanation. Interesting that the difference is also demarcated in colour too.

[Ichthyophthirius]

Hi Rik,

My understanding was that the highest resolution in insects is associated with the highest density of ommatidia (dragonflies). The chapter by Land (1997) is very interesting; there is obviously a huge body of knowledge about compound eyes.

This is what I was thinking of (p. 171):
"An increase in the detectability of small objects can be achieved either by reducing ?p, so that a small target causes a large change in the signal on the rhabdom that images it, or by increasing the numbers of photons available to the rhabdoms, thereby reducing the noise against which the signal must be detected. Either method requires a larger facet diameter D (Equation 7 and 11). In most known examples increases in facet diameter have evolved to reduce ?p. However, the male blowfly Chrysomyia megalocephala has a “bright zone” rather than an acute zone, where ?p is similar to the rest of the eye, but the photon catch per rhabdomere is enhanced roughly tenfold by an increase in both facet and rhabdomere diameter (81). Perhaps this enables the fly to mate in particularly dim conditions."

So maybe I was wrong.
Larger ommatidia mean fewer pixels and therefore lower resolution.
However, the insect can use the larger ommatidia
a) for larger photon catch (lower resolution but brigher image)
b) reduce the ?p (acceptance angle) of each ommatidium (better quality of each pixel and therefore potentially better image quality overall)

BTW, I found the big-headed flies on the same page:
"Although it is males that generally have acute zones, females of the pipunculid flies in the genus Chalarus, have greatly enlarged frontodorsal ommatidia (27). These flies parasitize leafhoppers, and the ovipositing females must locate these on the undersides of leaves. The males have no equivalent need for keen eyesight."

Kind regards,

Ichty

[rjlittlefield]

Larger ommatidia mean fewer pixels and therefore lower resolution.

Fewer pixels yes, but that means lower resolution only if the visual angle covered remains the same. My understanding is that in these flatter areas with larger ommatidia, the visual angle drops more than the pixel count does, leading to higher resolution in an angular sense.

the highest resolution in insects is associated with the highest density of ommatidia (dragonflies)

Again, we need to be careful about "density". Dragonflies have a high density of ommatidia in the angular sense, but that is spread across a very large eye to give a low density in terms of area. The eyes of fruit flies have much higher density in terms of ommatidia per mm, but much less in terms of ommatidia per radian. Compare the 1 mm wide section of dragonfly eye at http://www.photomacrography.net/forum/v ... hp?t=11271 against the 0.5 mm entire fruit fly eye at http://www.photomacrography.net/forum/v ... php?t=7379.

--Rik

[uczeke]

Hi Paul, hi All -

I love this thread. This image/post finally got me to sign up as a forum member. I've been an occasional visitor for a few years and I know a few forum members. I'm a biologist who works on insect visual system development.

The photo of the Big Headed flies, 10), is really great. I had only seen pictures of males previously and hadn't seen the enlarged facets of the female frontal region. It really does look like a "small motion target detector" or SMTD (as they are referred to in the literature). If similar SMTD regions are found only in one sex it is usually a male-specific feature, sometimes called the "love spot", which is used for detecting and pursuing females. This is something that my lab works on in the common house fly Musca domestica. A female-specific SMTD is really interesting, and presumably yes, as surmised in the thread, it is probably used in detecting hosts for oviposition. Very cool!

Paul, would you mind if I use this image in scientific talks? I would also love to display a print of it in my lab, where I have a range of patterns and shapes of insect eyes on display. Any usage or print would include your name.

[hayath]

What a delightful set, this!

The stick insect portrait and the mating flies stand out for me

[rjlittlefield]

uczeke, welcome aboard!

--Rik

[pbertner]

Hi Uczeke,

So glad that this could be a source of inspiration for you to join the forum, it sounds like you'd be a very welcome addition to the community. Thanks for letting me know, and I'd be happy to let you use the photo for educational purposes.

Cheers,
Paul