Calliphoridae

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Guppy
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Calliphoridae

Post by Guppy »

Hi

Four eyes see more than two and what about five, like in the picture,
or with eight eyes, as in the spiders?
The evolution has gone through the whole thing in its mind
and came to the conclusion:
Two eyes are enough, if the resolution is high enough.

Image
www.focus-stacking.ch/B/05285_00.JPG

Camera: Nikon D810
Lens: MITUTOYO M Plan Apo 20X/0.42 ∞/0 f=200
Tube lens: Nikon ITL200
ISO: 64
Lighting: 4 flashes, YONGNUO YN560III
Diffuser: White writing paper
Shooting file format (RAW/JPG): RAW
Tripod: Reprostand
Family: Calliphoridae
Multishot technique: Stack
Stacking Software / Method: Zerene Stacker / PMax
Imaging scale: 20:1
Number of stack steps: 475
Average stack step size (µm) with Cognisys StackShot: 3

Kurt

Lou Jost
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Re: Calliphoridae

Post by Lou Jost »

Beautiful photo.
The evolution has gone through the whole thing in its mind
and came to the conclusion:
Two eyes are enough, if the resolution is high enough.
Well, evolution had more time to work on the eyes in flies than it did with mammals. We tend to think of ourselves as the pinnacle of evolution, but we are not. If two high-res eyes were the best solution for flies, we might expect that the fly would have prioritised two of its eyes and increased their resolution. For things as small and as fast as flies, I think multiple, highly specialized eyes (including the compound eyes) might be optimal.

The big compound eyes have almost no moving parts so they are going to work practially instantly compared to eyes that have to move around and focus. Further, they constantly cover a much broader angle than just two eyes small enough to fit on a fly's head.

Those compound eyes are marvellous solutions for scanning the whole sky for females, and quickly detecting them, and they are probably pretty good for keeping the fly aware of obstacles in the three-dimensional space around it as it flies.

That said, there may be some developmental constraints in insect anatomy that keep them from finding the high-res two-eye solution. But jumping spiders come pretty close to moving towards the few-eye, hi-res solution. That suggests flies could have done so as well.

Guppy
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Re: Calliphoridae

Post by Guppy »

Hi Lou

Thanks for your thoughts, very interesting!

The eyes of insects are so well adapted to their way of life and environment that they do not die out, absolutely optimal does not have to be.
As long as the food and the opposite sex are perceived, a survival of the species is possible, can also perceive the enemies, then the species is even more successful.
For this it does not necessarily need highly developed eyes.
We are not objective enough.
Humans are ophthalmic animals and therefore judge other animals mainly by their ability to see.
Dogs would judge us by the sense of smell, there we are not perfect,
so we would not be highly developed in the opinion of dogs.
Animals can also have other sensors that we don't know or don't know enough.
For a species to exist, the eyes do not have to be optimal.

Kurt

Lou Jost
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Re: Calliphoridae

Post by Lou Jost »

For a species to exist, the eyes do not have to be optimal.
Yes, you are quite right, nothing has to be optimal.

But within a species, on the average, a successful individual has to be "better than most". It is not enough to be just good enough. There is always competition for mates and resources, and always selection to avoid predators. Eyes are critically important for these purposes in flies. Flies are highly visual species. Just flying fast in complex environments requires highly developed eyes, and flies with better eyes will live longer and find mates faster. Those with better genes will reproduce more.There is always selection pressure for better eyes. Not "optimal", necessarily, but headed in that direction. Fly eyes have been evolving so long that they are probably close to optimal for the tasks that flies need (subject to the developmental constraints I mentioned).

My main point is that a pair of high resolution eyes is really not better than what flies have, if one were a fly.

Guppy
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Re: Calliphoridae

Post by Guppy »

Hi Lou
The evolution is not yet finished.
Some species still have potential to develop further, they become better.
This means that they are not optimal now!
Other species have used up their development potential and will also die out sooner or later without intervention of the human being.
The nature will be better, if the development potential of the human being is used up.
If I were a fly I could fly without kerosene, that would be nice :D
Kurt

Lou Jost
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Re: Calliphoridae

Post by Lou Jost »

This means that they are not optimal now!
Yes yes, as I said, I agree with you about that.

Just saying that a fly's set of eyes are better (for what a fly needs) than two high-resolution eyes.

Troels
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Re: Calliphoridae

Post by Troels »

An interesting discussion showing how difficult it is for us humans to capture the essens of evolution without making it a matter of being at the higher branch of the tree of evolution.

Kurt writes:
"For a species to exist, the eyes do not have to be optimal." and:

"The evolution is not yet finished.
Some species still have potential to develop further, they become better.
This means that they are not optimal now!"

Kurt's wording indicates, that flies are on a lower evoultion step, kind of a failed trend in the struggle for perfect evolution towards something higher, like mammals, not to mention humans. That is the common and very popular way of thinking about evoulution. It is almost impossible for us not to think in terms of intentions, and processes with a direction and a goal. But that is precisely what scientists always must try to avoid.

From a scientific point of view I tend to agree more with Lou:
"We tend to think of ourselves as the pinnacle of evolution, but we are not. If two high-res eyes were the best solution for flies, we might expect that the fly would have prioritised two of its eyes and increased their resolution. For things as small and as fast as flies, I think multiple, highly specialized eyes (including the compound eyes) might be optimal."

Darwins greatest contibution to science was to explain, that there is no general evolutionary trend towards complexity or advances attributes. Evolution has no direction. It just looks that way because we consider ourselves the crown of the process. There is only a search for new niches with less competition and therefore a constant trend towards higher diversity. And this stimulates the creation of complex and advanced features as well as more simple or 'primitive' features. After each mass extinction in the history of earth there have been an explosion of diversity in all directions.

In some ecological niches you need to adapt very complex senses or other advanced anatomical features like spinnerets, brains, feathers or structural colors. In other ecological niches optimal adaptation means reduction of organs (like in parasites), simplification of metabolism or behavoir or reduction in size (bacteria are very successful).

It can not be said often enough: There are no animals or plants surviving till today because they are just 'good enough' but still lacking behind the rest. If rainwworms did not work perfect in their environment, they would have disappeared long ago.

From an evolutionary point of view every living species found on the planet today are perfect and optimally developed and adapted to their actual environment. There are no spots on the earth without severe challenges and without threats of extinction.

If a species disappears it is because the environment changes faster than they are able to adapt, not because they are 'primitive'. And 'environment' of course also includes other organisms (like human beeings). In fact less specialized 'generalist' species can easier adapt to changes than the highly specialized and anatomically very advanced. House Sparrows and Crows flourish in a fast changing world because they are less advanced in behaviour and less specialized in feather shapes than Paradise Birds from New Guinea.

We humans happen to be very effective competitors because our very advanced properties, big brains, multifunctional hands and advanced social communication are extremely flexible and adaptable to almost any environment. They are not too specialized (I hope!).
Troels Holm, biologist (retired), environmentalist, amateur photographer.
Visit my Flickr albums

Lou Jost
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Re: Calliphoridae

Post by Lou Jost »

Maybe just for completeness, I'd like to suggest some refinements that I think Troels would agree with.

1. Evolution rarely produces something that is perfectly optimal, but for traits of high importance for reproductive success, natural selection is always pushing them towards a local optimum. (The global optimum, if there is one, might not be reachable by small steps from a local optimum.) Each local optimum is a moving target, as Troels said; these are changing constantly as climate changes, length of the year gets shorter, and species composition changes.

2. Some traits are deleterious. These include deleterious traits that are necessary consequences of the evolution of other traits that are more important than the deleterious ones. In addition, natural selection does have limits, which depend on the size of a population and the ampunt of time available for evolution. A trait that is only very slightly deleterious cannot be eliminated by natural selection in a reasonable amount of time if a population is very small.

3. Many traits are neutral or nearly so. ("Neutral" here means "having no effect on reproductive success".) Much of the genome is also neutral or nearly so (how much is still a subject of hot debate in spite of what you might have heard one way or the other). Much evolution at the molecular level is neutral or nearly so.

mgausp
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Re: Calliphoridae

Post by mgausp »

Thank you for sharing this image with us. I really like the composition and lighting. And the detail is simply remarkable, I am very impressed!

Your discussion about evolutionary paths and goals is very interesting. I am currently doing a PhD in the evolution of the visual system and agree with Troels and Lou in everything they said. One important point I would like to add, is that vision is energetically very expensive. Having eyes that sample the visual space in high resolution and a cerebral system that constructs a neurological representation of the environment from visual (and other perceptual) cues is a luxury that probably is not too common among animals. For warm-blooded animals, the energy is generally much higher and they can therefore more likely "afford" a sophisticated visual system, but for cold-blooded animals, the return on such an investment is a serious factor that determines their evolutionary fitness. Zebra fish larva are estimated to use 50% on their energy for the visual system. They find prey solely by visual cues (probably mostly in the UV-spectrum, but this is a different story), so this is obviously a worthwhile investment.
I guess what I am trying to say is that any capability is not necessary developing towards higher performance, but towards higher evolutionary fitness of the organism as a whole. Generally, but for vision especially, the tradeoff is often performance vs. energy consumption.

Best,
Michael

Lou Jost
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Re: Calliphoridae

Post by Lou Jost »

Excellent additions, mgausp.

Guppy
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Re: Calliphoridae

Post by Guppy »

Hi Troels

"Kurt's wording indicates, that flies are on a lower evoultion step, kind of a failed trend in the struggle for perfect evolution towards something higher, like mammals, not to mention humans."

I do not!
You have misinterpreted my statements!
The human being is only a newer development.
Also with the development to the modern man (Homo sapiens), there were less successful developments which died out.
There are still newer developments (new species) for example with fishes (Cichlidae) in the lakes in the area of the Great African Rift Valley.

Also according to my opinion the development is not two-dimensional, but develops in all possible and impossible directions, thus successful and also less successful.
The evolution is not intelligent and goes only in successful directions, but there are also developments which turn out to be failures after some time, they are then not developed further. However, they can continue to exist if they are not counterproductive.
The species living today are not all perfect, because the development is still in progress, with successful, less successful and not successful results!

Do you believe that the flagellar motor (flagellum, Vibrio cholerae and V. parahaemolyticus) of bacteria evolved without failures?
Do you believe in a higher intelligence that can be developed only successfully?

Hi Lou. hi Michael
Thank you for your complementary explanations.

Yes, it is a very interesting topic.

Kurt

Troels
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Re: Calliphoridae

Post by Troels »

Beefore I forget i again: A very impressive picture.

Thanks to Michael and Lou for adding valuable details to the topic. My knowledge is on the more general level.

To Kurt:
Sorry if I misinterpreted you. I only tried to understand the meaning of your words. Obviously we use some termes in different ways.

I should perhaps have made it more clear that when I said 'perfect adapted' or 'success' I did not mean, that the eye was optically perfect or more capabel than other animal's eyes. I just ment, that under the actual environmental conditions those eyes were perfectly suited to make the animal survive the challenges while taking the energetic and physiological costs into consideration (as mentioned by Michael).

Success is not only about development.
The so-called 'living fossils' with no apparent changes for millions of years are locked in their niche by the evolutionary pressure. There are also groups of flowers (Orchids) and animals (Erebia butterflies) with fast ongoing evolution apparently creating new species and confusing the taxonomists. Both categories are successes in my book, because they have survived. Even if they disappear next year.

Connected to this: Since evolution has no strategy, no direction and no end goal I find it kind of 'off topic' (almost antropomorphic) to talk about evolutionary 'mistakes'. Humans make mistakes - and some animals. But of course you can use the term in a looser sense if you like, and you also mentioned that it was in hindsight. I would just prefer to call the decline or extinction of a species an evolutionary bad luck. Like the extinction of the non-flying dinosaurs.
Troels Holm, biologist (retired), environmentalist, amateur photographer.
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