https://www.researchgate.net/publication/329638966_Signal_or_cue_the_role_of_structural_colours_in_flower_pollination

You can see the site of European pigments

Best regards

Klaus:

Thought provoking question - Colors produced by ultrastructure and not by pigments is not totally understood, but has something to do with pollination and other unknown factors: Kindly see this link as well:

Article BOTANICAL BRIEFING Structural colour and iridescence in plan...

Best

Syed

I would like to add further, we have noted structural chromatic variants are different functionally as well. We have noted that pink variants in Teak and Tamarind populations have longer floral life (at least 30-40%), the extra floral nectaries are unique. This probably increases their male functions as they are open for longer duration. Sure they cascade pollination dynamics. Needs to be comprehended.

Dear Prof. Lunau,

These are some very interesting points that need much study!! Especially the last two questions that ask for teasing apart: i) effect of ambient illumination in shaping floral structure from other known genetic patterning in flower structures, and ii) signalling in structural colours from pigment colours.

There are certain doubts that come in my mind: a) How can we (if we could) differentiate, and tell morphologically that a particular flower type will display structural colour patterns (like iridescence)?

b) In terms of the pollinators, is it not going to be just the difference in whether the sensory perception is able to differentiate it from the non-structural display type? --- i.e. I am not sure if you mean that structural display such as iridescence would lead to some characteristic sensory signal?

Regards,

Eapsa

Dear Eapsa,

the regularity of ridges and its dimension will clearly tell you whether a flower is iridescent or not. Gloss arises from very flat surfaces; we use a simple glossmeter to quantify gloss; alternatively you may use microscopy or SEM or your eye.

These structural colours differ from pigment colours in that they change with the viewing angle. It is a matter of discussion whether changing colour upon approach will improve the ability to detect the flower by a flower vsitor or will impede discrimination due to the changing colour signal.

Klaus

Dear Prof. Lunau,

Thank you for the clarification!! It seems all the more interesting now in terms of the pollinator's reaction to changing colour signal!!

We need experimental lab/field studies to see how bees respond to these changes!

Furthermore, this makes me wonder: How these ridges develop in corolla of flowers?

[I know from my personal observations of SEM in Ruellia sp. (its corolla has wavy tubes with ridges and furrows; BUT I have no information about iridescence!) that the abaxial surface (the surface exposed to pollinator) seems to have more wax deposition in regions of furrows compared to the ridges. More morphological developmental studies would help understand such structural forms.]

Regards.

Eapsa

Klaus Lunau very interesting topic.

I have one question, are these variations in colors similar to those that we observe in butterfly wings or hummingbird feathers?

If the answer is yes, perhaps the pollinators and floral visitors are adapted to see those fine variations in the color changes of the flowers (more in those specialized pollinators).

Regards

Dear Eapsa,

yes it is indeed challenging to find the response of a natural flower visitor to a structurally coloured flower in the fileld.

And Christian, you are right, many butterfly wings and hummingbird feathers show a similar phenomenon.

Coloured flower & they attraction for some of pollinator - yes,

but it is not trou for all !!!

Best regards

Dear Marpha,

it is even worse: The is no evidence from the field (rather than from the laboratory) that any pollinator responds to a structural colour.

Best wishes,

Klaus

Dear Prof. Lunau,

that is very interesting topic!

Structural colours are very often displayed by flower-visiting insects (e.g. iridescence in wings of butterflies as mentioned above or many bees and flower-visiting flies such as Calliphoridae exhibit metallic shiny colour). Is it known if some pollinators are able to use these signals to recognize other insect? If so, maybe, plants could use glossing or iridescent colours in order to imitate the signals that pollinators use to perceive other insect.

I guess, for example in Ophrys, this could be the case. But I have no idea if something similar could happen in some "normal" flowers as well.

Best wishes,

Jiří

Dear Jiří ,

you are right. If mimicry of insects is involved we understand glossy patches on flowers. In Ophrys speculum it is the bluish and glossy wong of a female scoliid wasp that is mimicked. In some Gorteria inflorescences it is a bombylid fly that is mimicked including the sparkle of the fly body in the sun.

However in other flowers such as Erythranthera orchids and bird-pollinated Swainsonia formosa flower both extremely glossy we have no idea about the function and whether the pollination is involved here. Both examples are from Australia. Evidence from field observations / experiments are needed. Other hypothetical causes such as wettability, evaporation, grip for flower visitors have to be considered.

Klaus

Dear Prof. Klaus Lunau ,

It is an interesting possibility that gloss could aid in mimicry. I have a couple of questions along this line:

1) Does gloss (if it functions as hypothesized) tend to be a short-distance visual cue for the pollinator?

2) As known from earlier studies: glossy surface appears from flat epidermal cells: I am sort of confused as to the localization of these type of cells: a majority of the distal parts of the flower have papillate cells of various types (?)

Regards.

Eapsa

Dear Eapsa,

there is no evidence about the function of gloss, so we cannot tell wheter it is valid only at short distances.

To me it seems more important that structural colours and color patterns are a dynamic visual signal with its properties changing with the angle of view.

Moreover, gloss can be an honest signal indicating the spherical properties of an object (see attachment), although not protected against fake.

And you are right, many floral epidermis cells have a papillate structure, however, some flowers with flat epidermis cells are glossy. As I mentioned already, flat cells might serve different functions at the same time. Flowers might protect themselves against nectar-robbing by having flat and thus slippery robbing-sensitive flower parts.

Klaus