Why Rana arvalis turn blue?

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Re: Why Rana arvalis turn blue?

Postby Kristian Munkholm » Sun Feb 26, 2017 2:47 pm

Here in Denmark it varies from year to year - and seemingly also from population to population - to which extent they turn blue, from no more than temporaria to electric.

I don't know of any studies documenting it but it is widely acknowledged that this indeed correlates to weather and water temperature. This also corresponds with my own experience.

Further, in my experience it seems there is a second correlation with the level of breeding activity. When conditions are ideal we experience large choruses of blue males for a day or two whereas in less optimal conditions breeding seems to be spread out across a few days more with less activity and ditto colour each day.
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Re: Why Rana arvalis turn blue?

Postby Ilian Velikov » Mon Feb 27, 2017 1:03 am

Guillaume Gomard wrote:There was absolutely no form of criticism in my answer, I just tried to make a point on the fact that it's probably hard to evaluate this effect without a proper analysis on energy loss. I hope I did not give the impression that this topic should be closed, since I really like this kind of discussion.


No problem, Guillame. I like having these discussions as well and exactly because a lot of things that are being discussed are hard to prove or not proven yet I'm using phrases like "I think" and "it seems". Still no harm in talking about it.

Mario Schweiger wrote:DOI: 10.1007/s00265-012-1412-6 = PDF-10898 in db

Yes, thanks Mario! From this perspective it makes more sense for me personally.

There's been some interesting info from all of you guys. Just to summarize, it looks like the blue colouration is correlated to:
- presence of females
- presence (and number) of other males
- weather
- water temperature

It is not correlated to:
- physical fitness

Could it be that some of the factors correlating with the blue colouration have to do with the physical process of turning blue (any publications on this?) rather than the behavioral aspect of it, e.g. they might need certain temperature and conditions to change colour...?

For me one thing is sure neither the calling nor the colouration has anything to do with a female's choice of an individual male, simply because she obviously doesn't have such choice.

So far the best we have is that in breeding masses with males greatly outnumbering females it would be useful for males to turn different colour so they don't waste time and energy by trying to mate with other males. However, even if this is so I don't think it stops males of trying to dislodge other males that are already in amplexus with a female. There's one thing I find a bit unsettling with this scenario - male frogs and toads of explosive breeding species have been known to go into amplexus not only with other males but also with dead females, dead fish, salamanders, other frog species, bottles and other objects...one male Bufo bufo even grabbed my hand as I was trying to catch him (they squeeze quite hard). So how just a visual cue like colour would help a male who can't tell the difference between a female and a dead fish to distinguish between sexes? Which also makes me wonder what is a frog's perception of others of its kind? Surely there must be other, maybe chemical cues for a male to recognize a female, or not...?
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Re: Why Rana arvalis turn blue?

Postby Mario Schweiger » Mon Feb 27, 2017 6:55 am

some more observations ;)

In 2010 I have made a video of R.a. wolterstorffi near Vienna.

you may watch it in HD too ;)

You have to be very careful, not to frighten the frogs, so they will dive away. Immediately they turn to brown and it needs "hours" until they are bright blue again.
What you may watch in the video is, if one male "copulates", the other males don't care and try to grab the female too. But they don't grab males floating alone.
Males on the way to or from the pond often show a purple coloration.
pinkarvalis.jpg
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Re: Why Rana arvalis turn blue?

Postby Jeroen Speybroeck » Mon Feb 27, 2017 8:51 am

Mario Schweiger wrote:Immediately they turn to brown

Hmmm... That's not the case around here, I think.
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Re: Why Rana arvalis turn blue?

Postby Ilian Velikov » Mon Feb 27, 2017 2:06 pm

Mario Schweiger wrote:You have to be very careful, not to frighten the frogs, so they will dive away. Immediately they turn to brown and it needs "hours" until they are bright blue again.
What you may watch in the video is, if one male "copulates", the other males don't care and try to grab the female too. But they don't grab males floating alone.
Males on the way to or from the pond often show a purple coloration.


Thanks Mario! That's very interesting. I didn't know they are capable of such a rapid change of colour. It makes sense to loose the bright conspicuous colour when danger approaches. It's interesting that they loose the blue colour rapidly and then need much more time to regain it. It would be interesting to learn more about the mechanism with which they do it. I also noticed some of the males loose (to different extend) the blue once egg laying starts.
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Re: Why Rana arvalis turn blue?

Postby Kristian Munkholm » Mon Feb 27, 2017 10:17 pm

Ilian Velikov wrote:
Mario Schweiger wrote:You have to be very careful, not to frighten the frogs, so they will dive away. Immediately they turn to brown and it needs "hours" until they are bright blue again.
What you may watch in the video is, if one male "copulates", the other males don't care and try to grab the female too. But they don't grab males floating alone.
Males on the way to or from the pond often show a purple coloration.


Thanks Mario! That's very interesting. I didn't know they are capable of such a rapid change of colour. It makes sense to loose the bright conspicuous colour when danger approaches. It's interesting that they loose the blue colour rapidly and then need much more time to regain it. It would be interesting to learn more about the mechanism with which they do it. I also noticed some of the males loose (to different extend) the blue once egg laying starts.


It's the same here - makes trying to photograph them an absolute pain if they're in even a little less than a complete senseless breeding frenzy, particularly at sites where it is impossible to sneak up on them.
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Re: Why Rana arvalis turn blue?

Postby Tomas Klacek » Tue Feb 28, 2017 11:19 am

Kristian Munkholm wrote:
Ilian Velikov wrote:
Mario Schweiger wrote:You have to be very careful, not to frighten the frogs, so they will dive away. Immediately they turn to brown and it needs "hours" until they are bright blue again.
What you may watch in the video is, if one male "copulates", the other males don't care and try to grab the female too. But they don't grab males floating alone.
Males on the way to or from the pond often show a purple coloration.


Thanks Mario! That's very interesting. I didn't know they are capable of such a rapid change of colour. It makes sense to loose the bright conspicuous colour when danger approaches. It's interesting that they loose the blue colour rapidly and then need much more time to regain it. It would be interesting to learn more about the mechanism with which they do it. I also noticed some of the males loose (to different extend) the blue once egg laying starts.


It's the same here - makes trying to photograph them an absolute pain if they're in even a little less than a complete senseless breeding frenzy, particularly at sites where it is impossible to sneak up on them.


A year ago I would say same thing. But last spring I saw them (for a first time) in higher numbers and they were not shy at all. I came at my spot literally at the moment when males where moving from the forest to the water. I can move on the shore around them and they showed no signs of behavior what I knew from last years. No diving, they just wait on water surface for females. When I returned afternoon, some females were already there and also first spawns - same not shy behavior. Unfortunately I do not have a time to check them again day after.

In previous years I saw just few very shy individuals (after mating), they were diving for a long time at the slightest movement.

Also have an experience when a slightly purple male turns blue within 10 minutes during shooting. Sun definitely affects their colour.
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Re: Why Rana arvalis turn blue?

Postby Ilian Velikov » Tue Feb 28, 2017 4:06 pm

It looks like the colour change mechanism is neuro-hormonal and is affected by a lot of factors including presence of females or rival males, environmental conditions and stress. This would explain why lone males don't turn blue or why they rapidly loose the blue colour when there's a potential threat, and also the differences between populations or seasons.

Here's some interesting reading on the subject:

This one was already pointed out by Guillame, I think.
http://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0114120&type=printable

http://www.zobodat.at/pdf/HER_28_1_2_0106-0109.pdf

http://rspb.royalsocietypublishing.org/content/279/1748/4687
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Re: Why Rana arvalis turn blue?

Postby Mario Schweiger » Wed Mar 01, 2017 10:37 am

interesting reading.
put
Kindermann et al. (Plose One) = PDF-10917 and
Garcia-Roa et al. (Herpetozoa) = PDF-10916
into the database.
Bell & Zamudio (Proc. R. Soc.) is already in the db: PDF-7181
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Re: Why Rana arvalis turn blue?

Postby Bert Vandebosch » Wed Mar 15, 2017 9:26 pm

I have been reading this thread with interest. But did not want to involve in the discussion before I had been out in the field again this season to spot some blues.

Last weekend I managed to do so.
I'm surprised by Mario's observations of the rapid colour change seemingly due to stress. My experiences contradict this. In the past I managed to catch a blue one and it stayed blue for a photo session. I know others who did the same...

I do think as stated before that sunshine and/or consequential higher temperatures are important factors in the mechanism of turning blue.
But why or to which advantage? I find the above proposed theories a bit far-fetched. Also comparing it with mechanisms of colour changes in tropical frog species, (although interesting) does not explain anything to me.

My theory is much simpler. One of my searches last weekend was a combined family walk. Also my mother was there. I showed her some blue frogs through the binoculars and asked her: why do you think they turn blue?
What? Because the water is blue?
Exactly mama! There, you go: some grandmother's wisdom.

They turn the most blue on bright sunny days. With a lot of reflection of the sun on the water and a blue sky reflecting in the water. This is maybe not always obvious from our point of view. From the edge of a pond with some trees reflecting in the water they can seem very outspoken if you know what you are looking for.
But if you think about it: They evolved during glacial times in steppe/tundra like habitat. No shade of trees, so a lot of reflection on the water surfaces. From a bird's-eye view of flocks of migratory birds, populations of blue frogs might be far less conspicious than when they remain brown.
I also checked this at night and bluish, purplish male frogs (same for R. temporaria) appear greyish and are far more difficult to spot with a weak spot light than the 'normal coloured' females. But most of the time females have a male on their back and they spend far less time in the water anyway.

So to conclude: my theory is just plain old camouflage! What do you think?
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