Why Rana arvalis turn blue?

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Why Rana arvalis turn blue?

Postby Ilian Velikov » Thu Feb 23, 2017 2:26 pm

I've been thinking recently on the question of why do the males of mass breeding species of frog like arvalis and temporaria call or change color. Supposedly it has to do with sexual selection and that's probably the first thing to pop-up in one's mind but what exactly is its function?

It would be interesting to hear your thoughts.

Here's a publication I found which has some interesting info on the subject.

http://agris.fao.org/agris-search/search.do?recordID=US201301577102
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Re: Why Rana arvalis turn blue?

Postby Mario Schweiger » Thu Feb 23, 2017 3:08 pm

yes, that's it.
this (4194), as well as a shorter in german (3927) are in the db
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Re: Why Rana arvalis turn blue?

Postby Ilian Velikov » Thu Feb 23, 2017 4:05 pm

Mario Schweiger wrote:yes, that's it.


Are you talking about the paper? There was not really an answer to the question in it. They suggest males might turn blue to avoid attempting amplexus with each other but don't they have the call for that?
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Re: Why Rana arvalis turn blue?

Postby Berislav Horvatic » Thu Feb 23, 2017 10:43 pm

Ilian Velikov wrote:
Mario Schweiger wrote:yes, that's it.

Are you talking about the paper? There was not really an answer to the question in it. They suggest males
might turn blue to avoid attempting amplexus with each other but don't they have the call for that?

A very nice, honest, readable, clearly written paper - but unfortunately without the answer to the question
that troubles us all, not just Ilian...

... but don't they have the call for that?

The call is meant to attract the females, not to repel other males. After all, in a breeding frenzy with hundreds
or even thousands of closely packed males, all of them calling (to the females), a striking colour would be much
more conspicuous and effective as a "same-sex repellent" than a call, hopelessly lost within a huge chorus of
identical ones. In my experience, a chorus like that can be heard from half a kilometre away - useful to attract
the females, from afar, but really useless for any recognition of an individual caller at close quarters...
Not that I really endorse the idea of a striking colour being the "same-sex repellent" as the solution, but I also
have no better idea to come up with, just like anyone else... Or maybe someone has?
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Re: Why Rana arvalis turn blue?

Postby Ilian Velikov » Fri Feb 24, 2017 11:06 am

Berislav Horvatic wrote:The call is meant to attract the females, not to repel other males.


I didn't mean the "advertising" call. What I meant is that in most (if not all) mass breeding frog species in the frenzy males would try to grab other males and when this happens the male who has been grabbed quickly emits a short call (different from the other) so he is immediately recognized as a male and released by the other male. Now, the blue colouration as a "same-sex repellent" would make sense if it acted as an immediate cue preventing males from even trying to mate with each other just by seeing them, which might save them some valuable energy after a few months of starvation. However, male arvalis seem to try to grab other males as much as any other (drab-coloured) species of mass breeding frog.

Berislav Horvatic wrote: In my experience, a chorus like that can be heard from half a kilometre away - useful to attract
the females, from afar, but really useless for any recognition of an individual caller at close quarters...


This is true.The call of male mass breeding frogs does not have the same purpose as in other frog species (e.g. Hyla sp.) - to showcase health, strength and stamina in an individual, so a female chooses him as mate. In mass breeding frogs the call doesn't have any significance in terms of selecting an individual male, because as all of us have seen any female entering a pool is grabbed by many males as soon as she enters the water. It is obvious that she doesn't have any choice of a male whatsoever. So the most likely purpose of the mass breeder's call is, as you say, to attract females from far away to this pool rather than the other. This is also backed up by the fact that all males start and stop (e.g. if there's a predator) calling at the same time. They basically seem to join forces to attract females from the area to their particular "party". Individual selection is out of the question and it seems that's true for the blue colouration of arvalis too, so we can at least rule this out.
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Re: Why Rana arvalis turn blue?

Postby Jeroen Speybroeck » Fri Feb 24, 2017 2:09 pm

Nuptial colours in males mainly serve to impress the ladies, I'd say.
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Re: Why Rana arvalis turn blue?

Postby Guillaume Gomard » Fri Feb 24, 2017 4:38 pm

Ilian Velikov wrote: Now, the blue colouration as a "same-sex repellent" would make sense if it acted as an immediate cue preventing males from even trying to mate with each other just by seeing them.


Interestingly, this seems to be the case for other species, for instance by Litoria wilcoxii. I just report the relevant sections below:

"L. wilcoxii turn yellow after securing a female, and remain so for up to 6 h while pairing with a female"

"Colour change in L. wilcoxii in an intra-sexual signal occurs following amplexus. This signal is directed at other males once a female has been secured and prevents displacement by other males, reducing energy expenditure and potentially avoiding sperm competition."

Complete reading: DOI: 10.1007/s00265-016-2220-1

Jeroen Speybroeck wrote:Nuptial colours in males mainly serve to impress the ladies, I'd say.


Would have been my guess too. However Ries et al. did not (could not) demonstrate this.
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Re: Why Rana arvalis turn blue?

Postby Jeroen Speybroeck » Fri Feb 24, 2017 8:11 pm

Merci, Guillaume!
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Re: Why Rana arvalis turn blue?

Postby Ilian Velikov » Fri Feb 24, 2017 10:11 pm

Jeroen Speybroeck wrote:Nuptial colours in males mainly serve to impress the ladies, I'd say.

In what way do you mean? As I said it is obvious that females have no choice whatsoever of which male they are going to mate with. Ries et al. also didn't find any correlation between colour and physical condition in male arvalis.
Guillaume Gomard wrote:"L. wilcoxii turn yellow after securing a female, and remain so for up to 6 h while pairing with a female"

"Colour change in L. wilcoxii in an intra-sexual signal occurs following amplexus. This signal is directed at other males once a female has been secured and prevents displacement by other males, reducing energy expenditure and potentially avoiding sperm competition."

That's interesting but I'm not fully convinced...Why would other males not want to displace each other from a female. Yes, sure saving energy but 1) other species (including arvalis, bufo, temporaria) obviously have enough energy to wrestle and kick each other and go through with the whole mating frenzy (Is wilcoxii flimsier less resilient species?); and 2) finding a mate would be the single most important thing for males, much more important than having a rest. If they save energy and don't mate, what are they saving it for?
There's also the sex ration to consider in this case. In European mass-breeding species (and others like the N American Wood Frog) males outnumber females in the breeding pool by a lot, so each male must fight to get a female. Maybe the ratio in wilcoxii is the opposite or more balanced, so if a male sees that a female is already taken he could afford to both save energy and find another available one?

Anyway, slight on-subject detour, I'm not satisfied with the "same-sex repellent" theory for arvalis mainly because their blue colour doesn't seem to make them behave in any different way from other European mass-breeders - males still try to grab each other, and still try to displace other males.
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Re: Why Rana arvalis turn blue?

Postby Guillaume Gomard » Fri Feb 24, 2017 11:25 pm

Ilian Velikov wrote:There's also the sex ration to consider in this case. In European mass-breeding species (and others like the N American Wood Frog) males outnumber females in the breeding pool by a lot, so each male must fight to get a female.


You're right Ilian, I gave a second thought about your initial question and found in a 2012 a more nuanced view to explain this phenomenon:

"A conspicuous visual signal making breeding males distinguishable from females and non-breeding males can reduce mate-searching time by (1) facilitating the visual detection of females, (2) minimising unwanted clasping attempts with rivals and (3) reducing harassment by rivals."

, where searching time<=>energy loss

(from DOI: 10.1007/s00265-012-1412-6)

In that sense, when you write that:
the blue colouration as a "same-sex repellent" would make sense if it acted as an immediate cue preventing males from even trying to mate with each other just by seeing them, which might save them some valuable energy after a few months of starvation. However, male arvalis seem to try to grab other males as much as any other (drab-coloured) species of mass breeding frog.

you assume that the visual communication should be optimized to minimize energy loss. Herein the authors rather suggest that it just reduces those losses. You also write that male arvalis "seem to (...)": it would be interesting to check if someone ever tried to quantify this effect to figure out if it is significant, beyond the maybe misleading impression that one can get with "simple" observation in the field.
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