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will 
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Joined: 27 Feb 2007 Location: United Kingdom Status: Offline Points: 1830 |
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 Posted: 02 Jul 2014 at 2:49pm |
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...and also the vividness of the green could drive away other males, and be an indicator of testosterone levels?
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liamrussell
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Posted: 02 Jul 2014 at 4:23pm |
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I looked at this as part of my studies. The green is primarily a signal to other males of how fit they. A bright green male is signalling to others that there's no point in fighting him for females. The females aren't that picky and will generally mate with whoever is available - hence the mate guarding you see in the spring.
I looked at the RGB component of flank colour of photos of the males using photoshop and compared these animals to ones from Dorset and Holland. There is no significant difference in the green component of the flank colour between any of the sites. The differences we perceive are due to differing amounts of red and blue in the colour. These animals have significantly more red and less blue than the Dorset or Dutch animals (which were pretty similar).
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Peter
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Posted: 02 Jul 2014 at 5:14pm |
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My own non scientific field observations tally with Liam's comments. Females really aren't at all picky, and literally will mate with whatever is available regardless of size/status, including relatively small males. There are other species where the colouration appears to be mainly a signal/communication to other males, the European moor frog(Rana arvalis)being a well known example. The males turn blue for a very brief period during breeding.
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BLF Dragonscapes Habitats officer
Amphibian and Reptile Conservation e: peter.hill@arc-trust.org |
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will
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Posted: 02 Jul 2014 at 5:36pm |
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thanks guys - great to have such expertise on tap!
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Tom Omlette
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Posted: 02 Jul 2014 at 10:38pm |
fortunately for me that also applies to one or two human females or else i'd still be single! tom
Edited by Tom Omlette - 02 Jul 2014 at 10:38pm |
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will
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Posted: 03 Jul 2014 at 6:35am |
 - I reckon with me, it's the 'sneaky male' strategy that worked!
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Paul Ford
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Posted: 03 Jul 2014 at 11:33am |
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"The males turn blue for a very brief period during breeding"
Tempted, but I think I'll leave it
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Caleb
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Posted: 03 Jul 2014 at 2:22pm |
What did you use to calibrate between images for this, to compensate for lighting, exposure etc? I did something similar with soil colour many years ago- I had to get photos printed, cut them into pieces and pass them through a massive reflectometer. Would have been so much easier with digital photography and image editing software.
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liamrussell
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Posted: 03 Jul 2014 at 3:35pm |
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I had originally taken the photos for a different purpose, so didn't have this in mind at the time. Other studies controlled for this at the time of the photo (e.g. using special photo boxes) but I wans't thinking about this at the time.
They were all taken using the same camera with the same settings from the same angle in the shade (no flash), but other than that nothing specific. I took multiple measurements from each flank in order to try and minimise any differences due to reflections etc but there will be some effect.
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Caleb
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Posted: 03 Jul 2014 at 5:06pm |
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So were you able to compare intensity between images to say definitively that the northern males aren't more or less green than the southern ones? Can't see how you'd do that without some calibration.
For my soil samples, I photographed each one next to some red, green and blue tapes, so that any variation in intensity and colour of the light source, and any variation in the camera's response could be calibrated for- it was surprising how much this varied even under seemingly identical conditions.
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Peter wrote: