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mynewt
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Posted: 19 Jul 2006 Topic: How Common are Red frogs in England?



Hi Gemma and other Raukers

After having followed the various threads for a while on the site I thought it was time to take the plunge myself..

This is about the apparent increase in oddly coloured (common) frogs, especially in gardens.   Apart from simple observer bias, I wonder if this has little to do with inbreeding and genetic drift (if so, wouldn't most of the frogs around one breeding site be expected to show the same 'odd' colour ?) and more to do with increased survival of odd coloured frogs in the benign environment of the garden.

Most, if not all, of these odd coloured frogs are being observed as adults / subadults.   Maybe it's just that the same fraction of odd coloured froglets metamorphose in the wild and in suburbia, but the higher survival rate for odd coloured frogs can be greater in gardens due to a  lack of predation - especially by colour sensitive predators like herons (which do visit garden ponds, I know, but can't be as significant in this environment than in the 'wild').

To test this idea, it would be necessary to count the proportion of odd coloured froglets at metamorphosis in wild and garden populations, and see if there were differences in a) the proportions of odd coloured froglets in the 2 kinds of habitat and b) whether survival rates of odd coloured frogs were different post-metamorphosis in the 2 areas.

Has anyone done any work to test this ?   Any thoughts welcome.

I'll try to post a pic of a lovely near-black common frog from a site in Islington, north London, which I saw last week - as well as a similarly coloured crested newt from a few years back, to show that the same odd colours can happen in suburban GCN too..

Cheers

Mynewt



mynewt
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Posted: 19 Jul 2006 Topic: How Common are Red frogs in England?



Thanks for the reply Gemma.   Your point about the froglets not yet showing their 'true colours' is a good one.

I guess what I meant was that odd frogs - colour, shape etc - perhaps even the odd extra leg ! - might be no more common to start off with in gardens than in the wild, but that relaxed selection in gardens might allow them to persist for longer than in the 'tangled bank' of Darwinian realities out in the wild.   As a result, alleles which could be maladaptive in the wild are not ruthlessly selected against and become more prevalent in the garden habitats.   This is a separate although not mutually exclusive explanation from that offered by Trevor Beebee in which genetic drift (ie neutral selection) is held responsible for odd colours being more commonly observed in suburban than wild frog populations.

Mynewt

PS In my limited experience, 'round nosed' common frogs are very often older ones, and I would agree that this often correlates with odd colours and patterns - perhaps some frogs get more striking patterns as they age ?



mynewt
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Posted: 19 Jul 2006 Topic: How Common are Red frogs in England?





Here are the odd frog and GCN from London; apologies for the low quality of images, especially the GCN which is a photo of a photo..

I thought the frog had a particularly black slimy mud on it when first seen but in fact that black colour is  the frog's own

Mynewt



mynewt
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Posted: 19 Jul 2006 Topic: How Common are Red frogs in England?



Nice to see this illustration of at least one 'odd' / bright female common frog going back to the turn of the last century, from Boulanger's book 

Mynewt





mynewt
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Posted: 20 Jul 2006 Topic: How Common are Red frogs in England?



I guess you'd have to capture large numbers of froglets from wild vs suburban populations and raise them for a while til they show their true colours - not an easy thing to do !   If I'm right, there should be no significant difference between odd colours in frogs derived from wild areas and those from suburban areas, provided they're raised in identical conditions.

With reference to Trevor Beebee's work, I'm sure I remember reading somewhere that he did a genetic analysis of urban frogs looking for heterozygosity at specific gene loci, as an indication of inbreeding, and found more in urban than rural populations.   On the other hand, even an occasional input of fresh genes from a frog down the road can boost the variation in a population for a long while.   This raises the whole controversy of spawn swapping - inbreeding dangers vs red leg etc once again, of course.



mynewt
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Posted: 20 Jul 2006 Topic: How Common are Red frogs in England?



I agree Gemma - truth is, I just like the Boulanger illustration - there is definitely something more unusual than just an orange-ish female frog situation in some of these urban frogs.   But my main point is simply that  I think it might be worth investigating the hypothesis that this sort of maladaptive trait might be less selected against in the cosseted world of the back garden than in the rough and tough of 'the wild'.


mynewt
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Posted: 21 Jul 2006 Topic: How Common are Red frogs in England?



Good idea Gemma; one for the spring, perhaps - we could make a note of 'odd colours' in breeding frogs at 'wild' vs 'garden' sites, when there is a large sample size.

Of course it wouldn't tell us whether if there IS a significant difference whether this is due to inbreeding and genetic drift, or less natural selection against odd colours in suburbia, or a combination of both.   That would then need the tricky follow-up of raising loads of froglets in netted enclosures - MSc project anyone ?

And, as you say, there would be the problem of accurately defining what we mean by 'odd' colours and 'the wild' vs 'suburbia / gardens'; anyway, I'll try to do some work next spring - something to look forward to while we're all roasting at the moment..



mynewt
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Posted: 14 Aug 2006 Topic: August



Hi there

I've just seen something similar in Pembrokeshire, namely and courtship in palmate newts - a small pond in the gounds of a stately home had at least a dozen individuals, with males in full breeding condition, displaying to females who seemed willing to follow the males in turn.

has anyone seen active courtship / displaying in newts of any species this late in the season ?  Can anyone suggest why it's happening at this time ? - especially in mild south-west Wales ?

Cheers

Mynewt





mynewt
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Posted: 18 Aug 2006 Topic: Treatment of adder bite link



Here's a stupid question, but I've been wondering ...

Is there any evidence that anyone has been bitten often enough by adders, in the line of duty / pleasure to build up any degree of immunity to the venom ?   How long would such an immunity last ? I remember seeing a programme on TV where the guy had been bitten by venomous snakes so often that he was sensitised to the venom, but presumably this doesn't usually happen.   Also, would immunity to adder venom protect you from other European viper species' bites ?

Any of you pro's become adder-immune ?

Mynewt



mynewt
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Posted: 19 Aug 2006 Topic: Treatment of adder bite link



Thanks Wolfgang - a pretty clear answer !

Cheers



mynewt
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Posted: 20 Sep 2006 Topic: signal crayfish and newts



Hi there

I've just found signal (American) crayfish in a nice GCN pond - does anyone know whether they impact on our native newts - either by attacking adults or feeding on eggs in water plants ?   Is it too early to say - and is anyone studying this ?

In the Seychelles the biggest problem for hatching Aldabra tortoises is having their legs bitten off by land crabs, apparently - and crayfish have pretty big pincers too !




mynewt
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Posted: 25 Sep 2006 Topic: Markings



Hi there

GCN can bend their bodies banana-like to show warning colours to predators - it's called the 'unken reflex' - I guess from German herpetology.

I have always supposed that they're camouflaged on the top as an initial defence and then colourful underneath as a last resort, given that they're not highly poisonous like poison dart frogs, for instance.  




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