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The text below was in response to a post on a wildlife forum enquiring about a reddish coloured common frog. It can be seen in context here.
Hi KatinWales.
That is indeed a superb image of a common frog displaying particularly beautiful colouration. The animal is most likely female, although it is seldom possible to be 100% accurate when looking at images alone. Such beautiful colouration is far from uncommon however, as I shall attempt to demonstrate whilst simultaneously running a theory past you all.
That is indeed a superb image of a common frog displaying particularly beautiful colouration. The animal is most likely female, although it is seldom possible to be 100% accurate when looking at images alone. Such beautiful colouration is far from uncommon however, as I shall attempt to demonstrate whilst simultaneously running a theory past you all.
The common frog (Rana temporaria) has been referred to in the past as the “temporary frog”, hence it’s scientific name. It is most likely that the label; “temporary frog” came about due to the species explosive breeding strategy. The explosive breeding strategy is common among amphibians from temperate zones. The entire local population converges simultaneously upon a spawning site immediately following emergence from hibernation. Literally hundreds of individuals gather (sometimes more at particularly suitable sites) producing multiple clumps of spawn. A single spawn clump alone may contain over 2,000 individual eggs. The strategy relies entirely upon large numbers of animals converging simultaneously. Predators will gorge themselves until full on any of the unlucky ones, so in effect sheer numbers overwhelm predation so that some frogs make it. Once the vast numbers of eggs have been laid, there is no parental care. The adult frogs then have to run the sweepstake of migrating back to their terrestrial habitat, including the aquatically hibernating males, which disperse terrestrially until the time for hibernation once again returns. The colony completes spawning in a matter of days. To the casual observer, noticeably large numbers of frogs appear and then disappear once more. Temporary frogs!
Where circumstances dictate, considerable numbers of male frogs adopt the strategy of hibernating below the water in the mud and dead leaves at the bottom of the pond or ditch. They are able to do so due to the fact that amphibian skin is incredibly permeable, and the lowered rate of oxygen consumption during the torpor of hibernation means that sufficient oxygen can be diffused from the water through the skin to keep the hibernating males alive. Why do they do so? The number of males is always considerably greater than that of females, so the aquatically hibernating males most likely do so in order to be “onsite” to intercept the arriving females, the majority of which would appear to hibernate terrestrially and not aquatically.
Males that hibernate terrestrially are more likely to arrive at the spawning site to find that the aquatically hibernating males have monopolised the available females. Consequently terrestrially hibernating males are far less likely to breed successfully. It comes as no surprise therefore that the majority of successful breeding males are, at such times, coloured much like the grey mud in which they have spent the winter period, and nearly always with a conspicuous white throat.
Here are male frogs gathered at a site local to me two years ago (2009);
Where circumstances dictate, considerable numbers of male frogs adopt the strategy of hibernating below the water in the mud and dead leaves at the bottom of the pond or ditch. They are able to do so due to the fact that amphibian skin is incredibly permeable, and the lowered rate of oxygen consumption during the torpor of hibernation means that sufficient oxygen can be diffused from the water through the skin to keep the hibernating males alive. Why do they do so? The number of males is always considerably greater than that of females, so the aquatically hibernating males most likely do so in order to be “onsite” to intercept the arriving females, the majority of which would appear to hibernate terrestrially and not aquatically.
Males that hibernate terrestrially are more likely to arrive at the spawning site to find that the aquatically hibernating males have monopolised the available females. Consequently terrestrially hibernating males are far less likely to breed successfully. It comes as no surprise therefore that the majority of successful breeding males are, at such times, coloured much like the grey mud in which they have spent the winter period, and nearly always with a conspicuous white throat.
Here are male frogs gathered at a site local to me two years ago (2009);
Notice how the vast majority of them are of a colour much the same as the water, which has been disturbed due to the mass of male frogs emerging from the grey muddy bottom of the ditch and the ongoing breeding activity;
When the females arrive however, there is noticeable variation in body colour among them and the throat is nearly always mottled. Some individuals appear bright yellow. Here is an unusual sighting of a gravid (full of spawn) female arriving safely at the spawning site;
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I use the word unusual because it certainly is unusual to find a gravid female during the breeding season at a spawning site whilst not in amplexus (the term used to describe the “piggy back” style spawning embrace of male and female). The awaiting males immediately set upon the pictured female upon her arrival. Many more females however appear to be any one of a number of varying shades of red or orange such as the animal on the left.
Common frogs, especially females, can be especially beautiful at this time of year. Perhaps colour variation is determined by a reaction of the amphibian skin to varying soil conditions or other environmental factors. They certainly look very different to the males at spawning time. All of the following images depict pairs in amplexus and every one of the females depicted is a shade of red, orange or yellow;
Here`s a few more;
Here is an unattached reddish coloured male. Perhaps he hibernated terrestrially, hence the colouration?
Here, among a group of males we can see a pair in amplexus towards the top of the image and facing away from camera. You will notice the female is also a shade of red when compared to the muddy grey of the male. An unattached reddish coloured male stands out among the grey males at the top right hand side of the picture also;
Individuals vary in colour throughout the year. Although muddy grey during the explosive aquatic spawning season, the same individual male frog may appear bright yellow later in the year (during the summer) whilst occupying terrestrial habitat such as lush grass or mosses. Individuals of both sexes do vary greatly in colouration at different times of the year. Following spawning, the thousands of eggs produced turn into thousands of tadpoles that then face a considerably precarious aquatic development amidst an array of specialised aquatic predators. A fraction of the tadpoles produced make it to full term development and metamorphose into tiny versions of the adults. Despite heavy losses, considerable numbers of young frogs emerge in the summer, so the explosive breeding strategy, despite on appearance being wasteful, does work for this species. One example of a very different breeding strategy is that of the many species of South American poison dart frogs. Individual species strategies vary, but all produce a very small amount of eggs when compared to the quantity of spawn produced in the case of the explosive breeding temperate species. In general, in the case of the majority of dart frog species, less than 10 eggs are produced at a time. Parental care is displayed which greatly increases the survival odds for the tadpoles. Living in a tropical climate also means that the dart frogs can of course spawn at repeated intervals throughout the wet season rather than a single spawning as in the case of most temperate zone species.
Returning home once more to the common frog; until recently, we have experienced comparatively wet but mild winters. Consequently the strategy of aquatic hibernation in the common frog has, on the whole in recent years been a successful one, resulting in the majority of spawn clumps having been successfully fertilized by the aquatically hibernating males that were able to secure the bulk if not all of the available females prior to the terrestrially hibernating males even arriving at the spawning site.
There are disadvantages to the strategy however. Mild winters have meant that ponds and ditches have not been freezing over for extended periods of time. Last winter however was a different matter for the aquatically hibernating males. Long periods of oxygen starvation in the water due to ponds and ditches being iced over for a greater amount of time than was the case during the previous run of mild winters are likely to have killed off all of the aquatically hibernating males. This spring therefore, the scene at the spawning site at which the above images were taken two years previously was a very different one. It was plainly apparent that there were far less males than in previous years. Furthermore, the diversity in colour among the few males that were assembled was considerably more apparent than in the case of the previous few years. The hoards of “muddy grey” males were conspicuous by their absence.
It is not unlikely therefore that this year, it was the turn of the terrestrially hibernating males to fertilise the majority of spawn clumps due to the absence of the vast numbers of aquatically hibernating males that were present in previous breeding seasons. Perhaps terrestrially hibernating males produce a greater percentage of offspring that are more inclined to hibernate terrestrially than is produced by aquatically hibernating males.
If such is indeed the case, then we have a clear demonstration of how diversification of breeding strategy in a single species can maintain reproduction despite comparatively drastic changes of climatic conditions.
It would certainly make an interesting study, although how it would be implemented without unjust amounts of intrusion into the animals lives I shouldn`t like to say.
Returning home once more to the common frog; until recently, we have experienced comparatively wet but mild winters. Consequently the strategy of aquatic hibernation in the common frog has, on the whole in recent years been a successful one, resulting in the majority of spawn clumps having been successfully fertilized by the aquatically hibernating males that were able to secure the bulk if not all of the available females prior to the terrestrially hibernating males even arriving at the spawning site.
There are disadvantages to the strategy however. Mild winters have meant that ponds and ditches have not been freezing over for extended periods of time. Last winter however was a different matter for the aquatically hibernating males. Long periods of oxygen starvation in the water due to ponds and ditches being iced over for a greater amount of time than was the case during the previous run of mild winters are likely to have killed off all of the aquatically hibernating males. This spring therefore, the scene at the spawning site at which the above images were taken two years previously was a very different one. It was plainly apparent that there were far less males than in previous years. Furthermore, the diversity in colour among the few males that were assembled was considerably more apparent than in the case of the previous few years. The hoards of “muddy grey” males were conspicuous by their absence.
It is not unlikely therefore that this year, it was the turn of the terrestrially hibernating males to fertilise the majority of spawn clumps due to the absence of the vast numbers of aquatically hibernating males that were present in previous breeding seasons. Perhaps terrestrially hibernating males produce a greater percentage of offspring that are more inclined to hibernate terrestrially than is produced by aquatically hibernating males.
If such is indeed the case, then we have a clear demonstration of how diversification of breeding strategy in a single species can maintain reproduction despite comparatively drastic changes of climatic conditions.
It would certainly make an interesting study, although how it would be implemented without unjust amounts of intrusion into the animals lives I shouldn`t like to say.
Explosive Breeding strategy of the
comon frog-
WARNING! Lots of sex and violence!
Spawning time for the common frog can be a stressful time for the animals and there are often casualties. Some of the images are graphic.
As explained in the text above, the explosive breeding strategy of the common frog is an evolutionary reproductive tactic typical of temperate zone amphibians. No parental care negates the production of a vast amount of spawn, quite literally putting all their eggs in one basket! When a large population gathers to spawn, it really is a natural wonder, an experience not forgotten. It has to be seen to be believed, which is why I have included more images and videos of sizeable spawning gatherings. Here are some examples for you to experience. Turn up the volume on the videos and you will hear the male frogs calling in abundance, a beautiful and ancient sound that would have been heard far more often in times past than it is currently.
comon frog-
WARNING! Lots of sex and violence!
Spawning time for the common frog can be a stressful time for the animals and there are often casualties. Some of the images are graphic.
As explained in the text above, the explosive breeding strategy of the common frog is an evolutionary reproductive tactic typical of temperate zone amphibians. No parental care negates the production of a vast amount of spawn, quite literally putting all their eggs in one basket! When a large population gathers to spawn, it really is a natural wonder, an experience not forgotten. It has to be seen to be believed, which is why I have included more images and videos of sizeable spawning gatherings. Here are some examples for you to experience. Turn up the volume on the videos and you will hear the male frogs calling in abundance, a beautiful and ancient sound that would have been heard far more often in times past than it is currently.
The breeding season is a very risky and stressful time for amphibians. There are many factors that they have to deal with, predators, environmental factors plus the stress of the explosive breeding season itself.
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The "explosive" breeding strategy (i.e. large numbers of animals at the same time) makes it more likely for individual animals to be successful in breeding and avoid predation at this vulnerable time due to sheer numbers. If a steady flow of animals to the breeding pond/ditch occured instead, then large numbers would be picked off. It`s a tactic that works well, however there are disadvantages.
Males always outnumber females substantially, and "knots" of several males clinging on to one female may occur. In the worst case scenario, the female may be drowned or crushed.
The image on the right shows a knot of three males attached to one female taken at the same site as the previous images in this thread. On this occasion, this particular female did manage to shake off her surplus suitors.
Males always outnumber females substantially, and "knots" of several males clinging on to one female may occur. In the worst case scenario, the female may be drowned or crushed.
The image on the right shows a knot of three males attached to one female taken at the same site as the previous images in this thread. On this occasion, this particular female did manage to shake off her surplus suitors.
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The image on the left was taken at a different site a day later. Notice the orange colouration to the mud at the pond bottom. It`s a mine water treatment plant, the water comes from old mine shafts full of rusting abandoned mine works. More environmental factors for the frogs to deal with. Anyway, I
noticed the knot of frogs at the bottom of the pond. Females are generally considerably bigger than the average male as it is the females that carry the spawn, it makes sense to be larger. The female generally moves and the attached males move with her. In this instance the knot wasn`t moving much and I didn`t rate the female`s chances.
noticed the knot of frogs at the bottom of the pond. Females are generally considerably bigger than the average male as it is the females that carry the spawn, it makes sense to be larger. The female generally moves and the attached males move with her. In this instance the knot wasn`t moving much and I didn`t rate the female`s chances.
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The image on the right shows the knot brought out of the water in my net. A total of five males were attached to the female which was quite dead as you can see in the pic. Notice the orange gunge all over the frogs as well.
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OK, this is where it gets pretty nasty! Look away if you are squeamish.
The next images demonstrates the damage done to the long dead female from the above instance once the males had deserted. The combined strength of the males, spurred on by the competition had literally caused the female to burst.
The next images demonstrates the damage done to the long dead female from the above instance once the males had deserted. The combined strength of the males, spurred on by the competition had literally caused the female to burst.
As if this isn`t enough to contend with, the next image shows a predator waiting in the wings in the shape of a heron. The explosive breeding strategy is no doubt welcomed by many predators. At the end of a long hard winter, the protein boost of frog on the menu may be a life saver for some predators.
There is always evidence of predation at the spawning sites that I visit. In nearly every case discovered, the victims are female. Perhaps hibernating terrestrially and having to travel to the pond exposes females to predation to a greater extent than aquatically males. A heron wouldn`t have been the predator in the two cases photographed here, as they tend to swallow their prey whole. Perhaps corvids (crow family) may have been responsible for these attacks or a mustelid such as a polecat, otter or mink.
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The above images were taken at a third site. The frogs were spawning in temporary meadow pools shown below. A good deal of spawn was successfully laid however.
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Hopefully these images have not upset people too much. It is important that we recognize the varying high risk factors directed towards frogs during the breeding season.
It`s certainly not easy being green!
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The females that successfully breed are doubtful to have fed since prior hibernation and look to be emaciated when leaving the spawning site, like this one for instance.
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Compare her with this animal that has yet to spawn.
As discussed, male frogs no doubt hibernate at the pond bottom so as to be able to intercept the arriving females. There are instances recorded where the male frogs hibernate at the bottom of slow moving rivers which are close to breeding ponds to avoid suffocation due to long periods of still water icing over. Upon emergence the males then travel the short distance from river to pond.
Some females on route to the pond meet up with migrating males also. I have watched females actually arrive at the breeding site with a male on board. The pair can sometimes be intercepted by a gang of males at the water`s edge instantly, the males stimulated by the movement of the pair.
Another interesting fact that has been revealed is how a prolonged breeding period tends to produce evenly matched pairs size-wise. A shorter breeding period produces pairs that are not so well matched size-wise. Why? Well, a small male on a large female, or a large male on a small female leaves an "overlap" at which another male can wedge his head in and begin the process of dislodging the original male. Over a short breeding period, there is less time for other males to dislodge the original males of pairs already in amplexus (breeding embrace). A longer period allows time for this to happen and therefore more evenly matched pairs are apparent. If the animals in amplexus are more evenly matched size-wise, there are less opportunities for a second male to dislodge the original due to a lack of an "overlap" which provides the all important point at which the intruder can wedge his head and begin prising the original male from the female.
Perhaps the females "prefer" to run the risk of predation by migrating to the breeding site from their terrestrial hibernation spot rather than risk being part of a "knot" as they emerge from hibernation and drown as a result should they hibernate in the water alongside the hoards of amorous males. Just my own thoughts and not based on any scientific study, purely observation.
Some females on route to the pond meet up with migrating males also. I have watched females actually arrive at the breeding site with a male on board. The pair can sometimes be intercepted by a gang of males at the water`s edge instantly, the males stimulated by the movement of the pair.
Another interesting fact that has been revealed is how a prolonged breeding period tends to produce evenly matched pairs size-wise. A shorter breeding period produces pairs that are not so well matched size-wise. Why? Well, a small male on a large female, or a large male on a small female leaves an "overlap" at which another male can wedge his head in and begin the process of dislodging the original male. Over a short breeding period, there is less time for other males to dislodge the original males of pairs already in amplexus (breeding embrace). A longer period allows time for this to happen and therefore more evenly matched pairs are apparent. If the animals in amplexus are more evenly matched size-wise, there are less opportunities for a second male to dislodge the original due to a lack of an "overlap" which provides the all important point at which the intruder can wedge his head and begin prising the original male from the female.
Perhaps the females "prefer" to run the risk of predation by migrating to the breeding site from their terrestrial hibernation spot rather than risk being part of a "knot" as they emerge from hibernation and drown as a result should they hibernate in the water alongside the hoards of amorous males. Just my own thoughts and not based on any scientific study, purely observation.