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.
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 specie’s 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 porous, 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, 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;
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 mating 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;
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;
Common frogs 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.
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