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Common Frog

What our animals are doing this month… November 2020

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We’ve recently covered what our amphibians and reptiles are up to over the autumn months, the differences in their overwintering behaviour and where they may spend the colder seasons in structures such as hibernacula. 

It might surprise many however to hear that November can be a month for sighting Common Frogspawn in the south of England.  Common frogs usually begin breeding and laying spawn as spring commences – often with sightings in January and February into spring depending on their location in the UK.  But areas in Cornwall do report sightings of frogspawn before winter even fully commences.

This behaviour could be due to confusion during mild autumn and winter months that we can experience now in the UK or might be a strategy to get ahead of the game in terms of breeding times – albeit it with a huge risk of freezing temperatures affecting the survivability of the spawn.

This could be one sign of more to come in terms of our amphibians adapting to the effects of climate change and seasonal differences their behaviour isn’t quite adapted to.  It’s so important that we can monitor these yearly trends in our amphibian and reptile species to help inform our work at Froglife and you can help by submitting your sightings using the Dragon Finder App – available for free on Android and iPhone devices!

Frogspawn in November? Surely not! But this sighting can occur in mild autumns in the south of England

Croaking Science: Do frogs and toads change their colours and if so, why?

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Froglife have been running an enquiry line and an email advice service for a very long time now and some issues have been reappearing regularly over the years. Most of those have been incorporated in the FAQs on the website specifically to facilitate the rapid dissemination of information to people searching for it. However, other topics are more complex and there is no short answer to some questions. For example: Do amphibians change their colour and if so what is prompting that change? Is it an adaptation to match the background colour (i.e. a toad is brown on brown soil but becomes dark grey when moving onto a gravel substrate to blend in), is it a seasonal change (lighter in spring but dark in autumn), is it an indication of disease or stress or is it when they are breeding?

Common Frog in autumn Silviu
S. Petrovan

It has been well described how colour can change in many amphibian species due to environmental conditions such as humidity and especially temperature and often frogs and toads or even salamander larvae are much darker when their body temperature is low. The common toad (Bufo bufo) however can have significant variation in dominant colour depending on age and some salamander larvae become lighter as they age, probably because early in the season there is a clear advantage to be darker and warm up quicker in cold water but later on dark larvae are at higher risk of predation. There is equally some evidence that in some species, including the common toad there is a certain level of adaptation of the colour depending on the predominant substrate in the area where they live. Probably toads that stand out (brown toads in dark grey soils) are more in danger of predation and as such there is a level of predation selection. Complex mechanisms are involved in relation to the colour change in most amphibians, including the common frog (Rana temporaria) in relation to the background colour. Confusingly, tree frogs in Europe are known to change their colour dramatically between dark grey in early morning to bright green or light grey later by mid-day yet neither of these species is particularly adapt at changing their colour to match that of their environment. Similar species of treefrogs from North America however do change to adapt to their background.

Flickr, CC (Mumes World)
Flickr, CC (Mumes World)

Some amphibians also dramatically change colour during breeding, with the Moor frog (Rana arvalis) in continental Europe as the best example. Males become UV-blue during breeding and create an amazing visual spectacle at ponds and marshes where they congregate. However, the reasons for this colour change have remained relatively unclear given that the vast majority of social interactions between amphibians are auditory (males sing during the breeding season to attract a high density of females in a small patch). Recent research indicates that while females remain brown during breeding the males change colour at that time not just in the human visible spectrum but also in UV spectrum but neither intensity nor wave length of this blue colour are correlated with body condition of the males. As such the most plausible explanation is that the colour change might serve to communicate male-male competitive advantages or potentially to showcase the fact that they are indeed males and therefore to avoid potentially energetically expensive mistakes when males try to get in amplexus with other males due to confusion in a small area, full of frogs.

Colour change in amphibians is a highly complex and variable topic, with numerous species-specific adaptations. So the question Why do amphibians change colour? has a myriad answers and can vary to involve different species, life stages, predation pressure, ambient conditions, especially temperature, stress, UV light and intra-sexual communication between males.

 

References:

King, R. B., Hauff, S., & Phillips, J. B. (1994). Physiological color change in the green treefrog: responses to background brightness and temperature. Copeia, 422-432.

Ries C., Spaethe J., Sztatecsny M., Strondl C & Hodl W.(2008) Turning blue and ultraviolet: sex-specific colour change during the mating season in the Balkan moor frog Journal of Zoology 276, 229–236

 

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Flexibility of life history events in the Common Frog

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5. Getting bigger (Rob Williams, 2011)

Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

Croaking Sceince reporter Rhiannon Laubach looks at the history of Chytridiomycosis and it’s impacts on the Fire Salamanders in Europe

– See more at: http://www.froglife.org/2014/05/14/lethal-chytridiomycosis-salamandars/#sthash.ugsmA3E1.dpuf

Croaking science is a new way for student volunteers and scientist to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

Croaking Sceince reporter Rhiannon Laubach looks at the history of Chytridiomycosis and it’s impacts on the Fire Salamanders in Europe

– See more at: http://www.froglife.org/2014/05/14/lethal-chytridiomycosis-salamandars/#sthash.ugsmA3E1.dpuf

Croaking science is a blog for student volunteers and scientists to explore what’s occurring in the world of Science. Croaking Science looks at science facts, new research or old debates which are inspired by or affect amphibians and reptiles, and then communicates this in layman’s language to a wider audience. The aim of the feature is to provide a platform for those starting their foray into the world of science communications as well as established scientists. We welcome any submissions from students and scientists. Please note that the views expressed in the articles are not those of the Froglife Trust.

Croaking Science reporter Rhiannon Laubach looks at the flexibility of life history events and its significance for Common Frogs

Not all members of the same species undergo metamorphosis at the same rate. Metamorphosis can be described as a life history event, the transformation from the larva (tadpole) to the juvenile adult (froglet). The size of an animal, or the development stage it is at, can affect the chances of an individual surviving the winter, in temperate climates.

Most tadpoles metamorphose into froglets in the same year. However, some common frog tadpoles can over-winter in this larval stage and then transform into frogs the next spring. This phenomenon has been recorded with a greater frequency in recent years, being reported by both the media and scientific literature. There has not been much investigation into what causes this and it is not known at which point in its development an individual will determine if it will over-winter as a tadpole or not.

A recent report studied the growth and development of a population of common frogs (Rana temporaria) tadpoles throughout one year in order to see if the rate of development of tadpoles would influence in what form they over-winter. Laboratory studies were carried out to complement field work.

8. Long legs (Rob Williams, 2011)The methods of the study were as follows: between May and January of the following year, tadpole development at the field site was monitored by randomly collecting tadpoles and taking them back to the laboratory to be measured and their stage of development was noted. If an individual had not started metamorphosis by November it was considered to be over-wintering as a larva. Water temperature was continuously logged for the duration of the study. This data was used to calculate the mean fortnightly temperature. For the laboratory study, the tanks where kept at mean fortnightly temperatures and they had either a high or low food availability scenario. The tadpole’s development and condition were also recorded.

9. Front legs growing under skin (Rob Williams, 2011)The study confirmed that tadpoles do over-winter at the study site. At the site, shortly after hatching the larvae began to form two distinct development groups. One group consisted of waves of individuals that grew on and then metamorphosed. The second, smaller, group continued to grow but did not metamorphose and this decision to over-winter as tadpoles was carried out very early in their development.

It is unclear what causes this, it could be genetic or “local environmental cues triggering a particular developmental pathway in a genetic subset of the population” (Walsh& al 2008). Tadpoles that over-winter have an advantage, as they don’t have to invest so much energy into development and can use more energy for growth. Larger tadpoles will metamorphose into larger frogs. Larger frogs have an advantage. In the laboratory there was no over-wintering. The tanks where kept at a mean fortnightly temperature, which does not reflect the temperature fluctuations at the study site. Food availability was not shown to have an affect on over-wintering.

This study shows that the possibility of a tadpole over-wintering is determined very early in its development. Over-wintering of larvae might be the tadpoles’ response to local environmental conditions but temperature does not seem to be the main variable for determining this (Walsh& al 2008).

17. Freedom... (Rob Williams, 2011)

 

Reference
Walsh, P.,T., Downiel, J., R., Monaghan, P.. (2008). Larval over-wintering: plasticity in the timing of life history events in the Common Frog. Journal of Zoology. 276 , 394-401.

Photos: Rob Williams