frogs

Croaking Science: Chemical communication in frogs and toads

September 25, 2017 by admin

Chemical communication in frogs and toads

The use of chemical communication to facilitate courtship in salamanders and newts is well recognised. Since anurans (frogs and toads) predominantly use acoustic cues during courtship, the use of scent has previously been thought of as a less important form of communication. However, studies over the past two decades have shown that chemical cues are more important than was first realised in the lives of frogs and toads.

During the breeding season of frogs and toads, the male will often form amplexus with the female and to help facilitate a grip on the female’s back, male frogs develop keratinized, often spiny nuptial pads on their thumbs and forearms. Glands are present below the surface of the nuptial pads and these release a secretion onto the keratinized surface of the nuptial pads. It has been proposed that these produce glue-like substances to enhance the male’s grip on the female. In addition, they may also act as attractant pheromones for reproduction. A recent study on the common frog (Rana temporaria) has shown that these chemicals serve a purpose in reproduction. Willaert et al. (2013) have found that chemicals known as amplexins are secreted at the surface of the male’s nuptial pad, probably during amplexus. The small spines on the male’s nuptial pad causes wounds on the female and these may allow the secreted molecules to seep directly into the female’s circulatory system. Such a direct delivery of protein pheromones into the circulatory system is only known from some species of plethodontid salamanders from North America. In these species, males develop a special gland during the breeding season which they use to rub pheromones into the female’s skin. It is therefore possible that delivery of pheromones through the skin is more common than initially thought within anurans.

*Figure 1: A male painted reed frog (Hyperolius marmoratus) calling during the night in South Africa. The gular patch on the vocal sac produces pheromones which may be used to attract females.*

Chemical communication may be used to serve different purposes during courtship in anurans. The anuran family Hyperoliidae (reed frogs) is common in sub-Saharan Africa, Madagascar, and the Seychelles, and consists of over 200 species in 18 genera. Reed frogs develop a colourful gular patch on their vocal sac during the breeding season. The vocal sac is used to produce advertisement calls and results from experimental work on reed frogs by Starnberger et al. (2013) has shown that the colourful gular patch produces pheromones (Figure 1). This study confirmed the presence of volatile pheromones in the gular patch on the vocal sac of reed frogs from several of the genera known at present including the most species-rich ones (Hyperolius, Afrixalus, and Heterixalus). Starnberger et al. (2013) propose that the male produces volatile substances that are emitted while he is calling and these circulate in the air to attract females, and/or to keep rival males at a distance. Male reed frogs often call from females in mixed groups with other closely related species. Starnberger et al. (2013) propose that advertisement calls alone may not be sufficient for females to sufficiently identify males from their own species. Therefore the additional chemical cues emitted in the form of pheromones may aid in species recognition.

Male dwarf African clawed frogs (genus Hymenochirus) have also been observed to have an ability to attract females using pheromones. Members of this genus are highly aquatic and endemic to central Africa, occupying slow-moving water bodies within areas of rainforest. As with many other male frogs and toads, individuals within the genus Hymenochirus possess skin glands during the breeding season. The importance of these has remained unknown for many decades. However, Pearl et al. (2007) have found that the breeding glands of male dwarf African clawed frogs (Hymenochirus sp.) release a mate-attractant chemical. In an experimental y-maze, females showed a positive response to water housing males and to water containing homogenized breeding glands. Results from this study were among the first to demonstrate a mate-attractant function for anuran breeding glands. Since many anuran species possess breeding glands, these results suggest that pheromone communication could be more widespread among frogs and toads than previously believed.

Figure 2: Male mantellid frogs such as the golden mantella (Mantella aurantiaca) from Madagascar may use volatile pheromones emitted from glands on their thighs to attract females.

Since this discovery in 2007, further research has focused on searching for other anurans which use chemical signals. In the Mantelline subfamily of Mantellid frogs, males have enlarged femoral glands that cluster on their ventral thighs (Figure 2). An analysis of macroglands from several Mantelline species by Veneces et al. (2007) found species specific differences in the volatile compounds. The authors suggested that the chemicals help the frogs identify individuals of the same species in multi-species choruses. These and similar studies are adding to our knowledge and understanding of how anurans use chemical signals. The chemical systems used by amphibians are varied and complex and future research should look at further investigating the use of chemicals in anuran reproduction.

References

IUCN SSC Amphibian Specialist Group. 2014. Hymenochirus boettgeri. The IUCN Red List of Threatened Species 2014: e.T58154A18396612. http://dx.doi.org/10.2305/IUCN.UK.2014-3.RLTS.T58154A18396612.en. Downloaded on 08 September 2017.

Pearl, C.A. Cervantes, M., Chan, M., Ho, U., Shoji, R. and Thomas, E.O. (2007) Evidence for a mate-attracting chemosignal in the dwarf African clawed frog Hymenochirus. Hormonal Behaviour, 38 (1): 76-74.

Starnberger, I., Poth, D., Peram, P.S., Schulz, S., Vences, M., Knudsen, J., Barej, M.F., Rödel, M-O., Walzl, M. and Hödl, W. (2013) Take time to smell the frogs: vocal sac glands of reed frogs (Anura: Hyperoliidae) contain species-specific chemical cocktails. Biological Journal of the Linnean Society, 110 (4): 828–838, https://doi.org/10.1111/bij.12167.

Willaert, B., Bossuyt, F., Janssenswillen, S., Adriaens, D., Baggerman, G., Matthijs, C., Paulsels, E., Proost. E., Raepsaet, A., Schoof, L., Stegan, G., Treer. D., Van Hoorebeke, L., Vanderbergh, W. and Van Bocxlaer, I. (2013) Frog nuptial pads secrete mating season-specific proteins related to salamander pheromones. The Journal of Experimental Biology, 216: 4139-4143.

Vences, M., Walh-Boos, G., Hoegg, S., Glaw, F., Spinelli Oliveira, E., Meyer, A. & Perry, S., 2007. Molecular systematics of mantelline frogs from Madagascar and the evolution of their femoral glands. Biological Journal of the Linnean Society, London, 92: 529–539.

Woodley, S. (2015) Chemosignals, hormones, and amphibian reproduction. Hormones and Behaviour, 68: 3-13.

Gretton School are leaping for joy!

February 1, 2017 by admin

Froglife have been awarded a £19,836 grant from the Postcode Local Trust to develop an unused and publically accessible area of Gretton School’s grounds into a vibrant wildlife area and outdoor classroom.

We will be working with the school to create a network of ponds, providing stepping stone habitats for wildlife and linking to the surrounding countryside. A fire pit, wooded area for den building, natural seating areas for learning and a wooden hut will also be included in the project. Community involvement will be encouraged through wildlife workshops and an open day.

Froglife’s Head of Learning and Communications, Jenny Tse-Leon said “We’re hugely grateful to the Postcode Local Trust for awarding us this grant so that we can create this community resource”

frog in hands lcb After a chance meeting Froglife worked with Gretton School to develop plans to improve an overgrown area of land for the benefit of wildlife and people.

Assistant Headteacher, Victoria Howe, explains “Gretton School is a specialist school for children with high functioning autism. The children prefer to learn in a kinaesthetic way and having an outside area which they can have safe access to would motivate and inspire them to embrace the outdoors and to be able to practise invaluable life skills”.

“Leapfrog Girton” was developed from these ideas and aims to support children with additional needs to engage with the environment around them whilst also creating valuable habitats for wildlife and raising awareness among the school and local community about amphibians, reptiles and conservation efforts to protect them.

Froglife will be delivering the year-long project through their Leapfrog Schools Programme which offer schools a range of accessible and inclusive options to help them learn more about amphibians and reptiles.

Jenny Tse-Leon, said “We are delighted to be working with Gretton School on this project and have been impressed by their enthusiasm and commitment”.

You can find out more about our Leapfrog Schools project at www.froglife.org/leapfrog-schools/.

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

October 30, 2015 by admin

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.

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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Inspired by Nature: Digging Potatoes and holding frogs

July 31, 2015 by admin

^{Inspired by Nature is a themed Croak to entertain you with some of our favourite artwork based on nature and the outdoors. We hope it will stimulate you to get creative and produce something yourself. If you do and would like to share them with us, please post them on our Facebook page, Twitter account, or email us at info@froglife.org}

^{This months feature has been written by the poet Keely Mills who worked with Rebecca Neal our Conservation Youth Worker on the Peterborough Green Pathways project, funded by BBC Children in Need.}

Digging potatoes and holding frogs

None of us say much,

Questions hang like spider webs in the air,

they can’t catch the answers though.

Just a huh or a maybe.

Its an uncomfortable mood

& it seeps into every move we each make.

Even the fire we light, can’t stay aflame.

We split off, each of us an ember.

I am not sure that it will change.

Nature overtakes any doubt.

Within minutes, we are all digging potatoes.

We take it in turns to collect and wash them.

Back together again.

Choosing which of them we will take.

As if it were ready now, the fire is lit.

It reaches the sky and feeds off our new warmth.

We share cooking duties, stories about school.

Some of us hold tiny frogs,

Make badges and boil a kettle.

After we have eaten.

And the taxi has been called.

Each of us hold onto this green feeling for as long as we can.

Now more than ever, I understand that a bad start,

can be mended with dirt, love and growing.

By Keely Mills

July 2015

Last chance: Share your frog thoughts & enter our prize draw

March 5, 2014 by admin

Froglife’s national survey about perceptions of amphibians and reptiles is coming to an end on the 14^th of March. We are asking people what they think about snakes, newts, frogs, lizards and toads as part of a project supported by the Heritage Lottery Fund to investigate how the animals are viewed. We would love to know your thoughts about wildlife and charity, and you can find the online survey here.

Questions include your favourite animals and thoughts about wildlife conservation, your opinions on amphibians and reptiles, a bit of an ID quiz as well as about the charitable causes closest to your heart.

We’re not looking for right or wrong answers; we’re really interested in honest responses to help us get a better understanding of the challenges we face when talking about our work. You can find out more about the aims of The Scale of the Problem project here.

Through taking part, you can also enter a prize draw to win over £50 worth of goodies from the Froglife online shop, with a prize for over 18s and under 18s who take part.

Under 18s prize — *The prize for under 18s includes a cuddly frog, pond dipping kit and frog back pack from the online shop*

The results so far have been really interesting, with Hedgehogs the most popular answer to the favourite animal question. 95% of the respondents so far have seen a frog in the wild in the UK, compared to 64% having seen a snake. We are also hearing, perhaps unsurprisingly, that many people are affected by financial concerns when choosing to support charities, and have cut back donations. All of the information we gather through the survey will be analysed by marketing experts Emerald Frog to help us strengthen our fundraising and campaigning techniques, enabling us to better support amphibians and reptiles into the future.

It would be wonderful if you could take the time to share your thoughts and experiences before the 14^th of March, to help shape the future of Froglife’s communications and campaigns. Thank you!

Inspired by Nature: Limericks

January 27, 2014 by admin

Inspired by Nature is a new themed Croak to entertain you with some of my own and my favourite famous poems written about nature and the outdoors. I hope it will stimulate you to get creative with words and write something yourself. If you do and would like to share them with us, please post them on our facebook page.
Becca (Conservation Youth Worker: Green Pathways Project).

Everyone loves a limerick, but have you ever tried to write one yourself?

I attend a weekly creative writing class. One week, I had not done any homework and knocked these out after work to ensure I had something to hand in! I love being outdoors, so everything I wrote is true (except now I have my own handsome man and so obviously, only love that one!).

A limerick is a short funny poem with 5 lines where the first, second and fifth lines rhyme and the third and forth rhyme (in literary terms, this is described as the rhyme scheme AABBA). They are often rude and nonsense. The first line usually introduces a character and a place. There are complicated ways to talk about the rhythm which uses words like feet, syllables and meter but basically it goes like this:

da DUM da da DUM da da DUM
da DUM da da DUM da da DUM
da DUM da da DUM
da DUM da da DUM
da DUM da da DUM da da DUM

Here are mine:
There once was a girl in the fens
Who took teenagers out to build dens
She wrote poetry for fun
Read short stories she’s done
As they always contain handsome men
There once was a wildlife nerd
Whose specialist subject was birds
She also liked badgers
And searching for adders
And loved handsome men, so I’ve heard

What you can do:

Why not have a go yourself, perhaps inspired by a walk on your local nature reserve or watching the birds with your kids ? Please don’t share the really rude ones, but any that you would read to your mother we would love to see on our facebook page.

croak all about it

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