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Two talks at SICB2021

02 January 2021

Two very different talks for Society for Integrative and Comparative Biology (SICB) 2021

I’m co-author on two very different talks at this years’ SICB conference, held online. 

The first talk by Carla Madelaire takes the work she and Adriana did on CORT back in 2019 to another level by asking whether saliva assays work as well as blood. This work has particular relevance on repeating CORT levels on individuals. Great to see this being presented!

The second study uses some data collected by myself and Anthony Herrel many years back. We collected some burrowing data on various caecilian species. Now Aurélien Lowie, from Ghent University, has taken this and other data to look at how a number of different live caecilians perform in relation to their skull shape. 

See more on the SICB 2021 website (links below!).

Corticosterone levels in the saliva as a measure of stress in toads

CB Madelaire, D Dillon, AMG Barsotti, J Measey, FR Gomes, CL Buck

Glucocorticoids have been widely used as a physiological marker of stress, and elevated baseline glucocorticoids levels in vertebrates have been associated with environmental changes. The use of minimally invasive sampling techniques and analysis of non-traditional sample types to monitor stress in wild populations has increased due to the importance of understanding how animals respond to environmental disturbances. The use of saliva samples can be a powerful tool to monitor both endocrine shifts and responses to stressors in wild populations. This sampling method does not require a large amount of manipulation and it can be used to sample smaller species, contributing to an increase of studies in environmental endocrinology and conservation efforts of understudied species. This study validated corticosterone (CORT) measurements in the saliva of the guttural toad (Sclerophrys gutturalis) using samples collected in the field and after a standardized stress protocol. We show that small amounts of saliva (0.018±0.028 g) are sufficient to quantify CORT. Salivary CORT levels were higher after exposure to a standardized stress protocol when compared to field levels of CORT, indicating that saliva samples can reflect biologically meaningful levels of CORT in the guttural toad. Because levels of salivary and plasma CORT were not correlated in either the field sampled animals or following exposure to acute stress, we conclude that CORT in the saliva and plasma might show different response dynamics to stimuli.


conservation physiology, glucocorticoid, acute stress, anura, salivary glucocorticoids

9:47 AM - 9:48 AM SAST on Saturday, January 2

Under pressure: the relationship between cranial shape and in vivo maximal burrowing force in caecilians (Gymnophiona)

Co-Author(s): A Lowie, A Herrel, B De Kegel, M Wilkinson, GJ Measey, JC O'Reilly, N Kley, P Gaucher, J Brecko, T Kleinteich, D Adriaens

Caecilians are elongate and limbless amphibians. Except one aquatic family, they all have an at least partially fossorial lifestyle. It has been suggested that they evolved sturdy compact skulls with fusion of ancestrally separate bones and tight sutures as an adaptation for head-first burrowing. Although their cranial osteology is well described, relationships between form and function remain poorly understood. In this study, we report data on in vivo burrowing forces for more than 120 specimens belonging to 13 different species. Over 80 caecilians were µCT-scanned and their skulls segmented. Using fixed and semi-sliding anatomical landmarks, we performed 3D geometric morphometrics to quantify skull variability across species. Finally, using correlation tests, linear models and two-blocks partial least squares, we investigated the relationships between the overall cranial shape and in vivo burrowing force in caecilians. Surprisingly, results show that despite differences in the head morphology across species, there is no relation between overall skull shape and this particular measure of burrowing performance. Although a phylogenetic signal may partly obscure the results, our conclusions join previous studies using biomechanical models and suggest that any differences in their degree of fossoriality are not driving the correlated adaptive evolution of head shape and maximal burrowing force. As the cranium has multiple functions such as feeding, and houses major sensory organs, or respiratory systems, further studies are needed to fully understand the selective pressures shaping the evolution of skull form.


amphibian, burrowing, geometric morphometrics, gymnophiona, skull, performance, head-first burrowers, head shape

10:05 AM - 10:06 AM SAST on Saturday, January 2

Endocrinology of invasive Guttural toads

22 December 2020

Hormones tell us more about rapid adaptation of invasive Guttural Toads

Back in January 2019, the wonderful PhD student Adriana Barsotti visited Stellenbosch together with Dr Carla Madelaire (both from Fernando Ribeiro Gomes' lab in USP), to add some endocrinological studies to our ongoing work on invasive Guttural Toads in Cape Town (see blog post here). Within no time at all, the fab duo set to work on sampling invasive toads in Cape Town's exclusive Constantia suburb, and from there they travelled to Durban to sample native toads with MeaseyLab MSc student, Carla Wagener (see blog post here). Along the way, the two Braziliaras taught us some some useful caipirinha skills (see here). 

Now Adriana has published the paper resulting from all of her work in South Africa:

In this great paper, we learn:

Invasive toads have lower body condition and tend to become dehydrated in the more arid conditions of Cape Town;
Invasive toads have the highest BKA and N:L ratio which could favor dispersal in their novel environment;
Dehydration is a stressor for native and invasive toads;
BKA remains comparatively higher in invasive toads even after acute stressors.

...and all this after only 20 years of invasion!

Carla published her findings earlier this year, showing us that invasive Guttural Toads have changed the way that they think about water (see blog post here).

The expertise from Fernando's lab is a great example of how our understanding grows through collaborations. Not only that, but it was great fun to host Adriana and Carla in the MeaseyLab, and we look forward to hosting more of Fernando's brilliant lab members in the future.

Read the papers in full here:

Barsotti, A.M.G., Madelaire, C.B., Wagener, C., Titon Jr, B., Measey, J., Ribeiro Gomes, F. (in press) Challenges of a novel range: water balance, stress, and immunity in an invasive toad. Comparative Biochemistry and Physiology, pdf

Madelaire, C.B., Barsotti, A.M.G., Wagener, C., Sugano, Y., Baxter-Gilbert, J., Ribeiro Gomes, F., Measey, J. (2020) Challenges of dehydration result in a behavioral shift in invasive toads. Behavioral Ecology and Sociobiology74: 83. pdf

Lots of news coverage for tiny toads

09 December 2020

Shrinking toads attract lots of news coverage...

The publication of our Biology Letters note has garnered lots of press coverage all over the globe. The story that Guttural Toads introduced to Mauritius in 1922 have shrunk by nearly a third from their original size has led to a lot of interest. It ties into the fascination that people have with the role of islands in both dwarfism and gigantism. After all, Mauritius is probably best known for the evolution of a huge pigeon, commonly known as the Dodo, Raphus cucullatus.

Our finding that an invasive population of Guttural Toads had so quickly shrunk now raises questions about these other instances of gigantism and dwarfism. Is there a possibility that they also happened in only hundreds of years, instead of tens or hundreds of thousands, as previously thought?

There was another swathe of articles published after James' press release hit the web: read here

Animali Il record del rospo delle Mauritius:, 03 Dec 2020

Miniature guttural toads on Mauritius and Réunion stun researchers: Agenparl, 08 Dec 2020

Morphological reshaping in guttural toads in Mauritius in a short time: The Hindu, 28 Nov 2020

Miniature guttural toads on Mauritius and Réunion stun researchers: Scienmag: Latest Science and Health News 08 Dec 2020

Miniature guttural toads on Mauritius and Reunion stun researchers:, 09 Dec 2020

Los sapos africanos se miniaturizan en casi un siglo en las islas de Mauricio y La Reunión: LaSexta, 13 Dec 2020

Volverse enano en una isla: el caso de una especie de sapo: NCYT - Noticias de la Ciencia y la Technologia, 15 Dec 2020

Read the blog post about the paper here

Or read the original paper in Biology Letters here:

Baxter-Gilbert, J.H., Riley, J.L., Wagener, C., Mohanty, N.P., Measey, J.  (in press)  Shrinking before our isles: The rapid expression of insular dwarfism in two invasive populations of guttural toad    (Sclerophrys gutturalis). Biology Letters pdf

Tiny toads from Mauritius and Reunion

18 November 2020

Miniature toads on Mauritius and Réunion

From time to time you make a natural history observation that really blows your mind. This was the case when I visited Mauritius in 2017 (seehere). I was there to study their Guttural Toads which had been introduced to the island in 1922. I had already heard from Giovanni Vimercati who had visited Mauritius himself several years earlier that the toads were very small, but it wasn't until I saw them that I realized the full magnitude of what had happened. In less than 100 years since their introduction these toads had shrunk.

Guttural Toads,Sclerophrys gutturalis, are a familiar feature in large parts of sub-Saharan Africa. They regularly inhabit urban areas taking advantage of lights to capture attracted insect prey. I have seen these toads in Kenya and Tanzania and they always appear quite large no matter the altitude or setting. So it was quite startling to see these mini toads on Mauritius.

Last year James Baxter-Gilbert visited Mauritius together with other members of the MeaseyLab to measure guttural toads and conduct some experiments with them (seeblog post). James managed to measure a large number of toads on both Mauritius and Réunion measuring not just their size but also their limb and jaw lengths. When he analyzed the data, James found that not only had the size changed but the limbs had changed their relative lengths as well. Overall, limbs were shorter on the island toads suggesting that their dispersal capacity is reduced. 

There are of course many outstanding questions about these observations. Is this miniaturization and change in limb length a permanent evolutionary change or a plastic reaction that would see them swap back to the regular size if reared on the mainland? We are hoping to address this question in future with a common garden experiment in Durban (watch this space!).

Other outstanding questions concern the reason why the environments on Mauritius and Réunion caused the toads to miniaturise. There are several competing theories but of course it could be a combination of any of these. Toads that need to move less on the small islands don't need large sizes and limb lengths. When released from the usual predation regime toads may revert to a smaller size that would be more vulnerable to mainland predators. Reproduction may occur more regularly on the islands meaning that the toads do not need to store energy for single reproductive bouts. Instead they could reproduce many times with small batches of eggs during the year. 

As you can tell there is still plenty of research to be done on guttural toads. The publication of this natural history observation is simply the first of what we believe will be many exciting investigations into this island invasion system.

Read all about it here:

Baxter-Gilbert, J.H., Riley, J.L., Wagener, C., Mohanty, N.P., Measey, J.  (in press)  Shrinking before our isles: The rapid expression of insular dwarfism in two invasive populations of guttural toad   (Sclerophrys gutturalis).Biology Letters

James publishes a popular article

05 November 2020

What do invasive toads eat on Mauritius?

It feels like it was only last week that I was encouraging the MeaseyLab to write popular articles to help publicise their papers (among other reasons: see here). Today, James Baxter-Gilbert, post-doc in the MeaseyLab, published a really nice piece in The Conversation Africa, about his study on Guttural Toad diet in Mauritius.

Here, James makes the really important point that these toads are eating Mauritian endemic snails that are classified by the IUCN as Critically Endangerd, Omphalotropis plicosa. Indeed, if you look up this species on the Red List website today, you'll see that it's listed as Extinct. Indeed, Vincent and Claudia, our collaborators in Mauritius, thought that this snail was extinct until it was flushed out of the stomach of a Guttural Toad (see here). Like other species coming back from apparent extinction, it has been termed a "Lazarus species". As the snail is arboreal, they don't think that the toads are a direct threat, but it all goes to show how much information you can get from looking at an alien's diet!

Read James' great article on Guttural Toad diet here:

Baxter-Gilbert, J. (2020). The diet of invasive toads in Mauritius has some rare species on the menu. The Conversation - Africa November 5, 2020 149371

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