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Fortune favours the bold urban toad

04 September 2021

Urban toads show themselves to be bolder - before and after invasion

Many of us are now familiar with urban commensal species - those that have adapted to life in towns and cities and can be seen to exploit their new surroundings. The Guttural Toad,Sclerophrys gutturalis, is one such species that can be more easily found in urban areas of east and southern Africa than in rural situations. This toad readily adapts to feeding under street lights at night, and breeding in garden ponds. 

In this study, MeaseyLab postdoc James Baxter-Gilbert, collected toads from urban and rural areas in their native (Durban) and invasive (Reunion & Mauritius) ranges (see blog posts about the field work here and here). He then examined differences in boldness and exploration in toads from each site. Because the invasion route of these toads is already known (see blog post here), James was able to reconstruct whether trends in boldness along the invasion route. Have invasive toads become bolder than their native counterparts?

What he found was that urban toads were consistently more bold than those in rural situations. This means that along the invasion route, there has been a reversal from bold to not so bold when toads moved from urban situations into rural ones. This tells us that urban settings significantly benefit these bold traits, and that toads (at least) are able to switch between these different phenotypes no matter where they are introduced. 

This finding shows us more of the flexibility of these toads as invaders. If they are moved from native or invasive ranges, they will adapt for both urban and rural lives. 

Read the article in full here:

Baxter-Gilbert, J., Riley, J.L. & Measey, J. Fortune favors the bold toad: urban-derived behavioral traits may provide advantages for invasive amphibian populations. Behav Ecol Sociobiol 75, 130 (2021). pdf

Also see the blog entry at the CIB here: 

Sam catching toads in Durban

20 April 2021

Fieldwork at last for Sam 

Lockdown has taken it's toll on many projects in the MeaseyLab, and no more so than with Sam Peta who has been prevented from doing much of the fieldwork that was envisioned for his MSc. Happily, domestic travel was still an option for Sam, and so he has been able to conduct a trip to Durban this April to collect some needed samples for his work.

Despite it being very late in the toad season, Sam has done a fantastic job of getting all of the samples he needs to complete his second MSc chapter. 

Sam captures another Guttural toad for his work, and completes his sampling.

Shrinking bigger than we thought

16 April 2021

Battle of the dwarfs: Guttural Toads turn out to be the largest known shrinkage of any anuran island dwarf

Large analyses reveal a good idea of how major systems have shifted on an evolutionary scale. Yesterday a new paper published inNature Ecology & Evolutionby Ana Benítez-López and colleaguesbrought together more than a thousand species of vertebrates to explore the ‘island rule’:  insular dwarfism in large-bodied species and island gigantism in small-bodied species.

As keen readers of this blog will know we published a paper last year (Baxter-Gilbert et al 2020) about rapid shifts in the sizes of Guttural Toads introduced from Durban, South Africa to the islands of Mauritius and Réunion. That paper led by MeaseyLab postdoc, James Baxter Gilbert, revealed that female toads from Mauritius had significantly smaller snout vent length (SVL) than female toads from Durban by 33.9% (red data point below). Similarly female toads from Réunion had significantly smaller SVL than female toads from Durban by 25.9% (green data point below). For males the shift was somewhat smaller (and is not shown on the graph). 

We were quite surprised with the magnitude of these changes but we did not appreciate how large they really were until the publication of the study by Anna Bonita Lopez et al, yesterday.

Above I have graphed out their data on anuran SVL together with a one to one bar (blue) indicating size parity. Their data seems pretty globally comprehensive with 116 data points from 42 anuran species. You can see that most examples of frogs on islands show gigantism compared to their mainland counterparts. The two coloured data points represent mean size shifts between Durban and Mauritius (red) and Durban and Réunion (green). 

The biggest shift that they record for any taxon on from mainlands to islands is a 25% reduction from 43 mm to 32 mm from the Spanish mainland to Majorca for Alytes dickhilleni and A. muletensis, respectively (Arntzen & Garcia-Paris 1995). These sister taxa are believed to have been separated for more than 4 million years! 

As you can see, it is clear that the 33% shift we saw for female Guttural Toads (from Durban to Mauritius - red data point) in less than 100 years is not only remarkable but the largest reduction in body size of any anuran known on the planet! 

A nice fun fact for a Friday morning



Arntzen, J.W. and García-París, M., 1995. Morphological and allozyme studies of midwife toads (genus Alytes), including the description of two new taxa from Spain. Contributions to Zoology, 65(1), pp.5-34.

Baxter-Gilbert, J., Riley, J.L., Wagener, C., Mohanty, N.P. and Measey, J., 2020. Shrinking before our isles: the rapid expression of insular dwarfism in two invasive populations of guttural toad (Sclerophrys gutturalis). Biology letters, 16(11), p.20200651.

Benítez-López, A., Santini, L., Gallego-Zamorano, J. et al. The island rule explains consistent patterns of body size evolution in terrestrial vertebrates. Nat Ecol Evol (2021).

Graduation time

01 April 2021

Graduation time

Every graduation is a celebration of achievements, and each year I am moved by how much our students achieve during their (relatively) short postgraduate studies. This April we had a double celebration of two MSc students, both of whom graduatedcum laude. Sadly, because of the ongoing pandemic situation, neither was able to attend the graduation ceremony in person. 

Nolwethu Jubase-Tshaliworked full-time during her MSc, including receiving a promotion to becoming Western Cape Regional Coordinator in SANBI’s Directorate on Biodiversity Evidence (DBE). Because Nolwethu worked full-time at her day job, we didn’t see her often in the lab. Nolwethu was co-supervised by Dr Ross Shackleton, previously a PhD student and post-doc at the CIB, but now Maitre assistant at the University of Lausanne, Switzerland. 

Nolwethu’s MSc thesis consists of 2 chapters. In the first, she asks what motivates volunteers to remove alien invasive plants in the Western Cape. In the second, she finds out what people from 8 towns in the Berg River catchment know about alien invasive species. Both chapters are placed into the framework of how to practically manage alien invasive species in the Western Cape province. Each progresses our understanding in the important topic of biological invasions. 

The first chapter: "Motivations and contributions of volunteer groups in the management of invasive alien plants in South Africa’s Western Cape province", is currently in press withBothalia, African Biodiversity & Conservation

The second chapter is being prepared for a special issue. For more news on this, stay tuned on the blog. 

Nolwethu’s graduation provides an important milestone for me, as she is my first student to graduate with a degree in Botany!

Carla Wagenerdid her undergraduate degree in Botany & Zoology, she did both her Honours project and MSc in the lab. Consequently, Carla had been in the department in Stellenbosch longer than anyone else, and knew the answers to practically anything we could think of. Carla’s MSc work was co-supervised by Dr Morne du Plessis (then) of SANBI at the Pretoria Zoo. Carla also received the covetedcum laudefor her thesis and presentation of her MSc in Zoology.

You can read blog posts about Carla’s work: 


With Brazilian guests:Carla&Adriana

Doing toady things inMauritius&Durban

Carla’s MSc has two chapters. One compares the gut microbiome of 1 native and 3 invasive populations of Guttural Toad,Sclerophrys gutturalis. The second chapter contains an experiment to determine the effect of transplanting gut microbial fauna from invasive to native populations, and vice versa. The first chapter is currently under review, while you can read a preprint of the second chapter here: 

The gut microbiome facilitates ecological adaptation in an invasive vertebrate

Last, but not least, Lisa Mertens, also graduated as a PhD. Due to some difficulties during the course of her studies, Lisa finally graduated with John as her supervisor. They both attended graduation on April 1st. 

Graduating theses:

Jubase-Tshali, N. (2021) Evaluating the effectiveness of citizen science to detect, report and control alien and invasive species in Western Cape, South AfricaMSc thesisStellenbosch University

Wagener, C. (2021) Spill your guts: the invasive amphibian gut microbiome.MSc thesisStellenbosch University

Mertens, L. (2021) Assessing the evolutionary and physiological resilience of southern African marine speciesPhD ThesisStellenbosch University

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

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