The 10th World Congress of Herpetology in Kuching, Sarawak, Malaysia

It was a great pleasure to attend the 10th World Congress of Herpetology in Kuching this month. The congress was a great opportunity to catch up with herpetologists from across the planet, including many that I have known for many years as well as many many new faces. 

I presented my work on the gut microbiome of Xenopus laevis, and was pleased to see many former members of the MeaseyLab presenting their own work.

Burrowing in Snakes: a Comparative Study on the Performance and Mechanics of Snake Burrowing
Anthony Herrel, David J. Gower, James C. O’Reilly, Nathan J. Kley, Philippe Gaucher, Ilian Grima, John Measey and Marion Segall

Snakes are an incredibly diverse lineage of squamates that have radiated into a great diversity of habitats from a possibly fossorial ancestor. Fossoriality imposes strong constraints on obligatory head-first burrowers and this has been suggested to have impacted the morphological evolution of both head and cranial shape. The strength of constraints on head shape likely depend on the taxon and burrowing style but quantitative data on the forces exerted during burrowing or the kinematics of burrowing remain scarce. Preliminary data suggested that typhlopid snakes were capable of generating higher forces than other snakes for a given size and body diameter but taxon sampling was limited. Here, we present data on the three-dimensional burrowing forces for 26 species of snakes distributed across most major lineages. We further present the first X-ray data on the kinematics of locomotion through tunnels and soil for a subset of species including sand swimmers (Eryx) and true burrowers (Anilius, Xenopeltis, Cylindrophis, Homalopsis and Aspidelaps). Our data show significant differences in maximal resultant forces and force orientation in different species. Moreover, our kinematic data show that sand swimmers are unique in showing kinematics of subsurface locomotion similar to those observed in snakes swimming in water. Finally, we show that some snakes such as Anilius are capable of performing internal concertina locomotion documented previously only for caecilians. Overall our data shed new light on the diversity of burrowing performance and kinematics in snakes and help understand the evolution of this lifestyle and its constraints on form and function.

Does Plasticity or Genetic Adaptation Induce Variation in Thermal Sensitivity of an Invasive Frog (Xenopus laevis)? A Population Level Study, from Tadpoles to Adults
Laurie Araspin, John Measey and Anthony Herrel

Life history traits of organisms are modulated by the selective pressures of the environment, generating variation in phenotypes. This phenotypic diversity can be observed at the interspecific level but also at the intraspecific level in populations living in different environments. Temperature is a characteristic of an animal’s habitat and one of the dimensions of the ecological niche. It is a critical factor impacting all aspects of the biology of organisms, especially in ectotherms. Xenopus laevis is an aquatic frog that is invasive on four continents, with invasive populations inhabiting a diversity of environments. The objective of this study was to investigate the thermal adaptation ability of this species that is successfully established in dramatically different thermal environments. The use of thermal performance curves allowed to assess the relationship between temperature and locomotor performance and basal metabolic rate in individuals from two generations. Phenotypes from a F1 generation of the studied populations raised in a common garden environment were compared to the F0 phenotypes. This allowed to understand whether the observed differences among populations
are plastic or genetically based. This study demonstrated that populations exhibit a different thermal dependence of their performance, and that genetic and plastic processes are involved in the thermal adaptation, highlighted by a significant genotype by environment interaction. Variation in performance depending on temperature provides an insight into how this invasive species can survive and cope with different thermal environments, especially in the context of climate change.

Of Toads and Toxins: Shrinking Toxin Glands but Stable Toxin Composition Indicate Directions and Constraints of Adaptation in Invasive Populations of an African Toad
Max Mühlenhaupt, Cláudia Baider, James Baxter-Gilbert, André J. de Villiers, Nhlanhla S. Dludla, F. B. Vincent Florens, Buyisile G. Makhubo, Xavier Porcel, Julia L. Riley, Willem A. L. van Otterlo and John Measey

Many amphibian species use chemical defenses to avoid predation, yet, how these defenses vary between populations, or change as populations colonize novel habitats is not well understood. The Guttural Toad (Sclerophrys gutturalis) has established three invasive populations, located in Mauritius, Réunion, and Cape Town. All of these populations originated from a clade located at the port city of Durban in eastern South Africa, providing an excellent study system to examine how biological invasions drive phenotypic change. To investigate how toad chemical defenses may have shifted along their invasion path, we compared the relative size of the parotoid glands (as a correlate of toxin quantity) and the composition of the toxic secretions that exude from these glands (as an indicator of toxin potency) between native and invasive populations. While the two oldest invasive populations, Mauritius and Réunion, showed pronounced convergent decreases in gland size, the toxin composition remained stable between all populations. These results indicate that the invasive populations of this chemically defended toad may have experienced reduced predation pressure in their novel habitats, which resulted in reduced selection pressure for defense. Furthermore, within the native populations, gland size may also be a more variable trait than toxin composition. Integrating both quantitative as well as qualitative information will help us better understand the evolution of chemical defenses in animals and could aid in predicting if and how chemically defended invasive species colonize novel environments.

Home and Away: The Core Gut Microbiome of Xenopus laevis is Modified by its Environment
Measey, J., Ren, Q., Guille, M., Almojil, D., Araspin, L., Wagener, C., Boissinot, S., Watts, J. and Robson, S.

The vertebrate gut microbiome is a community largely composed of bacterial, fungal and viral components, whose molecular component equal that of the host. The influence of the microbiome is known to be significant both on an individual basis, and also on population scales in a wide range of host organisms. The gut microbiome is known to be involved with key attributes of animal health, including assimilation of nutrients, immuno-defensive functions and host behavior. In this study, we used bacterial 16S rRNA amplicon-based sequencing for metataxonomic classification of the gut microbiome of individuals from eight populations of Xenopus laevis. These populations were selected to represent an altitudinal gradient in the native range of the host species (0 to 3,000 m asl). From the 16S rRNA community profiles, we determine the components of the core microbiome of X. laevis , and ask whether deviations from the core are associated with the environmental context in which they live. In addition, we sampled four European invasive populations and a laboratory population from the European Xenopus Resource Centre (EXRC) in the UK, to determine what aspects of the core microbiome are retained by non-native populations. This represents the first time that the microbiome of X. laevis has been assessed across such diverse conditions, and provides data that will help understand the role played by the environment and inform monitoring of health within this model organism.

ROUNDTABLE "TAKING THE INVASIVE TOAD TOOLKIT GLOBAL"

John Measey, Georgia Ward-Fear & Angelica Crottini

Invasive toads are a global problem, and yet many solutions and mitigations are available –
particularly as a result of a large investment into cane toad invasions in Australia. But how
much of the “invasive toad toolkit” can be exported to other invasions? This round-table event
is aimed at stakeholders with an interest in toads and toad invasions to precise what parts of
the toad toolkit can be used in toad invasions worldwide.

The peculiar tale of Xenopus laevis in Hamamatsu City, Shizuoka Prefecture

There are a few pathways for invasive populations of African clawed frogs, Xenopus laevis. The first, and oldest, has been the accidental (or deliberate) release of animals associated with laboratories using animals for pregnancy testing or as lab models. More recently, the number of invasions due to released pets has been on the rise, and we have seen examples of this in the USA, Belgium and China. Most of the invasions in Japan also appear to be related to pets, but not the population in Hamamatsu City.

In addition to being the laboratory model amphibian, the tadpoles of Xenopus are also used in a method known as FETAX (Frog Embryo Teratogenesis Assay – Xenopus) where they are used to measure toxicity of the water. I presume that it was this reason that led the City of Hamamatsu to release Xenopus tadpoles into one of their polluted Lake Sanaru in 1982 (see Arao & Kitano 2006). This means that the population found by Arao & Kitano in 2005 in an aquaculture area raising eels was over 20 years old at that time, but is now over 40 years old.

I was reliably informed that the animals were still there 5 years ago, and so I teamed up with Dr. Hisanori Okamiya from the Museum of Natural and Environmental History in Shizuoka. After spending a frutless morning searching in Makinohara (which apparently also had a population 5 years ago), Hisanori and I started looking around the eel farms.

A farmer at the first farm that we asked at pointed to a dead floating frog floating in a newly sterilised eel tank and asked us if this was the type of frog we were looking for. I fished it out with a very long net, and could immediately see that it was indeed a (very) dead Xenopus laevis. 

The farmer confirmed that he gets these frogs in his eel tanks all the time, but that the population appeared to be getting smaller over the last 5-10 years. We placed out traps in a large outdoor pond, the presumed source of frogs, and came back the next day very disappointed to find that there were no animals at all inside. 

I suggested that we keep on asking at eel farms and see whether anyone else was finding animals, or perhaps could point to their source. As we headed down the row of farms along the road next to the bullet train track, sightings appeared to be getting less and less. We decided to take a break and have some lunch. It had been pouring with rain all night and all morning, and Hinasori and I had been getting very wet despite waterproofs. It seemed fitting that we have eel for lunch, and so I splashed out. 

After lunch, we headed back the way we came. We stopped in the neighbouring aquaculture farm (not an eel farm, but a farm for koi carp). We couldn't find anyone around. We searched around all of the buildings, but couldn't find anyone. As we were walking through a big puddle at the side of an eel pond, Hisanori saw a frog swimming in the water. Happily, I filmed what happened next, so you'd best watch the video below:

We managed to find the owners of the farm who allowed us to fish around in one of their empty fish ponds, where we found lots of tadpoles and lots more metamorphs, but no adults. 

So it seems that 42 years after releasing tadpoles into Lake Sanaru, African clawed frogs are still alive and well in Hamamatsu City.

Further Reading:

Arao, K. and Kitano, T., 2006. Xenopus laevis from Hamamatsu City, Shizuoka Prefecture, Japan. 爬虫両棲類学会報, 2006(1), pp.17-19. 

A new invasion of Xenopus laevis in Chiba City

Before my visit to Japan I was looking for information about current invasions in the country when I came across a citizen conservation group in Chiba City, who had recorded Xenopus laevis  in a river flowing through a conservation area in their city. I made arrangements to visit the site with Dr. Takaki Kurita from the Chiba Prefecture Natural History Museum, and was greeted by a band of entthusiastic conservationists who were all happy to jump into the river with us to capture some Xenopus.

It wasn't long before the first shout went up, and then another and another. In the 34 C heat, we were pulling lots of animals out of the river, including an array of native and invasive fish and American crayfish. 

It was great to work with such enthusiastic conservationists in Chiba Prefecture. 

Xenopus from the Tanabe peninsula

The invasive population of Xenopus on the Tanabe peninsula has been one that I have wanted to visit for many years. I was alterted to its presence through a paper by Kento Takata from the Wakayama Prefecture Natural History Museum (Takata et al. 2023).

I was really pleased to take this opportunity to visit the Tanabe Peninsula and meet up with Kento and Hiroshi Doei who has been working for 16 years to eliminate Xenopus laevis from the Tanabe Peninsula. Unfortunately for me, Doei has done such a good job that despite setting over 100 traps the night before I arrived, we did not capture a single individual. In fact, they had not seen any individuals in 2024, and only a handful in 2023, with the last tadpoles seen in 2022. 

If this invasive species really has been eliminated from the Tanabe peninsula, this would be a remarkable feat. I take my hat off to Hiroshi Doei who had come up with some truely inventive  ways to set traps and capture animals in more than 30 ponds on the peninsula. It was a great visit, even if I was not able to sample any Xenopus!

One of the key innovations that Hiroshi Doei made was to place traps on a pulley across the pond. This enabled him to set 30 or more traps at a single site with minimal effort..

To get an idea of just how bad the Xenopus population was on the Tanabe peninsula, take a look at this video.

Sampling the invasive population of Xenopus on Awaji Island

Japan has several invasive populations of Xenopus laevis and among them is the one on Awaji Island, South of Kobe City. Prof Takeshi Igawa kindly accompanied me to the site, making the trip possible. We were joined there by the amazing Nobuyuki Higashiguchi who has been catching Xenopus from this population for over 6 years. 

The island has a lot of rice paddys and small resevoirs that are needed to flood them. These present a myriad of habitats for Xenopus as they are all interconnected. 

We spent several days trapping in various different ponds and amassed a large number of animals. We were also treated to the mastery of a throw net as Nobuyi showed us how to catch tadpoles from one of the reservoirs.