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Plenary talk for SEH20

06 September 2019

The future of our planet’s amphibians and reptiles: a view from invasion science

I was asked to deliver a plenary to the 20th meeting of the Society for European Herpetology back in October 2018. This gave me a very long time to think about what soap box I wanted to get onto. This plenary invitation came with no strings, so I had the full gambit of subjects to consider. Given my current position and my recent reviews of the herp literature, it was clear to me that I wanted to give herpetologists more background and ideas about why invasion science is particularly important subject to be involved with.

I started my presentation with a reflection on the writing workshop of editors we had back in March 2019. It was John Wilson who suggested that for the last chapter of the book “Biological Invasions in South Africa” we should consider long-term trajectories of invasions, following the lead of Baum et al (2019). This gave us 4 outcomes for 2000 years’ time, and I began the plenary by describing each one and then explaining how we might expect invasion profiles to look in order to reach the outcomes.

In this slide, you’ll only see 3 outcomes as I ditched the ‘end of humanity’ trajectory as the planning for this is too similar to ‘pangea’.

You’ll be able to read more about the outcomes of this exercise in the forthcoming book chapter (Wilson et al 2019), but for the purposes of this blog post, the idea in both the plenary and the book chapter was to help people see how short-term planning needs to be in line with long-term thinking. This seems to be especially relevant now that we’ve lost the ability to think in the ‘long now’ that we had in the past.

This framework allowed me to place the Seebens et al (2017) revelation that there’s no saturation to alien introductions into the context of both alien reptiles and amphibians, and those other invasive populations that damage them (cf Nunes et al 2019).

I then continued by explaining the importance of the pet trade in future amphibian and reptile invasions (cf  Measey et al 2019; Mohanty & Measey in press), and especially the relevance of invasion debt in this; such that we should not expect to see invasive populations of all of these newly traded species, but that they will come in time.

I finished off the talk, by giving a few highlights of why studying invasive species is such fun. Special shout-outs were given to studies by Nick Telford, Nitya Mohanty, Gio Vimercati, Nicola van Wilgen and Carla Madelaire (among others).

If you’ve helped and are reading this blog, but didn’t get a chance to see the plenary, here’s the acknowledgement slide at the end, in which should be your pic!

 

Baum SD et al. (2019) Long-term trajectories of human civilization Foresight 21:53-83 doi:10.1108/fs-04-2018-0037

Measey J et al. (2019) Why have a pet amphibian? Insights from YouTube. Front. Ecol. Evol. 7: 52. doi: 10.3389/fevo.

Nunes AL et al. (2019) A global meta-analysis of the ecological impacts of alien species on native amphibians. Proceedings of the Royal Society B286(1897), p.20182528.

Seebens H et al. (2017) No saturation in the accumulation of alien species worldwide. Nature Communications8, p.14435.

Wilson JR et al. (2019) Potential Futures of Biological Invasions in South Africa. In van Wilgen et al. Biological Invasions in South Africa. Springer.

Other MeaseyLab talks at SEH20 were:

Ginal, P. Herrel, A., Measey, J., Mokhatla, M., Rodder, D. Ecophysiology predicts the fundamental niche of native and invasive populations of the African clawed frog Xenopus laevis. XX European Congress of Herpetology, Milan 2-6 September 2019

One main threat promoting the worldwide amphibian decline is the introduction of non-indigenous amphibians, like the African Clawed Frog Xenopus laevis, which is now one of the widest distributed amphibians occurring on four continents with ongoing expansion including large parts of Europe. Species Distribution Models (SDM’s) and the concept of ecological niche are essential to predict the invasive risk of those species. Previous efforts to predict distributions of invasive amphibians have mainly focussed on correlative approaches but these can be vulnerable to extrapolation errors when projecting species’ distributions in non-native ranges. Recently, more robust process-based models, which use physiological data like critical thermal limits, or hybrid models of both approaches were used for this purpose. Previous correlative SDM’s for Europe predict different patterns in the potential distribution but it is likely that these models do not access the full invasive potential. Based on physiological performance trials we calculated size and temperature depending response surfaces, which were scaled to the species’ range matching the critical thermal limits. These ecophysiological performance layers were used in a standard correlative SDM framework to predict the potential distribution in South Africa and Europe. We found thermal performance differed significantly among native and invasive populations indicating some degree of fundamental niche change, which lead to different potential distribution patterns for the native and invasive populations in the respective ranges. Our hybrid-SDMs revealed that X. laevis has a much higher invasive potential than previous correlative models predicted for Europe.

Measey, J. The future of our planet’s amphibians and reptiles: a view from invasion science XX European Congress of Herpetology, Milan 2-6 September 2019

In 2000 years, the future of our planet could have one of four potential outcomes: end of humanity, Pangea, use some/preserve others, and conservation earth. While we have already started along the trajectory toward Pangea, our actions in the near future will determine whether we can achieve a future where we retain areas that are preserved and herpetologically distinct. Among the global change drivers, invasion science is increasing in importance because of a continuing and near exponential increase in trade. We need all herpetologists to help generate the data needed to prevent the Floridarisation of herpetology. In this presentation, I outline a number of ways in which herpetologists can push back against herpetological Pangea: (i) characterising current invasive species, (ii) determining the breadth of invasion debt, and (iii) scoping the traits of all species to establish a rational basis for future trading. Although it was only conceived in the 1950s, invasion science now draws on almost all disciplines in biology, including phylogenetics, population biology, evolutionary ecology and modelling, to name but a few. However, our best chances of preventing herpetological Pangea may come from social science studies of what drives the trade in reptiles and amphibians. The challenge for us is to retain the potential for inspiring reptile and amphibian pets for coming generations, without peppering our environment with propagules of invasive species.

Vimercati, G., Davies, S. & Measey, J. Invasive subtropical toads allocate more resources to growth and maintenance over reproduction and storage in a mediterranean environment. XX European Congress of Herpetology, Milan 2-6 September 2019

Amphibians living in cold and seasonal environments allocate more resources to growth, maintenance and storage than do conspecifics from warmer and less seasonal environments. This sustained resource allocation may be obtained at the expense of reproduction, especially when low conditions of temperature and rainfall restrict breeding season length. Invasive populations act as experiments to explore how resources are allocated in novel environments. We studied the guttural toad Sclerophrys gutturalis, a synanthropic species which naturally inhabits subtropical areas of central and southern Africa. Guttural toads were introduced in the early 2000s to Cape Town, where they rapidly became invasive. Since Cape Town experiences a mediterranean climate, the species has been exposed to an environment that is cooler and presents a different rainfall pattern from that of the native range. We targeted the Cape Town invasive population and a native source population from Durban (South Africa). After dissection, lean structural mass (bones and muscles), gonadal mass, liver mass and body fat % were measured in 161 native and invasive animals sampled at the beginning and the end of the breeding season. As expected, male and female toads from the invaded range allocate more resources to growth and maintenance than their native counterparts, whereas invasive female toads direct fewer resources to reproduction than native ones. Unexpectedly, energy storage of guttural toads does not consistently differ between invaded and native ranges. Such allocation shift may be a response to the low temperature, reduced rainfall and heightened seasonality encountered by the invasive population.


Another Guttural Toad revelation

03 September 2019

Capital Breeding in Cooler Cape Town

A new study suggests that guttural toads are changing their breeding patterns to accommodate the cooler, drier Cape Town climate.

In this study, Giovanni Vimercati compared the mass of different organs from guttural toads from their native population in Durban (see post here) and the invasive population in the peri urban area of Constantia, near Cape Town. The relative masses of the different organs provide information about how these toads invest their energy. 

Native frogs in Cape Town save up much more energy in their storage organs prior to breeding, because of the inhospitable dry summers. Whereas the guttural toad in its native Durban, uses energy as they generate it during the breeding period. These two strategies are known as capital- and income-breeding, respectively. 

Giovanni's study suggests that even though they have only been in Cape Town for less than 20 years, they have already started moving toward a capital breeding strategy, typical of the native species in the area. However, he only found this difference in females and not males.

The MeaseyLab is conducting lots of interesting work on invasive populations of Guttural Toads at the moment. To see more blog posts about this work, click here.

Vimercati, G., Davies, S. & Measey, J. (2019) Invasive toads adopt marked capital breeding when introduced to a cooler, more seasonal environment. Biological Journal of the Linnnean Societyhttps://doi.org/10.1093/biolinnean/blz119 pdf




Where did the invasive Guttural Toads come from?

31 August 2019

Where did the invasive Guttural Toads come from?

The Guttural Toad, Sclerophrys gutturalis, has a large distribution in Africa, from Ethiopia in the North to South Africa in the South, and from Angola in the West to Mozambique in the East. That’s one of the largest distributions of any of Africa toad. No wonder then that there are also some invasive populations of Guttural Toads, which the MeaseyLab has been studying for the last 5 years or so (see more recent stories on Guttural Toads, click here).

Guttural toads have been invasive in Mauritius and Reunion for nearly 100 years (since ~1922), and have been in Constantia (near Cape Town) for another 20 years, but where did those colonising toads come from? This was the central question behind the MSc study of Nick Telford (now of SANBI, but then of UWC under the supervision of Alan Channing), and now a paper published today in Herpetological Conservation and Biology.

Nick took tissues of toads that had been collected from all over the continent (with some help from Alan and John), plus those sequences already published on Genbank, and to them he collected intensively in South Africa. We also obtained tissues from each of the invasive populations: Constantia, Mauritius and Reunion. He sequenced a common mitochondrial gene and made a phylogeny with all the sequences. The result was somewhat surprising: all of the invasive populations shared alleles which were naturally found around the South African port city of Durban.

The result fits in well with the historical information already published on the Guttural Toad invasions. A man called Gabriel Regnard, a Director of the dock management company in Mauritius, was known to have introduced them to Port Louis. It seems most likely that Regnard had sourced the animals from a nearby port. From there they were introduced to Reunion in 1927. Guttural Toads were first heard calling from the garden of Jonathan Ackerman, soon after the family relocated from Durban in 2000. The genetics suggests that the animals moved may have been eggs or tadpoles that were moved unwittingly with ornamental pond plants.

Knowing that all toads originated from Durban, has made it easier to study these invasions together, as we have been able to compare both invasive populations and those of the source in one study. With the publication of this genetic study we can continue to explore invasions of the Guttural Toad. There are also some oddities in the genetics which suggest some more investigation, like the most southerly records of animals from Port St Johns and Coffee Bay, which appear to have the genetic signature of animals from Gauteng.

You can find the publication Open Access here:

Telford, N., Channing, A. & Measey, J. (2019) Origin of invasive populations of the Guttural toad Sclerophrys gutturalis Herpetological Conservation & Biology. 14(2):380–392.


Île de La Réunion visited by toad team

20 July 2019

The Guttural Toad crew starts work on Île de La Réunion

 

We've seen recently how Mauritius was taken by storm when the MeaseyLab #Mascarenetoadteam visited (see blog entry here). Now they have moved to another island infested with the same toads for nearly 100 years. Their sampling was concentrated in two areas: the natural island forests and urban areas.

In the forest they saw toads climbing trees, and lots of different colour morphs, including the melanistic form (above). This tree climbing behaviour was specifically tested with a standardised climbing performance test which will be repeated in Cape Town and native Durban frogs. Will they all be able to climb?

Meanwhile, Carla was carefully swabbing forest toads to contrast with the urban cousins.

Meanwhile down town toads were getting dirty, and finding them wasn't always a pleasant experience. Can you spot the unlikely toad below? Note the champaign bottle - surely not the trash of our MeaseyLab #Mascarenetoadteam? 

 The MeaseyLab #Mascarenetoadteam found some time to relax among the larva fields at high altitude on Reunion. Pictured here with guest star Sohan Sauroy-Toucouère.


Tiny Toads meet their match on Mauritius

02 July 2019

Marauding Mauritius for Tiddly Toads

This month, the MeaseyLab has relocated to the Mascarene Islands of Mauritius and Reunion to conduct research on their invasions of Guttural Toads, Sclerophrys gutturalis. These toads were introduced, from the port city of Durban in South Africa, into Mauritius in 1922. Now, nearly 100 years later, they can be found nearly everywhere on the island. Intriguingly, they are a fraction of the size of the animals found in Durban. I visited Mauritius a while back (see blog post here), and worked with Claudia Baider and Vincent Florens to visit some toad populations in different parts of the island. Now the lab is back and working on the toads.

 

Carla has been seen with Guttural Toads before (see here and here), but this is her first time in Mauritius. Not only is she collecting faecal matter for her MSc on the Guttural Toad microbiome, but she’s using the opportunity to collect some skin swabs for our collaboration with Morne du Plessis at the National Zoological Garden, Pretoria (see here).

 

James only just started his post-doc in the MeaseyLab (see here). He’s using the model system of the Guttural Toad in Africa to understand their invasion success through the investigations of divergent phenotypic traits and rapid, localised evolution. Mauritius is his first field stop, and he’s making the most of every moment by putting the toads through their paces.

 

Nitya and Julia are helping out James and Carla with their work but adding their own research talents into the mix. We’ll come back to that in future when the publications start rolling out!

 

All together, the fab quartet make a talented team to take on the challenge of these invasive amphibians on Mauritius. You can be sure that those tiddly toads are no match for the four of them.

 

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