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Welcome Max Mühlenhaupt

18 November 2019

The MeaseyLab welcomes Max Mühlenhaupt

Max Mühlenhaupt (think windmill) comes from the Free University in Berlin (Freie Universität Berlin) where he is studying for a MSc in Biology (Masterstudiengang Biologie). Max previously spent time with Dr James Baxter-Gilbert, when James was conducting his PhD in Australia. Max was responsible for chasing dragons in circles. I know it sounds like a fantasy, but I'm assured that this is what he did.


Max Mühlenhaupt with Dr James Baxter-Gilbert outside the Department for Botany & Zoology, Stellenbosch University

Max is in Stellenbosch to conduct his project: Examining the potential for evolutionary drivers behind biological invasions of Guttural Toads. He will focus on the early life-history stages of these toads: tadpoles and metamorphs. This will take place in a mesocosm experiment in Durban. Watch this space to learn more of Max and his adventures in South Africa.

Max reminds us that he is not an intern, but a co-investigator, and of course we are very happy to have him on board in this capacity.


18th AAWG in George

08 October 2019

18th African Amphibian Working Group (AAWG)

My first AAWG was back in 1996, when I was still finishing my PhD at Bristol University. It was the only conference that I attended during the entirety of my PhD studies, and it happened in Bristol - yes, that exotic far flung location that I had been saving myself up for…

This year, the 18th AAWG was held in the town of George, in the Western Cape, South Africa from 7-8 October 2019. The venue was the Garden Route Botanical Gardens, George. George is close to the Outeniqua Mountains, and is the home to a range of interesting frogs includingBreviceps fuscus,Afrixalus knysnae(pictured above) andHeleophryne regis.

We had a lot of fun listening to lots of different talks about amphibians from all over the continent. The CIB was well represented with talks from Anneke Schoeman, Natasha Kruger, John Measey, Mac Mokhatla and Sarah Davies (see pic!).

There were a bunch of talks from the MeaseyLab. See below for titles:

Talks:

Natasha Kruger, Jean Secondi, Louis du Preez, Anthony Herrel, John Measey 2019. The local adaptation of development and survival of nativeXenopus laevistadpoles in different climatic regions in South Africa.18th African Amphibian Working Group, George, South Africa.

Mohlamatsane Mokhatla, Dennis Rödder, John Measey 2019. Using physiology and performance to predict climate driven distribution range shifts in three temperate African anurans species: a hybrid modelling approach. 18th African Amphibian Working Group, George, South Africa.

Sarah Davies, Dean Impson, Jonathan JA Bell, Clova Jurk-Mabin, Marco Meyer, Chandre Rhoda, Louise Stafford, Kirstin Stephens, Mfundo Tafeni, Andrew A Turner, Nicola J van Wilgen, John RU Wilson, Julia Wood, John Measey 2019. Coordinating invasive alien species management in a biodiversity hotspot: The CAPE Invasive Alien Animals Working Group. 18th African Amphibian Working Group, George, South Africa.

Francois Becker, Jasper Slingsby, John Measey, Krystal Tolley, Res Altwegg 2019. Searching for rare species and determining their absence for conservation applications. 18th African Amphibian Working Group, George, South Africa.

John Measey 2019. Rapid adaptation of an invasive African toad:Sclerophrys gutturalis.  18th African Amphibian Working Group, George, South Africa.


The HAA meeting 2019

13 September 2019

The HAA meeting at Cape St. Francis, Eastern Cape

Only 8 hours drive from Cape Town, and we arrived at Cape St. Francis in the Eastern Cape to attend the Herpetological Association of Africa's 14th conference.

Of course, once we were there, we all gave stunning talks from many members of the MeaseyLab, both those based at Stellenbosch University and elsewhere. Nitya got a special surprise when the paper on which his talk was based was accepted in the session before he talked! Very welcome news indeed!

It was good fun to get to the beach, meet up with plenty of herpers that we knew and meet new ones that we didn't know. A special mention to Alan Channing who received the HAA's highly prized life-time achievement award for his contribution to southern African frog taxonomy. More than 20 years ago (1998), I worked with Alan at UWC during my first Royal Society post-doc (see here). 

Here are some of the abstracts of the talks:

Kruger, N, Vimercati, G, Herrel, A, Secondi, J & Measey, J Spatial sorting on dispersal traits are stage dependent in the invasive amphibian Xenopus laevis in western France

Organisms are exposed to trade-offs constraining their anatomy, physiology, and behavior between dispersal and life-history traits. The spatial sorting theory predicts the enhancement of dispersal traits due to resource re-allocation at the periphery of expanding populations. A more nuanced view of spatial sorting emerges when one considers organisms with complex life cycles in which dispersal usually occurs at a particular ontogenic stage. It is currently not known if enhancement of dispersal traits in organisms with complex life cycle emerges only at the dispersal stage. In amphibians, larval development can influence life-history traits that directly influence dispersal in post-metamorphic juveniles. Spatial sorting for dispersal traits occurs in adults of the invasive African clawed frog, Xenopus laevis, in western France. Individuals have been expanding from a single introduction point since the 1980s colonizing an area of ~2000 km2. The mass of reproductive organs is reduced at the range periphery while the dispersal rate, probability and distance are increased. In X. laevis all stages are aquatic and dispersal is terrestrial. We predict that the enhancement or adaptation of dispersal traits due to spatial sorting occurs at the onset of their development regardless of dispersal ability of tadpoles. To test this, we conducted experiments in outdoor mesocosms and in microcosms in the lab. We surveyed tadpole development for 10 weeks from hatching to metamorphosis. We observed no effect of site position (core vs. periphery) on morphology, development, and survival of tadpoles. This study shows that spatial trait variation in pre-dispersal and dispersal stages are decoupled to a large extent in species with complex life cycles. In amphibians, tadpole development is constrained by factors such as initial density, food availability, and predation whereas in adults, resource allocation to dispersal can be enhanced at the dispersing stage and not at the pre-dispersal stage.

Measey, J, Baxter-Gilbert, J, Davies S, Kruger, N, Mohanty N How do herpetologists study invasions?

Invasion Biology is a young discipline, Charles Elton only coined the term in 1958. Although the subject was generally ignored by most people for 40 years, the last 20 years has seen a near exponential rise in papers by herpetologists on alien reptiles and amphibians (and not only by Rick Shine!). But how do herpetologists go about studying invasions? In this study, we reviewed 836 publications on alien herps and compared their objectives with 30 well known hypotheses from invasion biology. We found that although the field is rapidly expanding, very few researchers had specified any of the invasion hypotheses, but 26% had the data to test one or more. The most commonly tested hypothesis resembled the concept of the ‘ideal weed’, that invasion success of a non-native species depends on its specific traits (3.8%). Other popular hypotheses referred to habitat filtering (1.7%), preadaptation through human commensalism (1.8%), novel weapons (1.3%), novel associations (1.4%) and invasion meltdown (1.5%). Perhaps more excitingly, are the new hypotheses that herpetologists can donate to invasion biology, including spatial sorting, invasion hubs and hybridisation. We conclude that herpetologists need to pay more attention to existing hypotheses in invasion biology, many of which stem from classical questions in ecology. Better transdisciplinary communication will likely lead to increased impact of studies which could teach invasion biologists more about reptiles, amphibians and their amazing invasions.

Mohanty, N & Measey, J The global pet trade in amphibians: Species traits, taxonomic bias, and future directions

The burgeoning global pet trade in vertebrates has multi-pronged conservation implications, including overexploitation of native populations, spread of diseases, and invasions. The majority of amphibian invasions are due to the pet trade pathway and current lists of extra-limital amphibians (including those in trade) suggest that future invasions will encompass a broader taxonomic diversity than is known. Given that trade is dynamic, it is essential to move beyond currently traded species and understand which species are likely to be traded in the future and serve as candidates for invasions. In this study, we systematically assess amphibian species in the pet trade, i) characterising taxonomic bias, ii) evaluating species-traits as predictors of traded species and trade volume, and iii) forecasting likely future pets. We collated a global list of 443 traded amphibians and a regional dataset (USA) on trade volume. Species-traits (body size, native range size, clutch size, and breeding type) and conservation status, were considered as predictors of traded species and volume. Six Families contributed disproportionately to the amphibian pet trade; the likelihood for species to be traded was positively associated with body size, range size, and a ‘larval’ breeding type. However, species-traits performed poorly in predicting trade volume, suggesting an overriding effect of socio-economic aspects of the trade. The identified species-traits and taxonomic bias of the trade were then used to predict species likely to be traded as pets in the future. This study formalizes the knowledge on amphibian species that are traded as pets. We found a strong bias for certain Families, along with a preference for large-bodied and widely distributed species with a larval phase. Our results pave way for more trait-based approaches to forecast amphibians entering the trade. Such understanding of the pet trade can help pre-emptively tackle the pathway responsible for most invasions and disease spread in amphibians.

Peta, STP, Engelbrecht, GD & Measey, J Reptile and avian assemblage along a gradient of invasive alien plants in the critically endangered Woodbush Granite Grassland

Invasive alien plants species (IAPs) are a significant problem in South Africa and can pose complex and far-reaching challenges to biodiversity, with impacts on fauna poorly understood. The study aimed for multi-site comparison of reptile and bird assemblages between pristine grassland, alien plant invaded and plantation habitats. Reptiles and birds were surveyed using standard Y-shape trap array and fixed-point counts respectively. Vegetation structure and invasion intensity was determined using point-intercept method. Five IAPs were identified: Acacia mearnsii, Eucalyptus grandis, Pennisetum clandestinum, Pinus patula and Solanum mauritianum. Reptiles (23 individuals from 5 species) were recorded, with highest abundance and diversity in the grassland. Birds (2113 individuals from 67 species) showed the greatest abundance, diversity and richness in the invaded habitat. Trachylepis varia was a common reptile species, showing overlap between grassland and invaded habitat. Lygodactylus methuen was the only identified endemic reptile species. Grassland bird specialists (i.e. Anthus similisCisticola lais, and Sphenoeacus afer) were observed in more open and moderately invaded habitat but absent in denser and heavily invaded habitat. The study demonstrated that reptiles and birds respond differently to alien plants invasion. Reptiles were mostly supported by low vegetation cover, availability of microhabitats e.g. rocks and bare ground for thermoregulation while birds responded to rich vegetation stratification. Clearing of invasive alien plants can be considered as management strategy if it is to promote biodiversity. Clearing can create more thermal opportunities for reptiles and accommodate open habitat bird species.

Telford, N, Channing, A & Measey, J Origin of invasive populations of the Guttural Toad, Sclerophrys gutturalis

The Guttural toad, Sclerophrys gutturalis, has three established invasive populations on Mauritius, Reunion and in Constantia, a peri-urban area of Cape Town, South Africa. The native range of this toad covers much of central and southern Africa. Here we use mitochondrial DNA (mtDNA) to sample across the range of the natural distribution (from Kenya to South Africa) and compare ND2 and 16S sequences to those from animals sampled from each of the three invasive populations. We show that all invasive populations refer to the same mtDNA clade, which is naturally distributed in north-eastern South Africa, but not from adjoining Mozambique or southernmost Eastern Cape areas. Our findings corroborate previous reports of deliberate introductions from South Africa to Mauritius, and from Mauritius to Reunion. Similarly, our results suggest a single accidental translocation within South Africa from the northeast to Constantia. Our findings highlight the combination of anthropophilic behavior, and extreme long-distance dispersal occurring with accidental translocation for this species. We caution that accidental pathways are likely to continue into the future, with increasing numbers of invasive populations of this species.

Wagener, C, Kruger, N & Measey, J Xenopus laevis progeny display local adaptation of physiological performance to environmental extremes

Altitudinal variation of environmental temperatures is expected to shape the evolution of physiological functions of widespread populations. Adaptation to thermal extremes can create altitudinal differentiation in ectotherm physiological performance. In this study, a common garden experimental approach was employed to determine whether thermal adaptations to contrasting environmental regimes are heritable and how these thermal adaptations affect performance. To address this, we compared the critical thermal limits and swimming performance of African clawed frog (Xenopus laevis) tadpoles bred from two adult populations captured from high (~ 2000 m above sea level) and low (~ 5 m above sea level) altitudinal extremes. Parental-origin significantly affected tadpoles’ critical thermal minima (CTmin), maximum velocity, maximum acceleration, total distance and distance travelled in the first 200 m.s-1. Tadpoles with low-altitude parental-origins had a higher optimal temperature (Topt) for swimming performance and CTmin than tadpoles with high-altitude parental-origins. Performance of tadpoles bred from high-altitude adults was significantly higher at cooler temperatures and lower at the highest test temperature, in comparison with tadpoles bred from low-altitude adults. These results suggest that thermal performance curves of X. laevis tadpoles have adapted in response to contrasting local environmental conditions experienced by adults. Future studies should focus on whether similar thermal performance trait variations are present in other populations of the widely distributed African clawed frogs (X. laevis).

Jordaan, PR, Measey, J, Hanekom, CC, Greend, AN, Woolcocke, AB, Combrink, X Grassland and savanna fossorial herpetofaunal densities

Ecological data on soil living amphibians and reptiles are largely lacking. Specialised methods relying on substrate excavation are required to adequately quantify fossorial herpetofaunal densities as surveying techniques which rely on surface movement (e.g. pitfall or funnel trap surveys) are biased against soil-living species which infrequently move over the soil surface. As part of a larger study, we quantified baseline densities for fossorial herpetofauna in grassland at Sileza Nature Reserve and in savanna at Tembe Elephant Park. All sites were underlain by aeolian sand. Grassland surveys were conducted at two adjoining sites, one during summer, and one in winter while both savanna sites were only surveyed during winter. Quadrats of 4 m2 (2 m x 2 m) were excavated to a mean depth of 0.25 m (volume of 1 m3) as most species of fossorial herpetofauna are considered to live at shallow soil depths. The excavated substrate was momentarily stored in 20 litre buckets before being sifted through a 2 mm x 2 mm (4 mm2) metal mesh, exposing soil living reptiles and amphibians. Grassland fossorial herpetofaunal densities were marginally lower during winter (0.56 individuals.m-2) compared to the summer (0.67 individuals.m-2) survey. Grassland species richness consisted of a single amphibian, Breviceps mossambicus, as well as five reptile species. Although amphibian species richness was considerably lower in grassland compared to reptiles, densities were higher especially during summer. Inter-seasonal demographic variability was observed in the grassland amphibian population with higher numbers of juveniles present during the summer. Herpetofaunal fossorial densities at savanna sites were on average more than four times lower (0.11 and 0.14 individuals.m-2 respectively) compared to grassland. Once again, the only amphibian present was B. mossambicus, but in much lower densities (0.01 and 0.02 individuals.m-2). It is hoped that the outcomes of this study will contribute to a better ecological understanding of soil megafauna in grassland and savanna ecosystems.


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



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