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Eggs, toads or tadpoles & the hydra effect

22 December 2021

All toads are equal, but some are more equal than others

When conducting an eradication campaign, it seems obvious that you should go out and collect all the individuals you can find. But could collecting some individuals be more important than others? This question is especially important when it comes to animals with complex life-cycles where the larvae and adults inhabit different parts of the ecosystem. We asked this question of the Guttural toad eradication in Cape Town, and received some surprising answers. 

Guttural toads lay large numbers of eggs, and their tadpoles inhabit garden ponds in the low-density, high-income suburb of Constantia. Meanwhile, the adults cruise around the gardens looking for insects and snails to snack on. For the people charged with their control, they can either spend their time cruising in the shrubberies looking for adult toads, or go to the ponds with nets and scoop up tadpoles and strings of eggs. Or of course, they could do both. But what is the best strategy?

Giovanni Vimercati built a mathematical model of the Guttural toad population in Constantia to answer this problem (see also Vimercati et al. 2017a,b). Recently, Gio used this same model to answer the question of which life-history stage of these toads should be targeted by people trying to control the population. Because there is strong competition between tadpoles and metamorphs, Gio found that any attempts to remove these aquatic life-history stages resulted in an increased number of toads in the population. The counter-intuitive result is known as the ‘hydra effect’ - where cutting off some heads simply makes more grow. In the case of the Guttural toad, the removal of some of the aquatic stages increases the rate of survival and fitness of those that remain. 

The model has the advantage that it can be run forwards to see what happens to the population given different control regimes. The mathematical model results told us that to maximise the impact of time spent controlling toads, concentrate on collecting adults. Adult removal has a far greater impact on the total population. 

To read more:

Vimercati G, Davies SJ, Hui C, Measey J (2021) Cost-benefit evaluation of management strategies for an invasive amphibian with a stage-structured model. NeoBiota 70: 87–105.https://doi.org/10.3897/neobiota.70.72508 

Other publications on this model are:

Vimercati, G., Davies, S.J., Hui, C. & Measey, J. (2017) Does restricted access limit management of invasive urban frogs? Biological Invasions19: 3659-3674.https://doi.org/10.1007/s10530-17-1599-6

Vimercati, G., Davies, S.J., Hui, C. & Measey, J. (2017) Integrating age structured and landscape resistance models to disentangle invasion dynamics of a pond-breeding anuran. Ecological Modelling 356: 104–116https://doi.org/10.1016/j.ecolmodel.2017.03.017 


Another online CIB-ARM

19 November 2021

Centre for Invasion Biology - Annual Research Meeting - online again

By May 2021 it seemed that we could have started planning for an in-person Annual Research Meeting (ARM) for the Centre for Invasion Biology (CIB), but decided to err on the side of caution and keep it online only. That turned out to be the best plan as the third wave of COVID hit us in July and still hadn't entirely left by September. 

We managed to fit all CIB students into 4 pods led by all remaining post-docs, and had some great presentations from all members of the MeaseyLab. Below you will find images of everyone giving their talks. 

Sam Peta, M.Sc. An army marches on its stomach: diet composition and prey preference of guttural toad (Sclerophrys gutturalis) populations along a native-invasive and natural-urban gradient. 

John Measey How to write a PhD in Biological Sciences - book launch

SESSION 03: Distribution, spreading and impacts of invasive species Introduced and chaired by
Dr Andrea Melotto

Dan Van Blerk, M.Sc. Impacts of invasive fish on amphibians in lentic and lotic systems: a meta-analysis 

Laurie Araspin, Ph.D. Temperature dependence of locomotor performance across an altitudinal gradient in an invasive frog, Xenopus laevis

Of course, you can watch the full meeting (only 7.5 hours) on YouTube (below) if you want!


Do toads shit in the woods?

05 November 2021

Expanding populations of toads shit in the woods

A recent study by CIB MSc student, Carla Wagener, and CIB researcher John Measey, found that the gut microbiome on invasive toads shifts in expanding populations. 

The study, published this month inMicrobial Ecology, examined the faecal microbiome of three invasive populations of the Guttural Toad,Sclerophrys gutturalis, Mauritius, Reunion and Cape Town, as well as their origin population in Durban. The Mauritius and Reunion populations, despite being introduced ~100 years ago, contained a microbiome that most closely resembled the native Durban population. 

Guttural toads from Cape Town had the most distinct microbiome recorded for these toads. Although this population is only ~20 years old, the animals are believed to have arrived accidentally in Cape Town as eggs or tadpoles. This would mean that the gut microbiome of the adults was acquired after metamorphosis in their new environment. Moreover, toads collected from the periphery of the invasion were found to have a microbiome that had shifted from those at the invasion core. 

This is the first time that a study has shown rapid alteration of the faecal microbiome during a population expansion, such as that during the movement of individuals during an invasion. It seems likely that this difference is due to the proximity of other Guttural Toads during the expansion process. 

Read the article here:

Wagener, C., du Plessis, M., Measey, J. (2021) Invasive amphibian gut microbiota and functions shift differentially in an expanding population but remain conserved across established populations.Microbial Ecologyhttps://doi.org/10.1007/s00248-021-01896-4


Talks at the Conservation Symposium

04 November 2021

A session dedicated to the Guttural Toad (Sclerophrys gutturalis)

The Conservation Symposium (1-4 November 2021) had a special session on the morning of 4 November 2021 where five MeaseyLab members presented their work on Guttural Toads. Because these presentations were recorded ahead of time, we are able to share them for your interest in a playlist here.

The humble guttural toad (Sclerophrys gutturalis): Lessons of plasticity and adaptation following invasion: John Measey

Introduction of guttural toads (Sclerophrys gutturalis) produces marked shifts in the endemic western leopard toad (Sclerophrys pantherina) gut microbiome: Carla Wagener

Does urban adaptation enhance invasiveness? A case study of tadpoles of a successful invasive amphibian: Max Mühlenhaupt

Conqueror toads: Comparing behaviour, performance and competitive potential in a successful invader and its native congeners: Andrea Melotto

An army marches on its stomach: Diet composition and prey preference of guttural toad (Sclerophrys gutturalis) populations along a native-invasive and natural-urban gradient: Sam Peta

The session was well attended with 140 people online. You may recognise some of the people below who showed up to face the questions...
 
Measey, J. 2021. The humble guttural toad (Sclerophrys gutturalis): Lessons of plasticity and adaptation following invasion. The Conservation Symposium, 1-5 November 2021

Wagener, C., Measey, J. 2021. Introduction of guttural toads (Sclerophrys gutturalis) produces marked shifts in the endemic western leopard toad (Sclerophrys pantherina) gut microbiome. The Conservation Symposium, 1-5 November 2021

Mühlenhaupt, M., Baxter-Gilbert, J., Riley, J., Makhubo, B., Measey, J. 2021. Does urban adaptation enhance invasiveness? A case study of tadpoles of a successful invasive amphibian. The Conservation Symposium, 1-5 November 2021

Melotto, A. 2021. Conqueror toads: Comparing behaviour, performance and competitive potential in a successful invader and its native congeners. The Conservation Symposium, 1-5 November 2021

Peta, S., Baxter-Gilbert, J., Measey, J. 2021. An army marches on its stomach: Diet composition and prey preference of guttural toad (Sclerophrys gutturalis) populations along a native-invasive and natural-urban gradient. The Conservation Symposium, 1-5 November 2021

Tadpoles of guttural toads also adapt

20 October 2021

Growing up in a new world

In a new paper published in Neobiota, Max Mühlenhaupt and colleagues bring tadpoles from invasive and native (both urban and rural) populations of the Guttural Toad (Sclerophrys gutturalis) into a common garden. You may remember the exploits of Max back in late 2019 and early 2020 (if not, then you can read about them here, here and here).

Max looked at lots of traits of the tadpoles as they developed over time. This included morphology swimming performance and developmental rate. What he found is that animals from all populations were identical morphologically and their performance did not diverge. However animals from the invasive population in Cape Town developed significantly more slowly.

In the video clip below, you can see how Max stimulated the tadpoles to perform. From videos such as this, he was able to measure swimming performance of individuals.

Although the COVID-19 pandemic interrupted the end of this experiment, we expect that the slow development of tadpoles from Cape Town would have resulted in their larger size at metamorphosis. This is yet another example of adaptation in an extremely short period of time. Guttural Toads were first discovered in Cape Town in the year 2000. Just under 20 years from when Max started his experiment.

Read more here:

Mühlenhaupt M, Baxter-Gilbert J, Makhubo BG, Riley JL, Measey J (2021) Growing up in a new world: trait divergence between rural, urban, and invasive populations of an amphibian urban invader. NeoBiota  69: 103–132. https://doi.org/10.3897/neobiota.69.67995

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