How do fish invasions change fynbos amphibian communities?

Back in 2017, Naas Terblanche visited me in my office in Stellenbosch. A retired agriculturalist (with an MSc in animal nutrition) turned winemaker, Naas had spent the first 16 years of his retirement in Stanford developing a passion for the frogs that he found there. He explained that he wanted to conduct a scientific study on the different communities of frogs that he found in the area near where he lived, using the skills of sampling and identification that he had developed.

We put together a study that tested the influence of invasive fish on various different habitat types in the region. Spread across two watersheds in the Overstrand, Naas used satellite data to select 200 different freshwater sites and categorise them into different waterbody types. From these we selected 50 that represented a balanced number of each category type.

Naas spent the next two winters visiting each of these 50 sites in turn, identifying the amphibian communities therein. It was long and hard work as he had to visit each site once during each year, and spend the afternoon and evening conducting the surveys so that he saw, captured or heard every species present.

The data showed convincingly that invasive fish were important in determining the composition of amphibian communities. Perhaps unsurprisingly, toads (Raucous toads and Western Leopard toads) that have toxic eggs and larvae are particularly tolerant of invasive fish, while the most intolerant was the plantanna, X. laevis, perhaps because they spend most of their time in the water.

Secondly, the resulting data demonstrated some interesting trends in freshwater habitat types. First, we confirmed that different habitat types contain different amphibian assemblages in the fynbos, with those most valuable being from temporary aquatic habitats. Permanent habitats, such as garden ponds and dams, were not particularly useful for local amphibians, but more for widespread common species. This means that if you want to create a freshwater habitat for conservation purposes in the fynbos, you need to make sure that it is temporary (not permanent), drying out in the summer months and filling in the winter.

Read the paper in full:

Terblanche, N., Measey, J. (2023) The conservation value of freshwater habitats for frog communities of lowland fynbos. PeerJ 11: e15516 https://doi.org/10.7717/peerj.15516

Getting high to work out how low they can go

The Cape Fold Mountains are the centre of African Clawed Frog genetic diversity

I'm really pleased to see this paper finally emerge. It's a fantastic study that took many years (more than 10!) to assemble all of the tissue samples used. A great many people helped assemble all of these, and the detailed resolution we now have of genetic diversity of this most widely distributed amphibian in southern Africa is excellent. 

What did we find?

In contrast to previous studies, we found that there are 5 mitochondrial clades of Xenopus laevis in southern Africa. You can see how these are distributed in the following map (Fig 2 below). 

Here you can see (on the right) that most of the area colonised by this species is from a single (yellow) clade. This shows signs of rapid expansion suggesting that even in it's native southern Africa, X. laevis  is a very successful species that has recently spread throughout a very large area. The next largest clade (blue) is from the winter rainfall area of the Cape. This includes animals that were sent all over the world for pregnancy testing (Van Sittert & Measey, 2016) and that are currently in the pet trade (Measey, 2017). The Cape Fold Mountains harbour the greatest genetic diversity of this species, and this includes a (green) clade that occurs in the lower Karoo. In the same area is the new (brown) clade, that appears to be co-distributed with the yellow clade up South Africa's east coast. But by far the most different animals in this species come from Nieuwoudtville (purple clade - see Fig 3 below) and adjacent areas of the northwest Karoo. This area is known for having many relict species, but how and why X. laevis  became isolated there so long ago is probably related to the large wetland areas that occur along the escarpment. Presumably these remained wet even when lowland areas dried up.

Overall, the picture of the distribution of this species in southern Africa is one of opportunism. These animals readily move into permanent water (e.g. irrigation dams) that is associated with modern farming practices. This has allowed expansion of this species into many arid areas where they might otherwise only appear after unusual rainfall events.

Our data is also the first to examine the entire genome of this model species. In the figure above you can see how the two different subgenomes differ (as X. laevis  is a tetraploid species). There is very little difference between the two genomes, suggesting that they are both under selection throughout its range. 

This is not the last study on the geographical differences of X. laevis,  but it is a great advance from our existing knowledge. 

Read More:

Premachandra, T., Cauret, C.M.S., Conradie, W., Measey, J., Evans, B.J. (2022) Population genomics of Xenopus laevis  in southern Africa. G3 Genes|Genomes|Genetics,  https://doi.org/10.1093/g3journal/jkac325 pdf

Measey, J. (2017). Where do African clawed frogs come from? An analysis of trade in live Xenopus laevis imported into the USA. Salamandra 53: 398-404. pdf

Van Sittert, L. & Measey, G.J. (2016) Historical perspectives on global exports and research of African clawed frogs (Xenopus laevis). Transactions of the Royal Society of South Africa  71: 157-166. https://doi.org/10.1080/0035919X.2016.1158747pdf

Invasive Xenopus in Chile

I was privileged to join members of Claudio Soto Azat's lab in Chile this month for two weeks of intensive field work. It was amazing to work with such a dedicated group of young researchers who were so keen to join in the collecting and processing of their invasive population of Xenopus laevis. 

Some of you will recognise Tyrone Hayes pictured above, who visited the MeaseyLab in September of this year. Tyrone was on a similar mission in Chile to capture animals for his work on Atrazine. 

More on this to come...

The CIB holds its final ARM as a hybrid event

Every year the CIB holds an Annual Research Meeting as an opportunity for students to present their work to an audience of peers and the CIB network of Core Team Members, affiliates and associates. This year sees the last meeting in the role of the CIB under the DSI-NRF Centre of Excellence. The 2020 and 2021 events were both online affairs. 

Three MeaseyLab students presented their research findings at the meeting:

Laurie Araspin started the show by presenting a chapter from her PhD work on "Locomotor performance in Xenopus laevis".  Laurie is a co-tutelle student with Anthony Herrel's MECADEV lab at the Natural History Museum in Paris.

Next Dan van Blerk presented a chapter of his MSc work on "The impact of invasive fish on ghost frog tadpoles", work that he conducted in collaboration with Josie Pegg from SAIAB. 

Lastly, Jonathan Bell presented some preliminary results from his MSc work on "Optimising conditions for controlling the invasive guttural toad". Jonathan is conducting his MSc at the CIB, but also works full time for the City of Cape Town invasive species unit.

Congratulations go to Laurie and Dan, both of whom won runners up prizes in their categories for best presentation.