PeerJ Expert Curations: Rapid Evolution

I was asked to curate a set of PeerJ articles around a topic, and chose to do this on Rapid Evolution. You can read the summary that I wrote and the articles I picked on this blog at PeerJ.

Curation Summary

Darwin’s (1859) theory of evolution involved ‘slow steps’ that precluded the concept of ‘sudden leaps’, instead advancing by ‘taking advantage of slight successive variations’. Although Darwin’s ideas still form the basis of our modern understanding of evolutionary processes, we now have examples of how the process can occur in the sudden leaps that Darwin himself eschewed. Documenting and investigating how these rapid evolutionary processes occur has become an important theme in 21st century life sciences. In this small selection of papers published in PeerJ Life and Environment, I highlight how scientists have gained insight on rapid evolutionary processes from multiple evidential sources, and how this has led to a better understanding of evolution today.

Rapid evolution as evidenced in PeerJ Life & Environment

Perhaps the best examples of rapid evolutionary processes are provided by the smallest living organisms. For example, Gutiérrez-Escobar et al. (2018) document how changes in genetic sequences of Helicobacter pylori sampled from patients in Columbia result in physical changes in the protein AlpA. Genetic mutations resulting in differences to transcribed proteins represent the most widely understood of evolutionary mechanisms. In their study, Gutiérrez-Escobar et al. show how the evolutionary mechanisms of gene conversion and purifying selection have diverged for this important gastric carcinogenic bacterium across a small spatial scale of Columbian cities during its short post-colonial history.

Dufour et al. (2018) use an invasion of Anolis lizards to study the evolutionary consequences on communication and behavior between native populations (A. oculatus) with and without an invasive congener (A. cristatellus). They found that in the 15 years since the introduction of A. cristatellus, populations in sympatry had decreased the proportion of display-time spent displaying (dewlapping), stressing how behavioral traits might be the first visible signs of rapid evolutionary processes taking place.

Invasive species are vulnerable to native species that may prey upon them. The ways in which these communities evolve can be surprising, especially when similar species are already present in the recipient environment. Schilthuizen et al. (2016) document how the native insect community on invasive cherries (Prunus serotina) is more diverse (but less dense) than those on native (Sorbus aucuparia) in a park in the Netherlands. Moreover, a beetle (Gonioctena quinquepunctata) collected from native and invasive trees displays different preferences in a choice test.

Regular collections of black rats (Rattus rattus) from Anacapa Island (USA) over a period of 60 years allowed Pergams et al. (2015) to make a series of detailed morphological measurements to track changes in cranial measurements. In this short period, the rats’ skulls had increased in size by between 3 and 10%, probably as a result of their island diet. Meanwhile, endemic deer mice (Peromyscus maniculatus) on the island became smaller after the introduction of the rats, likely through competition and predation.

The immune system must have the ability to respond rapidly to potential pathogens but this response is energetically expensive, and is predicted to be downregulated in invasive populations. Previous studies had shown immune response differences between populations of Rhinella marina from the core and at the invasion front in Australia. Selechnik et al. (2017) tried to replicate these results, using an experimental approach, but failed to find a difference between these two invasive populations. This reminds us that despite the overwhelming evidence for rapid evolutionary processes, we still need to proceed with caution when accepting results of previously published studies. More importantly, we need to be able to publish negative results in order for science to advance.

These exemplars also serve to demonstrate the utility of invasions to study rapid evolutionary processes in situ. While the impacts of these invasions are widely acknowledged to be largely detrimental to the recipient environment, they can serve as analogies to the impending changes to global climate due to anthropogenically mediated climate change. Why do some species thrive while others decline? Moreover, they offer scientists an opportunity to gain insight on the most fascinating and fundamental of all topics in life sciences and the environment: evolution.

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

How to Start your PhD

In some parts of the world the time-line is just getting started for new PhD students. This will be a very busy time for those involved, but it also needs to be a time to take stock and consider the bigger questions. In this video I provide some pointers to key issues for you to think about when starting your PhD. 

Graduation time for Dan

Dan van Blerk has been in the MeaseyLab since his Honours project in 2019 (see here), when he conducted a literature review on the impacts of invasive lizards around the world. In late 2019, Dan and I met with Olaf Weyl to plan Dan’s MSc fieldwork over the next two years. With all three of us filled with enthusiasm for the upcoming adventure and what it would achieve, we were about to find out that fate had other plans.

Very sadly, Olaf died later that same year, and subsequently did not get to participate in any of the plans. He is greatly missed, and we continue to remember his initial enthusiasm for the project. Happily, Josie Pegg was soon on hand to take over from the SAIAB side, and in doing so saved the project. However, just as we were about to deploy Dan into the streams of the Western Cape, we were hit by another big setback. The world suddenly shut down, and with it Dan was confined to quarters and we decided that we’d have to conduct at least one of his chapters as a literature review instead of in the field as planned.

During 2021, Dan managed to get two notes published on natural history observations that he’d made during his time in the MeaseyLab (van Blerk 2021 a,b).

Eventually, Dan did get out into the field and surveyed many locations in many streams for ghost frog tadpoles and invasive fish. The work was a real advance for conservation evidence in the impacts of invasive fish on these frogs. Dan presented his work in the Conservation Symposium (see here). We got used to seeing Dan presenting online and in person (see here and here). His findings have already been submitted to Aquatic Invasions, and we hope to announce publication of his chapter soon. Watch this space. Dan defended his MSc work in February this year (see here).

It was great having Dan in the lab, even if he didn’t spend much of the three years physically with us. We wish him all the best in his subsequent career and hope that he’ll keep in touch.

Read more:

van Blerk, D. (2023) The Impacts of Invasive Fish on Ghost Frog tadpoles. MSc thesis, Stellenbosch University. http://hdl.handle.net/10019/32356

Van Blerk, D., Reissig, J., Riley, J.L., Measey, J., Baxter-Gilbert, J. (2021) Observations of infanticide and cannibalism in four species of cordylid lizard (Squamata: Cordylidae) in captivity and the wild. Herpetology Notes 14: 725-729. pdf

Van Blerk, D., Measey, J., Baxter-Gilbert, J.H. (2021) Predation by a Brown Widow Spider, Latrodectus geometricus (Koch, 1841), on a Common Dwarf Gecko, Lygodactylus capensis (Smith, 1849), with a review of the herpetofaunal diet of Latrodectus spp. Herpetology Notes 14: 291-296. pdf