Dan van Blerk's study on Ghost Frog tadpoles is published

Readers of this blog will know that Dan van Blerk spent an entire summer season out in the streams of the Western Cape catching alien fish and Ghost frog tadpoles. If you've already forgotten see here and here.

Now Dan's first chapter of his MSc is published

This study shows unequivocally that invasive fishes have a negative impact on Ghost Frog tadpole abundance, something that we only knew before from anecdotal studies. Dan went to 111 sites across 26 streams finding that tadpole abundance decreases by around 18 times in the presence of invasive fish species.

The other thing that Dan uncovered is the real lack of data on the distribution of invasive fish in streams of the fynbos. This meant that they were absent from places where he thought they would be present and present in places where he thought they would be absent. 

This publication will be important in adding evidence for conservation decisions on the removal of invasive fishes from streams in the fynbos.

Van Blerk, D., Melotto, A., Pegg, J., Measey, J. (2023) Invasive fishes negatively impact ghost frog tadpole abundance. BioInvasions Records 12(4): 1121-1138. https://doi.org/10.3391/bir.2023.12.4.24 pdf

There's a frog in my tadpole

Sometimes a photograph can instantly give you a whole lot more information on a topic than you ever knew. 

This is a cropped close-up of a picture that I showed on the blog a few weeks back (see here). At the time that I took the picture, and later when I selected it for the blog post, I had completely failed to spot this metamorphosing frog in the image. I had never fully appreciated how the new frog in a metamorphosing tadpole was formed. Perhaps because of the colour of this Xenopus laevis frog from an invasive population in Tucson, Arizona, is so stark, you can clearly see through the transparent tadpole flesh the form of the frog coming through.

Note how the head of the tadpole and head of the frog appear to be completely different, yet the sensory organs (eyes, nares, etc.) are functioning on the tadpole and joined by nerves to those same sites on the frog head. Note also the way in which the fore-limbs (that always appeared to come at an odd place on the tadpole) are perfectly situated in relation to the frog head. 

Over the next week or so, the tadpole head will regress in size and the tail will start to shrink as the final stages of metamorphosis take place. Sensory organs will relocate into the frog head. 

Laurie presents at the 22nd European Congress of Herpetology

The 22nd European Congress of Herpetology took place in Wolverhampton UK and Laurie Araspin presented her PhD work on Xenopus acclimation:

Locomotion and physiology depending on temperature in Xenopus laevis native and invasive populations
Araspin, L., Measey, J. & Herrel, A.

Ectothermic species are dependent on temperature, which drives many aspects of their physiology. The distribution of native and invasive populations of the frog Xenopus laevis is characterised by an exceptional latitudinal and altitudinal range. Along these gradients, the thermal environment changes and populations experience different temperatures. We assessed phenotypes depending on the temperature of individuals coming from six native and one invasive populations. We measured the thermal dependence of locomotor performance in adults given its relevance to dispersal, predator escape, and prey capture. Results show that the thermal performance optimum differs among populations, and the minimum critical temperature varies among populations coming from different altitudes. Then, we compared the standard metabolic
rate (energetic cost of organismal maintenance; SMR) depending on temperature, as locomotor performance strongly relies on metabolic activity. We tested SMR in populations from the native range, inhabiting low (South Africa) and high altitudes (Lesotho), and from the invasive range (France). Regarding the contrasting climatic environments of the studied populations, differences in the SMR depending on temperature are expected. We found that populations exhibit different energetic costs in metabolic activity and that populations show reduced metabolic activity in the temperature range the most encountered in their environment (i.e., in cold temperatures for
populations from colder environments and in hot temperatures for populations from warmer environments). The ability of this species to change its optimal temperature for locomotor performance and its metabolic activity across extremely different climatic environments may help explain its invasive potential. These findings highlight the extraordinary thermal adaptation ability of the species. This ability to cope with a wide range of variation in environmental temperatures suggests that the species may be particularly good at invading novel climatic areas.

A demanding way to spend your weekend

While at the Amphibian Foundation at the end of my trip to the USA, I took advantage of an offer to conduct a snake handling course (level 1) that they offer (see here). I've been in situations that have called for venomous snake handling in the past, and have always felt a little under prepared. Now with the course completed I know how to be safer when faced with a venomous snake on the ground, and a group of people that want it moved away.

Looking a little overgrown (after 2 months in the field without a haircut), I was outfitted with gaiters to prevent fangs going through my trousers. Guided by a set of expert instructors I learned how to handle heavy snakes on hooks (notice the braced position of the hooks under the forearms), and importantly how to safely get the snake into a tied bag and sealed bucket keeping it more than arms length at all times. 

Being in Atlanta, we became familiar with several of the regions most venomous snakes including the Eastern Timber Rattlesnake (Crotalus horridus - above), the Eastern Copperhead (Agkistrodon contortrix), Cottonmouth (Agkistrodon piscivorus), and Eastern Diamondback Rattlesnake (Crotalus adamanteus  - below). 

As you can see, the snakes were all very beautiful and it was a great pleasure working with them. Carefully following each of the steps according to instructions allowed us to bag up the snakes in a very safe manor. Run by the Rattlesnake Conservancy, these courses offer experienced and professional tuition in a relaxed and friendly environment.

As you can see, I gained my certificate of competence and feel a lot more confident about how to tackle venomous snakes in future.