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Welcome Siya!

08 January 2021

The MeaseyLab welcomes Siya Aggrey to

start his PhD on invasive House Crows

In our current state of turmoil surrounding the global pandemic of COVID-19, it seems amazing that Siya Aggrey has managed to make it from his home in Uganda to South Africa for the start of the academic year. Siya was recruited at the end of 2019 to receive a CIB bursary to study the invasion of House Crows in Cape Town. Days after getting his visa at the start of 2020, Siya was prevented from travelling as the pandemic spread across the globe and the university was closed. 

But Siya has managed to survive the year of COVID (2020) by conducting field studies in rural Uganda on COVID, AIDS and Ebola. He's also managed to remain preductive by adding to his increasing number of publications in 2020.

Siya will be working on invasive House Crows, which have also been having a great year by expanding their distribution vastly in South Africa. We are really looking forward to getting some more information on this situation as we move forward on their eradication programmes.


Finally I know my Erdős number

04 January 2021

My Erdős Number conforms to 6 degrees of separation

Paul Erdős was a Hungarian mathematician who authored or co-authored hundreds of publications across a wide variety of disciplines. He was so prolific that a certain level of prestige is associated to having co-authored a paper with him. The idea for the Erdős Number came from another mathemetician, Casper Goffman. This has now turned into a kind of science cult, in the same way that the Bacon number (actually a newer concept stemming from the Erdős Number) has in acting (see here). Those who have co-authored with Erdős are given an Erdős number of 1. Someone who has never written a paper with Erdős, but who has co-authored a paper with one of his co-authors are given an Erdős number of 2, and so on with increasing degrees of separation. As noted by Lenski, while the ranks of those with 6 degrees of separation from Erdős and Bacon are quite high, very few people have an Erdős-Bacon Number. 

For a long time, I've been pestering my mathatically inclined collaborators to find out what their Erdős number is so that I can plot my own. It turns out that I need not have bothered as my line is more direct than I had thought. 

My six degrees of separation:

Daniel Kleitman published many papers with Erdős, and has an Erdős number of 1

Lior Pachter has an Erdős number of 2, having co-authored a publication with Daniel Kleitman.

Richard Lenski has an Erdős number of 3, having co-authored a publication with Lior Pachter.

Jonathan Losos has an Erdős number of 4, having co-authored a publication with Richard Lenski.

Anthony Herrel has an Erdős number of 5, having co-authored a publication with Jonathan Losos.

I therefore have an Erdős number of 6, having co-authored a publication with Anthony Herrel

Thus my collaborators have either an Erdős number of 7 or lower (if they've got a more direct line to Erdős). It could be that my Erdős number is lower, or will get lower. Stay tuned for any updates!

Here are the relevant publications:

Beerenwinkel, N., Pachter, L., Sturmfels, B., Elena, S.F. and Lenski, R.E., 2007. Analysis of epistatic interactions and fitness landscapes using a new geometric approach. BMC Evolutionary Biology7(1), 1-12.

Blount, Z.D., Lenski, R.E. and Losos, J.B., 2018. Contingency and determinism in evolution: Replaying life’s tape. Science362  (6415).

Erdös, P. and Kleitman, D.J., 1968. On coloring graphs to maximize the proportion of multicolored k-edges. Journal of Combinatorial Theory5(2), pp.164-169.

Kleitman, D. and Pachter, L., 1998. Finding convex sets among points in the plane. Discrete & Computational Geometry19(3), pp.405-410.

Measey, G.J., & Herrel, A. 2006. Rotational feeding in caecilians: putting a spin on the evolution of cranial design. Biology Letters 2, 485-487.

  Lab  Writing

Two talks at SICB2021

02 January 2021

Two very different talks for Society for Integrative and Comparative Biology (SICB) 2021

I’m co-author on two very different talks at this years’ SICB conference, held online. 

The first talk by Carla Madelaire takes the work she and Adriana did on CORT back in 2019 to another level by asking whether saliva assays work as well as blood. This work has particular relevance on repeating CORT levels on individuals. Great to see this being presented!

The second study uses some data collected by myself and Anthony Herrel many years back. We collected some burrowing data on various caecilian species. Now Aurélien Lowie, from Ghent University, has taken this and other data to look at how a number of different live caecilians perform in relation to their skull shape. 

See more on the SICB 2021 website (links below!).

Corticosterone levels in the saliva as a measure of stress in toads

CB Madelaire, D Dillon, AMG Barsotti, J Measey, FR Gomes, CL Buck

Glucocorticoids have been widely used as a physiological marker of stress, and elevated baseline glucocorticoids levels in vertebrates have been associated with environmental changes. The use of minimally invasive sampling techniques and analysis of non-traditional sample types to monitor stress in wild populations has increased due to the importance of understanding how animals respond to environmental disturbances. The use of saliva samples can be a powerful tool to monitor both endocrine shifts and responses to stressors in wild populations. This sampling method does not require a large amount of manipulation and it can be used to sample smaller species, contributing to an increase of studies in environmental endocrinology and conservation efforts of understudied species. This study validated corticosterone (CORT) measurements in the saliva of the guttural toad (Sclerophrys gutturalis) using samples collected in the field and after a standardized stress protocol. We show that small amounts of saliva (0.018±0.028 g) are sufficient to quantify CORT. Salivary CORT levels were higher after exposure to a standardized stress protocol when compared to field levels of CORT, indicating that saliva samples can reflect biologically meaningful levels of CORT in the guttural toad. Because levels of salivary and plasma CORT were not correlated in either the field sampled animals or following exposure to acute stress, we conclude that CORT in the saliva and plasma might show different response dynamics to stimuli.


conservation physiology, glucocorticoid, acute stress, anura, salivary glucocorticoids

9:47 AM - 9:48 AM SAST on Saturday, January 2

Under pressure: the relationship between cranial shape and in vivo maximal burrowing force in caecilians (Gymnophiona)

Co-Author(s): A Lowie, A Herrel, B De Kegel, M Wilkinson, GJ Measey, JC O'Reilly, N Kley, P Gaucher, J Brecko, T Kleinteich, D Adriaens

Caecilians are elongate and limbless amphibians. Except one aquatic family, they all have an at least partially fossorial lifestyle. It has been suggested that they evolved sturdy compact skulls with fusion of ancestrally separate bones and tight sutures as an adaptation for head-first burrowing. Although their cranial osteology is well described, relationships between form and function remain poorly understood. In this study, we report data on in vivo burrowing forces for more than 120 specimens belonging to 13 different species. Over 80 caecilians were µCT-scanned and their skulls segmented. Using fixed and semi-sliding anatomical landmarks, we performed 3D geometric morphometrics to quantify skull variability across species. Finally, using correlation tests, linear models and two-blocks partial least squares, we investigated the relationships between the overall cranial shape and in vivo burrowing force in caecilians. Surprisingly, results show that despite differences in the head morphology across species, there is no relation between overall skull shape and this particular measure of burrowing performance. Although a phylogenetic signal may partly obscure the results, our conclusions join previous studies using biomechanical models and suggest that any differences in their degree of fossoriality are not driving the correlated adaptive evolution of head shape and maximal burrowing force. As the cranium has multiple functions such as feeding, and houses major sensory organs, or respiratory systems, further studies are needed to fully understand the selective pressures shaping the evolution of skull form.


amphibian, burrowing, geometric morphometrics, gymnophiona, skull, performance, head-first burrowers, head shape

10:05 AM - 10:06 AM SAST on Saturday, January 2

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