André is a PhD student at the Research Centre in Biodiversity and Genetic Resources, Portugal. He is an ecologist with special focus on biogeography, for which he combines historical and conservation perspectives. Here, André shares his recent work on the evolution of lizards inhabiting the most arid habitats of the Sahara Desert.
André during his Ph.D. sampling in the ergs (sand dune fields) of Ouarane, Mauritania.
Institute. CIBIO/InBIO, Research Centre in Biodiversity and Genetic Resources, University of Porto.
Academic life stage. PhD student.
Major research themes. Biogeography and phylogeography interface between comparative and conservation approaches. During my Ph.D. (ongoing), I investigate spatial biodiversity patterns in the Sahara Desert, aiming at (1) understanding the origin of the desert’s unique fauna and (2) synthesizing knowledge that can be used to minimize the impacts of the unprecedented climatic emergency on species’ persistence.
Current study system. Because they are intensely arid and bare, Saharan hyper-arid habitats (like the dune “erg” fields) appear to be virtually devoid of life, but such empty-desert rule is to some extent misleading given that some organisms successfully persist within these habitats. Beyond desert-flagship invertebrates (such as scorpions and beetles), the best example are spiny-footed lizards, Acanthodactylus scutellatus complex. These are conspicuous and widespread dwellers of sandy fields, wherein they have thrived for millions of years under extreme dryness thanks to their remarkable tolerance towards aridity constraints. These singularities make spiny-footed lizards unique pieces to understand the Sahara puzzle.
Vegetated patches and rocky outcrops contrast with the endless desert sand. Photo Credits: José Carlos Brito.
Recent JBI paper. Liz, A. V., Rödder, D., Gonçalves, D. V., Velo‐Antón, G., Tarroso, P., Geniez, P., Crochet, P.-A., Carvalho, S. B., & Brito, J. C. (2022). Overlooked species diversity in the hyper‐arid Sahara Desert unveiled by dryland‐adapted lizards. Journal of Biogeography 23(1), 101–115. https://doi.org/10.1111/jbi.14510
Motivation behind this paper. We know very little about hyper-arid habitats in the Sahara Desert, despite the area’s vastness (it is larger than the whole Australian continent!) and key role in global dynamics (like dust exportation to feed the Amazon rainforest). Indeed, filling existing knowledge gaps is important from both a natural-history and conservation perspective; first, because the paleoclimatic cycles that affected the desert’s extent make it a unique natural system to understand biodiversity responses to steep environmental shifts; and second, because the expected drastic impact of global warming in the region urges efficient measures to protect its unique wildlife. These reasons led us to study the biogeography of spiny-footed lizards, bearing in mind that, through the analysis of present-day species’ distribution and evolutionary patterns, we could infer historical landscape dynamics (such as shifts in sandy habitats and surface humidity) and verify the magnitude of regional biodiversity shortfalls (how many species have not been properly described?).
Key methodologies. One strength of this paper was the integration of different methodologies, namely ecological modelling, phylogeography and population genetics, to obtain a rather complete picture of the evolutionary history of spiny-footed lizards across the Sahara, and partially overcome sampling biases towards the more accessible areas. For instance, through ecological modelling and spatial interpolations of genetic data, we were able to obtain information from unexplored areas – which species are likely to occur therein? where should we expect higher diversity?
Specimen of Long Fringe-fingered Lizard, Acanthodactylus longipes, a conspicuous dweller of Saharan ergs. Photo Credits: José Carlos Brito.
Unexpected challenges. Certainly, the main challenge was to compile a representative set of samples that were relatively well distributed across the Sahara, considering that it would take us ages to survey the whole region or reach remote areas far from the main human settlements. The Sahara spans over 10 countries, some of them affected by long-lasting armed conflicts and political instability, which adds another layer of difficulty to field campaigns. To solve these issues, we focused sampling on the most accessible hyper-arid habitats, which could be reached in “only” a few days of driving, and by complementing it with natural-history collection samples. Finally, after over a decade of intermittent fieldwork and countless car breakdowns, we were able to build a rich dataset of ~700 samples to start the analyses.
Major results. The most exciting result was the amount of diversity still to be described from the group, which we had far underestimated. Even for taxa that are linked to habitats that are super common in the Sahara, most widespread “species” are in fact a collection of range-restricted species. You take sand specialists, there is sand everywhere and they are present everywhere, yet they have diverged (mostly until speciation) to a level totally crazy! And yet some candidate species are going from the Red Sea to nearly the Atlantic coast… This is very interesting both in terms of natural history (which environmental/geological mechanisms are responsible for such great diversity and connectivity?) and conservation (because the hyper-arid Sahara harbours many more species than what is often realised).
Next steps for this research. I would like to dig more into the biogeographic role of hyper-arid habitats in shaping local species structure, especially during “Green Sahara” phases – did sandy/gravel lowlands become the single pockets of suitable habitats for dryland specialists? were mountains more efficient shelters instead? or was it a mix between these two scenarios, where species persisted in the edge of hyper-arid habitats? are there differences according to functional groups (for instance, would reptiles and arthropods show the same trend)? Understanding these issues would help clarify the ecological value of these historically neglected habitats in the origin of the desert’s unique diversity.
An old truck near Bir Moghrein, which could not make it through the harsh desert conditions. Photo Credits: José Carlos Brito.
If you could study any organism on Earth, what would it be? I am fascinated by tropical habitats and the explosion of life present therein. Prior to my Ph.D., I spent two years in southern Brazil; this experience really marked me both at the professional and personal level. There, I learned to appreciate the symphonic communities of the Atlantic Forest, but also became aware of the conflicting context of dramatic environmental destruction that imperils their perpetuation. I would love to move back there one day and contribute to the conservation of these habitats.