Name: Gonçalves DV
Biodeserts supervisor: Brito JC
Co-supervisors: Carranza S
Title: Integrative inference of evolutionary patterns of desert biodiversity: a spatial and temporal multiscale approach using herpetofauna from North-Africa
Institution: University of Porto
Status: Completed
Abstract
North Africa is a region of high biogeographic importance, increasingly recognized as a biodiversity and diversification hotspot, and with a close historical connection with the European biological diversity. Most of the region is occupied by the Sahara and Sahel, also two of the major ecoregions of Africa, which comprise the world’s largest warm desert and the neighbouring arid regions to the south. The range of both areas has widely fluctuated in the last few million years, due to 20-to-100 thousand-years arid-humid cycles that have made the desert come and go, which, together with a series of geological events and a topographically varied landscape, provide a rich scenario to study evolutionary mechanisms shaping the local biodiversity.
In spite of a recently increasing body of studies on Sahara-Sahel biodiversity, there is still a huge knowledge gap regarding biodiversity distribution, species limits, or the evolutionary processes that led to the currently observed patterns of biodiversity. The general aim of this thesis was to increase the knowledge on the biodiversity and biogeographic history of arid North Africa, as well as the evolutionary processes shaping it. Four main goals were delineated for that purpose: 1) increase the available sampling data for the region, and describe biodiversity patterns; 2) development and optimization of tools and protocols targeted at studying local biodiversity; 3) assessment of evolutionary patterns at large spatial and temporal scales; and 4) assessment of evolutionary patterns at local spatial (and temporal) scales. This was achieved by integrating phylogeographic and eco-geographic tools in the analysis of distribution, genetic, and ecological data pertaining representatives of North African herpetofauna, including species of the Agama genus, Psammophis schokari and Hoplobatrachus occipitalis.
The known distribution ranges of several species have been extended and better detailed, both in terms of presence records and genetic diversity. Parapatry was the dominant pattern in the distribution of species and genetic lineages of the study subjects. Climate has been shown to have played a major role in shaping the biodiversity patterns and evolution in the region, by shaping distributional ranges, causing demographic fluctuations and local extinctions, restricting dispersal, which ultimately led to diversification and speciation events. The hypothesis of climate-induced vicariance as lead diversification motor was tested in Agama genus, by assessing the occurrence of expected biogeographic patterns and using ecological niche comparisons. Results seem to support this hypothesis. Examples of particular vicariant agents that were detected were sand deposition that covers rock outcrops (for A. boulengeri), or the Tamanrasset paleoriver basin (for P. schokari). The hypothesis of trans-Saharan corridors allowing gene flow among populations of mesic species was assessed using P. schokari. The permanence of the Atlantic Sahara mesic corridor was supported, at least for the species tending to the xeric and high-dispersal end, like P. schokari, possibly working as refugium as well. The connectivity between Mediterranean coast and southern Algerian mountains was higher than expected. The local scale biogeographic assessment of A. boulengeri revealed a complex scenario, possibly involving multiple refugia, recurrent bottlenecks, landscape connectivity and male-biased dispersal, demonstrating in one species the richness of evolutionary processes that can intervene in the region.
Non-climate related diversification mechanisms were also identified in the region, with a possible allopolyploidization in H. occipitalis, which isolated in a diploid mountain-endemic population in Mauritania, surrounded by a widespread tetraploid lowland one. Selective pressures towards adaptation to novel conditions are expected to have played a role in species diversification as well, although in the study cases here presented no strong indication of divergent adaptation was found. Technical contributions were also made with the development of microsatellite markers for A. boulengeri and other species in the genus, which could allow pursuing questions regarding gene flow, variable landscape connectivity or systems of mating and dispersal.
Evidence is provided for the importance of mountain regions as biodiversity hotspots and refugia during climatic cycles in the Plio-Pleistocene. The Djouk valley, separating the Tagant and Assaba in Mauritania, seems to be of particular interest for conservation given the biodiversity richness and the importance for preserving evolutionary processes and gene-flow among neighbouring mountain systems. Considering the range of questions addressed and the diversity of relatable subjects, I expect the contribution here presented will prove useful for future works on disciplines as varied as phylogeography, evolutionary ecology or biodiversity conservation.