Name: Pissarra J

Biodeserts supervisors: Brito JC, Velo-Antón G

Title: Phylogenetic and ecological characterization of Monitor lizards in Northern Africa

Institution: University of Porto

Status: Completed




The ongoing biodiversity crisis of direct and indirect anthropogenic causes highlights the urgency to study global biodiversity. A particularly understudied region is Northern Africa where political instability, social conflicts, low development index, and generic inaccessibility hamper scientific work. Northern Africa (above the equator) harbours multiple ecoregions with a wide range of climatic and topographic conditions, from the hyper-arid deserts to the water-saturated rainforests. Recent studies show that Northern Africa is more biologically diverse than previously thought due to its rich history of climatic shifts like the formation of the Sahara and the periodic oscillations between arid and humid climates of the Plio-Pleistocene, and due to multiple barriers to gene flow like mountain ranges and rivers. In this study, three monitor lizard species (genus Varanus) were selected as model systems to better understand the patterns of genetic structure and diversity of large and highly mobile reptiles of Northern Africa. Each selected species of Varanus is adapted to different ecological conditions with V. griseus being adapted to arid regions, V. exanthematicus to mesic environments, and V. niloticus being dependent of permanent water bodies. In order to understand the genetic structure and patterns of diversity of the three Varanus species, to resolve incongruencies regarding the species range, and to aid future conservation planning of these exploited species, the work leading to this dissertation was developed under the frame of the following objectives: 1) update the geographic distribution; 2) determine the genetic structure and intraspecific genetic diversity; 3) map the spatial genetic diversity and potential barriers to gene flow; and 4) characterise the ecological niche of all target species and potential intraspecific lineages.
Exhaustive literature research and data collected during past field trips allowed to calculate the extent of occurrence of each species according to IUCN Red List norms. Phylogenetic analysis of a segment of 627 bp of the mitochondrial genome from samples collected during past field work and sequences from NCBI GenBank revealed a total of 18 lineages grouped into six clades among the three species. One clade of V. griseus, two of V. exanthematicus (West and East) and the three clades already described in the literature of V. niloticus (West, North and South). Three nuclear genetic markers, totalling 1218 bp, were also analysed to create haplotype networks of
the available samples. In these networks, V. griseus showed no diversity, and V. exanthematicus and V. niloticus presented very little diversity without clear structure. A Spatial Principal Component Analysis of nine topoclimatic variables of Africa was created to access the ecological niche of the species and respective clades. The resulting comparisons revealed some ecological differences between species and none between clades.
Distinct spatial distribution, genetic structure and percentual differences among the mtDNA clades, suggest the existence of potential cryptic diversity within V. exanthematicus and V. niloticus that likely appeared due to strong climatic events that shaped Northern Africa in the past. However, analyses of the nuclear genetic markers and ecological niche revealed little support in favour of new cryptic species suggesting that more work is needed to properly address this issue. This work was important to fill in knowledge gaps regarding the distribution and genetic structure of the three species, and to path the way for future studies and the conservation of these species.