Name: Barros M

Biodeserts supervisors: Martínez-Freiría F, Velo-Antón G

Title: Reconstructing the evolutionary history of desert-adapted Cerastes vipers in North Africa and the Arabian Peninsula

Institution: University of Porto

Status: Completed

Abstract

Pleistocene climatic oscillations have influenced biogeographical patterns of species worldwide, affecting their distributional ranges and shaping their genetic diversity. Desert environments have been mistakenly characterized as regions extremely poor in biodiversity and with low variability. However, the opposite has been proven, in major deserts such as the Sahara and Arabian deserts and its surrounding regions, which present several types of ecoregions. This great variety of ecoregions exist due to the wide range of climatic and topographical conditions that characterize North Africa and the Arabian Peninsula. These characteristics demonstrate the potential that these outstanding regions have for conducting scientific research. In addition, recent studies have shown the importance of the climate influence in the genetic structure and variability of species given their accentuated and dynamic climatic history, and diverse life history and habitat traits of taxa inhabiting such extreme regions. This study aims to address the role of Pleistocene climatic oscillations in the evolutionary history of the three Cerastes species (Viperinae), C. cerastes and C. vipera from the Sahara Desert, and C. gasperettii from the Arabian Peninsula deserts. Phylogenetic structure and variability were inferred using Bayesian inference over sequences (68 samples) for one mtDNA (COI) and three nuDNA (PRLR, NT3, VIM) gene markers. Paleoclimatic models combined 318 occurrences and five climatic variables in Maxent to infer climatic suitability for current and past (mid Holocene, Last Glacial Maximum and Last Inter Glacial) events, and stability over time. Paleoclimatic models were conduct in two different scales, the first carried for all three species at a 10x10 kms scale, covering the total range of the genus, and the second at a 1x1kms scale conducted only in North West Africa. Mitochondrial inferences show C. cerastes and C. gasperettii as sister taxa, while C. vipera is identified as a phylogenetically more distant species, which is concordant with previously recent studies. The three nuDNA genes analysed in this study (PRLR, NT3 and VIM) well differentiated C. gasperettii from the other two taxa. However, PRLR and NT3 showed extensive haplotype sharing between C. cerastes and C. vipera. The different results obtained using mitochondrial and nuclear markers raise questions on the true phylogenetic relationships between Cerastes vipers. Further levels of mtDNA structure within the three species originated along the middle and late Pleistocene. A clear division between C. cerastes and C. vipera populations was found between eastern and western areas of North Africa. In the phylogenetic reconstruction was also possible to observe structuration within each lineage of C. cerastes and C. vipera. Within the western group, two distinct population were recovered for C. cerastes (West-North and West-South) and for C. vipera (West-west and West-Central). C. gasperettii shown to be the species with the most recent divergence and for which two lineages (North and South) were recovered. Due to the vast intraspecific diversity found for C. cerastes in western North Africa, and since this region has been hypothesized to have acted as a refuge and corridor for several other species with different ecological requirements through time, further paleoclimatic modelling was conducted for Western populations of this species. Paleoclimatic models identified Inter Glacial events as major drivers of range reduction and isolation in the three species. Distinct areas of high climatic stability across the Sahara and Arabian deserts fit spatial patterns of genetic structure and likely acted as Pleistocene climatic refugia for species and lineages. Mito-nuclear discordances are discussed in the light of morphological and ecological traits of species. This multidisciplinary approach allows to propose biogeographic scenarios for the evolution of these desert-adapted species.