Assessing the role of aridity-induced vicariance and ecological divergence in species diversification in North-West Africa using Agama lizards

Abstract

Diversification events in the Sahara-Sahel have mostly been attributed to regional aridification and subsequent arid-humid fluctuations, through vicariance or adaptation. However, no study has attempted to test these contrasting hypotheses. Here, we assess the importance of aridity-induced vicariance (as opposed to adaptation to new conditions) on diversification processes in NorthWest African Agama lizards. To test the hypothesis of vicariance as the main driver of diversification, we assessed the occurrence of the following three patterns expected to occur under the proposed scenario: (1) prevalent allopatric or parapatric distributions; (2) allopatric climatic refugia coincident with current distributions; and (3) niche similarity decreasing with increasing phylogenetic distance. We also reconstructed the centre of origin and range expansion dynamics for the Sahelian species to verify the congruence of the genetic signal with the vicariance scenario. All patterns expected from a neutral, non-adaptive niche divergence scenario were present. The diffusion models for the Sahelian species identified similar points of origin, corresponding to the areas of highest genetic diversity, topographic heterogeneity and climatic stability. Other patterns, such as mountain-isolated lineages, also indicate isolation by aridity. Our results support vicariance as the main driver of diversification in NW African Agama at both large and local scales. The importance of southern Mauritania for the conservation of biodiversity and the evolutionary process is highlighted.

Second Sahelian amphibian endemism suggested by phylogeography of Groove crowned Bullfrog ( Hoplobatrachus occipitalis ) in western Sahel and hints of polyploid species formation

“…The Djouk valley between Assaba and Tagant seems to be of particular importance for species persistence during arid phases, since it is where “highland” diversity is highest, but also considering similar evidence found in lizards (Gonçalves et al, ) and crocodiles (Velo‐Antón, Godinho, Campos, & Brito, ). As for the “lowland” lineage, the fact that only one mitochondrial allele is found in most of Mauritania (including Afollé and Adrar‐Atar) is consistent with a recent expansion, but the fact that all nuclear POMC alleles in Adrar‐Atar are private also suggests a refugium there.…”

“…The Djouk valley between Assaba and Tagant seems to be of particular importance for species persistence during arid phases, since it is where "highland" diversity is highest, but also considering similar evidence found in lizards (Gonçalves et al, 2018) and crocodiles (Velo-Antón, Godinho, Campos, & Brito, 2014). As for the "lowland" lineage, the fact that only one mitochondrial allele is found in most (Spieler & Linsenmair, 1998), and rapid development allowed by tadpole carnivory (Grosjean, Vences, & Dubois, 2004).…”

The correspondence between environmental similarity and geographical sympatry in Uromastyx species

“…Both overlap measurements are also uncorrelated (Pearson r = 0.48; p = 0.14). These results suggest that the degree of geographical overlap is lower than the degree of environmental sharing; a pattern reinforcing the hypothesis of a speciation process mainly based on geographical isolation processes (Gonçalves et al, 2018;Tamar et al, 2018).…”

Climate change, range shifts, and the disruption of a pollinator-plant complex

“…In addition, A. asperrima as well as L. nivalis exhibited less contraction of suitable area under RCP 8.5 both in 2050 and 2070. This suggests that species currently adapted to high aridity are slightly less impacted than less arid adapted species [36][37][38] .…”