Abstract
The Namib Desert is a biodiversity hotspot for many invertebrates, including spiders. Tube‐dwelling spiders belonging to the Ariadna genus are widespread in gravel plains. These sit‐and‐wait predators share a particular behavior, as they spend their life in tunnels in the soil, surrounding the entrance of their burrow with stone rings. We investigated five spider populations taking into account environmental parameters, functional traits, and molecular data. We have chosen the temperature at the soil surface and at the bottom of the burrow, the air humidity, and the soil granulometry to define the environment. The chosen functional traits were the diameter and depth of the burrows, the ratio between weight and length, the thermal properties of their silks, and the number of ring elements. The molecular branch lengths and the evolutionary distance emerging from cytochrome oxidase I gene sequences summarized the molecular analysis. Our study highlights a strong coherence between the resulting evolutionary lineages and the respective geographical distribution. Multivariate analyses of both environmental and molecular data provide the same phylogenetic interpretation. Low intrapopulation sequence divergence and the high values between population sequence divergence (between 4.9% and 26.1%) might even suggest novel taxa which deserve further investigation. We conclude that both the Kimura distance and the branch lengths are strengthening the environmental clustering of these peculiar sites in Namibia.
Highlights
Namibia is one of the world's drylands at greatest risk of large rain‐ fall changes, and urgent actions are needed to prepare the coun‐ try for further decreases in rainfall (Chadwick, Good, Martin, &Rowell, 2016)
Quaternary reconstructions of aridity and trade‐wind strength in southwestern Africa clearly show that eolian erosion in Namibia is remarkably high and the long‐term combination between such an extreme erosion, huge aridity and direct and intense solar radiation is a major environmental driver for any living organism
It is estimated that 11% of arachnids in Namibia are endemic and about 90% of the occurring invertebrates might not have been described yet (Ministry of Environment & Tourism, 2014)
Summary
Namibia is one of the world's drylands at greatest risk of large rain‐ fall changes, and urgent actions are needed to prepare the coun‐ try for further decreases in rainfall About 25 years ago, Costa, Petralia, Conti, Hänel, and Seely (1993) re‐ corded the existence of numerous and large tube‐dwelling spider pop‐ ulations on the gravel plains of the Namib Desert These populations were identified as belonging to the genus Ariadna (Segestriidae). The taxonomy of Segestriidae seems to be quite chaotic (World Spider Catalog, 2018) This makes an integrated approach based on molecular data as well as ecological features and functional traits the best response to highlight how different popula‐ tions can face different environmental conditions especially in such extreme habitats. The purpose of this work is to understand to what extent ecological factors in a hyperarid envi‐ ronment might have led to a specific differentiation within the genus Ariadna with site‐specific behavioral features
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