Ariadna spider as potential bioindicator of heavy metal exposure in the Namib Desert

Human activities are strongly affecting the health of ecosystems, so even organisms from natural environments are more and more frequently exposed to increasing concentrations of pollutants. Among these, heavy metals represent persistent components and have therefore a strong impact on both plant and animal populations. Mining activity is the biggest contributor to Namibia’s economy in terms of revenue and includes copper, gold, lead, zinc, uranium, diamonds, semi-precious gemstones and minerals. Various spider populations belonging to undescribed Ariadna species are widespread in gravel plains within the Central Namib Desert. These sit-and-wait predators spend their life in individual tunnels dug in the soil so, as it has already been demonstrated for other spiders, they seem to be good candidates as bioindicators of heavy metals. We first analysed the effect of mining activity on three Ariadna populations along a N/S and W/E transect at different distances from mining areas. Three sites were selected at various distance from the mining area. An average number of 35 spiders were collected from each site and shipped alive to Italy. Diameter of entrance and depth of the burrows of single spider were calculated on site. Oxidative stress parameters, selected enzymes involved in metal biotransformation as CAT, GST, MDA and total MT have been investigated as well as gene expression profile of related genes as gst, hsp70 and mt. Cholinesterases have been also characterized in order to use their inhibition as a potential marker of heavy metal exposure. Heavy metal concentrations in both soils and animal tissue were also determined. The diameter of the burrow entrance and their depth show statistical differences among sites. Enzymatic assays as well as gene expression profile also highlight differences among sites. The results obtained show that the Namibian Ariadna spiders is a good candidate as bioindicator of heavy metal exposure in Namib Desert.