Brightness discrimination in the day- and night-adapted wandering spider Cupiennius salei.

Cupiennius salei is a nocturnal spider with eight eyes, which undergo a remarkable circadian cycle: the rhabdomeric membrane of the photoreceptor cells is dismantled during the day and rebuilt at the beginning of the night. Such drastic changes might influence the brightness discrimination ability. We tested this hypothesis by presenting square-shaped flickering stimuli with certain luminances on stationary backgrounds with other luminances to spiders with day- or night-adapted eyes. When the spider, through its three pairs of so-called secondary eyes, perceives a visible contrast between the stimulus and the background, its principal eye muscle activity should increase. We therefore recorded this activity in vivo to assess the brightness discrimination ability of Cupiennius salei. Our results show that this spider has good brightness discrimination ability, which is significantly better with dark-adapted eyes. A Michelson contrast of 0.1 to 0.2 at night, and of 0.2 to 0.3 for day-adapted eyes, is sufficient to elicit a significant response, except below a critical value of luminance (~16 cd m(-2)), where the minimal perceivable contrast needs to be higher. In the Discussion we compare these performances with those of other animals, in particular with jumping spiders.

Soil sampling and isolation of extracellular DNA from large amount of starting material suitable for metabarcoding studies.

DNA metabarcoding refers to the DNA-based identification of multiple species from a single complex and degraded environmental sample. We developed new sampling and extraction protocols suitable for DNA metabarcoding analyses targeting soil extracellular DNA. The proposed sampling protocol has been designed to reduce, as much as possible, the influence of local heterogeneity by processing a large amount of soil resulting from the mixing of many different cores. The DNA extraction is based on the use of saturated phosphate buffer. The sampling and extraction protocols were validated first by analysing plant DNA from a set of 12 plots corresponding to four plant communities in alpine meadows, and, second, by conducting pilot experiments on fungi and earthworms. The results of the validation experiments clearly demonstrated that sound biological information can be retrieved when following these sampling and extraction procedures. Such a protocol can be implemented at any time of the year without any preliminary knowledge of specific types of organisms during the sampling. It offers the opportunity to analyse all groups of organisms using a single sampling/extraction procedure and opens the possibility to fully standardize biodiversity surveys.