There are many questions regarding what influences the emergence of new species. Firstly and above all, is the appearance of differences within a certain specie, where a certain part is isolated from the group and continues its own evolution. One of these differences appear between the surface- and cave-dwelling Asellus aquaticus, as the ability to hold on to their surface.
The discovery of these differences was carried out using a method of experiment, namely on the cave-dwelling Asellus aquaticus from Planinska jama and Zelške jame and on surface-dwelling Asellus aquaticus from Ljubljana (near Biotehniška fakulteta) and Planinsko polje. With the experiment I tried to determine the maximum limit of the current velocities in which Asellus aquaticus can no longer hold on to their ground. For this purpose I had to built a contraption (PVC tube with a »slide«) that would allow me to do the experiment. The slide is wrapped with coarse paper, so that it represents a surface on which the organsms can hold on to. After an Asellus aquaticus is placed on that surface, the slide is pulled by a string on one side. On the other side, a different pull of the slide causes different tensions to the elastic, therefore causing different velocities. The movement of the slide along the contraption simulates the water flow, in where the initial tension of the elastic, determines the speed. Then I measured and recorded the expansion of the elastic string, each time the specimen let go of the surface. After many repetitions, I calculated the average speed of the water current during the release.
Before the actual experiment, I measured the speed the slide without Asellus aquaticus and created graphs of speed in dependence to the elongation of the weaker and stronger elastic. I presented the results of the measurements in form of a box plot and checked the differences in the grip between groups by using nonparametric statistical tests. Those have shown that there are significant differences between surface- and cave-dwelling Asellus aquaticus and no differences within the populations themselves.
The results have shown that cave-dwelling Asellus aquaticus are better adapted to gripping to the substrate, if the intensity of the water flow suddenly increases. These findings will help understand the behavioral differences which, together with other factors of evolution, affect the proces of formation of new underground species, despite the close vicinity to the surface ancestor populations.
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