02.05.2021

Tarantula sperm is "packed"!

Theraphosid sperm is called "caenosperm" when transferred into the bulb and also later when transferred into the spermatheca,, i.e. many sperm are collected in a sheath and these secretion sheaths then swim around in the sperm fluid in great numbers, as can be seen in the Pic 1. This secretion envelope provides a certain protection of the spermatozoa from external influences, because under certain circumstances the spermatozoa - protected in this way - have to remain in the receptacles of the spermatheca for weeks if not months before fertilization of the oocytes in the uterus externus occurs. In some cases, the sheaths are so large that they contain up to 100 spermatozoa (Pic 1, red arrows). Occasionally, however, there are also exposed spermatozoa in the sperm fluid, which are probably no longer needed for fertilization (Pic 2, red circles). If fertilization of the oocytes in the uterus externus is to occur, the membrane first dissolves and releases the sperm contained in it for fertilization.

These caenosperm are found in Theraphosidae and the Mesothelae, and therefore it is believed that this state of "sperm packing" is the more phylogenetically plesiomorphic state. Higher spiders, in fact, have a slightly different type of sperm packing, in which only one sperm at a time is found in a secretory sheath.

The Pic 1 & 2 show the caenosperm of Caribena versicolor (Walckenaer, 1837).

Another possibility for sperm examination came from the sperm net of a Pamphobeteus sp. "Zaruma" male, from which we were able to collect the sperm after the male had ingested the majority of the sperm and moved away. This was done as follows:

A slide was slid under the sperm net and pressed from below against the net with its attached sperm droplet, causing the tissue and sperm to adhere to the slide. We then dribbled several drops of saline (0.9% NaCl) onto the area with the sperm on the slide to wash the sperm out of the web. By gently pressing the web onto the slide, the washing out of the sperm was accelerated.

Afterwards, the web was removed from the slide and a coverslip was placed on top of the NaCL solution containing the sperm and this was placed under our microscope and the sperm was photographed at 400' and 600' magnification. Again, as expected, the typical "sperm packets" ( =Caenospermia) appeared (Pic 3 & 4), but on average these appear somewhat larger than in Caribena versicolor. We also noticed a clump that apparently contained some burst caenosperm (Pic 5 & 6, red arrows), from which the actual sperm had visibly leaked. To what extent such leaked sperm would still be useful for a successful fertilization remains unclear for the time being.