Bio professor details ‘spermcasting spermballs’

By Dan Jurcisin

James Stockel visited the College on Friday to lead a presentation regarding the mating habits and fertilization of mussels and crayfish. The presentation described two experiments that were conducted by Stockel and his colleagues.

The presentation, titled “Spermcasting Spermballs and Carapace Cleaning Worms: Adventures In Mussel and Crayfish Ecology,” began by introducing a concept called the Allee effect. As some biology students may know, the Allee effect is a phenomenon in which a small population grows at a faster rate when the population size is at a state of greater density.

Stockel then described his first experiment. It consisted of placing mussels in a pond at different distances and determining whether or not the distance, or current, created by using an airlift, impacted their fertility.  His hypothesis was that fertilization would decrease when distance from males was increased, and more strongly in the absence of current.  The results of the experiment found that current did not make a difference in fertilization, fertilization was not a product of sperm storage or hermaphroditism, and there were adaptations for long distance fertilization.

The conclusion of the experiment was that mussels to not need a dense population to fertilize.  As Stockel remarked, density, “Does not seem to hinder long distance fertilization.”  Additionally, the study found that sex ratio may be an important factor to fertilization, and that spermcasting reduces the Allee effect.

The next experiment that was described was a two-part study regarding crayfish and branchiobdellida worms.  These worms use crayfish in order obtain food, and to reproduce.  The question of part one of the experiment was whether or not worms improve crayfish survivorship and growth in surface and/or underground environments.

For the experiment, Stockel and others constructed surface and underground environments in which to place the worms and crayfish.  For the surface environments, the study found that there was no difference in terms of crayfish survivorship, and there was a high reproduction of worms.

The second part of the study placed the crayfish and worms in the underground environment. The results were that the worms did not significantly affect crayfish growth, mortality or the burrow area.

Therefore, the results of the two-part study were that worms increased crayfish growth in surface waters, but did not affect the growth in the underground environment.