Our understanding of sexual selection is advancing with new technologies
that tag individuals or their sperm, revealing how females use
post-copulatory processes to discriminate between competing mates. Many
tagging methods have been devised primarily for model insect organisms
like Drosophila or Gryllidae. Developing such novel methods, however, is
expensive and requires intensive investment. In this experiment, we
trial the use of Rhodamine B and Rhodamine 110 in a small arachnid, the
bulb mite Rhizoglyphus echinopus, for pre and post copulatory
observations as it is a relatively inexpensive and simple way to tag
individuals and their ejaculate proteins. First, we tested whether
Rhodamine B and Rhodamine 110 applied to food can be used as a tagging
method to track and distinguish between individuals. Second, we explored
whether Rhodamine applied in this way can be used to track sperm
transfer. We found that both tagging probes worked well in tagging
individuals and that we were able to distinguish between individuals
using both LED and fluorescent microscopy. We also found that Rhodamine
degraded rapidly in the animals, likely due to their fast metabolism.
Due to the rapid degradation, we observed variable results in the sperm
transfer trials. We suggest multiple uses for Rhodamine and highlight
other invertebrates where this method may come into use for the study of
sexual selection.