The red-swamp crayfish, Procambarus clarkii, is an invasive species in the freshwater streams of the Santa Monica Mountains. Entocytherid ostracods have been found to live on, P. clarkii, a suggested commensalistic relationship with the ostracod’s life cycle taking place in and on P. clarkii. P. clarkii outcompetes the California newt, T. torosa, through habitat destruction, and the consumption of T. torosa eggs, larvae, and juveniles despite the presence of the potent neurotoxin, tetrodotoxin (TTX), which is excreted on the skin, and is present in the eggs of T. torosa. Previous research has discovered that the production of TTX slows down movement of an invasive snail, speeds up mosquito larval growth, and effects benthic macroinvertebrate behavior. Unlike other invertebrates, the presence of TTX does not affect P. clarkii viability. We had two experimental goals: define the relationship between Entocytherid ostracods and chemical cues, specifically TTX, present in the Santa Monica Mountains’ freshwater ecosystems, and determine whether Entocytherid ostracods deposited their eggs in a non-random pattern on the gills of P. clarkii. We hypothesized that, like other invertebrates, ostracod movement would decrease as TTX concentration increased. We additionally hypothesized that there would be a significant deviation from a 1:1:1:1:1:1:1 distribution of observed eggs at the meeting of P. clarkia gills and appendages. We created four different ecologically relevant concentrations of TTX, in addition to a control and stock solution of TTX. We subjected ostracods to both the control solutions of TTX and the ecologically relevant solutions of TTX and observed appendage movement underneath an ECHO Rebel™ Microscope. We also observed and recorded the location of 923 Entocytherid ostracod eggs distributed on five different crawfish.
Results/Conclusions
We found no significant difference in appendage movement across the experimentally tested treatments compared to the control, and no significant trend of appendage movement frequency within or between any treatment group. We did not find a significant reduction of appendage movement at ecologically present concentrations of TTX. However, we found ostracod appendage movement to be significantly less in the stock solution treatment. We therefore concluded that ostracods are unaffected by ecologically encounterable concentrations of TTX, suggesting an incidence of parallel evolution of a similar trait in P. clarkii and commensalistic Entocytherid ostracod species. Furthermore, we did find a significant deviation from a 1:1:1:1:1:1:1 distribution of Entocytherid ostracod eggs with 35:20:10:15:6:1:1 better representing their distribution.