Abstract
Nematodes have sensitive olfactory perception, which is used to detect and differentiate many volatile odorants. Some odorants are attractive, others repulsive, and yet others evoke no particular response. Chemotaxis assays can be used to determine the role of certain odors in many different behaviors including foraging, predator avoidance, and mate attraction. In addition to chemotaxis, some species of nematodes in the entomopathogenic genus Steinernema can jump, which is thought to play an important role in host-seeking and dispersal (Dillman and Sternberg, 2012). Jumping and chemotaxis assays have been successfully used to identify odorants that stimulate these behaviors in a variety of nematodes (Bargmann et al., 1993; Campbell and Kaya, 1999; Hallem et al., 2011; Dillman et al., 2012; Castelletto et al., 2014). Here a detailed protocol for chemotaxis and jumping assays is provided based on the growing body of literature.
Keywords: Entomopathogenic, Chemotaxis, Jumping, Behavior, Nematodes
Materials and Reagents
Equipment
Procedure
Representative data
Notes
These experiments can show some variability and are highly sensitive to changes in temperature, humidity, and the introduction of transient odors (e.g. perfume, cologne, soap, food, etc.) I have noticed that foods being cooked or eaten nearby, especially fragrant food such as popcorn, which smells like the attractant diacetyl, can affect chemotaxis and jumping behavior. Because of the high sensitivity and variability of these behavioral assays it is important that test runs and controls are run in parallel, using the same conditions. Having many replicates can help increase the behavioral signal. Although behavioral experiments tend to have high sensitivity and variability, I have found that observed phenotypes using these techniques are robust over many days of experiments and between different batches of nematodes, both for jumping and chemotaxis, though there are occasional batches with unusual behavior. The proclivity for chemotaxis assay is an interesting extension of the regular chemotaxis assay that provides more data and finer resolution into chemotaxis behavior. While previous work shows high chemotaxis indices for several species, which leads the reader to conclude that the species have similar chemoattractive preferences and abilities (e.g. Hallem et al. 2011; Dillman et al. 2012), a PCI assay might reveal differences in the proclivity for chemotaxis between these species. For example, whereas Steinernema glaseri and S. carpocapsae may both have a high CI toward waxworm odors, perhaps only 20% of the S. carpocapsae population being tested participates in the behavior while 80% of S. glaseri may be participating. The PCI is another way to explore the behavioral ecology of nematode olfactory responses.
Recipes
Acknowledgments
This laboratory protocol is a free adaptation of various published and unpublished protocols and has evolved over time (Ward, 1973; Bargmann et al., 1993; Campbell and Kaya, 2000; Hallem et al., 2011; Dillman et al., 2012; Castelletto et al., 2014). A.R.D. was funded by initial lab startup funds from the University of California, Riverside.
References
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