Planarian Phototactic Assay Reveals Differential Behavioral Responses Based on Wavelength

Abstract

Planarians are free-living aquatic flatworms that possess a well-documented photophobic response to light. With a true central nervous system and simple cerebral eyes (ocelli), planarians are an emerging model for regenerative eye research. However, comparatively little is known about the physiology of their photoreception or how their behavior is affected by various wavelengths. Most phototactic studies have examined planarian behavior using white light. Here, we describe a novel planarian behavioral assay to test responses to small ranges of visible wavelengths (red, blue, green), as well as ultraviolet (UV) and infrared (IR) which have not previously been examined. Our data show that planarians display behavioral responses across a range of wavelengths. These responses occur in a hierarchy, with the shortest wavelengths (UV) causing the most intense photophobic responses while longer wavelengths produce no effect (red) or an apparent attraction (IR). In addition, our data reveals that planarian photophobia is comprised of both a general photophobic response (that drives planarians to escape the light source regardless of wavelength) and wavelength-specific responses that encompass specific behavioral reactions to individual wavelengths. Our results serve to improve the understanding of planarian phototaxis and suggest that behavioral studies performed with white light mask a complex behavioral interaction with the environment.

Photokinesis and Djopsin gene expression analysis during the regeneration of planarian eyes

“…Not surprisingly, the analysis of the spectral sensitivity showed that planarian eyes were more sensitive to blue light (495 nm), as reported previously (Brown et al 1968;Azuma et al 1999;Paskin et al 2014), which is known to parallel the absorption spectrum of rhodopsin in both vertebrates and invertebrates (Yokoyama 1997). Unexpectedly, the planarian eyes were also sensitive to yellow light (635 nm) under the same experimental conditions.…”

Mechanics dictate where and how freshwater planarians fission

“…No induction mechanism has been identified, although decapitation has been shown to increase fission probability (2)(3)(4). Furthermore, planarians are photophobic (5), fission occurs primarily in the dark (4,6), and even slight disturbances cause it to stop, complicating real-time imaging of the process. Finally, in the planarian species most commonly used in stem cell research, fission occurs on average approximately once per month per worm (7) and only lasts from a few minutes to tens of minutes (this study).…”

Temporal regulation of planarian eye regeneration

“…To determine the timeline of when the regenerating eye first becomes functional, we analyzed regenerates using a light avoidance assay we previously developed (Paskin et al. ) (Fig. ).…”

“…However, this does not necessarily correspond to equivalent functional recovery times, especially since worms needing to regrow their brain as well may recover function slower than worms just regrowing an optic cup. To determine the timeline of when the regenerating eye first becomes functional, we analyzed regenerates using a light avoidance assay we previously developed (Paskin et al 2014) (Fig. 5).…”

“…Planarians have a well-established photophobic response and will seek cover when exposed to light. Their phototactic responses vary by wavelength, with green wavelengths causing a moderate behavioral response where worms turn to avoid traveling through the light (Paskin et al 2014). Functional recovery of visual phototransduction was tested starting at 4 days post ablation (when pigment spots were first visible, Fig.…”