Characterization of tmt-opsin2 in Medaka Fish Provides Insight Into the Interplay of Light and Temperature for Behavioral Regulation

Abstract

One of the big challenges in the study of animal behavior is to combine molecular-level questions of functional genetics with meaningful combinations of environmental stimuli. Light and temperature are important external cues, influencing the behaviors of organisms. Thus, understanding the combined effect of light and temperature changes on wild-type vs. genetically modified animals is a first step to understand the role of individual genes in the ability of animals to cope with changing environments. Many behavioral traits can be extrapolated from behavioral tests performed from automated motion tracking combined with machine learning. Acquired datasets, typically complex and large, can be challenging for subsequent quantitative analyses. In this study, we investigate medaka behavior of tmt-opsin2 mutants vs. corresponding wild-types under different light and temperature conditions using automated tracking combined with a convolutional neuronal network and a Hidden Markov model-based approach. The temperatures in this study can occur in summer vs. late spring/early autumn in the natural habitat of medaka fish. Under summer-like temperature, tmt-opsin2 mutants did not exhibit changes in overall locomotion, consistent with previous observations. However, detailed analyses of fish position revealed that the tmt-opsin2 mutants spent more time in central locations of the dish, possibly because of decreased anxiety. Furthermore, a clear difference in location and overall movement was obvious between the mutant and wild-types under colder conditions. These data indicate a role of tmt-opsin2 in behavioral adjustment, at least in part possibly depending on the season.

Light wavelength modulates search behavior performance in zebrafish

“…As we observed changes in the magnitude of search motor outputs, yet not transition latency, suggests potentially independent neural actions driven by photo-mediated signaling and general G-protein coupled receptor signaling 95 – 98 . Supporting this idea, the loss of non-visual opsins valopa/b or tmt2 disrupt early development and neuromodulatory functions, respectively, in a seemingly light independent manner, implicating deep-brain photoreceptors may exert physiological roles outside of active photoreception 99 , 100 . Altogether, our work complements prior studies showing chromatic inputs differentially drive activity in the brain by establishing new and distinct behavioral changes instructed by wavelengths across the visual spectrum.…”

Diversity and Molecular Evolution of Nonvisual Opsin Genes across Environmental, Developmental, and Morphological Adaptations in Frogs

“…It is possible that TMT3, rather than NEUR1, is contributing to seasonal sensitivity and reproductive changes in frogs. TMT2, a very closely related opsin, has been implicated in behavioral adjustment of medaka fish in response to the onset of cold temperatures ( Zekoll et al 2021 ), creating a precedent for seasonally linked function within the tmt-opsin group. If TMT3 is playing a role in the seasonal response, we would expect that this elevated ω is the product of adaptive selection in nontropical species due to the greater seasonal variation in the photoperiod they experience.…”

All Light, Everywhere? Photoreceptors at Nonconventional Sites

“…All these aspects show the complexity of nonvisual photoreceptors and their differential signaling in animals, which we have only started to understand, especially considering the complexity of their combinatoric ( 53 ) and other environmental cues, such as temperature ( 71 ).…”