A three-dimensional habitat for C. elegans environmental enrichment

Abstract

As we learn more about the importance of gene-environment interactions and the effects of environmental enrichment, it becomes evident that minimalistic laboratory conditions can affect gene expression patterns and behaviors of model organisms. In the laboratory, Caenorhabditis elegans is generally cultured on two-dimensional, homogeneous agar plates abundantly covered with axenic bacteria culture as a food source. However, in the wild, this nematode thrives in rotting fruits and plant stems feeding on bacteria and small eukaryotes. This contrast in habitat complexity suggests that studying C. elegans in enriched laboratory conditions can deepen our understanding of its fundamental traits and behaviors. Here, we developed a protocol to create three-dimensional habitable scaffolds for trans-generational culture of C. elegans in the laboratory. Using decellularization and sterilization of fruit tissue, we created an axenic environment that can be navigated throughout and where the microbial environment can be strictly controlled. C. elegans were maintained over generations on this habitat, and showed a clear behavioral bias for the enriched environment. As an initial assessment of behavioral variations, we found that dauer populations in scaffolds exhibit high-frequency, complex nictation behavior including group towering and jumping behavior.

Mechanosensory Systems and Sensory Integration Mediate C. elegans Negative Gravitaxis

“…Under normal laboratory growth conditions in which C. elegans are cultivated on flat agar surfaces in Petri dishes, dauers of the laboratory N2 strain of C. elegans do not nictate unless contaminated by fungi or when grown on three dimensional habitable scaffolds 37 ; however, 3-D scaffolds are not convenient for studying migratory behavior. To address this issue, we adapted a setup used to study neuromuscular integrity in C. elegans 38 to investigate whether C. elegans dauers exhibit directional bias in response to gravity (see Methods).…”

“…Under normal laboratory growth conditions where C. elegans are cultivated on flat agar surface in petri dishes, C. elegans dauers do not nictate unless contaminated by fungi. Nictation behavior is also observed when grown on three dimensional habitable scaffolds [37]; however, 3D scaffolds are not very convenient to study migratory behavior.…”

Automatically tracking feeding behavior in populations of foraging C. elegans

“…Recent work has succeeded in building a scaffolded 3D environment where C. elegans dauer larvae were observed 61 , indicating that behaviors are richer than in the typical 2D culturing environments. Our method, combined with animal tracking in 3D, could enable assays for feeding in these naturalistic contexts, while traditional grinder-tracking optical methods would likely be difficult due to the size and orientation changes of the pharynx in 3D.…”

Combining Animal Welfare With Experimental Rigor to Improve Reproducibility in Behavioral Neuroscience

“…While one can argue that there are not enough studies strengthening this assertion, the low quality of life of captive animals, the low reproducibility of studies, and the poor translational rate of preclinical research reinforce the necessity of a paradigm shift related to the welfare of animals ( Akkerman et al, 2014 ; Voelkl et al, 2020 ). This debate should not be restricted to rodents and shall include avians ( Melleu et al, 2016 ; Campbell et al, 2018 ), reptiles ( Burghardt et al, 1996 ), fishes ( Turschwell and White, 2016 ; Fong et al, 2019 ; Masud et al, 2020 ), and even invertebrate animals ( Ayub et al, 2011 ; Mallory et al, 2016 ; Bertapelle et al, 2017 ; Wang et al, 2018 ; Guisnet et al, 2021 ). We bring two practical examples (or recommendations) of improvements that we (the neuroscientific community) could do: (1) when using animal models we should implement environmental enrichment as the standard in the animal facilities (especially for those animal models that attempt to simulate central nervous system disorders), as raising animals in impoverished environments provides suboptimal sensory, cognitive and motor stimulation, making them too reactive to any kind of intervention (i.e., “noise amplifiers”) ( Nithianantharajah and Hannan, 2006 ); (2) when proposing alternative organisms to study behavior (e.g., zebrafish), we should learn from past and present mistakes (mostly in rodents), keeping in mind the ethological and natural needs of the species ( Branchi and Ricceri, 2004 ; Lee et al, 2019 ; Stevens et al, 2021 ).…”