Responses of different Drosophila species to temperature changes

Evolution of temperature preference in flies of the genus Drosophila

The preference for a particular thermal range is a key determinant of the distribution of animal species. However, we know little on how temperature preference behaviour evolves during the colonization of new environments. Here we show that at least two distinct neurobiological mechanisms drive the evolution of temperature preference in flies of the genus Drosophila. Fly species from mild climates (D. melanogaster and D. persimilis) avoid both innocuous and noxious heat, and we show that the thermal activation threshold of the molecular heat receptor Gr28b.d precisely matches species-specific thresholds of behavioural heat avoidance. We find that desert-dwelling D. mojavensis are instead actively attracted to innocuous heat. Notably, heat attraction is also mediated by Gr28b.d (and by the antennal neurons that express it) and matches its threshold of heat activation. Rather, the switch in valence from heat aversion to attraction correlates with specific changes in thermosensory input to the lateral horn, the main target of central thermosensory pathways and a region of the fly brain implicated in the processing of innate valence1-5. Together, our results demonstrate that, in Drosophila, the adaptation to different thermal niches involves changes in thermal preference behaviour, and that this can be accomplished using distinct neurobiological solutions, ranging from shifts in the activation threshold of peripheral thermosensory receptor proteins to a substantial change in the way temperature valence is processed in the brain.

Behavioral Assays for Optogenetic Manipulation of Neural Circuits in Drosophila melanogaster

Optogenetics has become a fundamental technique in neuroscience, enabling precise control of neuronal activity through light stimulation. This study introduces easy-to-implement setups for applying optogenetic methods in Drosophila melanogaster. Two optogenetic tools, CsChrimson, a red-light-activated cation channel, and GtACR2, a blue-light-activated anion channel, were employed in four experimental approaches. Three of these approaches involve single-fly experiments: (1) a blue-light optogenetic thermotactic positional preference assay targeting temperature-sensitive heating cells, (2) a red-light optogenetic positional preference assay activating bitter sensing neurons, and (3) a proboscis extension response assay activating the sweet-sensing neurons. The fourth approach (4) is a fly maze setup to assess avoidance behaviors using multiple flies. The ability to manipulate neural activity temporally and spatially offers powerful insights into sensory processing and decision-making, underscoring the potential of optogenetics to advance our knowledge of neural function. These methods provide an accessible and robust framework for future research in neuroscience to enhance the understanding of specific neural pathways and their behavioral outcomes.

Elevated sleep quota in a stress-resilient Drosophila species

Sleep is broadly conserved across the animal kingdom but can vary widely between species. It is currently unclear which selective pressures and regulatory mechanisms influence differences in sleep between species. The fruit fly Drosophila melanogaster has become a successful model system for examining sleep regulation and function, but little is known about the sleep patterns in many related fly species. Here, we find that fly species with adaptations to extreme desert environments, including D. mojavensis, exhibit strong increases in baseline sleep compared with D. melanogaster. Long-sleeping D. mojavensis show intact homeostasis, indicating that desert flies carry an elevated drive for sleep. In addition, D. mojavensis exhibit altered abundance or distribution of several sleep/wake-related neuromodulators and neuropeptides that are consistent with their reduced locomotor activity and increased sleep. Finally, we find that in a nutrient-deprived environment, the sleep patterns of individual D. mojavensis are strongly correlated with their survival time and that disrupting sleep via constant light stimulation renders D. mojavensis more sensitive to starvation. Our results demonstrate that D. mojavensis is a novel model for studying organisms with high sleep drive and for exploring sleep strategies that provide resilience in extreme environments.

Functional labeling of individualized postsynaptic neurons using optogenetics and trans-Tango in Drosophila (FLIPSOT)

A population of neurons interconnected by synapses constitutes a neural circuit, which performs specific functions upon activation. It is essential to identify both anatomical and functional entities of neural circuits to comprehend the components and processes necessary for healthy brain function and the changes that characterize brain disorders. To date, few methods are available to study these two aspects of a neural circuit simultaneously. In this study, we developed FLIPSOT, or functional labeling of individualized postsynaptic neurons using optogenetics and trans-Tango. FLIPSOT uses (1) trans-Tango to access postsynaptic neurons genetically, (2) optogenetic approaches to activate (FLIPSOTa) or inhibit (FLIPSOTi) postsynaptic neurons in a random and sparse manner, and (3) fluorescence markers tagged with optogenetic genes to visualize these neurons. Therefore, FLIPSOT allows using a presynaptic driver to identify the behavioral function of individual postsynaptic neurons. It is readily applied to identify functions of individual postsynaptic neurons and has the potential to be adapted for use in mammalian circuits.

Cool and warm ionotropic receptors control multiple thermotaxes in Drosophila larvae

Animals are continuously confronted with different rates of temperature variation. The mechanism underlying how temperature-sensing systems detect and respond to fast and slow temperature changes is not fully understood in fly larvae. Here, we applied two-choice behavioral assays to mimic fast temperature variations and a gradient assay to model slow temperature changes. Previous research indicates that Rhodopsin 1 (Rh1) and its phospholipase C (PLC) cascade regulate fast and slow temperature responses. We focused on the ionotropic receptors (IRs) expressed in dorsal organ ganglions (DOG), in which dorsal organ cool-activated cells (DOCCs) and warm-activated cells (DOWCs) rely on IR-formed cool and warm receptors to respond to temperature changes. In two-choice assays, both cool and warm IRs are sufficient for selecting 18°C between 18°C and 25°C but neither function in cool preferences between 25°C and 32°C. The Rh1 pathway, on the other hand, contributes to choosing preferred temperatures in both assays. In a gradient assay, cool and warm IR receptors exert opposite effects to guide animals to ∼25°C. Cool IRs drive animals to avoid cool temperatures, whereas warm IRs guide them to leave warm regions. The Rh1 cascade and warm IRs may function in the same pathway to drive warm avoidance in gradient assays. Moreover, IR92a is not expressed in temperature-responsive neurons but regulates the activation of DOWCs and the deactivation of DOCCs. Together with previous studies, we conclude that multiple thermosensory systems, in various collaborative ways, help larvae to make their optimal choices in response to different rates of temperature change.