A linear neural circuit for light avoidance in Drosophila larvae

Understanding how neural circuits underlie behaviour is challenging even in the era of the connectome because it requires a combined approach encompassing anatomical and functional analyses. This is exemplified in studying the circuit underlying the light-avoidance behaviour displayed by the larvae of the fruit fly Drosophila melanogaster. While this behaviour is robust and the nervous system relatively simple, only bits and pieces of the circuit have been delineated1. Indeed, some studies resulted in contradicting conclusions regarding the contributions of various neuronal types to this behaviour2,3. Here we devise trans-Tango MkII, a new version of the transsynaptic circuit tracing and manipulation tool trans-Tango4. We implement trans-Tango MkII in anatomical tracing and combine it with circuit epistasis analysis. We use neuronal inhibition to test necessity of particular neuronal types for light-avoidance. We complement these experiments by selective neuronal activation to examine sufficiency in rescuing light-avoidance deficiencies exhibited by photoreceptor mutants. Together, our studies reveal a four-order, linear circuit for light-avoidance behaviour connecting the light-detecting photoreceptors with a pair of neuroendocrine cells via two types of clock neurons. Our combined approach could be readily expanded to other larval circuits. Further, this strategy provides the framework for studying more complex nervous systems and behaviours.

Transcriptional Analysis of C-Repeat Binding Factors in Fruit of Citrus Species with Differential Sensitivity to Chilling Injury during Postharvest Storage

Citrus fruit are sensitive to chilling injury (CI) during cold storage, a peel disorder that causes economic losses. C-repeat binding factors (CBFs) are related to cold acclimation and tolerance in different plants. To explore the role of Citrus CBFs in fruit response to cold, an in silico study was performed, revealing three genes (CBF1, CBF2, and CBF3) whose expression in CI sensitive and tolerant cultivars was followed. Major changes occurred at the early stages of cold exposure (1–5 d). Interestingly, CBF1 was the most stimulated gene in the peel of CI-tolerant cultivars (Lisbon lemon, Star Ruby grapefruit, and Navelina orange), remaining unaltered in sensitive cultivars (Meyer lemon, Marsh grapefruit, and Salustiana orange). Results suggest a positive association of CBF1 expression with cold tolerance in Citrus cultivars (except for mandarins), whereas the expression of CBF2 or CBF3 genes did not reveal a clear relationship with the susceptibility to CI. Light avoidance during fruit growth reduced postharvest CI in most sensitive cultivars, associated with a rapid and transient enhance in the expression of the three CBFs. Results suggest that CBFs-dependent pathways mediate at least part of the cold tolerance responses in sensitive Citrus, indicating that CBF1 participates in the natural tolerance to CI.

Drosophila larval light avoidance is negatively regulated by temperature through two pairs of central brain neurons

Animal’s innate avoidance behavior is crucial for its survival. It subjects to modulation by environmental conditions in addition to the commanding sensorimotor transformation pathway. Although much has been known about the commanding neural basis, relatively less is known about how innate avoidance behavior is shaped by external conditions. Here in this paper, we report that Drosophila larvae showed stronger light avoidance at lower temperatures than at higher temperatures. Such negative regulation of light avoidance by temperature was abolished by blocking two pairs of central brain neurons, ACLPR60F09 neurons, that were responsive to both light and temperature change, including cooling and warming. ACLPR60F09 neurons could be excited by pdf-LaN neurons in the visual pathway. On the downstream side, they could inhibit the CLPNR82B09 neurons that command light induced reorientation behavior. Compared with at warm temperature, ACLPR60F09 neurons’ response to light was decreased at cool temperature so that the inhibition on CLPNR82B09 neurons was relieved and the light induced avoidance was enhanced. Our result proposed a neural mechanism underlying cross-modal modulation of animal innate avoidance behavior.

Influence of color and brightness on ontogenetic shelter preference by prawns (Macrobrachium rosenbergii)

The giant river prawn (Macrobrachium rosenbergii), native to rivers and river mouths of different Asian countries, is a heavily widespread species that has been introduced around the world due to its great commercial importance. These prawns are farmed under many different conditions that might translate to a great range of light environments, which impact their behavior and productivity. Here, as a contribution for prawns’ welfare and economical productivity, we present the first study employing both visual modeling and behavioral data to evaluate ontogenetic changes on color preference of juveniles and adults of M. rosenbergii. For this purpose, we offered ten shelters of different colors to juveniles and adults and registered their preference. Our results showed that the criterion for shelter preference changed with ontogeny, since juveniles chose shelters based on chromaticity (preference for blue), while adults based their decisions on brightness (preference for dark gray). This preference of adults for dark colors is probably associated with a light avoidance behavior. We recommend providing blue shelters for juveniles and dark shelters for adults.

Discrete escape responses are generated by neuropeptide-mediated circuit logic

Animals display a plethora of escape behaviors when faced with environmental threats. Selection of the appropriate response by the underlying neuronal network is key to maximize chances of survival. We uncovered a somatosensory network in Drosophila larvae that encodes two escape behaviors through input-specific neuropeptide action. Sensory neurons required for avoidance of noxious light and escape in response to harsh touch, each converge on discrete domains of the same neuromodulatory hub neurons. These gate harsh touch responses via short Neuropeptide F, but noxious light avoidance via compartmentalized, acute Insulin-like peptide 7 action and cognate Relaxin-family receptor signaling in connected downstream neurons. Peptidergic hub neurons can thus act as central circuit elements for first order processing of converging sensory inputs to gate specific escape responses.One Sentence SummaryCompartment-specific neuropeptide action regulates sensory information processing to elicit discrete escape behavior in Drosophila larvae.

In vivo photoprotection mechanisms observed from leaf spectral absorbance changes showing VIS–NIR slow-induced conformational pigment bed changes

Regulated heat dissipation under excessive light comprises a complexity of mechanisms, whereby the supramolecular light-harvesting pigment–protein complex (LHC) shifts state from light harvesting towards heat dissipation, quenching the excess of photo-induced excitation energy in a non-photochemical way. Based on whole-leaf spectroscopy measuring upward and downward spectral radiance fluxes, we studied spectrally contiguous (hyperspectral) transient time series of absorbance A(λ,t) and passively induced chlorophyll fluorescence F(λ,t) dynamics of intact leaves in the visible and near-infrared wavelengths (VIS–NIR, 400–800 nm) after sudden strong natural-like illumination exposure. Besides light avoidance mechanism, we observed on absorbance signatures, calculated from simultaneous reflectance R(λ,t) and transmittance T(λ,t) measurements as A(λ,t) = 1 − R(λ,t) − T(λ,t), major dynamic events with specific onsets and kinetical behaviour. A consistent well-known fast carotenoid absorbance feature (500–570 nm) appears within the first seconds to minutes, seen from both the reflected (backscattered) and transmitted (forward scattered) radiance differences. Simultaneous fast Chl features are observed, either as an increased or decreased scattering behaviour during quick light adjustment consistent with re-organizations of the membrane. The carotenoid absorbance feature shows up simultaneously with a major F decrease and corresponds to the xanthophyll conversion, as quick response to the proton gradient build-up. After xanthophyll conversion (t = 3 min), a kinetically slower but major and smooth absorbance increase was occasionally observed from the transmitted radiance measurements as wide peaks in the green (~ 550 nm) and the near-infrared (~ 750 nm) wavelengths, involving no further F quenching. Surprisingly, in relation to the response to high light, this broad and consistent VIS–NIR feature indicates a slowly induced absorbance increase with a sigmoid kinetical behaviour. In analogy to sub-leaf-level observations, we suggest that this mechanism can be explained by a structure-induced low-energy-shifted energy redistribution involving both Car and Chl. These findings might pave the way towards a further non-invasive spectral investigation of antenna conformations and their relations with energy quenching at the intact leaf level, which is, in combination with F measurements, of a high importance for assessing plant photosynthesis in vivo and in addition from remote observations.