Neural Architecture of Hunger-Dependent Multisensory Decision Making in C. elegans

Little is known about how animals integrate multiple sensory inputs in natural environments to balance avoidance of danger with approach to things of value. Furthermore, the mechanistic link between internal physiological state and threat-reward decision making remains poorly understood. Here we confronted C. elegans worms with the decision whether to cross a hyperosmotic barrier presenting the threat of desiccation to reach a source of food odor. We identified a specific interneuron that controls this decision via top-down extrasynaptic aminergic potentiation of the primary osmosensory neurons to increase their sensitivity to the barrier. We also establish that food deprivation increases the worm's willingness to cross the dangerous barrier by suppressing this pathway. These studies reveal a potentially general neural circuit architecture for internal state control of threat-reward decision making

Global patterns in endemicity and vulnerability of soil fungi

Fungi are highly diverse organisms, which provide multiple ecosystem services. However, compared with charismatic animals and plants, the distribution patterns and conservation needs of fungi have been little explored. Here, we examined endemicity patterns, global change vulnerability and conservation priority areas for functional groups of soil fungi based on six global surveys using a high-resolution, long-read metabarcoding approach. We found that the endemicity of all fungi and most functional groups peaks in tropical habitats, including Amazonia, Yucatan, West-Central Africa, Sri Lanka, and New Caledonia, with a negligible island effect compared with plants and animals. We also found that fungi are predominantly vulnerable to drought, heat and land-cover change, particularly in dry tropical regions with high human population density. Fungal conservation areas of highest priority include herbaceous wetlands, tropical forests, and woodlands. We stress that more attention should be focused on the conservation of fungi, especially root symbiotic arbuscular mycorrhizal and ectomycorrhizal fungi in tropical regions as well as unicellular early-diverging groups and macrofungi in general. Given the low overlap between the endemicity of fungi and macroorganisms, but high conservation needs in both groups, detailed analyses on distribution and conservation requirements are warranted for other microorganisms and soil organisms

Global patterns in endemicity and vulnerability of soil fungi

Fungi are highly diverse organisms, which provide multiple ecosystem services. However, compared with charismatic animals and plants, the distribution patterns and conservation needs of fungi have been little explored. Here, we examined endemicity patterns, global change vulnerability and conservation priority areas for functional groups of soil fungi based on six global surveys using a high-resolution, long-read metabarcoding approach. We found that the endemicity of all fungi and most functional groups peaks in tropical habitats, including Amazonia, Yucatan, West-Central Africa, Sri Lanka, and New Caledonia, with a negligible island effect compared with plants and animals. We also found that fungi are predominantly vulnerable to drought, heat and land-cover change, particularly in dry tropical regions with high human population density. Fungal conservation areas of highest priority include herbaceous wetlands, tropical forests, and woodlands. We stress that more attention should be focused on the conservation of fungi, especially root symbiotic arbuscular mycorrhizal and ectomycorrhizal fungi in tropical regions as well as unicellular early-diverging groups and macrofungi in general. Given the low overlap between the endemicity of fungi and macroorganisms, but high conservation needs in both groups, detailed analyses on distribution and conservation requirements are warranted for other microorganisms and soil organisms

Multisensory integration in Caenorhabditis elegans behavioral ecology

To optimize foraging in natural environments, animals continuously make complex decisions about the suitability of their surroundings. These decisions require simultaneously processing sensory information, usually of different types (e.g., visual, auditory, etc.) about the environment, as well as an assessment of internal physiological state. How animals make these decisions is incompletely understood. I used the nematode worm Caenorhabditis elegans in two distinct contexts to investigate how multisensory integration contributes to foraging decisions. Like any animal, while foraging C. elegans must approach and obtain food while avoiding various threats, which for them include toxic chemicals and hyperosmotic concentrations of otherwise innocuous solutes. Little is known, however, in any animal about cellular and molecular mechanisms underlying decisions balancing avoidance of danger with approach to things of value. I confronted worms with a decision whether to cross a hyperosmotic barrier, presenting the threat of desiccation, to reach a source of food odor. I found that activation of a neuropeptide receptor in the higher-order "RIM" interneuron biases the worm against crossing the barrier. Unexpectedly, however, RIM controls this decision not by synaptic signaling to downstream motor command circuits, but rather by top-down extrasynaptic aminergic signaling directly onto the primary osmosensory neuron to tune its sensitivity to the barrier. Furthermore, I found that food deprivation increases the worm's willingness to cross the dangerous barrier by suppressing this pathway. Overall this work reveals a potentially general neural circuit basis for internal state control of threat-reward decision making. Using another behavioral paradigm, I have found that contrary to expectations, worms possess a color discrimination system that guides their foraging decisions despite lacking any opsin or other photoreceptor genes. C. elegans live in decomposing organic matter where they feed on microorganisms, some of which secrete colorful pigments. However, it was unknown whether worms use light information, potentially including color, to inform foraging behaviors in environments containing colorful food sources. Interestingly, I found that simulated daylight guides C. elegans foraging decisions with respect to harmful bacteria that secrete a blue pigment toxin. By absorbing yellow-orange light, this blue pigment toxin alters the color of light sensed by the worm, and thereby triggers an increase in avoidance of harmful bacteria. Not only does this work reveal an unexpected contribution of visual stimuli to worm behavioral ecology, it also establishes the existence of a color detection system that is distinct from those of other animals

C. elegans discriminates colors to guide foraging

Color detection is used by animals of diverse phyla to navigate colorful natural environments and is thought to require evolutionarily conserved opsin photoreceptor genes. We report that Caenorhabditis elegans roundworms can discriminate between colors despite the fact that they lack eyes and opsins. Specifically, we found that white light guides C. elegans foraging decisions away from a blue-pigment toxin secreted by harmful bacteria. These foraging decisions are guided by specific blue-to-amber ratios of light. The color specificity of color-dependent foraging varies notably among wild C. elegans strains, which indicates that color discrimination is ecologically important. We identified two evolutionarily conserved cellular stress response genes required for opsin-independent, color-dependent foraging by C. elegans, and we speculate that cellular stress response pathways can mediate spectral discrimination by photosensitive cells and organisms—even by those lacking opsins.NIH (Grants R01GM024663, R01GM098931

Effects of ether vs. ester linkage on lipid bilayer structure and water permeability.

The structure and water permeability of bilayers composed of the ether-linked lipid, dihexadecylphosphatidylcholine (DHPC), were studied and compared with the ester-linked lipid, dipalmitoylphosphaditdylcholine (DPPC). Wide angle X-ray scattering on oriented bilayers in the fluid phase indicate that the area per lipid A is slightly larger for DHPC than for DPPC. Low angle X-ray scattering yields A=65.1A(2) for DHPC at 48 degrees C. LAXS data provide the bending modulus, K(C)=4.2x10(-13)erg, and the Hamaker parameter H=7.2x10(-14)erg for the van der Waals attractive interaction between neighboring bilayers. For the low temperature phases with ordered hydrocarbon chains, we confirm the transition from a tilted L(beta') gel phase to an untilted, interdigitated L(beta)I phase as the sample hydrates at 20 degrees C. Our measurement of water permeability, P(f)=0.022cm/s at 48 degrees C for fluid phase DHPC is slightly smaller than that of DPPC (P(f)=0.027cm/s) at 50 degrees C, consistent with our triple slab theory of permeability.</p