Connectomic reconstruction predicts visual features used for navigation.

Many animals use visual information to navigate1-4, but how such information is encoded and integrated by the navigation system remains incompletely understood. In Drosophila melanogaster, EPG neurons in the central complex compute the heading direction5 by integrating visual input from ER neurons6-12, which are part of the anterior visual pathway (AVP)10,13-16. Here we densely reconstruct all neurons in the AVP using electron-microscopy data17. The AVP comprises four neuropils, sequentially linked by three major classes of neurons: MeTu neurons10,14,15, which connect the medulla in the optic lobe to the small unit of the anterior optic tubercle (AOTUsu) in the central brain; TuBu neurons9,16, which connect the AOTUsu to the bulb neuropil; and ER neurons6-12, which connect the bulb to the EPG neurons. On the basis of morphologies, connectivity between neural classes and the locations of synapses, we identify distinct information channels that originate from four types of MeTu neurons, and we further divide these into ten subtypes according to the presynaptic connections in the medulla and the postsynaptic connections in the AOTUsu. Using the connectivity of the entire AVP and the dendritic fields of the MeTu neurons in the optic lobes, we infer potential visual features and the visual area from which any ER neuron receives input. We confirm some of these predictions physiologically. These results provide a strong foundation for understanding how distinct sensory features can be extracted and transformed across multiple processing stages to construct higher-order cognitive representations.

The putative functions of lysogeny in mediating the survivorship of Escherichia coli in seawater and marine sediment.

Escherichia coli colonizes various body parts of animal hosts as a commensal and a pathogen. It can also persist in the external environment in the absence of fecal pollution. It remains unclear how this species has evolved to adapt to such contrasting habitats. Lysogeny plays pivotal roles in the diversification of the phenotypic and ecologic characters of E. coli as a symbiont. We hypothesized that lysogeny could also confer fitness to survival in the external environment. To test this hypothesis, we used the induced phages of an E. coli strain originating from marine sediment to infect a fecal E. coli strain to obtain an isogenic lysogen of the latter. The three strains were tested for survivorship in microcosms of seawater, marine sediment and sediment interstitial water as well as swimming motility, glycogen accumulation, biofilm formation, substrate utilization and stress resistance. The results indicate that lysogenic infection led to tractable changes in many of the ecophysiological attributes tested. Particularly, the lysogen had better survivorship in the microcosms and had a substrate utilization profile resembling the sediment strain more than the wild type fecal strain. Our findings provide new insights into the understanding of how E. coli survives in the natural environment.