Regulation of specialists and generalists by neural variability improves pattern recognition performance

This is the author’s version of a work that was accepted for publication in Neurocomputing. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Neurocomputing, VOL 151, Part 1, (2015), DOI 10.1016/j.neucom.2014.09.073To analyze the impact of neural threshold variability in the mushroom body (MB) for pattern recognition, we used a computational model based on the olfactory system of insects. This model is a single-hidden-layer neural network (SLN) where the input layer represents the antennal lobe (AL). The remaining layers are in the MBs that are formed by the Kenyon cell (KC) layer and the output neurons that are responsible for odor learning. The binary code obtained for each odorant in the output layer by unsupervised learning was used to measure the classification error. This classification error allows us to identify the neural variability paradigm that achieves a better odor classification. The neural variability is provided by the neural threshold of activation. We compare two hypotheses: a unique threshold for all the neurons in the MB layer, which leads to no variability (homogeneity), and different thresholds for each MB layer (heterogeneity). The results show that, when there is threshold variability, odor classification performance improves. Neural variability induces populations of neurons that are specialists and generalists. Specialist neurons respond to fewer stimulus than the generalists. The proper combination of these two neuron types leads to performance improvement in the bioinspired classifier.This work was supported by the Spanish Government project TIN2010-19607 and predoctoral research grant BES-2011- 049274. R.H. acknowledges partial support by NIDCDR01DC011422- 01

Roadmap on biology in time varying environments

Biological organisms experience constantly changing environments, from sudden changes in physiology brought about by feeding, to the regular rising and setting of the Sun, to ecological changes over evolutionary timescales. Living organisms have evolved to thrive in this changing world but the general principles by which organisms shape and are shaped by time varying environments remain elusive. Our understanding is particularly poor in the intermediate regime with no separation of timescales, where the environment changes on the same timescale as the physiological or evolutionary response. Experiments to systematically characterize the response to dynamic environments are challenging since such environments are inherently high dimensional. This roadmap deals with the unique role played by time varying environments in biological phenomena across scales, from physiology to evolution, seeking to emphasize the commonalities and the challenges faced in this emerging area of research

Host location in a specialist parasitoid wasp via olfactory cues – a physiological, behavioural and morphological study

For successful host location, parasitoids are thought to have evolved different strategies to filter relevant olfactory cues which indicate the presence of the host. Because of their versatility in their ecology and behaviour, as well as their fine tuned olfactory system to volatile compounds of the host and host plant, they have gained increasing recognition as model organisms to study learning and behaviour in an adaptive ecological context. However, neural and cellular mechanisms of olfactory detection and processing in parasitoids are mainly unknown.In this thesis physiological, behavioural and morphological experiments were used to determine neural and behavioural mechanisms of host location via olfactory cues in the specialist parasitoid Cotesia vestalis. C. vestalis showed significant antennal responses to a range of odour compounds. Behavioural experiments, however, have demonstrated that only the herbivore-induced plant volatile linalool attracts C. vestalis males and females, but 1-nonanol has a repulsive effect on females. A morphological study of the antennal lobe, the first brain area where olfactory information is processed, revealed 40 ordinary glomeruli in both males and females. In addition, a complex of 2-3 enlarged glomeruli (MGC) was found in males. The courtship behaviour observed in males and the MGC suggest that males could use sex pheromones to locate females. Finally, calcium imaging studies showed glomerular activity to olfactory stimulation in bees but not in parasitoids. In conclusion, the degree of host specialisation in C. vestalis appears to influence olfactory learning in males and females, which favours learning of volatiles related to its host and host plant, as well as the morphological organisation of the antennal lobe. Larger, fewer and possibly specialised glomeruli could enhance processing of odour cues which are important for this parasitoid

Cracking the Odor Code: Molecular and Cellular Deconstruction of the Olfactory Circuit of Drosophila Larvae

The Drosophila larva offers a powerful model system to investigate the general principles by which the olfactory system processes behaviorally relevant sensory stimuli. The numerically reduced larval olfactory system relieves the formidable molecular and cellular complexity found in other organisms. This thesis presents a study in four parts that investigates molecular and neuronal mechanisms of larval odor coding. First, the larval odorant receptor (OR) repertoire was characterized. ORs define the olfactory receptive range of an animal. Each of the 21 larval olfactory sensory neurons (OSNs) expresses one or rarely two ORs, along with the highly conserved olfactory co-receptor Or83b. Second, odor response profiles of 11 larval OSNs were characterized by calcium imaging. A subset of larval neurons showed overlapping responses to the set of odorants tested, while other neurons showed either very narrow or very broad tuning. Third, the olfactory circuit for ethyl butyrate was investigated in detail. Three OSNs, expressing Or35a, Or42a and Or42b, responded with different sensitivity to ethyl butyrate. Second order projection neurons synapsing with each of these OSNs showed similar concentration tuning, but inhibitory interneurons showed high response thresholds and were only activated at high odor concentrations. We correlated these concentration-dependent response properties with larval chemotaxis behavior. Fourth, the relevance of olfaction to animals was investigated in competitive rearing experiments. Or83b mutants experienced a selective disadvantage when they had to forage for limiting food sources, particularly when competing against larvae with normal olfactory function. Thus, odor coding is achieved both by peripheral tuning and central circuit modulation

The Taste of Blood

Human blood and floral nectar are both appetizing meals to a hungry female mosquito, yet each meal fulfills a distinct nutritional requirement. While protein obtained from blood is required for females to develop eggs and successfully reproduce, carbohydrates supplied from plant nectar are sufficient for energy metabolism in both females and males. To procure essential nutrients from these distinct food sources, females employ two mutually exclusive feeding programs with unique sensory appendages, meal sizes, digestive tract targets, and metabolic fates. When a female is ready to reproduce, she must selectively seek the taste of blood and ignore the sweet taste of nectar. How does she flexibly modify her preference for the taste of blood to select the feeding program that satisfies her current metabolic needs

Developmental and Genetic Mechanisms of Ovariole Number Evolution in Drosophila

The goal of the "Quantitative Trait Gene" (QTG) program is to identify genes and mutations that underlie natural phenotypic variation. My goal with this work was to contribute an additional model to the program: ovariole number evolution in Drosophila. In this thesis I describe the progress I have made towards identifying a specific genetic change that contributed to the divergence of ovariole number between two Drosophila lineages. I identify specific developmental mechanisms relevant to establishing ovariole number in different Drosophila lineages by detailing ovarian cell-type specific specification, proliferation, and differentiation. I test specific candidates of genetic regulators of these developmental mechanisms with mutational analysis in D. melanogaster. I show that independent evolution of ovariole number has resulted from changes in distinct developmental mechanisms, each of which may have a different underlying genetic basis in Drosophila. I use the interspecies comparison of D. melanogaster versus D. sechellia to test for functional differences in insulin/insulin-like growth factor (IIS) signaling between the two species. I show that IIS activity levels and sensitivity have diverged between species, leading to both species-specific ovariole number and species-specific nutritional plasticity in ovariole number. Moreover, plastic range of ovariole number correlates with ecological niche, suggesting that the degree of nutritional plasticity may be an adaptive trait. My work and quantitative genetic analyses strongly support the hypothesis that evolution of the Drosophila insulin-like receptor (InR) gene, specifically, is at least partially responsible for the divergence in ovariole number and nutritional plasticity of ovariole number between D. melanogaster and D. sechellia. I detail ongoing experiments to test this hypothesis explicitly via cross-species transgenesis