Flower diversification across “pollinator climates”: Sensory aspects of corolla color evolution in the florally diverse south american genus Jaborosa (Solanaceae)

Flower phenotype may diverge within plant lineages when moving across “pollinator climates” (geographic differences in pollinator abundance or preference). Here we explored the potential importance of pollinators as drivers of floral color diversification in the nightshade genus Jaborosa, taking into account color perception capabilities of the actual pollinators (nocturnal hawkmoths vs. saprophilous flies) under a geographic perspective. We analyzed the association between transitions across environments and perceptual color axes using comparative methods. Our results revealed two major evolutionary themes in Jaborosa: (1) a “warm subtropical sphingophilous clade” composed of three hawkmoth-pollinated species found in humid lowland habitats, with large white flowers that clustered together in the visual space of a model hawkmoth (Manduca sexta) and a “cool-temperate brood-deceptive clade” composed of largely fly-pollinated species with small dark flowers found at high altitudes (Andes) or latitudes (Patagonian Steppe), that clustered together in the visual space of a model blowfly (Lucilia sp.) and a syrphid fly (Eristalis tenax). Our findings suggest that the ability of plants to colonize newly formed environments during Andean orogeny and the ecological changes that followed were concomitant with transitions in flower color as perceived by different pollinator functional groups. Our findings suggest that habitat and pollination mode are inextricably linked in the history of this South American plant lineage.Fil: Moré, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Ibañez, Ana Clara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Drewniak, María Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Cocucci, Andrea Aristides. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; ArgentinaFil: Raguso, Robert A.. Cornell University; Estados Unido

Neurons against Noise : Neural adaptations for dim light vision in hawkmoths

All animals perceive the world through their senses, which form the basis for their decisions and motor actions. However, when these all-important senses reach their limit and cease to provide reliable information, the animal’s survival is threatened. Among the senses, vision is brought to its limits on a daily basis, because its signal strength is diminished as night falls, and increases again as the sun rises. In this thesis, I investigated adaptations that enable the visual system of hawkmoths, a group of insects, to cope with the low light intensities they face at night. I have focused on neural adaptations, manifested in the processing of visual neurons, in contrast to anatomical adaptations, such as modifications of the eye. I showed that neural adaptations exist in the motion vision system of hawkmoths, in the form of integration of visual information in space and time. Furthermore, I demonstrated that a combination of such spatial and temporal summation increased sensitivity and information content in dim light (Paper I). The amount of spatial and temporal summation matched the ecological needs of different hawkmoth species, as well as their anatomical adaptations for visual sensitivity: night active species, and species with less sensitive eyes had more extensive spatial and temporal summation than day-active species and species with very sensitive optics (Paper II). Furthermore, I identified and characterised candidate neurons that carry out spatial and temporal summation in the brain of hawkmoths (Paper III). Finally, I quantified the effects of temporal summation on the ability of hawkmoths to track flowers in hovering flight at different light levels, and showed that a subset of the observed behavioural phenomena could be explained by temporal processing in the nervous system (Paper IV). Taken together, this work has provided detailed insight into how neural processing can increase visual reliability in dim light. The results presented are not only relevant to hawkmoths, since neural summation is also expected to increase visual sensitivity in other species of nocturnal insects, and can be compared to similar mechanisms in vertebrates. Furthermore, this work is instructive for the development of artificial visual systems, for which insect brains have proven to be a successful biomimetic model

Characterization and regulation of insect odorant receptors

The olfactory world of insects is highly dynamic. Volatiles, once emitted from the source, are dispersed and diluted in the ambient air. Using a set of ∼60 odorant receptors (ORs), the fruit fly Drosophila melanogaster is able to extract valuable information from the plume in terms of odor identity and intensity. ORs are heteromeric complexes constituted by an odor-specific OrX and a co-receptor termed Orco. These are expressed in olfactory sensory neurons (OSNs) housed in the antenna and maxillary palps. They are capable of resolving fast changes in odor pulses and can adjust their sensitivity based on previous odor stimuli. This work is dedicated to the characterization and regulation of insect ORs. We have done so in heterologous expression systems and in the ORs native environment combining genetic and pharmacological manipulations with functional imaging techniques and electrophysiology. Our results highlight the importance of understanding signal processing at the periphery, considering the different players involved in the olfactory response

Neuroethology of olfactory-guided behavior and its potential application in the control of harmful insects

Harmful insects include pests of crops and storage goods, and vectors of human and animal diseases. Throughout their history, humans have been fighting them using diverse methods. The fairly recent development of synthetic chemical insecticides promised efficient crop and health protection at a relatively low cost. However, the negative effects of those insecticides on human health and the environment, as well as the development of insect resistance, have been fueling the search for alternative control tools. New and promising alternative methods to fight harmful insects include the manipulation of their behavior using synthetic versions of "semiochemicals", which are natural volatile and non-volatile substances involved in the intra-and/or inter-specific communication between organisms. Synthetic semiochemicals can be used as trap baits to monitor the presence of insects, so that insecticide spraying can be planned rationally (i.e., only when and where insects are actually present). Other methods that use semiochemicals include insect annihilation by mass trapping, attract-and-kill techniques, behavioral disruption, and the use of repellents. In the last decades many investigations focused on the neural bases of insect's responses to semiochemicals. Those studies help understand how the olfactory system detects and processes information about odors, which could lead to the design of efficient control tools, including odor baits, repellents or ways to confound insects. Here we review our current knowledge about the neural mechanisms controlling olfactory responses to semiochemicals in harmful insects. We also discuss how this neuroethology approach can be used to design or improve pest/vector management strategies.Fil: Reisenman, Carolina Esther. University of California at Berkeley; Estados UnidosFil: Lei, Hong. University of Arizona; Estados UnidosFil: Guerenstein, Pablo Gustavo. Provincia de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Universidad Autónoma de Entre Ríos. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Centro de Investigaciones Científicas y Transferencia de Tecnología a la Producción; Argentina. Universidad Nacional de Entre Ríos. Facultad de Ingeniería; Argentin

The chemosensory ecology of a foraging hawkmoth

While foraging, all animals need to balance their energetic cost and gains. The sensory systems provide the information, which form the bases for these energy-economic decisions and thus, link the sensory input directly to the fitness of the animal. Night-active hawkmoth species particularly rely on their olfactory system which detects the volatiles emitted by those plants visited by the moth. This dissertation examined the olfactory system and the foraging decisions of the hawkmoth Manduca sexta to gain further insights into the ecological pressures which might have directed the evolution of the olfactory system in hawkmoths and their coevolution with the flowers they visit. In order to address these questions we first studied the odour guided flight of M. sexta to flowers of different Nicotiana species, which matched the length of the moth proboscis to different degrees. It was found that the moth already selected the best matching flower at the first encounter with the odour plume emitted by this flower and that foraging on these matching flowers did result in the highest energy gain for the moth. We could further show that M. sexta recognise a plant headspace based on the composition of this blend rather than on its concentration. However, flower odours are readily intermixed with other volatiles and their detection is hence most reliable close to the flower. Here, we show that the moth uses specific olfactory neurons on the tip of its proboscis to evaluate flowers, and that this close range detection is crucial both for foraging as well as pollination. Finally, the effect of flower orientation on the foraging of M. sexta was analysed, finding that the synchronisation of floral volatiles and orientation is crucial for this moth-plant interaction. Taken together our studies on the foraging of hawkmoth might not only help to gain new insights into the evolution of sensory systems, but also on how these systems shapes the interaction between different species

Colour Vision in Birds : Comparing behavioural thresholds and model predictions

Birds use colour vision for many biologically relevant behaviours such as foraging and mate choice. Bird colour vision is mediated by four types of single cones, giving them an extra dimension of colour information compared to trichromatic humans. The cone photoreceptors of birds have coloured oil droplets that are assumed to increase the discriminability of colours in bright light at the cost of dim light sensitivity. In this thesis I present four studies where we have trained chickens to perform colour discrimination and tested the limits of their behavioural performance. In paper I we tested how small colour differences chickens can discriminate. This allowed us to test the predictions of the most well established model for bird colour vision, the receptor noise limited model. There was a reasonably good fit between model and behaviour. Furthermore, we tested in how dim light chickens could discriminate colours and found that the intensity threshold was affected by the colour difference between the stimuli and their intensity. In Paper II we continued testing colour discrimination in dim light and tested the hypothesis that chickens sum the signals from many photoreceptors to increase contrast sensitivity at the cost of spatial resolution in dim light, so called spatial pooling. We used food containers covered with larger, smaller, more or fewer colour patches. Supporting the hypothesis, the containers covered by more colour could be discriminated in dimmer light. In Paper III we tested colour constancy, the ability to maintain colour perception in different spectral illuminations that would otherwise confuse colour perception. Our aim was to find the largest illumination change that chicken colour constancy could tolerate. We found that chicken colour constancy could tolerate larger illumination changes when discriminating stimuli that were more different from each other. In paper IV we continued the work on colour constancy but allowed the chickens to use relative colour learning, which was specifically excluded in paper III. In Paper IV we found that their colour constancy could tolerate larger illumination changes. In nature relative colour cues are available and may be an important aspect of colour learning and perception. These results suggest that such cues can make colour constancy more robust to larger illumination changes. In both experiments chicken colour constancy was improved if they were adapted for 5 minutes in the tested illumination before performing the discrimination task. We compared the illuminations for which chickens retained colour constancy, to the difference between natural illuminations and we can conclude that chickens are well equipped to maintain accurate colour perception when changing between habitats in the wild. Objects are detected both by their chromatic and achromatic contrasts. The receptor noise limited model can be used to predict discriminability through both chromatic and achromatic vision. To use the model reliably its assumptions and predictions must be compared to behavioural results. This has been done for the chromatic version of the model but not the achromatic. In Paper V we compiled all known chromatic and achromatic contrast detection thresholds, and used them to derive the limiting noise level to be used when predicting visual discrimination in a range of animals. We discuss the limitations of using modelling in the wild such as the need to consider the spatial pattern of the stimuli and the light intensities in which the modelling occurs