Large-scale assessment of olfactory preferences and learning in Drosophila melanogaster: behavioral and genetic components

Exploring the Therapeutic Potential of Camellia longii Orel & Luu Leaf Extracts for Memory Loss in Alzheimer's Disease: Novel Findings and Functional Food Applications

Novel research on the chemical compositions and biochemical activities of Camellia longii Orel and Luu leaf extracts revealed valuable resources with potential applications in Alzheimer's disease treatment. Qualitative phytochemicals detected various compound groups, including polyphenols, saponins, tannins, flavonoids, alkaloids, amino acids, coumarins, and polysaccharides. HPLC-MS identified 23 compounds in C. longii leaves with compounds found at significant levels, including epicatechin gallate (17.12%), tryptophan (13.73%), isovitexin (12.91%), gallic acid (3.06%), and quercetin (3.06%). Interestingly, the ethanol extract (CLL-Ew) exhibited the highest extraction yield (26.6%) and potent antioxidant and acetylcholinesterase (AChE) inhibitory effects in vitro. In the Drosophila melanogaster model, CLL-Ew improved longevity, movement, and memory by reducing malondialdehyde and increasing glutathione levels. Docking simulations suggested that the above compounds bind tightly to AChE's active site, potentially contributing to memory enhancement. Interestingly, observations of male and female mice after administration of a dose of 5000 mg/kg C. longii leaf extract were recorded normally throughout the 14 day experiment. These findings highlight the potential of C. longii leaf extracts in functional foods and therapeutic interventions for memory impairment prevention and treatment.

Bayesian updating during development predicts genotypic differences in plasticity

Interactions between genotypes and environments are central to evolutionary genetics, but such interactions are typically described, rather than predicted from theory. Recent Bayesian models of development generate specific predictions about genotypic differences in developmental plasticity (changes in the value of a given trait as a result of a given experience) based on genotypic differences in the value of the trait that is expressed by naïve subjects. We used these models to make a priori predictions about the effects of an aversive olfactory conditioning regime on the response of Drosophila melanogaster larvae to the odor of ethyl acetate. As predicted, across 116 genotypes initial trait values were related to plasticity. Genotypes most strongly attracted to the odor of ethyl acetate when naïve reduced their attraction scores more as a result of the aversive training regime than those less attracted to the same odor when naïve. Thus, as predicted, the variance across genotypes in attraction scores was higher before than after the shared experience. These results support predictions generated by Bayesian models of development and indicate that such models can be successfully used to investigate how variation across genotypes in information derived from ancestors combines with personal experience to differentially affect developmental plasticity in response to specific types of experience.

Naïve Chicks Prefer Hollow Objects

Biological predispositions influence approach and avoid responses from the time of birth or hatching. Neonates of species that require parental care (e.g. human babies and chicks of the domestic fowl) are attracted by stimuli associated with animate social partners, such as face-like configurations, biological motion and self-propulsion. The property of being filled is used as a cue of animacy by 8-month-old human infants but it is not known whether this reflects the effect of previous experience. We used chicks of the domestic fowl (Gallus gallus) to investigate whether the property of being filled vs. hollow elicits spontaneous or learned preferences. To this aim we tested preferences of naïve and imprinted chicks for hollow and closed cylinders. Contrary to our expectations, we documented an unlearned attraction for hollow stimuli. The preference for hollow stimuli decreased when chicks were imprinted on filled stimuli but did not increase when chicks were imprinted on hollow stimuli, suggesting that hollowness is not crucial to determine affiliative responses for imprinting objects. When chicks were imprinted on occluded stimuli that could be either filled or hollow, the preference for hollow stimuli emerged again, showing that imprinting does not disrupt the spontaneous preference for hollow objects. Further experiments revealed that hollow objects were mainly attractive by means of depth cues such as darker innards, more than as places to hide or as objects with high contrast. Our findings point to predisposed preferences for hollow objects, and suggest that early predispositions might be driven by factors different from animacy cues.

The complexity of learning, memory and neural processes in an evolutionary ecological context

The ability to learn and form memories is widespread among insects, but there exists considerable natural variation between species and populations in these traits. Variation manifests itself in the way information is stored in different memory forms. This review focuses on ecological factors such as environmental information, spatial aspects of foraging behavior and resource distribution that drive the evolution of this natural variation and discusses the role of different genes and neural networks. We conclude that at the level of individual, population or species, insect learning and memory cannot be described as good or bad. Rather, we argue that insects evolve tailor-made learning and memory types; they gate learned information into memories with high or low persistence. This way, they are prepared to learn and form memory to optimally deal with the specific ecologies of their foraging environments.

Physiological and behavioral responses in Drosophila melanogaster to odorants present at different plant maturation stages

The fruit fly Drosophila melanogaster feeds and oviposits on fermented fruit, hence its physiological and behavioral responses are expected to be tuned to odorants abundant during later stages of fruit maturation. We used a population of about two-hundred isogenic lines of D. melanogaster to assay physiological responses (electroantennograms (EAG)) and behavioral correlates (preferences and choice ratio) to odorants found at different stages of fruit maturation. We quantified electrophysiological and behavioral responses of D. melanogaster for the leaf compound β-cyclocitral, as well as responses to odorants mainly associated with later fruit maturation stages. Electrophysiological and behavioral responses were modulated by the odorant dose. For the leaf compound we observed a steep dose-response curve in both EAG and behavioral data and shallower curves for odorants associated with later stages of maturation. Our data show the connection between sensory and behavioral responses and are consistent with the specialization of D. melanogaster on fermented fruit and avoidance of high doses of compounds associated with earlier stages of maturation. Odor preferences were modulated in a non-additive way when flies were presented with two alternative odorants, and combinations of odorants elicited higher responses than single compounds.

Using Drosophila to study the evolution of herbivory and diet specialization

Herbivory evolved many times independently across the insect phylogeny, and its evolution is linked with increased rates of diversification. Plants present many barriers to potential herbivores, among them are the so-called secondary chemicals and other molecular defenses such as protease inhibitors that deter herbivores. To understand the mechanisms behind the emergence of herbivory and subsequent species radiations of insects driven largely by diet specialization, it is important to identify the molecular basis associated with these evolutionary transitions. However, most herbivore species lack the genomic information and genetic tools required to identify functionally important genes. The notable exception is the genus Drosophila in which herbivory evolved at least three times independently, and for which abundant genomic data are available. Furthermore, contained within the family Drosophilidae is Drosophila melanogaster, the first genetic model animal. Here, we provide a synthesis of the salient tools that the D. melanogaster system provides to identify functionally important genes required for herbivory and subsequent diet specialization across insects.

Origins of Knowledge: Insights from Precocial Species

Behavioral responses are influenced by knowledge acquired during the lifetime of an individual and by predispositions transmitted across generations. Establishing the origin of knowledge and the role of the unlearned component is a challenging task, given that both learned and unlearned knowledge can orient perception, learning, and the encoding of environmental features since the first stages of life. Ethical and practical issues constrain the investigation of unlearned knowledge in altricial species, including human beings. On the contrary, precocial animals can be tested on a wide range of tasks and capabilities immediately after birth and in controlled rearing conditions. Insects and precocial avian species are very convenient models to dissect the knowledge systems that enable young individuals to cope with their environment in the absence of specific previous experience. We present the state of the art of research on the origins of knowledge that comes from different models and disciplines. Insects have been mainly used to investigate unlearned sensory preferences and prepared learning mechanisms. The relative simplicity of the neural system and fast life cycle of insects make them ideal models to investigate the neural circuitry and evolutionary dynamics of unlearned traits. Among avian species, chicks of the domestic fowl have been the focus of many studies, and showed to possess unlearned knowledge in the sensory, physical, spatial, numerical and social domains. Solid evidence shows the existence of unlearned knowledge in different domains in several species, from sensory and social preferences to the left-right representation of the mental number line. We show how non-mammalian models of cognition, and in particular precocial species, can shed light into the adaptive value and evolutionary history of unlearned knowledge.