Genetic architecture of the toxicological response to eucalyptol and citronellal in Drosophila melanogaster.

The excessive and indiscriminate use of synthetic insecticides has led to environmental pollution, wildlife destruction, and adverse effects on human health, while simultaneously giving rise to resistance in insect pest populations. This adaptive trait is expressed through various mechanisms, such as changes in the cuticle, heightened activities of detoxifying enzymes, and alterations in the sites of action that reduce their affinity for insecticides. In this context, we associate variation in toxicological response with genomic variation, to identify genetic polymorphisms underlying the different steps of the insect (genotype)-response (phenotype)-insecticide (environment) interaction. Under this framework, our objective was to investigate the genetic factors involved in the toxicological response of D. melanogaster lines when exposed to citronellal and eucalyptol vapors (monoterpenes of plant origin). We quantified KT50 in adult males, representing the time necessary for half of the exposed individuals to be turned upside down (unable to walk or fly). Since the genomes of all lines used are completely sequenced, we perform a Genome Wide Association Study to analyze the genetic underpinnings of the toxicological response. Our investigation enabled the identification of 656 genetic polymorphisms and 316 candidate genes responsible for the overall phenotypic variation. Among these, 162 candidate genes (77.1%) exhibited specificity to citronellal, 45 (21.4%) were specific to eucalyptol, and 3 candidate genes (1.5%) namely CG34345, robo2, and Ac13E, were implicated in the variation for both monoterpenes. These suggest a widespread adaptability in the response to insecticides, encompassing genes influenced by monoterpenes and those orchestrating resistance to the toxicity of these compounds.

Oviposition behaviour in Drosophila melanogaster: Genetic and behavioural decoupling between oviposition acceptance and preference for natural fruits.

In phytophagous insects, oviposition behaviour is an important component of habitat selection and, given the multiplicity of genetic and environmental factors affecting its expression, is defined as a complex character resulting from the sum of interdependent traits. Here, we study two components of egg-laying behaviour: oviposition acceptance (OA) and oviposition preference (OP) in Drosophila melanogaster using three natural fruits as resources (grape, tomato and orange) by means of no-choice and two-choice experiments, respectively. This experimental design allowed us to show that the results obtained in two-choice assays (OP) cannot be accounted for by those resulting from no-choice assays (OA). Since the genomes of all lines used are completely sequenced, we perform a genome-wide association study to identify and characterize the genetic underpinnings of these oviposition behaviour traits. The analyses revealed different candidate genes affecting natural genetic variation of both OA and OP traits. Moreover, our results suggest behavioural and genetic decoupling between OA and OP and that egg-laying behaviour is plastic and context-dependent. Such independence in the genetic architectures of OA and OP variation may influence different aspects of oviposition behaviour, including plasticity, canalization, host shift and maintenance of genetic variability, which contributes to the adoption of adaptive strategies during habitat selection.

Functional analysis of PHYB polymorphisms in Arabidopsis thaliana collected in Patagonia.

Arabidopsis thaliana shows a wide range of natural genetic variation in light responses. Shade avoidance syndrome is a strategy of major adaptive significance that includes seed germination, elongation of vegetative structures, leaf hyponasty, and acceleration of flowering. Previously, we found that the southernmost Arabidopsis accession, collected in the south of Patagonia (Pat), is hyposensitive to light and displays a reduced response to shade light. This work aimed to explore the genetic basis of the shade avoidance response (SAR) for hypocotyl growth by QTL mapping in a recently developed 162 RIL population between Col-0 and Pat. We mapped four QTL for seedling hypocotyl growth: WL1 and WL2 QTL in white light, SHADE1 QTL in shade light, and SAR1 QTL for the SAR. PHYB is the strongest candidate gene for SAR1 QTL. Here we studied the function of two polymorphic indels in the promoter region, a GGGR deletion, and three non-synonymous polymorphisms on the PHYB coding region compared with the Col-0 reference genome. To decipher the contribution and relevance of each PHYB-Pat polymorphism, we constructed transgenic lines with single or double polymorphisms by using Col-0 as a reference genome. We found that single polymorphisms in the coding region of PHYB have discrete functions in seed germination, seedling development, and shade avoidance response. These results suggest distinct functions for each PHYB polymorphism to the adjustment of plant development to variable light conditions.