Organization of Foraging Behavior in Larvae of Cosmopolitan, Widespread, and Endemic Drosophila Species

The behavior of adult Drosophila in the wild

Little is known about how Drosophila adults behave in the wild, including mating, allocation of food and space, and escape from predators. This lack of information has negative implications for our ability to understand the capabilities of the nervous system to integrate sensory cues necessary for the adaptation of organisms in natural conditions. We characterized a set of behavioral routines of D. melanogaster and D. simulans adults in three ecologically different orchards: grape, apple and prickly pear. We also investigated how the flies identify conspecifics and aliens in the wild to better understand relationships between group formation and adaptation of Drosophila to breeding sites. We characterized the locations by recording in each orchard humidity, temperature, illumination conditions, pH of fruits, the presence/absence of other Drosophila species and the predator ant Linepithema humile. Our findings suggest that the home range of these species of Drosophila includes decaying fruits and, principally, a variety of microhabitats that surround the fruits. The ecological heterogeneity of the orchards and odors emitted by adult D. melanogaster and D. simulans influence perch preferences, cluster formation, court and mating, egg-laying site selection, and use of space. This is one of the first large examinations of the association between changing, complex environments and a set of adult behaviors of Drosophila. Therefore, our results have implications for understanding the genetic differentiation and evolution of populations of species in the genus Drosophila.

Development of a PCR-RFLP assay to identify Drosophila melanogaster among field-collected larvae

The fruit fly Drosophila melanogaster is a model organism to study several aspects of metazoan biology. Most of the work has been conducted in adult fruit flies, including laboratory and field-derived specimens, but Drosophila melanogaster larvae recently became a valuable model to better understand animal physiology, development, or host-microbe interactions. While adult flies can be easily assigned to a given Drosophila species based on morphological characteristics, such visual identification is more intricate at the larval stage. This could explain the limited number of studies focusing on larvae, especially field-derived samples. Here, we developed a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay that discriminates D. melanogaster from other ecologically relevant Drosophila species at the larval stage. The method, which targets the cytochrome oxidase I (COI) gene, was validated using laboratory-derived larvae from seven D. melanogaster populations originating from different geographic areas as well as six Drosophila species. We further validated this PCR-RFLP assay in a natural context, by identifying wild larvae collected in two locations in France. Notably, among all PCR-RFLP profiles that matched the D. melanogaster species, 100% were correctly identified, as confirmed by COI sequencing. In summary, our work provides a rapid, simple, and accurate molecular tool to identify D. melanogaster from field-collected larvae.

The genetics and development of mandibles and hypopharyngeal sclerite and cornua in larvae of Drosophila gaucha

The genetics and epigenetic processes associated with morphological organization are a principal aim of biology, ranging from cohesion between cells to shape and size of organisms. We investigate the post-embryonic development of Hypopharyngeal sclerite and cornua HPC and mandibles M of Drosophila gaucha larva. Integrated functioning of these Cephalopharyngeal skeleton parts of D. gaucha larva is essential for food acquisition, participating in locomotion and microhabitat selection. We examined two isolates by recording the growth of the HPC and M every 24 h for 8 days in parental, F₁, F₂ and backcross larvae. In F₁ larvae, the HPC and M growth was similar to the parental. In F₂ and backcross larvae, the growth was slower. Epistasis and dominance are the principal sources upon which the growth of HPC and M are based. Pleiotropic genes seem also to be involved in integrating the development of M and HPC. Our data suggest that hybridization of the isolates modified epigenetic processes involved in the development of those morphological structures of D. gaucha larva.

Ectotherms in Variable Thermal Landscapes: A Physiological Evaluation of the Invasive Potential of Fruit Flies Species

Climate change and biological invasions pose one of the greatest threats to biodiversity. Most analyses of the potential biological impacts have focused on changes in mean temperature, but changes in thermal variance may also impact native and invasive organisms, although differentially. We assessed the combined effects of the mean and the variance of temperature on the expression of heat shock protein (hsp90) in adults of the invasive fruit fly Drosophila melanogaster and the native Drosophila gaucha in Mediterranean habitats of central Chile. We observed that, under these experimental conditions, hsp90 mRNA expression was higher in the invasive species but absent in the native one. Apparently, the biogeographic origin and niche conservatisms are playing a role in the heat shock response of these species under different putative scenarios of climate change. We suggest that in order to develop more realistic predictions about the biological impact of climate change and biological invasions, one must consider the interactions between the mean and variance of climatic variables, as well as the evolutionary original conditions of the native and invasive species.

Genetic dissection of a regionally differentiated network for exploratory behavior in Drosophila larvae

An efficient strategy to explore the environment for available resources involves the execution of random walks where straight line locomotion alternates with changes of direction. This strategy is highly conserved in the animal kingdom, from zooplankton to human hunter-gatherers. Drosophila larvae execute a routine of this kind, performing straight line crawling interrupted at intervals by pause turns that halt crawling and redirect the trajectory of movement. The execution of this routine depends solely on the activity of networks located in the thoracic and abdominal segments of the nervous system, while descending input from the brain serves to modify it in a context-dependent fashion. I used a genetic method to investigate the location and function of the circuitry required for the different elements of exploratory crawling. By using the Slit-Robo axon guidance pathway to target neuronal midline crossing defects selectively to particular regions of the thoracic and abdominal networks, it has been possible to define at least three functions required for the performance of the exploratory routine: (1) symmetrical outputs in thoracic and abdominal segments that generate the crawls; (2) asymmetrical output that is uniquely initiated in the thoracic segments and generates the turns; and (3) an intermittent interruption to crawling that determines the time-dependent transition between crawls and turns.

Plasticity and genotype × environment interactions for locomotion in Drosophila melanogaster larvae

Locomotion is a primary means by which animals interact with the world. To understand the contribution of genotype × environment interactions to individual differences in D. melanogaster larval locomotion we investigated phenotypic sensitivity to environmental changes in four strains of this species and their F1 hybrids. We also investigated to what extent flexibility and plasticity of locomotion depend upon larval age. Specifically, we examined larval locomotion at 48 and 96 h of development on three different substrates. Locomotion was influenced by the structure of the substrate, but this depended on both the genotype and larval age. At 48 h of larval development phenotypic variation in locomotion was attributable to both genotype × environment interactions and genotypic differences among the larvae, while at 96 h of age, differences were mainly due to genotype × environment interactions. An analysis of variance of the 4 × 4 diallel cross made at 48 and 96 h of development showed, depending on the cross, either dominance to increase/decrease locomotion, overdominance to increase/decrease locomotion, or no dominance to increase/decrease locomotion. Furthermore, the diversity of behavioral responses in the F1 hybrids was greater at 96 than at 48 h of larval development. Our results demonstrate that genotype × environment interactions result in plasticity of D. melanogaster larval locomotion, which makes sense in light of the fact that larvae, in the wild, develop in heterogeneous and rapidly changing environments.

Genetics analysis of larval foraging behavior in Drosophila funebris

To understand the genetics and evolution of foraging in larvae of Drosophila funebris, we examined two strains reared at different breeding sites in the wild. Larvae of the Til-Til strain breed in necrotic cactus tissue, while those of the Pelequén strain rear in necrotic prickly pear cladodes. We measured feeding, locomotion, turning behavior, and latency of D. funebris. Til-Til and Pelequén larvae, at 8 days of age show very similar rates in all behaviors. Crosses between Til-Til and Pelequén strains decrease feeding rate and increase locomotion, turning, and latency in F(1) and F(2) larvae. Backcross larvae show a behavior similar to that of their parental strains. The behavioral similarities observed between the Til-Til and Pelequén strains are product of two different co-adapted gene pools. Epistasis and dominance are the principal sources upon which adaptation of the gene pools of each population are based.