Drosophila glue protects from predation

Abstract

Animals can be permanently attached to a substrate for several days, weeks or months in aerial environments at certain stages of their development such as eggs and pupae. Pupa adhesion has evolved multiple times in insects and is thought to maintain the animal in a place where it is not detectable by predators. Here, we investigate whether pupa adhesion in Drosophila could also protect the animal by preventing potential predators from detaching the pupa. We measured the adhesion of Drosophila species originating from the same area and found that pupa adhesion varies among species, which can be explained by different glue production strategies. Then, we compared attached and manually detached pupae in both field and laboratory assays to investigate the role of pupa adhesion to prevent predation. First, we found that attached pupae remain on site 30 % more than detached pupae in the field after three days, probably because they are less predated. Second, we observed that attached pupae are less efficiently predated by ants in the laboratory, because they are not carried back to the ant nest and because more ants are needed to consume them onsite. Our results show that pupa adhesion is a crucial mechanical trait for Drosophila fly survival that can prevent the animal from being taken away by predators.

Glue genes are subjected to diverse selective forces during Drosophila development

“…While A5 and B4 lines are from locations with similar climates (hot summer, little rain in winter), A7 (hot summer, heavy rain in winter) and B6 (hot summer, warm and dry winter) lines are not. As glue protects from predation (Borne et al, 2021), glue could also be adapted to the local predation pressure. More lines should be tested to examine possible correlations between adhesion force and specific environmental factors.…”

“…The high variance could be due to individual variation in the position or the shape of the pupa, the way glue spreads over the substrate, or to stochastic variation in glue production, in glue composition, or in very local conditions at the moment when the glue was excreted. It could also be due to variation in the position of the initial crack in the glue, which leads to detachment (Borne et al, 2020; Borne et al, 2021). Nonetheless, we found that 26% of the variation is explained by genotype and could thus reflect adaptation of the glue to the natural climatic conditions experienced by flies.…”

“…Pupae attached to glass slides (Menzel Superfrost microscope glass slide from ThermoScientific™ #AGAB000080) were prepared as previously described (Borne et al, 2021(Borne et al, , 2020. Adhesion force of an individual pupa was measured by detaching individual pupa from the glass slides using a universal test machine (LS1S/H/230V Lloyd Instruments, Ametek®) with a 5N force sensor (YLC-0005-A1 Lloyd Instruments TM , Ametek®) as previously described (Borne et al, 2021). Force-time curves were recorded using NEXYGENPlus software (Lloyd Instruments TM ).…”

“…In Drosophila, pupation site choice during the larval stage depends on various environmental conditions such as light (Rizki and Davis Jr, 1953), temperature (Schnebel and Grossfield, 1992), and humidity (Sokolowski, 1980) but is also influenced by intra- and interspecific competition (Beltramí et al, 2012; Da Silva et al, 2019). Insects have evolved different mechanisms to protect pupa from predation such as coloration, production of toxins, aggregation (Lindstedt et al, 2019), and pupal adhesion (Borne et al, 2021). For example, in both Drosophila simulans and D. suzukii , attached pupae survive longer in laboratory assays in the presence of ants compared to manually detached pupae (Borne et al, 2021).…”

“…Insects have evolved different mechanisms to protect pupa from predation such as coloration, production of toxins, aggregation (Lindstedt et al, 2019), and pupal adhesion (Borne et al, 2021). For example, in both Drosophila simulans and D. suzukii , attached pupae survive longer in laboratory assays in the presence of ants compared to manually detached pupae (Borne et al, 2021). The ability of pupae to successfully adhere to a diverse array of surfaces thus represents an important trait subjected to selection in fruit flies.…”