Biology subjects

Armand, M.

Publications and source records attributed to Armand, M..

7 recordsLinked to original sources

bioRxiv2025

No decoy effect in bees: rewardless flowers do not increase bumblebees' preference for neighbouring flowers

Nectarless flowers are common among flowering plants, which often retain colour-changed, rewardless flowers instead of shedding them. Yet, how these flowers influence pollinators foraging choices within an inflorescence remains unclear. We hypothesised that rewardless flowers in an inflorescence may act as "decoys", causing the rewarding flowers in the inflorescence to be perceived as more valuable by contrast. Using artificial inflorescences, we presented individual bumblebees (Bombus terrestris) with a binary choice between two equally rewarding inflorescences, one of which included additional unrewarded, differently coloured flowers. We found that the presence of rewardless flowers did not increase bees preference for neighbouring flowers, nor did it affect their overall choice between inflorescences. However, bees quickly learned to avoid the unrewarded flowers, drastically reducing visits and probing within a few foraging bouts. We review research on decoy effects in bees, and find very little support for their presence. Our findings contribute to the growing body of evidence that rewardless flowers do not induce decoy effects in bees, and highlight the need for further research into the ecological role of nectarless flowers within floral patches. It may be time to abandon the search for classical decoy effects in pollinators.

animal behavior and cognition↗

bioRxiv2025

Bumblebees do not prefer consistent floral scents over variable ones

To attract pollinators, flowering plants evolve diverse sensory traits into compelling signals. Floral scent, in particular, plays a key role in drawing bees from a distance and shaping their foraging choices. Scent composition varies widely, including across flowers of the same plant species. Yet, it is unclear whether scent variability influences bee flower choices, and thus whether plants would be under selection to minimise variation in their scent composition. Since bees typically avoid variability in rewards, we hypothesised they would favour flowers with more consistent scents. To test this, we trained individual bumblebees (Bombus terrestris) on two equally rewarding flower arrays: one with a consistent scent blend across flowers, and the other with variable scent blends between flowers. Contrary to expectations, bees showed no preference for scent consistency. They readily foraged from both arrays across bouts and did not favour either flower type in the binary choice test. To the best of our knowledge, this is the first study to examine how bees respond to scent variability. A better understanding of scent profile preferences in pollinators could offer new insights into their co-evolution with plants and the development of floral traits. More broadly, further research is needed on how pollinators respond to variability and unpredictability in neutral cues like scent or colour, a largely overlooked aspect of foraging decision-making.

animal behavior and cognition↗

bioRxiv2024

Interindividual variability in flower pickiness by foraging bumblebees

Pollinators navigate complex and heterogeneous "flower markets", where floral resources vary in quality, availability, and spatial distribution. Bumblebees, as generalist foragers, visit numerous flowers during their foraging bouts, yet the factors influencing their flower choices and the individual differences in foraging behaviour remain poorly understood. Here, we tested how bees adjust their foraging in response to different reward structures. Bombus terrestris workers completed three foraging bouts in two artificial flower environments: one simulating a favourable environment with patches alternating high- and low-quality flowers (40% vs. 20% w/w sucrose solution), and the other a challenging environment with high-quality flowers alongside unrewarded ones (40% w/w sucrose solution vs. plain water). We hypothesised that bees would improve their foraging efficiency in both environments, but more rapidly in the more extreme one, where the greater reward difference creates stronger pressure to learn quickly. In both conditions, bees increased their sucrose intake per unit time over bouts. We also observed consistent differences in flower selectivity among individuals: in the favourable environment, bees that first visited high-quality flowers focused on them and avoided low-quality ones (became "picky"), while bees that first visited low-quality flowers kept visiting both types. Despite these differences, bees across environments and pickiness levels all reached similar sucrose intake rates by the third foraging bout, either by becoming more selective, collecting more sucrose solution, or reducing time spent foraging. These findings highlight the adaptability of bee foraging and suggest that early flower experiences may contribute to lasting individual differences in foraging behaviour. Significance statementBumblebees are highly efficient pollinators of wild plants and commercial crops, yet their foraging behaviour varies notably among individuals. Understanding why bees differ in their foraging decisions is crucial, as it affects how they collect resources. We show that individual Bombus terrestris workers rapidly adapt to flower patches with different reward qualities. Remarkably, a bees first flower visits have lasting effects: individuals that started with high-quality flowers consistently favoured them and avoided low-quality ones, while those that started with low-quality flowers continued to visit both types over time. Despite these differences, bees reached similar nectar intake rates after just three foraging trips, regardless of how selective they were. Our findings show that bees can quickly adjust their foraging behaviour, and that early experiences play a key role in how they exploit resources across different environments.

animal behavior and cognition↗

bioRxiv2024

Testing the peak-end rule in bumblebees: lack of preference for a higher-reward sequence when the final reward is disappointing

The peak-end rule describes the tendency to evaluate experiences by their most intense and final moments, rather than considering the entire experience as a whole. While this cognitive bias is well-established in humans, studies on nonhuman animals are very limited. Bumblebees make foraging decisions largely based on past experiences, but whether peak-end effects influence their subsequent flower choices is still unknown. Here, we trained individual Bombus terrestris workers on two artificial flower types, alternating blue and yellow, over 12 consecutive foraging bouts. One flower type offered a sequence of three high-quality rewards (25 L drops of 50% w/w sucrose solution: "consistent" sequence), while the other provided the same sequence but ended with an additional, lower-quality reward (25 L drop of 20% w/w sucrose solution: "poor end" sequence). We then tested the bees flower type preference in a final binary choice. Bees showed a strong preference for blue flowers, both in their initial and overall visits. Across all visits during a 1-minute period, they also favoured flowers associated with the "consistent" sequence, though this preference was significant only when these flowers were yellow. Interestingly, despite offering more sucrose per foraging bout, bees did not favour the "poor end" sequence flower. This study is, to our knowledge, the first to investigate peak-end effects in an insect. How bees evaluate sequential rewards when foraging remains largely unexplored, yet could provide valuable insights into nectar distribution and plant-pollinator co-evolution.

animal behavior and cognition↗

bioRxiv2022

DNA methylation restricts coordinated germline and neural fates in embryonic stem cell differentiation

Somatic DNA methylation is established early during mammalian development, as embryonic cells transition from naive to primed pluripotency. This precedes the emergence of the three somatic germ layers, but also the segregation of the germline that undergoes genome-wide DNA demethylation after specification. While DNA methylation is essential for embryogenesis, the point at which it becomes critical during differentiation and whether all lineages equally depend on it is unclear. Using culture modeling of cellular transitions, we found that DNA methylation-free embryonic stem cells (ESCs) with a triple DNA methyltransferase knockout (TKO) normally progressed through the continuum of pluripotency states, but demonstrated skewed differentiation abilities towards neural versus other somatic lineages. More saliently, TKO ESCs were fully competent for establishing primordial germ cell-like cells (PGCLCs), even showing temporally extended and self-sustained capacity for the germline fate. By mapping chromatin states, we found that the neural and germline lineages are linked by a similar enhancer dynamics during priming, defined by common sets of methyl-sensitive transcription factors that fail to be decommissioned in absence of DNA methylation. We propose that DNA methylation controls the temporality of a coordinated neural-germline axis of preferred differentiation route during early development.

developmental biology↗

bioRxiv2022

Inside-out tracking and projection mapping for robot-assisted transcranial magnetic stimulation

Transcranial Magnetic Stimulation (TMS) is a neurostimulation technique based on the principle of electromagnetic induction of an electric field in the brain with both research and clinical applications. To produce an optimal neuro-modulatory effect, the TMS coil must be placed on the head and oriented accurately with respect to the region of interest within the brain. A robotic method can enhance the accuracy and facilitate the procedure for TMS coil placement. This work presents two system improvements for robot-assisted TMS (RA-TMS) application. Previous systems have used outside-in tracking method where a stationary external infrared (IR) tracker is used as a reference point to track the head and TMS coil position. This method is prone to losing track of the coil or the head if the IR camera is blocked by the robotic arm during its motion. To address this issue, we implemented an inside-out tracking method by mounting a portable IR camera on the robot end-effector. This method guarantees that the line of sight of the IR camera is not obscured by the robotic arm at any time during its motion. We also integrated a portable projection mapping device (PPMD) into the RA-TMS system to provide visual guidance during TMS application. PPMD can track the head via an IR tracker, and can project a planned contact point of the TMS coil on the head or overlay the underlying brain anatomy in real-time.

bioengineering↗

bioRxiv2021

DNMT3A-dependent DNA methylation is required for spermatogonial stem cells to commit to spermatogenesis

DNA methylation plays a critical role in spermatogenesis, as evidenced by the male sterility of DNA methyltransferase (DNMT) mutant mice. Here, we report a striking division of labor in the establishment of the methylation landscape of male germ cells and its functions in spermatogenesis: while DNMT3C is essential for preventing retrotransposons from interfering with meiosis, DNMT3A broadly methylates the genome--at the exception of DNMT3C-dependent retrotransposons--and controls spermatogonial stem cell (SSC) plasticity. By reconstructing developmental trajectories through single-cell RNA-seq and by profiling chromatin states, we found that Dnmt3A mutant SSCs can only self-renew and no longer differentiate due to spurious enhancer activation that enforces an irreversible stem cell gene program. We therefore provide a novel function for DNA methylation in male fertility: the epigenetic programming of SSC commitment to differentiation and to life-long spermatogenesis supply.

developmental biology↗