Stress-Mediated Allee Effects Can Cause the Sudden Collapse of Honey Bee Colonies.

The recent rapid decline in global honey bee populations could have significant implications for ecological systems, economics and food security. No single cause of honey bee collapse has yet to be identified, although pesticides, mites and other pathogens have all been shown to have a sublethal effect. We present a model of a functioning bee hive and introduce external stress to investigate the impact on the regulatory processes of recruitment to the forager class, social inhibition and the laying rate of the queen. The model predicts that constant density-dependent stress acting through an Allee effect on the hive can result in sudden catastrophic switches in dynamical behaviour and the eventual collapse of the hive. The model proposes that around a critical point the hive undergoes a saddle-node bifurcation, and that a small increase in model parameters can have irreversible consequences for the entire hive. We predict that increased stress levels can be counteracted by a higher laying rate of the queen, lower levels of forager recruitment or lower levels of natural mortality of foragers, and that increasing social inhibition can not maintain the colony under high levels of stress. We lay the theoretical foundation for sudden honey bee collapse in order to facilitate further experimental and theoretical consideration

Doctor of Philosophy

dissertationChapter 1 introduces a classic question from optimal foraging theory regarding space-use strategies of a forager, and gives context for addressing similar questions in groups of foraging ants. Chapter 2 generalizes the marginal value theorem (MVT) model by describing a rate-maximizing forager searching for pointwise resources with a specific searching distribution around previous resource finds, and giving-up value (GUV) strategy at resources. The model shows that the optimal ARS breadth increases, and the optimal GUV decreases, with increased dispersion of the resource distribution. Chapter 3 builds an agent-based model (ABM) and corresponding PDE model derived from an isotropic diffusion limit. The model links individual movement biases in the presence of pheromone to the colony-wide searching distribution. Parameterized with movement data obtained from Tetramorium caespitum (the pavement ant), the model predicts bistability in pheromonal recruitment at resource distances of 3 - 6 m; the onset-distance of bistability increases with colony size. Data collected from the field are used to estimate parameters of the PDE model for T. caespitum in Chapter 4. The ability of T. caespitum to find autocorrelated resources during recruitment is analyzed using a Cox proportional hazards model, the results of which are compared to those predicted by the PDE model developed in Chapter 3. Finally, Chapter 5 develops a simulation to assess the effect of individual trail fidelity on the ability of a colony to capitalize on autocorrelated resources in different resource scenarios; the results suggest that T. caespitum is tuned to exploit large, nonautocorrelated resource distributions

Optimal balance of individual and collective in honeybee foraging

Purpose. Previously, we developed a minimal foraging model in a honey bee colony that is applicable to describe both the decision-making process and the phase transition between two behavioral modes of the colony, individual and collective. In this paper, we show that this model is also applicable to determine the optimal division of labor in the colony, namely, to determine the optimal proportions between different types of foragers, scouts and recruits. Model. We represent the steps in the foraging process as reactions of chemical kinetics, which leads to reaction–diffusion equations. The reaction part describes the dynamic modes of the foraging process: the recruitment of unemployed foragers to profitable food sources, that have become unprofitable as a result of their exploitation, and scouting. Diffusion describes the transfer of information in a honey bee colony. We assume almost perfect accuracy in the transmission and use of information about food sources in the colony, which is modeled by a very small diffusion coefficient of working foragers in the information space. On the contrary, the diffusion coefficient of unemployed foragers is chosen large to ensure their full mixing in the information space. This models the equal accessibility to transmitted information for all unemployed foragers in the hive. Results. We consider the profit of a colony on an exploited food source as the number of foragers working on that source, weighted by its value to the colony. It was found that with an increase in the intensity of scouting, the profit of the colony first grows, and then begins to fall, thus illustrating that there is an optimal balance of scouts and recruits, which ensures the greatest influx of food resources into the colony. Conclusion. An optimal division of labor in a honey bee colony, defining a dynamic balance between exploration and exploitation in a constantly changing environment, is essential to the survival of the colony. Considering that scouts use exclusively personal information, and recruits take advantage of social information, we can say that our model describes the optimal balance between the individual and the collective in the colony

Cross-inhibition leads to group consensus despite the presence of strongly opinionated minorities and asocial behaviour

Strongly opinionated minorities can have a dramatic impact on the opinion dynamics of a large population. Two factions of inflexible minorities, polarised into two competing opinions, could lead the entire population to persistent indecision. Equivalently, populations can remain undecided when individuals sporadically change their opinion based on individual information rather than social information. Our analysis compares the cross-inhibition model with the voter model for decisions between equally good alternatives, and with the weighted voter model for decisions among alternatives characterised by different qualities. Here we show that cross-inhibition, differently from the other two models, is a simple mechanism, ubiquitous in collective biological systems, that allows the population to reach a stable majority for one alternative even in the presence of asocial behaviour. The results predicted by the mean-field models are confirmed by experiments with swarms of 100 locally interacting robots. This work suggests an answer to the longstanding question of why inhibitory signals are widespread in natural systems of collective decision making, and, at the same time, it proposes an efficient mechanism for designing resilient swarms of minimalistic robots

Heritabilnost negovateljskog ponašanja sive medonosne pčele (Apis mellifera Carnica)

Grooming behavior is considered an important defensive mechanism of honey bees against Varroa mites. The aim of this study was to reveal whether grooming behavior is a useful criterion in breeding of Varroa-tolerant bees. To obtain a reliable evaluation the environmental influences were excluded. The degree of grooming potential was estimated by the percentage of damaged mites in the total number of fallen mites. The heritability of grooming behavior throughout the three consecutive generations of queens was assessed by mother-daughter regression method. Among unselected queens, expressed grooming behavior was recorded only in colonies with F1 queens (36.27%), but not in colonies with P queens and F2 queens (33.69%, 31.66%, respectively). Significant differences in grooming behavior were found between colonies of P and F1 queens (p lt 0.001), and between colonies of P and F2 queens (p lt 0.05). However, all of the three generations of selected queens showed expressed grooming behavior (37.99%, 39.42% and 38.58% in Ps, F1s and F2s, respectively) without significant (p>0.05) difference among them. Nevertheless, the relatively low heritability of grooming behavior in the three generations of queens examined (h2yx=0.49±0.02; h2zx=0.18±0.01; h2zy=0.16±0.01) indicate that breeding colonies for grooming behavior only cannot be advised to beekeepers whose aim is to breed bees highly tolerant to Varroa mites.Negovateljsko ponašanje se smatra značajnim mehanizmom odbrane pčela od Varroa krpelja. Cilj ovog rada je bilo ispitivanje negovateljskog ponašanja, procena njegove heritabilnosti i mogućnosti povećanja ekspresije te osobine putem selekcije. Radi dobijanja pouzdanih rezultata korišćenja je metodologija kojom se uticaj spoljašnjih faktora isključuje. Ispoljenost negovateljskog ponašanja procenjivana je na osnovu procenta oštećenih u ukupnom broju otpalih krpelja. Heritabilnost negovateljskog ponašanja praćena na kroz generacije matica i procenjivana metodom regresije majka-ćerka. Među neselekcionisanim maticama, negovateljsko ponašanje bilo je izraženo samo kod matica F1 generacije (36,27%), ali ne i kod P (33,69%) i F2 generacije (31,66%). Statistički značajne razlike u negovateljskom ponašanju zabeležene su između društava P i F1 matica (p lt 0,001) i između društava P i F2 matica (p lt 0,05). Međutim, selekcionisane matice sve tri generacije (Ps, F1s, F2s) su imale izraženo negovateljsko ponašanje (37,99%, 39,42% i 38,58%) bez statistički značajnih (p>0,05) razlika među njima. Ipak, nizak koeficijent heritabilnosti praćene osobine (h2yx=0,49±0,02; h2zx=0,18±0,01; h2zy=0,16±0,01) ukazuje da se pčelarima ne može preporučiti selekcija pčela samo na negovateljsko ponašanje ako je njihov cilj uzgoj pčelinjih zajednica povećane otpornosti na Varroa krpelje

Self-organisation of plasticity and specialisation in a primitively social insect

Biological systems have the capacity to not only build and robustly maintain complex structures but also to rapidly break up and rebuild such structures. Here, using primitive societies of Polistes wasps, we show that both robust specialization and rapid plasticity are emergent properties of multi-scale dynamics. We combine theory with experiments that, after perturbing the social structure by removing the queen, correlate time-resolved multi-omics with video recordings. We show that the queen-worker dimorphism relies on the balance between the development of a molecular queen phenotype in all insects and colony-scale inhibition of this phenotype via asymmetric interactions. This allows Polistes to be stable against intrinsic perturbations of molecular states while reacting plastically to extrinsic cues affecting the whole society. Long-term stability of the social structure is reinforced by dynamic DNA methylation. Our study provides a general principle of how both specialization and plasticity can be achieved in biological systems. A record of this paper’s transparent peer review process is included in the supplemental information

The impact of interaction models on the coherence of collective decision-making : a case study with simulated locusts

A key aspect of collective systems resides in their ability to exhibit coherent behaviors, which demonstrate the system as a single unit. Such coherence is assumed to be robust under local interactions and high density of individuals. In this paper, we go beyond the local interactions and we investigate the coherence degree of a collective decision under different interaction models: (i)Â how this degree may get violated by massive loss of interaction links or high levels of individual noise, and (ii)Â how efficient each interaction model is in restoring a high degree of coherence. Our findings reveal that some of the interaction models facilitate a significant recovery of the coherence degree because their specific inter-connecting mechanisms lead to a better inference of the swarm opinion. Our results are validated using physics-based simulations of a locust robotic swarm