• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 21
  • 3
  • 2
  • Tagged with
  • 33
  • 16
  • 8
  • 7
  • 5
  • 5
  • 4
  • 4
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • 3
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Fuels for Winter: The Role of Proline in Overwintering Bumblebee Queens (Bombus impatiens)

Rondot, Ariane 10 June 2020 (has links)
The common eastern bumblebee queens (Bombus impatiens) endure cold winter months by entering a diapausal state post-fertilization. During this overwintering period, these animals use stored energy reserves while maintaining a low metabolic rate. Bumblebees are thought to use primarily lipids to fuel this critical overwintering period, despite the fact that bee mitochondria do not appear equipped to break down this metabolic fuel. For some insects, lipids stored in the fat body can be converted to the amino acid proline, and this metabolic fuel has recently been discovered to be readily oxidized by bumblebee workers. My research, therefore, investigates the role of proline during overwintering in bumblebee queens. Using cellular respirometry, I determined the metabolic capacity of the muscle cells of queens to use various fuels, and if this capacity changes throughout overwintering. Surprisingly, the tested queens showed a much lower potential to oxidize proline than workers, and their capacity did not change during a four-month overwintering period. The metabolic properties of muscle tissue were further characterized using metabolic enzymes activity profile. These results further demonstrate the low potential for proline metabolism and the limitations of bumblebee queens’ capacity to oxidize lipids. Body composition was measured to determine how the various energy stores (lipid, glycogen, protein) change during overwintering; however, no decrease in concentration was observed. Overall, this work clarifies the constraints of B. impatiens metabolism during overwintering.
2

Critical Thermal Maxima of Bombus impatiens: from Castes to Colonies

Bretzlaff, Tiffany 04 December 2023 (has links)
Bumblebees are experiencing declines and range contractions globally that are, in some cases, independent of anthropogenic pesticide- or land-use change, leaving rising global temperatures as the primary driver of such loses. With ambient temperature (Ta) and thermal limitations being a crucial component in these observed declines, I sought to determine the physiological limitations that high Ta imposes on both individuals and colonies of a temperate bumblebee species, Bombus impatiens. Through Chapter 2, I first established the upper thermal tolerance (CTmax) of the species, testing both adults and larvae to determine which of these colony castes are most thermally sensitive to heat. Collective thermoregulation at the colony-level is then important to ensure that the most heat sensitive individuals are protected from changes in optimal nest temperature (Tn). I thus identified the energetic costs associated with colonial thermoregulation and whether large colonies could successfully achieve thermal homeostasis under various Ta. Chronic bouts of heat stress are also of concern as colonies invest time and energy into thermoregulation, especially given that heatwave events are becoming more frequent. In Chapter 3, I examined whether there exists a trade-off between thermoregulation and foraging effort for colonies under chronic heat stress and how various measures of colony success are impacted. Finally, foraging requires individuals to employ flight for the procurement of resources. In Chapter 4, I investigated if the temperate adaptation of an insulative pile layer would hinder flight performance under high Ta by assessing the metabolic rates of adult castes during flight. I found that larvae were more thermally sensitive compared to bumblebee adults, which emphasizes the importance of colonial thermoregulation – a task successful at low Ta. Under heat stress, however, Tn could not be maintained despite elevated energetic investments (Chapter 2). These findings suggest that Ta which exceeds optimal Tn may pose significant challenges to colonies; not only energetically but also to the health of thermally sensitive larvae within. A trade-off between thermoregulation and foraging effort did not emerge for colonies experiencing chronic exposure to high Ta. Instead, only high incidences of thermoregulation were observed which failed to prevent increases in Tn. Furthermore, a greater number of individuals were found to abandon the colony at high Ta, and fewer offspring were produced (Chapter 3). Here, findings suggest that chronic high Ta may pose the greatest risk to the production of thermally sensitive offspring by way of reduced worker population and failed thermoregulation. Finally, the metabolic output during flight at high Ta was not found to be affected by an insulative layer of pile (Chapter 4), indicating that either pile may play a role in limiting other measures of flight performance at high Ta, or that alternate physiological mechanisms may be responsible instead. Together the findings from this thesis broaden the understanding of how a temperate species of bumblebee responds physiologically to high Ta both at the individual and colonial level, providing further evidence on thermal limitations in a changing climate.
3

Emerging viral diseases of pollinating insects

Manley, Robyn Anna January 2017 (has links)
The risks posed by rapidly evolving RNA viruses to human and animal health are well recognized. Epidemics in managed and wildlife populations can lead to considerable economic and biodiversity losses. Yet, we lack understanding of the ecological and evolutionary factors that promote disease emergence. Host-switching viruses may be a particular threat to species important for human welfare, such as pollinating bees. Both honeybees and wild bumblebees have faced sharp declines in the last decades, with high winter mortality seen in honeybees. Infectious and emerging diseases are considered one of the key drivers of declines, acting in synergy with habitat loss and pesticide use. Here I focus on multihost viruses that pose a risk to wild bumblebees. I first identify the risk factors driving viral spillover and emergence from managed honeybees to wild bumblebees, by synthesising current data and literature. Biological factors (i.e. the nature of RNA viruses and ecology of social bees) play a clear role in increasing the risk of disease emergence, but anthropogenic factors (trade and transportation of commercial honeybees and bumblebees) creates the greatest risk of viral spillover to wild bees. Basic knowledge of the pathogenic effect of many common pollinator viruses on hosts other than A. mellifera is currently lacking, yet vital for understanding the wider impacts of infection at a population level. Here, I provide evidence that a common bumblebee virus, Slow bee paralysis virus (SBPV), reduces the longevity of Bombus terrestris under conditions of nutrition stress. The invasion of Varroa destructor as an ectoparasitic viral vector in European honeybees has dramatically altered viral dynamics in honeybees. I test how this specialist honeybee vector affects multi-host pathogens that can infect and be transmitted by both honeybees and wild bumblebees. I sampled across three host species (A. mellifera, B. terrestris and B. pascuorum) from Varroa-free and Varroa-present locations. Using a combination of molecular and phylogenetic techniques I find that this specialist honeybee vector increases the prevalence of four multi-host viruses (deformed wing virus (type A and B), SBPV and black queen cell virus) in sympatric wild bumblebees. Furthermore, wild bumblebees are currently experiencing a DWV epidemic driven by the presence of virus-vectoring Varroa in A. mellifera. Overall this thesis demonstrates that wild bumblebees are at high risk of viral disease emergence. My research adds to the ever-expanding body of evidence indicating that stronger disease controls on commercial bee operations are crucial to protect our wild bumblebees.
4

Segregation of Visual Information in the Bee Brain

Paulk, Angelique January 2008 (has links)
Photoreceptors in the eye basically provide information about light intensities from which brains extract different kinds of visual cues (e.g. color, movement, pattern). How do the properties and response characteristic of visual interneurons differ from the periphery to the central brain? I intracellularly recorded from neurons in the second and third optic ganglia (medulla and lobula) and the central brain (protocerebrum) of bees (mainly bumblebees; Bombus impatiens) while presenting color and motion stimuli. Bees rely on such stimuli during flight and foraging and show sophisticated visual learning abilities. We found that neurons in the distal medulla are color specific while ones in the proximal medulla show complex, often antagonistic color responses. Neurons in the distal lobula (layers 1-4) mainly process motion information while the proximal lobula (layers 5 and 6) seems to combine color and motion responses. Anterior parts of the central brain receive complex input representing combinations of motion and color information characterized by specific temporal properties (e.g. temporal precision, 'novelty' information or entrainment). This kind of often sparsely coded information is also represented in the mushroom bodies, learning and memory centers in the insect brain. In contrast, posterior parts of the central brain receive mainly motion information and show more reliable responses yet less precise spike timing. While the former kind of information (temporally precise or novelty in anterior pathways) is suited to form stimulus associations relevant during foraging, the latter, more reliable information is thought to support fast optomotor flight control maneuvers and other less plastic behaviors.
5

Similar but Different: How Foraging Bumblebees ('Bombus Impatiens') Treat Flowers and Pictures of Flowers

Thompson, Emma January 2016 (has links)
Flowers, the sole natural source of pollen and nectar for bees, present many similar features, in colour, shape, size and scent, which facilitate pollinator attraction. This similarity among stimuli requires perception of commonality but also a capacity for differentiation between similar but different stimuli. While many flowers of a similar type will elicit approach and foraging, failure to access resources on any individual flower in an array (e.g. due to depletion) will not necessarily generalize and deter further foraging. Such conditions demand that bees respond to both the similarity and differences among stimuli which may share many common features but differ individually in available resources. Two questions are raised by this challenge and will herein be addressed: how do bees perceive and respond to ‘similar but different’ stimuli? And, how do bees use such cues to find rewarding flowers? Picture-object correspondence has not been previously specifically studied in invertebrates. The correspondence between picture-cue and object stimuli may offer a unique opportunity to trigger memory for corresponding targets while still retaining an important distinction between unrewarding cue and rewarding targets. Perception of pictures is not always perceived by animals as either the same as or equivalent to the intended subject. According to Fagot et al. (2000) the perceived relationship may result in confusion, independence or equivalence and is dependent upon experience. The objectives of this thesis are twofold: first, determine how bumblebees (Bombus impatiens) perceive the relationship between objects and corresponding pictures and secondly, to determine whether or not bees may be able to attend to and use pictures as cues while foraging. The correspondence of picture and object by bees was evaluated with four experiments of preference: (1) learned differentiation; spontaneous association to (2) colour, and (3) achromatic, impoverished images; and (4) learned picture cue use. Firstly, results show that bees do not confuse an object with a corresponding picture but nevertheless do perceive a relationship between them if colour cues are retained. Altered, achromatic images were not consistently treated as corresponding to coloured objects. Secondly, bees can learn to use a picture cue in a delayed matching foraging task. Results further suggest a role of three contributing factors in bumblebee picture cue use: (i) conditions of high inconsistency as to which target will be rewarding; (ii) stable target locations; and (iii) individual foraging experience. It appears that bumblebees can learn to use cues, in a delayed matching task, when the location of the corresponding target is known and stable, the individual bee has acquired some experience in successful foraging, and reward is otherwise unpredictable without the use of the cue. Bees may disregard secondary cues as noise under conditions of high target predictability whereby floral constancy or target perseveration may be most efficient, but attend to and learn such cues as signals if target reward is highly unpredictable. The conditions for this sensitivity may coincide with naturally occurring floral cycles.
6

Artificial pollen dispensing flowers and feeders for bee behaviour experiments

Russell, Avery L., Papaj, Daniel R 03 1900 (has links)
The study of foraging behaviour in plant-pollinator mutualisms has benefitted from the use of artificial flowers to manipulate floral display traits and the delivery of floral rewards. The two most common floral rewards are pollen and nectar; some pollinators, such as bees, are obliged to collect both for survival and reproduction. While flexible designs for artificial flowers providing nectar rewards abound, useful designs for artificial flowers that dispense pollen are few. This disparity mirrors a heavy emphasis on nectar collection in the study of pollinator foraging behaviour. In this study we describe a novel, easily constructed and modifiable artificial flower that dispenses flexible amounts of pollen via an ‘anther’ composed of a chenille stem. Using controlled lab assays, we show that more pulverized honeybee pollen is collected by bumblebee (Bombus impatiens) workers at chenille stem feeders than at dish-type feeders. We suggest that the paucity of studies examining pollinator cognition in the context of pollen rewards might be partly remedied if researchers had access to inexpensive and easily adjustable pollen-offering surrogate flowers.
7

Designing a realistic virtual bumblebee

Marsden, Timothy 09 February 2016 (has links)
Optimal Foraging Theory is a set of mathematical models used in the field of behavioral ecology to predict how animals should weigh foraging costs and benefits in order to maximize their food intake. One popular model, referred to as the Optimal Diet Model (ODM), focuses on how individuals should respond to variation in food quality in order to optimize food selection. The main prediction of the ODM is that low quality food items should only be accepted when higher quality items are encountered below a predicted threshold. Yet, many empirical studies have found that animals still include low quality items in their diet above such thresholds, indicating a sub-optimal foraging strategy. Here, we test the hypothesis that such ‘partial preferences’ are produced as a consequence of incomplete information on prey distributions resulting from memory limitations. To test this hypothesis, we used agent-based modeling in NetLogo to create a model of flower choice behavior in a virtual bumblebee forager (SimBee). We program virtual bee foragers with an adaptive decision-making algorithm based on the classic ODM, which we have modified to include memory. Our results show that the probability of correctly rejecting a low quality food item increases with memory size, suggesting that memory limitations play a significant role in driving partial preferences. We discuss the implications of this finding and further applications of our SimBee model in research and educational contexts.
8

Designing a realistic virtual bumblebee

Marsden, Timothy 09 February 2016 (has links)
Optimal Foraging Theory is a set of mathematical models used in the field of behavioral ecology to predict how animals should weigh foraging costs and benefits in order to maximize their food intake. One popular model, referred to as the Optimal Diet Model (ODM), focuses on how individuals should respond to variation in food quality in order to optimize food selection. The main prediction of the ODM is that low quality food items should only be accepted when higher quality items are encountered below a predicted threshold. Yet, many empirical studies have found that animals still include low quality items in their diet above such thresholds, indicating a sub-optimal foraging strategy. Here, we test the hypothesis that such ‘partial preferences’ are produced as a consequence of incomplete information on prey distributions resulting from memory limitations. To test this hypothesis, we used agent-based modeling in NetLogo to create a model of flower choice behavior in a virtual bumblebee forager (SimBee). We program virtual bee foragers with an adaptive decision-making algorithm based on the classic ODM, which we have modified to include memory. Our results show that the probability of correctly rejecting a low quality food item increases with memory size, suggesting that memory limitations play a significant role in driving partial preferences. We discuss the implications of this finding and further applications of our SimBee model in research and educational contexts.
9

Bumblebee learning flights at a flower : viewing direction on departure is influenced by landmark position on approach

Plante-Ajah, Michael January 2019 (has links)
Bumblebees, like other Hymenopterans, perform learning flights when departing their nest for the first few times or when departing from a newly discovered food source. As bees can learn about the landmarks around a flower both on approach and on departure, it is possible that what they see and learn on approach affects what they focus on during their learning flight on departure. In the present study, bumblebees from a commercial colony placed in a greenhouse were allowed to land at an artificial flower next to a single cylindrical landmark in one of three different positions (west, north or east), while all bees departed the flower with all three landmarks present in each position. Bumblebees approaching the flower with the landmark in the west position (WEST bees) faced mostly in a westerly direction and toward that landmark on departure, while NORTH bees faced mostly in an easterly direction and toward the east landmark and EAST bees faced mostly in a northerly direction and toward the north landmark. Thus, each group was consistent but favoured a different direction and faced toward a different landmark compared to the other groups, though these differences were most prominent during the early phase of the learning flight. On the other hand, all three groups faced the flower during the late phase of the learning flight. I therefore conclude that bumblebees do learn about the landmarks around a flower on approach, and this affects the direction they face during their learning flight in a consistent way.
10

Climate Change and Land-use Change Impacts on Bumblebees

Soroye, Peter 10 January 2022 (has links)
Biodiversity is declining across the globe, and human-driven climate change and land-use change are among the primary drivers of this loss. Understanding the mechanisms causing declines is critical for developing effective conservation and management strategies which will not only slow biodiversity loss, but reverse it. This is relevant for virtually all species on the planet, but given the ecosystem services that they provide, pollinators are an especially important group in which to study this. Among the wild pollinators native to North America and Europe, bumblebees (Bombus) are a particularly important and beautiful group. In this thesis, I identify how climate change and land-use change interact to influence population and community change in North American and European bumblebees, and I explore the potential role of protected areas in mitigating declines. I find that climate change has increased local extinction risk for bumblebees by exposing them to temperatures beyond their historic tolerances, and I introduce a broadly applicable method which improves prediction of this climate change-related risk (Chapter 2). Examining the interactions between climate change and land-use change shows that the risk from increasing temperatures and temperature extremes is worse in historically degraded areas, and that climate change and land-use change may be driving biotic homogenization in bumblebee communities. Yet, landscape-scale patterns suggest that human land-use can be managed to have minimal, or even positive, effects on pollinators (Chapter 3). In the face of these global pressures, protected areas represent one way to conserve species. I find that increasing the amount of protected area in a region, regardless of size or management category of the protected areas, is related to reduced local extinction risk for bumblebees across North America and Europe. This benefit is especially strong in areas with high human land-use, highlighting the importance of protected areas in highly human-dominated landscapes (Chapter 4). The work within my thesis improves our understanding of how climate change and land-use change drive shifts in species and communities, and can inform on the effectiveness of specific conservation actions from gardens and urban greenspaces, to Other Effective Area-Based Conservation Measures (Chapter 5).

Page generated in 0.0397 seconds