Time and energy constraints and the relationships between currencies in foraging theory

Measured foraging strategies often cluster around values that maximize the ratio of energy gained over energy spent while foraging (efficiency), rather than values that would maximize the long-term net rate of energy gain (rate). The reasons for this are not understood. This paper focuses on time and energy constraints while foraging to illustrate the relationship between efficiency and rate-maximizing strategies and develops models that provide a simple framework to analyze foraging strategies in two distinct foraging contexts. We assume that while capturing and ingesting food for their own use (which we term feeding), foragers behave so as to maximize the total net daily energetic gain. When gathering food for others or for storage (which we term provisioning), we assume that foragers behave so as to maximize the total daily delivery, subject to meeting their own energetic requirements. In feeding contexts, the behavior maximizing total net daily gain also maximizes efficiency when daily intake is limited by the assimilation capacity. In contrast, when time available to forage sets the limit to gross intake, the behavior maximizing total net daily gain also maximizes rate. In provisioning contexts, when daily delivery is constrained by the energy needed to power self-feeding, maximizing efficiency ensures the highest total daily delivery. When time needed to recoup energetic expenditure limits total delivery, a low self-feeding rate relative to the rate of energy expenditure favors efficient strategies. However, as the rate of self-feeding increases, foraging behavior deviates from efficiency maximization in the direction predicted by rate maximization. Experimental manipulations of the rate of self-feeding in provisioning contexts could be a powerful tool to explore the relationship between rate and efficiency-maximizing behavio

Dynamic changes in host-virus interactions associated with colony founding and social environment in fire ant queens (Solenopsis invicta)

Funding Information US Department of Agriculture AFRI Award. Grant Number: 2009‐35302‐05301 Marie Curie International Incoming Fellowship. Grant Number: FP7‐PEOPLE‐2013‐IIF‐625487Peer reviewedPublisher PD

Construction and characterization of a BAC-library for a key pollinator, the bumblebee Bombus terrestris L

Abstract.: The primitively social bumblebee Bombus terrestris is an ecological model species as well as an important agricultural pollinator. As part of the ongoing development of genomic resources for this model organism, we have constructed a publicly available bacterial artificial chromosome (BAC) library from males of a field-derived colony. We have shown that this library has a high coverage, which allows any particular sequence to be retrieved from at least one clone with a probability of 99.7%. We have further demonstrated the library's usefulness by successfully screening it with probes derived both from previously described B. terrestris genes and candidate genes from another bumblebee species and the honeybee. This library will facilitate genomic studies in B. terrestris and will allow for novel comparative studies in the social Hymenopter

The Darwin cure for apiculture? Natural selection and managed honeybee health

Recent major losses of managed honeybee, Apis mellifera, colonies at a global scale have resulted in a multitude of research efforts to identify the underlying mechanisms. Numerous factors acting singly and/or in combination have been identified, ranging from pathogens, over nutrition to pesticides. However, the role of apiculture in limiting natural selection has largely been ignored. This is unfortunate, because honeybees are more exposed to environmental stressors compared to other livestock and management can severely compromise bee health. Here, we briefly review apicultural factors that influence bee health and focus on those most likely interfering with natural selection, which offers a broad range of evolutionary applications for field practice. Despite intense breeding over centuries, natural selection appears to be much more relevant for the health of managed A. mellifera colonies than previously thought. We conclude that sustainable solutions for the apicultural sector can only be achieved by taking advantage of natural selection and not by attempting to limit it

Floral temperature and optimal foraging: is heat a feasible floral reward for pollinators?

As well as nutritional rewards, some plants also reward ectothermic pollinators with warmth. Bumble bees have some control over their temperature, but have been shown to forage at warmer flowers when given a choice, suggesting that there is some advantage to them of foraging at warm flowers (such as reducing the energy required to raise their body to flight temperature before leaving the flower). We describe a model that considers how a heat reward affects the foraging behaviour in a thermogenic central-place forager (such as a bumble bee). We show that although the pollinator should spend a longer time on individual flowers if they are warm, the increase in total visit time is likely to be small. The pollinator's net rate of energy gain will be increased by landing on warmer flowers. Therefore, if a plant provides a heat reward, it could reduce the amount of nectar it produces, whilst still providing its pollinator with the same net rate of gain. We suggest how heat rewards may link with plant life history strategies

Larvae act as a transient transmission hub for the prevalent bumblebee parasite Crithidia bombi

Disease transmission networks are key for understanding parasite epidemiology. Within the social insects, structured contact networks have been suggested to limit the spread of diseases to vulnerable members of their society, such as the queen or brood. However, even these complex social structures do not provide complete protection, as some diseases, which are transmitted by workers during brood care, can still infect the brood. Given the high rate of feeding interactions that occur in a social insect colony, larvae may act as disease transmission hubs. Here we use the bumblebee Bombus terrestris and its parasite Crithidia bombi to determine the role of brood in bumblebee disease transmission networks. Larvae that were artificially inoculated with C. bombi showed no signs of infection seven days after inoculation. However, larvae that received either an artificial inoculation or a contaminated feed from brood-caring workers were able to transmit the parasite to naive workers. These results suggest that the developing brood is a potential route of intracolonial disease transmission and should be included when considering social insect disease transmission networks

Demasculinization of male guppies increases resistance to a common and harmful ectoparasite

Parasites are detrimental to host fitness and therefore should strongly select for host defence mechanisms. Yet, hosts vary considerably in their observed parasite loads. One notable source of inter-individual variation in parasitism is host sex. Such variation could be caused by the immunomodulatory effects of gonadal steroids. Here we assess the influence of gonadal steroids on the ability of guppies (Poecilia reticulata) to defend themselves against a common and deleterious parasite (Gyrodactylus turnbulli). Adult male guppies underwent 31 days of artificial demasculinization with the androgen receptor-antagonist flutamide, or feminization with a combination of flutamide and the synthetic oestrogen 17 β-estradiol, and their parasite loads were compared over time to untreated males and females. Both demasculinized and feminized male guppies had lower G. turnbulli loads than the untreated males and females, but this effect appeared to be mainly the result of demasculinization, with feminization having no additional measurable effect. Furthermore, demasculinized males, feminized males and untreated females all suffered lower Gyrodactylus-induced mortality than untreated males. Together, these results suggest that androgens reduce the ability of guppies to control parasite loads, and modulate resistance to and survival from infection. We discuss the relevance of these findings for understanding constraints on the evolution of resistance in guppies and other vertebrates

Colorectal cancer testing rates after implementation of an organised screening programme in Vaud, Switzerland

AIMS OF THE STUDY: Canton Vaud, Switzerland, implemented an organised colorectal cancer  screening programme with colonoscopy and faecal occult blood tests in 2015, 4 to 6 years ahead of neighbouring cantons. Before its implementation, nearly half of Swiss citizens were already up to date with screening, primarily from opportunistic colonoscopies. We hypothesised that earlier implementation of an organised programme would be associated with greater increases in colorectal cancer testing rates. METHODS: We analysed Swiss health insurance claim data from CSS, a Swiss health insurer covering 16% of the Swiss population and 10% of canton Vaud. We stratified 50–69-year-olds into groups from Vaud, its four neighbouring cantons (Fribourg, Geneva, Neuchâtel and Valais), and the rest of Switzerland. We analysed overall, faecal occult blood test and colonoscopy testing rates for each year between 2010 and 2018. RESULTS: The overall testing rate increased from 7.6% in 2010 to 11.6% in 2018 (+4.0%) in Vaud, from 6.1% to 9.3% (+3.2%) in neighbouring cantons and from 7.4% to 8.6% (+1.2%) in the rest of Switzerland. The faecal occult blood test rate increased between 2016 and 2018 from 2.9% to 4.1% (+1.2%) in Vaud and from 1.7% to 2.6% (+0.9%) in neighbouring cantons, but it decreased from 3.1% to 1.5% (–1.6%) in the rest of Switzerland. The colonoscopy rate increased in all cantons, from 4.7% to 7.5% in Vaud (+2.8%), from 4.4% to 6.7% in neighbouring cantons (+2.3%) and from 4.3% to 7.1% in the rest of Switzerland (+2.8%). By 2018, 40% of faecal occult blood tests and 26% of colonoscopies in Vaud occurred in the organised programme. Those who completed an faecal occult blood test within the Vaud programme were younger, had fewer comorbidities and were more likely to have a high-deductible health plan than those tested outside the programme. CONCLUSIONS: Colorectal cancer testing rates increased between 2010 and 2018, with greater absolute increases in Vaud than in neighbouring cantons or the rest of Switzerland. Faecal occult blood test use increased in both Vaud and neighbouring cantons, possibly reflecting changes in testing patterns by general practitioners. By 2018, 40% of colonoscopies and 26% of faecal occult blood tests occurred within the screening programme

Infection by the castrating parasitic nematode <i>Sphaerularia bombi </i>changes gene expression in <i>Bombus terrestris </i>bumblebee queens

Parasitism can result in dramatic changes in host phenotype, which are themselves underpinned by genes and their expression. Understanding how hosts respond at the molecular level to parasites can therefore reveal the molecular architecture of an altered host phenotype. The entomoparasitic nematode Sphaerularia bombi is a parasite of bumblebee (Bombus) hosts where it induces complex behavioural changes and host castration. To examine this interaction at the molecular level, we performed genome-wide transcriptional profiling using RNA-Seq of S. bombi-infected Bombus terrestris queens at two critical time-points: during and just after overwintering diapause. We found that infection by S. bombi affects the transcription of genes underlying host biological processes associated with energy usage, translation, and circadian rhythm. We also found that the parasite affects the expression of immune genes, including members of the Toll signaling pathway providing evidence for a novel interaction between the parasite and the host immune response. Taken together, our results identify host biological processes and genes affected by an entomoparasitic nematode providing the first steps towards a molecular understanding of this ecologically important host-parasite interaction

Host allometry influences the evolution of parasite host-generalism: theory and meta-analysis

Parasites vary widely in the diversity of hosts they infect: some parasite species are specialists - infecting just a single host species, while others are generalists, capable of infecting many. Understanding the factors that drive parasite host-generalism is of basic biological interest, but also directly relevant to predicting disease emergence in new host species, identifying parasites that are likely to have unidentified additional hosts, and assessing transmission risk. Here, we use mathematical models to investigate how variation in host body size and environmental temperature affect the evolution of parasite host-generalism. We predict that parasites are more likely to evolve a generalist strategy when hosts are large-bodied, when variation in host body size is large, and in cooler environments. We then explore these predictions using a newly updated database of over 20,000 fish-macroparasite associations. Within the database we see some evidence supporting these predictions, but also highlight mismatches between theory and data. By combining these two approaches, we establish a theoretical basis for interpreting empirical data on parasites' host specificity and identify key areas for future work that will help untangle the drivers of parasite host-generalism