An immune response in the bumblebee, Bombus terrestris leads to increased food consumption

BACKGROUND: The concept of a costly immune system that must be traded off against other important physiological systems is fundamental to the burgeoning field of ecological immunity. Bumblebees have become one of the central models in this field. Although previous work has demonstrated costs of immunity in numerous life history traits, estimates of the more direct costs of bumblebee immunity have yet to be made. RESULTS: Here we show a 7.5% increase in energy consumption in response to non-pathogenic immune stimulation. CONCLUSION: This increase in energy consumption along with other results suggests that immunity is one of the most important physiological systems, with other systems being sacrificed for its continuing efficiency. This increased consumption and maintained activity contrasts with the sickness-induced anorexia and reduced activity found in vertebrates

Large-scale structure of brown rat (Rattus norvegicus) populations in England: effects on rodenticide resistance

The brown rat (Rattus norvegicus) is a relatively recent (<300 years) addition to the British fauna, but by association with negative impacts on public health, animal health and agriculture, it is regarded as one of the most important vertebrate pest species. Anticoagulant rodenticides were introduced for brown rat control in the 1950s and are widely used for rat control in the UK, but long-standing resistance has been linked to control failures in some regions. One thus far ignored aspect of resistance biology is the population structure of the brown rat. This paper investigates the role population structure has on the development of anticoagulant resistance. Using mitochondrial and microsatellite DNA, we examined 186 individuals (from 15 counties in England and one location in Wales near the Wales–England border) to investigate the population structure of rural brown rat populations. We also examined individual rats for variations of the VKORC1 gene previously associated with resistance to anticoagulant rodenticides. We show that the populations were structured to some degree, but that this was only apparent in the microsatellite data and not the mtDNA data. We discuss various reasons why this is the case. We show that the population as a whole appears not to be at equilibrium. The relative lack of diversity in the mtDNA sequences examined can be explained by founder effects and a subsequent spatial expansion of a species introduced to the UK relatively recently. We found there was a geographical distribution of resistance mutations, and relatively low rate of gene flow between populations, which has implications for the development and management of anticoagulant resistance

Sexual morph specialisation in a trioecious nematode balances opposing selective forces

The coexistence of diferent mating strategies, whereby a species can reproduce both by selfng and outcrossing, is an evolutionary enigma. Theory predicts two predominant stable mating states: outcrossing with strong inbreeding depression or selfng with weak inbreeding depression. As these two mating strategies are subject to opposing selective forces, mixed breeding systems are thought to be a rare transitory state yet can persist even after multiple speciation events. We hypothesise that if each mating strategy plays a distinctive role during some part of the species life history, opposing selective pressures could be balanced, permitting the stable co-existence of selfng and outcrossing sexual morphs. In this scenario, we would expect each morph to be specialised in their respective roles. Here we show, using behavioural, physiological and gene expression studies, that the selfng (hermaphrodite) and outcrossing (female) sexual morphs of the trioecious nematode Auanema freiburgensis have distinct adaptations optimised for their diferent roles during the life cycle. A. freiburgensis hermaphrodites are known to be produced under stressful conditions and are specialised for dispersal to new habitat patches. Here we show that they exhibit metabolic and intestinal changes enabling them to meet the cost of dispersal and reproduction. In contrast, A. freiburgensis females are produced in favourable conditions and facilitate rapid population growth. We found that females compensate for the lack of reproductive assurance by reallocating resources from intestinal development to mate-fnding behaviour. The specialisation of each mating system for its role in the life cycle could balance opposing selective forces allowing the stable maintenance of both mating systems in A. freiburgensis

Sexual morph specialisation in a trioecious nematode balances opposing selective forces

The coexistence of different mating strategies, whereby a species can reproduce both by selfing and outcrossing, is an evolutionary enigma that has long intrigued biologists (Darwin, 1877). Theory predicts only two stable mating states : outcrossing with strong inbreeding depression or selfing with weak inbreeding depression. As these two mating strategies are subject to opposing selective forces, mixed breeding systems are thought to be a rare transitory state, yet they have been found to persist even after multiple speciation events. We hypothesise that if each mating strategy plays a distinctive role during the species life history, opposing selective pressures could be balanced, permitting the stable co-existence of selfing and outcrossing sexual morphs. In this scenario, we would expect each sexual morph to be specialised in their respective roles. Here we show, using a combination of behavioural, physiological and gene expression studies, that the selfing (hermaphrodite) and outcrossing (female) sexual morphs of the trioecious nematode Auanema freiburgensis have distinct adaptations optimised for their different roles during the life cycle. A. freiburgensis hermaphrodites are produced under stressful conditions, are specialised for dispersal to new habitat patches and exhibit metabolic and intestinal changes that enable them to meet the energetic cost of dispersal and reproduction. In contrast, A. freiburgensis females are produced in favourable conditions, facilitate rapid population growth and compensate for the lack of reproductive assurance by reallocating resources from intestinal development to robust mate-finding behaviour. The specialisation of each mating system for their role in the life cycle could balance opposing selective forces allowing the stable maintenance of both outcrossing and selfing mating systems in A. freiburgensis

Differential gene expression and alternative splicing in insect immune specificity

Background: Ecological studies routinely show genotype-genotype interactions between insects and their parasites. The mechanisms behind these interactions are not clearly understood. Using the bumblebee Bombus terrestris/trypanosome Crithidia bombi model system (two bumblebee colonies by two Crithidia strains), we have carried out a transcriptome-wide analysis of gene expression and alternative splicing in bees during C. bombi infection. We have performed four analyses, 1) comparing gene expression in infected and non-infected bees 24 hours after infection by Crithidia bombi, 2) comparing expression at 24 and 48 hours after C. bombi infection, 3) determining the differential gene expression associated with the bumblebee-Crithidia genotype-genotype interaction at 24 hours after infection and 4) determining the alternative splicing associated with the bumblebee-Crithidia genotype-genotype interaction at 24 hours post infection. Results: We found a large number of genes differentially regulated related to numerous canonical immune pathways. These genes include receptors, signaling pathways and effectors. We discovered a possible interaction between the peritrophic membrane and the insect immune system in defense against Crithidia. Most interestingly, we found differential expression and alternative splicing of immunoglobulin related genes (Dscam and Twitchin) are associated with the genotype-genotype interactions of the given bumblebee colony and Crithidia strain. Conclusions: In this paper we have shown that the expression and alternative splicing of immune genes is associated with specific interactions between different host and parasite genotypes in this bumblebee/trypanosome model

The genomes of two key bumblebee species with primitive eusocial organization

Background: The shift from solitary to social behavior is one of the major evolutionary transitions. Primitively eusocial bumblebees are uniquely placed to illuminate the evolution of highly eusocial insect societies. Bumblebees are also invaluable natural and agricultural pollinators, and there is widespread concern over recent population declines in some species. High-quality genomic data will inform key aspects of bumblebee biology, including susceptibility to implicated population viability threats. Results: We report the high quality draft genome sequences of Bombus terrestris and Bombus impatiens, two ecologically dominant bumblebees and widely utilized study species. Comparing these new genomes to those of the highly eusocial honeybee Apis mellifera and other Hymenoptera, we identify deeply conserved similarities, as well as novelties key to the biology of these organisms. Some honeybee genome features thought to underpin advanced eusociality are also present in bumblebees, indicating an earlier evolution in the bee lineage. Xenobiotic detoxification and immune genes are similarly depauperate in bumblebees and honeybees, and multiple categories of genes linked to social organization, including development and behavior, show high conservation. Key differences identified include a bias in bumblebee chemoreception towards gustation from olfaction, and striking differences in microRNAs, potentially responsible for gene regulation underlying social and other traits. Conclusions: These two bumblebee genomes provide a foundation for post-genomic research on these key pollinators and insect societies. Overall, gene repertoires suggest that the route to advanced eusociality in bees was mediated by many small changes in many genes and processes, and not by notable expansion or depauperation

Antimicrobial peptides play a functional role in bumblebee anti-trypanosome defense

Bumblebees, amongst the most important of pollinators, are under enormous population pressures. One of these is disease. The bumblebee and its gut trypanosome Crithidia bombi are one of the fundamental models of ecological immunology. Although there is previous evidence of increased immune gene expression upon Crithidia infection, recent work has focussed on the bumblebee’s gut microbiota. Here, by knocking down gene expression using RNAi, we show for the first time that antimicrobial peptides (AMPs) have a functional role in anti-Crithidia defense

Evidence of capacitation in the parasitoid wasp, Nasonia vitripennis, and its potential role in sex allocation

The allocation of resources to the production of one sex or another has been observed in a large variety of animals. Its theoretical basis allows accurate predictions of offspring sex ratios in many species, but the mechanisms by which sex allocation is controlled are poorly understood. Using previously published data, we investigated whether alternative splicing, combined with differential gene expression, was involved with sex allocation in the parasitoid wasp, Nasonia vitripennis . We found that sex allocation is not controlled by alternative splicing but changes in gene and transcript‐specific expression, which were identified to be involved with oviposition, were shown to be similar to those involved in sperm motility and capacitation. Genes involved in cholesterol efflux, a key component of capacitation, along with calcium transport, neurotransmission, trypsin, and MAPKinase activity were regulated in ovipositing wasps. The results show evidence for regulation of sperm motility and of capacitation in an insect which, in the context of the physiology of the N. vitripennis spermatheca, could be important for sex allocation.</p

Immune response inhibits associative learning in insects.

In vertebrates, it is well established that there are many intricate interactions between the immune system and the nervous system, and vice versa. Regarding insects, until now little has been known about the link between these two systems. Here, we present behavioural evidence indicating a link between the immune system and the nervous system in insects. We show that otherwise non-infected honeybees whose immune systems are challenged by a non-pathogenic immunogenic elicitor lipopolysaccharide (LPS) have reduced abilities to associate an odour with sugar reward in a classical conditioning paradigm. The cost of an immune response therefore not only affects survival of the host, as previously shown, but also everyday behaviour and memory formation