Parasites delay worker reproduction in bumblebees: consequences for eusociality

Workers in eusocial insects usually tend the brood of the queen and so achieve representation in the next generation through aiding relatives to reproduce. However, workers of some eusocial species, such as bumblebees, are capable of reproductive activity even in the presence of the queen (in queen-right colonies), and worker reproduction is associated with aggressive behaviors and egg cannibalism, both of which reduce colony efficiency. Thus, factors that affect worker ovariandevelopment, a precondition for reproduction, can influence social harmony and colony productivity. Parasites are a ubiquitous and important part of the biotic environment of all organisms. Here we show that parasites play an important role in the reproductive physiology of worker bumblebees in queen-right colonies of Bombus terrestris, affecting the pattern and timing of ovarian development and oviposition. Workers from colonies parasitized with the intestinal trypanosome Crithidia bombi had less developed ovaries than workers of the same age from unparasitized colonies. In addition, parasitized colonies were smaller than unparasitized colonies for about the first half of colony development. This generated further demographic effects such that workers were on average younger in parasitized than in unparasitized colonies around the time of the onset of worker oviposition, and worker oviposition occurred significantly later in parasitized colonies. Workers in parasitized colonies therefore had lower individual reproductive potential and were cooperative for a larger proportion of the colony cycle than those in unparasitized colonies. In this system, where transmission of the parasite between years probably occurs only in infested, young queens, this effect may represent an adaptation on the part of the parasite to ensure its successful passage through the winter. Parasites, by reducing the cost of worker cooperation, may facilitate queen control over her worker force and play an important role in moderating the social organization of eusocial insect colonie

Cognitive effects of hypercapnia on immersed working divers

Cognitive effects of inspired doses of CO2 during submerged working dives have previously not been explored. Three experiments using male volunteer Navy divers in the NEDU test pool under 12 feet of fresh water explored: (1) dose-related and on/off effects of 1.5% (Phase 1a, N=20) and 3% (Phase 1b, N=16) inspired CO2; (2) questions of whether switching to gas free of CO2 results in further changes in performance or restoration to baseline (Phase 2, N=34); and (3) differences in the effects of CO2 in air vice in O2 (Phase 3, N=16). End tidal CO2 was collected from all divers and correlated with cognitive performance. The Automated Neuropsychological Assessment Metrics, version 4 (ANAM4), was used before and four times during each dive — with three intermittent periods of mild or moderate exercise during each dive — to measure nine cognitive domains. No dose-related effect of CO2 was found. Basic cognitive domains of simple reaction time, visual scanning, visuo-spatial processing, and learning were unaffected, while fatigue and the higher cognitive functions of short-term memory (STM), long-term memory (LTM), working memory (WM), math processing, and sustained attention produced perplexing results. Most consistent of all differences was the decrease in LTM while divers were on CO2, a decrease that persisted in Phase 1 even after divers were removed from CO2 and returned to O2. Math processing, WM, and sustained attention increased among divers both during and after breathing CO2. STM decreased on CO2 in Phase 1 but not in Phase 2. No cognitive changes were detected on air, when end tidal CO2 remained closer to normal than on O2. While some participants reported mild to moderate symptoms (e.g., headache, shortness of breath, irritability, and lack of concentration), end tidal CO2 levels were mostly \u3c7% Surface Equivalent Value (SEV). Because subjects were not hypercapnic, we cannot address the question of the study. Further investigation of the effects of inspired CO2 on higher cognitive domains — along with consideration of breathing resistance — is recommended

Genotype-specific interactions and the trade-off between host and parasite fitness

<p>Abstract</p> <p>Background</p> <p>Evolution of parasite traits is inextricably linked to their hosts. For instance one common definition of parasite virulence is the reduction in host fitness due to infection. Thus, traits of infection must be viewed in both protagonists and may be under shared genetic and physiological control. We investigated these questions on the oomycete <it>Hyaloperonospora arabidopsis </it>(= <it>parasitica</it>), a natural pathogen of the Brassicaceae <it>Arabidopsis thaliana</it>.</p> <p>Results</p> <p>We performed a controlled cross inoculation experiment confronting six lines of the host plant with seven strains of the parasite in order to evaluate genetic variation for phenotypic traits of infection among hosts, parasites, and distinct combinations. Parasite infection intensity and transmission were highly variable among parasite strains and host lines but depended also on the interaction between particular genotypes of the protagonists, and genetic variation for the infection phenotype of parasites from natural populations was found even at a small spatial scale within population. Furthermore, increased parasite fitness led to a significant decrease in host fitness only on a single host line (Gb), although a trade-off between these two traits was expected because host and parasite share the same resource pool for their respective reproduction. We propose that different levels of compatibility dependent on genotype by genotype interactions might lead to different amounts of resources available for host and parasite reproduction. This variation in compatibility could thus mask the expected negative relationship between host and parasite fitness, as the total resource pool would not be constant.</p> <p>Conclusion</p> <p>These results highlight the importance of host variation in the determination of parasite fitness traits. This kind of interaction may in turn decouple the relationship between parasite transmission and its negative effect on host fitness, altering theoretical predictions of parasite evolution.</p

Breathing 100% oxygen during water immersion improves postimmersion cardiovascular responses to orthostatic stress

Physiological compensation to postural stress is weakened after long-duration water immersion (WI), thus predisposing individuals to orthostatic intolerance. This study was conducted to compare hemodynamic responses to postural stress following exposure to WI alone (Air WI), hyperbaric oxygen alone in a hyperbaric chamber (O2HC), and WI combined with hyperbaric oxygen (O2WI), all at a depth of 1.35 ATA, and to determine whether hyperbaric oxygen is protective of orthostatic tolerance. Thirty-two healthy men underwent up to 15 min of 70° head-up tilt (HUT) testing before and after a single 6-h resting exposure to Air WI (N = 10), O2HC (N = 12), or O2WI (N = 10). Heart rate (HR), blood pressure (BP), cardiac output (Q), stroke volume (SV), forearm blood flow (FBF), and systemic and forearm vascular resistance (SVR and FVR) were measured. Although all subjects completed HUT before Air WI, three subjects reached presyncope after Air WI exposure at 10.4, 9.4, and 6.9 min. HUT time did not change after O2WI or O2HC exposures. Compared to preexposure responses, HR increased (+10 and +17%) and systolic BP (-13 and -8%), and SV (-16 and -23%) decreased during HUT after Air WI and O2WI, respectively. In contrast, HR and SV did not change, and systolic (+5%) and diastolic BP (+10%) increased after O2HC. Q decreased (-13 and -7%) and SVR increased (+12 and +20%) after O2WI and O2HC, respectively, whereas SVR decreased (-9%) after Air WI. Opposite patterns were evident following Air WI and O2HC for FBF (-26 and +52%) and FVR (+28 and -30%). Therefore, breathing hyperbaric oxygen during WI may enhance post-WI cardiovascular compensatory responses to orthostatic stress

Positive effects of cyanogenic glycosides in food plants on larval development of the common blue butterfly

Cyanogenesis is a widespread chemical defence mechanism in plants against herbivory. However, some specialised herbivores overcome this protection by different behavioural or metabolic mechanisms. In the present study, we investigated the effect of presence or absence of cyanogenic glycosides in birdsfoot trefoil (Lotus corniculatus, Fabaceae) on oviposition behaviour, larval preference, larval development, adult weight and nectar preference of the common blue butterfly (Polyommatus icarus, Lycaenidae). For oviposition behaviour there was a female-specific reaction to cyanogenic glycoside content; i.e. some females preferred to oviposit on cyanogenic over acyanogenic plants, while other females behaved in the opposite way. Freshly hatched larvae did not discriminate between the two plant morphs. Since the two plant morphs differed not only in their content of cyanogenic glycoside, but also in N and water content, we expected these differences to affect larval growth. Contrary to our expectations, larvae feeding on cyanogenic plants showed a faster development and stronger weight gain than larvae feeding on acyanogenic plants. Furthermore, female genotype affected development time, larval and pupal weight of the common blue butterfly. However, most effects detected in the larval phase disappeared for adult weight, indicating compensatory feeding of larvae. Adult butterflies reared on the two cyanogenic glycoside plant morphs did not differ in their nectar preference. But a gender-specific effect was found, where females preferred amino acid-rich nectar while males did not discriminate between the two nectar mimics. The presented results indicate that larvae of the common blue butterfly can metabolise the surplus of N in cyanogenic plants for growth. Additionally, the female-specific behaviour to oviposit preferably on cyanogenic or acyanogenic plant morphs and the female-genotype-specific responses in life history traits indicate the genetic flexibility of this butterfly species and its potential for local adaptatio

Phylogeography of the Bradyrhizobium spp. associated with peanut, Arachis hypogaea: Fellow travellers or new associations?

International audienceLegume plants have colonized almost all terrestrial biotopes. Their ecological success is partly due to the selective advantage provided by their symbiotic association with nitrogen-fixing bacteria called rhizobia, which allow legumes to thrive on marginal lands and nitrogen depleted soils where non-symbiotic plants cannot grow. Additionally, their symbiotic capacities result in a high protein content in their aerial parts and seeds. This interesting nutritional value has led to the domestication and agricultural exploitation of several legumes grown for seeds and/or fodder for human and domestic animal consumption. Several cultivated legume species are thus grown far beyond their natural geographic range. Other legume species have become invasives, spreading into new habitats. The cultivation and establishment of legume species outside of their original range requires either that they are introduced or cultivated along with their original symbiotic partner or that they find an efficient symbiotic partner in their introduced habitat. The peanut, Arachis hypogaea, a native of South America, is now cultivated throughout the world. This species forms root nodules with Bradyrhizobium, but it is unclear whether these came with the seeds from their native range or were acquired locally. Here we propose to investigate the phylogeography of Bradyrhizobium spp. associated with a number of different wild and cultivated legume species from a range of geographical areas, including numerous strains isolated from peanut roots across the areas of peanut cultivation. This will allow us to address the question of whether introduced/cultivated peanuts associate with bacteria from their original geographic range, i.e., were introduced together with their original bacterial symbionts, or whether they acquired their current associations de novo from the bacterial community within the area of introduction. We will base the phylogenetic analysis on sequence data from both housekeeping and core genes and a symbiotic gene (nif). Differences between the phylogenetic signal of symbiotic and non-symbiotic genes could resultfrom horizontal transfer of symbiosis capacity. Thus this study will also allow us to elucidate the processes by which this symbiotic association has evolved within this group of Bradyrhizobium spp

Influence of multiple infection and relatedness on virulence: Disease dynamics in an experimental plant population and its castrating parasite. PLoS One 2014

Abstract The level of parasite virulence, i.e., the decrease in host&apos;s fitness due to a pathogen, is expected to depend on several parameters, such as the type of the disease (e.g., castrating or host-killing) and the prevalence of multiple infections. Although these parameters have been extensively studied theoretically, few empirical data are available to validate theoretical predictions. Using the anther smut castrating disease on Silene latifolia caused by Microbotryum lychnidis-dioicae, we studied the dynamics of multiple infections and of different components of virulence (host death, non-recovery and percentage of castrated stems) during the entire lifespan of the host in an experimental population. We monitored the number of fungal genotypes within plants and their relatedness across five years, using microsatellite markers, as well as the rates of recovery and host death in the population. The mean relatedness among genotypes within plants remained at a high level throughout the entire host lifespan despite the dynamics of the disease, with recurrent new infections. Recovery was lower for plants with multiple infections compared to plants infected by a single genotype. As expected for castrating parasites, M. lychnidis-dioicae did not increase host mortality. Mortality varied across years but was generally lower for plants that had been diseased the preceding year. This is one of the few studies to have empirically verified theoretical expectations for castrating parasites, and to show particularly i) that castrated hosts live longer, suggesting that parasites can redirect resources normally used in reproduction to increase host lifespan, lengthening their transmission phase, and ii) that multiple infections increase virulence, here in terms of non-recovery and host castration

Diversity of thermal aptitude of Middle Eastern and Mediterranean Puccinia striiformis f. sp. tritici isolates from different altitude zones

The worldwide spread of wheat yellow rust lineage PstS1/S2 adapted to higher temperatures prompted us to investigate how diverse temperature responses of this lineage are in the Middle East, where diversity was previously observed within this lineage for pathotypes and genotypes. Here we highlight the diversity of response to temperature within a PstS1/S2 population. Twenty-six isolates from eight countries and different altitudes, which were tested under four combinations of cold and warm incubation and postincubation temperature conditions, showed diversity for infection efficiency (IE) and latency period (LP). IE of the various isolates ranged from 5.8% to 13.7% under cold (5°C) and 0.04% to 1% under warm (20°C) incubation temperatures. LP varied from 10.2 days under warm to 4.43 days under cold incubation. LP of isolates from the same country could differ by 2 days. Significant differences in thermal aptitudes of the isolates were observed between and within countries. IE and LP diversity was not related to altitude origin of the isolates on the whole; however, a trade-off between IE and LP was observed for isolates from low altitude (<400 m) under a warm regime. We showed diversity for thermal aptitude for IE and LP of isolates belonging to the same PstS1/S2 lineage. Understanding Pst temperature aptitude among geographically distant isolates of the same clonal lineage may help to identify the geographic range of pathogens and also to improve forecast models or breeding programmes

The impacts of predators and parasites on wild bumblebee colonies

1. The study of wild bumblebee nests has been hindered by the difficulty in locating and observing them. Here, 47 wild nests were located using a sniffer dog and volunteers. The entrances to 32 nests were filmed continuously to identify successful nests (those that produced gynes) and observe vertebrate species interactions. &nbsp; 2. Of the 47 nests, 71% and 21% produced gynes in 2010 and 2011, respectively.&nbsp; 3. A total of 39 vertebrate species were filmed at entrances but the majority did not interact with the nests. Great tits (Parus major) depredated or attempted to depredate bees on 32 occasions at the entrances to 10 nests, something that has not previously been described. Small mammals were very often recorded accessing entrances to bumblebee nests, but whether they depredated bees was not known, and frequently visited nests were no less likely to produce gynes. Eight nests were entered by adult wax moths,Aphomia sociella.&nbsp; 4. The faeces of 1179 workers from 29Bombus terrestrisnests were screened microscopically for parasites.Crithidia bombiinfections were apparent in 49% of worker bees, whileNosema bombiandApicystis bombiwere present in 5.5% and 0.68% of bees, respectively. Nests with a high prevalence ofC. bombiinfection were less likely to produce gynes, the first evidence of a direct impact of this common parasite on bumblebee colony reproduction in wild nests.&nbsp; 5. Overall, our data indicate that bumblebee nests are at the heart of a rich web of interactions between many different predator and parasite species

Light availability affects sex lability in a gynodioecious plant

PREMISE OF THE STUDY: Sex lability (i.e., gender diphasy) in plants is classically linked to the larger resource needs associated with the female sexual function (i.e., seed production) compared to the male function (i.e., pollen production). Sex lability in response to the environment is extensively documented in dioecious species, but has been largely overlooked in gynodioecious plants. METHODS: Here, we tested whether environmental conditions induce sex lability in the gynodioecious Geranium sylvaticum. We conducted a transplantation experiment in the field where plants with different sex expression were reciprocally transplanted between high light and low light habitats. We measured plants’ reproductive output and sex expression over four years. KEY RESULTS: Our results show that sex expression was labile over the study period. The light level at the destination habitat had a significant effect on sexual expression and reproductive output, because plants decreased their reproductive output when transplanted to the low light habitat. Transplantation origin did not affect any parameter measured. CONCLUSIONS: This study shows that sex expression in Geranium sylvaticum is labile and related to light availability. Sexually labile plants did not produce more seeds or pollen, and thus, there was no apparent fitness gain in sexually labile individuals. Sex lability in gynodioecious plants may be more common than previously believed because detection of sex lability necessitates data on the same individuals over time, which is rare in sexually dimorphic herbaceous plants