Ecological determinants of prevalence of the male-killing bacterium Arsenophonus nasoniae.

Male-killing bacteria are found in a broad range of arthropods. Arsenophonus nasoniae is a male-killing bacterium, causing a 80% reduction of the male progeny in infected Nasonia vitripennis wasps. Although the discovery of A. nasoniae dates from the early 80's, knowledge about the biology and ecology of this endosymbiont is still scarce. One of these poorly studied features is the ecological factors underlying A. nasoniae incidence on its Nasonia spp. hosts in different geographical locations. Here, we studied the prevalence of A. nasoniae in Iberian wild populations of its host N. vitripennis. This wasp species is a common parasitoid of the blowfly Protocalliphora azurea pupae, which in turn is a parasite of hole-nesting birds, such as the blue tit (Cyanistes caeruleus). We also examined the effects of bird rearing conditions on the prevalence of A. nasoniae through a brood size manipulation experiment (creating enlarged, control and reduced broods). Both the wasp and bacterium presence were tested through PCR assays in blowfly pupae. We found A. nasoniae in almost half (47%) of nests containing blowflies parasitized by N. vitripennis. The prevalence of A. nasoniae was similar in the two geographical areas examined (central Portugal and southeastern Spain) and the probability of infection by A. nasoniae was independent of the number of blowfly pupae in the nest. Experimental manipulation of brood size did not affect the prevalence of A. nasoniae nor the prevalence of its host, N. vitripennis. These results suggest that the incidence of A. nasoniae in natural populations of N. vitripennis is high in the Iberian Peninsula, and the infestation frequency of nests by N. vitripennis carrying A. nasoniae is spatially stable in this geographical region independently of bird rearing conditions.

The son-killer microbe Arsenophonus nasoniae is a widespread associate of the parasitic wasp Nasonia vitripennis in Europe.

Heritable microbes that exhibit reproductive parasitism are common in insects. One class of these are the male-killing bacteria, which are found in a broad range of insect hosts. Commonly, our knowledge of the incidence of these microbes is based on one or a few sampling sites, and the degree and causes of spatial variation are unclear. In this paper, we examine the incidence of the son-killer microbe Arsenophonus nasoniae across European populations of its wasp host, Nasonia vitripennis. In preliminary work, we noticed two female N. vitripennis producing highly female biased sex ratios in a field study from the Netherlands and Germany. When tested, the brood from Germany was revealed to be infected with A. nasoniae. We then completed a broad survey in 2012, in which fly pupal hosts of N. vitripennis were collected from vacated birds' nests from four European populations, N. vitripennis wasps allowed to emerge and then tested for A. nasoniae presence through PCR assay. We then developed a new screening methodology based on direct PCR assays of fly pupae and applied this to ethanol-preserved material collected from great tit (Parus major) nests in Portugal. These data show A. nasoniae is found widely in European N. vitripennis, being present in Germany, the UK, Finland, Switzerland and Portugal. Samples varied in the frequency with which they carry A. nasoniae, from being rare to being present in 50% of the pupae parasitised by N. vitripennis. Direct screening of ethanol-preserved fly pupae was an effective method for revealing both wasp and A. nasoniae infection, and will facilitate sample transport across national boundaries. Future research should examine the causes of variation in frequency, in particular testing the hypothesis that N. vitripennis superparasitism rates drive the variation in A. nasoniae frequency through providing opportunities for infectious transmission.

Habitat-dependent Culicoides species composition and abundance in blue tit (Cyanistes caeruleus) nests.

Wild birds are hosts of Culicoides from as early on as the nesting stage when constrained to their nests. However, the environmental factors which determine the abundance and composition of Culicoides species within each bird nest are still understudied. We sampled Culicoides from Eurasian blue tit (Cyanistes caeruleus) nests found in 2 types of forests located in southern Spain. Firstly, we monitored the abundance of Culicoides species in bird nests from a dry Pyrenean oak deciduous forest and a humid mixed forest comprising Pyrenean and Holm oaks throughout 2 consecutive years. During the 3rd year, we performed a cross-fostering experiment between synchronous nests to differentiate the role of rearing environment conditions from that of the genetically determined or maternally transmitted cues released by nestlings from each forest. We found 147 female Culicoides from 5 different species in the birds' nests. The abundance of Culicoides was higher in the dry forest than in the humid forest. Culicoides abundance, species richness and prevalence were greater when the nestlings were hatched later in the season. The same pattern was observed in the cross-fostering experiment, but we did not find evidence that nestling's features determined by the forest of origin had any effect on the Culicoides collected. These results support the notion that habitat type has a strong influence on the Culicoides affecting birds in their nests, while some life history traits of birds, such as the timing of reproduction, also influence Culicoides abundance and species composition.

Oxidative status of blue tit nestlings varies with habitat and nestling size.

Oxidative status has been proposed as an important ecological and evolutionary force given that pro-oxidant metabolites damage molecules, cells and tissues, with fitness consequences for organisms. Consequently, organisms usually face a trade-off between regulating their oxidative status and other physiological traits. However, environmental stressors and the availability of dietary-derived antioxidants vary according to local conditions and, thus, organisms inhabiting different habitats face different oxidative pressures. Still, there is little information on how different environmental conditions influence the oxidative status of animals inhabiting terrestrial environments. In this work, we examined the variation in oxidative status in the blue tit (Cyanistes caeruleus), a bird species with hatching asynchrony. Specifically, we examined the oxidative status of the largest and the smallest nestlings in the brood, inhabiting four forests differing in food availability and ectoparasite prevalence. We measured lipid peroxidation (malondialdehyde; MDA) as a marker of oxidative damage, total antioxidant capacity (Trolox-equivalent antioxidant capacity; TEAC) and antioxidant enzymatic activity (catalase, glutathione S-transferase, glutathione peroxidase) in blood samples. The glutathione peroxidase (GPX) activity differed among the forests, being the highest in the pine forest and the lowest in a mixed oak (Quercus) forest in the most humid area. Lipid peroxidation was higher in larger nestlings, suggesting higher oxidative damage with an increasing growth rate. Neither brood size, laying date, nor ectoparasites were related to the oxidative status of nestlings. These results suggest that nest rearing conditions might shape the oxidative status of birds, having consequences for habitat-dependent variation in regulation of oxidative status.

Variation in parasitoidism of Protocalliphora azurea (Diptera: Calliphoridae) by Nasonia vitripennis (Hymenoptera: Pteromalidae) in Spain.

Parasitoid wasps may act as hyperparasites and sometimes regulate the populations of their hosts by a top-down dynamic. Nasonia vitripennis (Walker, 1836) is a generalist gregarious parasitoid that parasitizes several host flies, including the blowfly Protocalliphora Hough, 1899 (Diptera, Calliphoridae), which in turn parasitizes bird nestlings. Nonetheless, the ecological factors underlying N. vitripennis prevalence and parasitoidism intensity on its hosts in natural populations are poorly understood. We have studied the prevalence of N. vitripennis in Protocalliphora azurea (Fallén, 1817) puparia parasitizing wild populations of pied flycatcher (Ficedula hypoleuca) and blue tit (Cyanistes caeruleus) birds in two Mediterranean areas in central and southern Spain. We found some evidence that the prevalence of N. vitripennis was higher in moist habitats in southern Spain. A host-dependent effect was found, since the greater the number of P. azurea puparia, the greater the probability and rate of parasitoidism by the wasp. Our results also suggest that N. vitripennis parasitizes more P. azurea puparia in blue tit nests than in pied flycatcher nests as a consequence of a higher load of these flies in the former. Based on the high prevalence of N. vitripennis in P. azurea puparia in nature, we propose that this wasp may regulate blowfly populations, with possible positive effects on the reproduction of both bird species.