Infectious Offspring: How Birds Acquire and Transmit an Avian Polyomavirus in the Wild

Detailed patterns of primary virus acquisition and subsequent dispersal in wild vertebrate populations are virtually absent. We show that nestlings of a songbird acquire polyomavirus infections from larval blowflies, common nest ectoparasites of cavity-nesting birds, while breeding adults acquire and renew the same viral infections via cloacal shedding from their offspring. Infections by these DNA viruses, known potential pathogens producing disease in some bird species, therefore follow an ‘upwards vertical’ route of an environmental nature mimicking horizontal transmission within families, as evidenced by patterns of viral infection in adults and young of experimental, cross-fostered offspring. This previously undescribed route of viral transmission from ectoparasites to offspring to parent hosts may be a common mechanism of virus dispersal in many taxa that display parental care

Host Responses in Life-History Traits and Tolerance to Virus Infection in Arabidopsis thaliana

Knowing how hosts respond to parasite infection is paramount in understanding the effects of parasites on host populations and hence host–parasite co-evolution. Modification of life-history traits in response to parasitism has received less attention than other defence strategies. Life-history theory predicts that parasitised hosts will increase reproductive effort and accelerate reproduction. However, empirical analyses of these predictions are few and mostly limited to animal-parasite systems. We have analysed life-history trait responses in 18 accessions of Arabidopsis thaliana infected at two different developmental stages with three strains of Cucumber mosaic virus (CMV). Accessions were divided into two groups according to allometric relationships; these groups differed also in their tolerance to CMV infection. Life-history trait modification upon virus infection depended on the host genotype and the stage at infection. While all accessions delayed flowering, only the more tolerant allometric group modified resource allocation to increase the production of reproductive structures and progeny, and reduced the length of reproductive period. Our results are in agreement with modifications of life-history traits reported for parasitised animals and with predictions from life-history theory. Thus, we provide empirical support for the general validity of theoretical predictions. In addition, this experimental approach allowed us to quantitatively estimate the genetic determinism of life-history trait plasticity and to evaluate the role of life-history trait modification in defence against parasites, two largely unexplored issues

Sampling frequency and accuracy of SPM flux estimates in two contrasted drainage basins

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Helper contributions to antiparasite behavior in the cooperatively breeding bell miner

Cooperatively breeding bell miners (Manorina melanophrys) have numerous male helpers assisting at multiple nests. Helpers are often related to the brood they aid, consistent with kin selection. However, there are also unrelated helpers for which other direct fitness benefits are likely to accrue. Bell miner nestlings can become infested by the larvae of a parasitic fly (Passeromyia indecora), which reduce growth and can be fatal. We investigated the amount of time that breeding pairs and helpers closely inspected nests and preened nestlings, behaviors apparently directed at detecting and removing parasites, a form of helping previously unstudied in a cooperative bird. Female breeders provided the greatest antiparasite effort, with breeding males and helpers not differing in effort regardless of their relatedness to the breeding female or brood. We also experimentally infested nests with nonparasitic flies and larvae. All individuals removed the introduced "parasites" if and when they encountered them. Compared with control sessions, inspection effort increased for all birds immediately after the experimental infestations, but only for a short, 5-min period. Further, we detected no changes in helper antiparasite behaviors after the temporary experimental removal of either breeding females or males. Such consistent helping behavior, independent of relatedness and potential audience effects, suggests that antiparasite behavior in bell miners is not particularly kin directed or operating as a signal of helper quality. Our results instead suggest that helper antiparasite effort appears to represent adaptive investment in the welfare of the brood, consistent with direct fitness benefits from group augmentation. Copyright 2008, Oxford University Press.