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Rhabdoviruses in two species of Drosophila: vertical transmission and a recent sweep.

Longdon B, Wilfert L, Obbard DJ, Jiggins FM - Genetics (2011)

Bottom Line: Males transmit lower viral titers through sperm than females transmit through eggs, and a lower proportion of their offspring become infected.In natural populations of D. obscura in the United Kingdom, we found that 39% of flies were infected and that the viral population shows clear evidence of a recent expansion, with extremely low genetic diversity and a large excess of rare polymorphisms.In light of this and earlier studies of a related virus in D. melanogaster, we conclude that vertically transmitted rhabdoviruses may be common in insects and that these host-parasite interactions can be highly dynamic.

View Article: PubMed Central - PubMed

Affiliation: Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK. b.longdon@ed.ac.uk

ABSTRACT
Insects are host to a diverse range of vertically transmitted micro-organisms, but while their bacterial symbionts are well-studied, little is known about their vertically transmitted viruses. We have found that two sigma viruses (Rhabdoviridae) recently discovered in Drosophila affinis and Drosophila obscura are both vertically transmitted. As is the case for the sigma virus of Drosophila melanogaster, we find that both males and females can transmit these viruses to their offspring. Males transmit lower viral titers through sperm than females transmit through eggs, and a lower proportion of their offspring become infected. In natural populations of D. obscura in the United Kingdom, we found that 39% of flies were infected and that the viral population shows clear evidence of a recent expansion, with extremely low genetic diversity and a large excess of rare polymorphisms. Using sequence data we estimate that the virus has swept across the United Kingdom within the past ∼11 years, during which time the viral population size doubled approximately every 9 months. Using simulations based on our lab estimates of transmission rates, we show that the biparental mode of transmission allows the virus to invade and rapidly spread through populations at rates consistent with those measured in the field. Therefore, as predicted by our simulations, the virus has undergone an extremely rapid and recent increase in population size. In light of this and earlier studies of a related virus in D. melanogaster, we conclude that vertically transmitted rhabdoviruses may be common in insects and that these host-parasite interactions can be highly dynamic.

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Viral titers in embryos that were infected either maternally or paternally. Titers were measured as in Figure 2. Error bars show the standard deviation of technical replicates.
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fig3: Viral titers in embryos that were infected either maternally or paternally. Titers were measured as in Figure 2. Error bars show the standard deviation of technical replicates.

Mentions: To investigate the viral titers transmitted through eggs and sperm, the viral titer in early stage embryos was examined by qRT-PCR. Virgin females and males (with either the female or the male being infected) were placed together and allowed to lay eggs in bottles with a small amount of yeast paste on the surface of apple or grape juice agar. Embryos were collected twice daily and homogenized in Trizol (Invitrogen), using a microscope to ensure that the embryo was successfully crushed. Thirty embryos were collected for each cross. RNA was extracted and reverse-transcribed (see above), and qRT-PCR was used to measure the viral titer relative to an endogenous control (RpL32) using the delta delta CT method. If one or two of the technical replicates failed to amplify virus, these were given CT values of 40 for the statistical analysis. Any samples in which all three technical replicates failed to amplify using the viral PCR primers were classed as uninfected and excluded from the statistical analysis (i.e., the viral titers of infected embryos were compared). These samples are still present in Figure 2 and Figure 3. Two data points were removed from the DAffSV cross where the cDNA was of poor quality (RpL32 CT values >30). This did not affect the outcome of the analysis.


Rhabdoviruses in two species of Drosophila: vertical transmission and a recent sweep.

Longdon B, Wilfert L, Obbard DJ, Jiggins FM - Genetics (2011)

Viral titers in embryos that were infected either maternally or paternally. Titers were measured as in Figure 2. Error bars show the standard deviation of technical replicates.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3120147&req=5

fig3: Viral titers in embryos that were infected either maternally or paternally. Titers were measured as in Figure 2. Error bars show the standard deviation of technical replicates.
Mentions: To investigate the viral titers transmitted through eggs and sperm, the viral titer in early stage embryos was examined by qRT-PCR. Virgin females and males (with either the female or the male being infected) were placed together and allowed to lay eggs in bottles with a small amount of yeast paste on the surface of apple or grape juice agar. Embryos were collected twice daily and homogenized in Trizol (Invitrogen), using a microscope to ensure that the embryo was successfully crushed. Thirty embryos were collected for each cross. RNA was extracted and reverse-transcribed (see above), and qRT-PCR was used to measure the viral titer relative to an endogenous control (RpL32) using the delta delta CT method. If one or two of the technical replicates failed to amplify virus, these were given CT values of 40 for the statistical analysis. Any samples in which all three technical replicates failed to amplify using the viral PCR primers were classed as uninfected and excluded from the statistical analysis (i.e., the viral titers of infected embryos were compared). These samples are still present in Figure 2 and Figure 3. Two data points were removed from the DAffSV cross where the cDNA was of poor quality (RpL32 CT values >30). This did not affect the outcome of the analysis.

Bottom Line: Males transmit lower viral titers through sperm than females transmit through eggs, and a lower proportion of their offspring become infected.In natural populations of D. obscura in the United Kingdom, we found that 39% of flies were infected and that the viral population shows clear evidence of a recent expansion, with extremely low genetic diversity and a large excess of rare polymorphisms.In light of this and earlier studies of a related virus in D. melanogaster, we conclude that vertically transmitted rhabdoviruses may be common in insects and that these host-parasite interactions can be highly dynamic.

View Article: PubMed Central - PubMed

Affiliation: Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK. b.longdon@ed.ac.uk

ABSTRACT
Insects are host to a diverse range of vertically transmitted micro-organisms, but while their bacterial symbionts are well-studied, little is known about their vertically transmitted viruses. We have found that two sigma viruses (Rhabdoviridae) recently discovered in Drosophila affinis and Drosophila obscura are both vertically transmitted. As is the case for the sigma virus of Drosophila melanogaster, we find that both males and females can transmit these viruses to their offspring. Males transmit lower viral titers through sperm than females transmit through eggs, and a lower proportion of their offspring become infected. In natural populations of D. obscura in the United Kingdom, we found that 39% of flies were infected and that the viral population shows clear evidence of a recent expansion, with extremely low genetic diversity and a large excess of rare polymorphisms. Using sequence data we estimate that the virus has swept across the United Kingdom within the past ∼11 years, during which time the viral population size doubled approximately every 9 months. Using simulations based on our lab estimates of transmission rates, we show that the biparental mode of transmission allows the virus to invade and rapidly spread through populations at rates consistent with those measured in the field. Therefore, as predicted by our simulations, the virus has undergone an extremely rapid and recent increase in population size. In light of this and earlier studies of a related virus in D. melanogaster, we conclude that vertically transmitted rhabdoviruses may be common in insects and that these host-parasite interactions can be highly dynamic.

Show MeSH
Related in: MedlinePlus