Altered within- and between-host transmission under coinfection underpin parasite co-occurrence patterns in the wild

Interactions among parasite species coinfecting the same host individual can have far reaching consequences for parasite ecology and evolution. How these within-host interactions affect epidemics may depend on two non-exclusive mechanisms: parasite growth and reproduction within hosts, and parasite transmission between hosts. Yet, how these two mechanisms operate under coinfection, and how sensitive they are to the composition of the coinfecting parasite community, remains poorly understood. Here, we test the hypothesis that the relationship between within- and between-host transmission of the fungal pathogen, Phomopsis subordinaria, is affected by co-occurring parasites infecting the host plant, Plantago lanceolata. We conducted a field experiment manipulating the parasite community of transmission source plants, then tracked P. subordinaria within-host transmission, as well as between-host transmission to naïve recipient plants. We find that coinfection with the powdery mildew pathogen, Podosphaera plantaginis, causes increased between-host transmission of P. subordinaria by affecting the number of infected flower stalks in the source plants, resulting from altered auto-infection. In contrast, coinfection with viruses did not have an effect on either within- or between-host transmission. We then analyzed data on the occurrence of P. subordinaria in 2018 and the powdery mildew in a multi-year survey data set from natural host populations to test whether the positive association predicted by our experimental results is evident in field epidemiological data. Consistent with our experimental findings, we observed a positive association in the occurrence of P. subordinaria and historical powdery mildew persistence. Jointly, our experimental and epidemiological results suggest that within- and between-host transmission of P. subordinaria depends on the identity of coinfecting parasites, with potentially far-reaching effects on disease dynamics and parasite co-occurrence patterns in wild populations.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10682-022-10182-9.

Carrier detection in X-linked retinitis pigmentosa

X-linked retinitis pigmentosa (XLRP) is manifested in affected males in their first decade and results in blindness by the third or fourth decade. Carrier detection is difficult since most carrier females show no or only equivocal signs well into or beyond their reproductive years. The genes, or the mutations causing RP have not been identified but at least two have been localised to the short arm of the X chromosome provisionally named RP2 and RP3. Identifying inheritance of one or other of these genes must be done by linkage in families using close, informative DNA markers. Here we report the localisation of a highly informative polymerase chain reaction (PCR) detectable microsatellite marker DXS538 using a previously studied family with X-linked RP3 in which recombination had occurred in the region of importance. The DXS538 dinucleotide repeat locus was previously localised to Xp21.1-p11.21 to study RP3 in one XLRP family. Using published RFLP data we narrowed the localisation of DXS538 to the region Xp21.1-p11.23. Thus DXS538 is now a convenient diagnostic tool, aiding carrier detection of XLRP in females, as shown in the family presented here.

Ethanol kinetics: extent of error in back extrapolation procedures

1. Plasma ethanol concentrations were measured in 24 male volunteers for 9 h after a single oral dose of 710 mg kg-1. 2. The rate of decline of the plasma ethanol concentration (k0; mean +/- s.d.), was 186 +/- 26 mg l-1 h-1. 3. In each individual, three elimination rates were used to back-extrapolate plasma ethanol concentrations over 3 and 5 h periods from observed values at 4 h and 6 h post-dosing assuming zero-order kinetics. The extrapolated values were then compared with the observed concentrations. 4. Using the mean k0 values for the subjects the mean error in back extrapolation was small but highly variable. The variability in the error increased with the length of the extrapolation period. 5. When a k0 value of 150 mg l-1 h-1 (a value often cited as a population mean) was used for back extrapolation this resulted in significant under-estimation of actual values whereas the use of a k0 value of 238 mg l-1 h-1 (the highest value observed in the present study) resulted in significant over-estimation of actual values. 6. These results indicate that because the kinetics of ethanol are associated with substantial inter-subject variability the use of a single slope value to back calculate blood concentrations can give rise to considerable error.

Linkage heterogeneity between X-linked retinitis pigmentosa and a map of 10 RFLP loci

In nine families in which X-linked retinitis pigmentosa (XLRP) is segregating, the lod scores of XLRP in a map of 10 RFLP loci were obtained by multipoint linkage analysis. The XLRP locus was located telomeric to DXS7 in seven of the families and centromeric to DXS7 in two of the families. Under the hypothesis of two XLRP loci, a heterogeneity (admixture) test was performed, providing significant evidence of heterogeneity in XLRP (P less than .01). No correlation was detected between the clinical manifestations of XLRP and the two different disease loci.

Localization of the X-linked retinitis pigmentosa locus between DXS7 and DXS84 in a family showing tapetal reflex in heterozygotes

The linkage relationships between the X-linked retinitis pigmentosa (XLRP) locus and seven Xp loci: DXS14, DXS7, OTC, DXS141, DXS148, DXS84 and DXS206 were analysed in one large family in which the heterozygotes exhibited the tapetal reflex. Evidence drawn from two-point and multipoint linkage analysis and a number of triply informative crossovers suggests that the XLRP locus in this family is between DXS7 and DXS84. The putative order of loci on the short arm of the X chromosome is: centromere - DXS14 - DXS7 - OTC - XLRP/DXS141 - DXS148 - DXS84 - DXS206 - telemere.