Dale, A. S. | bioRxiv Science

bioRxiv2023

Periodic shifts in viral load increase risk of spillover from bats

Prediction and management of zoonotic pathogen spillover requires an understanding of infection dynamics within reservoir host populations. Transmission risk is often assessed using prevalence of infected hosts, with infection status based on the presence of genomic material. However, detection of viral genomic material alone does not necessarily indicate the presence of infectious virus, which could decouple prevalence from transmission risk. We undertook a multi-faceted investigation of Hendra virus shedding in Pteropus bats, combining insights from virus isolation, viral load proxies, viral prevalence, and longitudinal patterns of shedding, from 6,151 samples. In addition to seasonal and interannual fluctuation in prevalence, we found evidence for periodic shifts in the distribution of viral loads. The proportion of bats shedding high viral loads was higher during peak prevalence periods during which spillover events were observed, and lower during non-peak periods when there were no spillovers. We suggest that prolonged periods of low viral load and low prevalence reflect prolonged shedding of non-infectious RNA, or viral loads that are insufficient or unlikely to overcome dose barriers to spillover infection. These findings show that incorporating viral load (or proxies of viral load) into longitudinal studies of virus excretion will better inform predictions of spillover risk than prevalence alone. Significance statementWe present a comprehensive analysis of a high-profile bat-virus system (Hendra virus in Australian flying-foxes) to demonstrate that both prevalence and viral loads can shift systematically over time, resulting in concentrated periods of increased spillover risk when prevalence and viral loads are high. We further suggest that prolonged periods of low-prevalence, low-load shedding may not reflect excretion of infectious virus, resolving the outstanding puzzle of why spillovers have not been observed during periods of low off-season prevalence in subtropical Australia, or more frequently in tropical Australia despite consistent low-prevalence shedding. The consideration of viral loads (or proxies of viral load) along with prevalence may improve risk inference from longitudinal surveys of zoonotic viruses across wildlife reservoir hosts.

ecology↗

bioRxiv2022

Re-assessing niche partitioning in MacArthur's Warblers: foraging behavior, morphology, and diet metabarcoding in a phylogenetic context

Due in large part to MacArthurs classic 1958 paper, wood-warblers (Parulidae) are ecological icons, textbook protagonists of a story of competition and niche partitioning. As the story goes, subtle differences in foraging behavior are the principal means by which these nearly morphologically indistinguishable species are able to co-occur and avoid extinction. Yet, MacArthurs study was in fact quite limited in scale, and he said little about the relevance of evolution to the study system. Here, we reassess MacArthurs conclusions across an expanded set of syntopic warbler species in a forest in northern New York. We combine morphometrics, quantitative foraging data, and fecal metabarcoding--a direct measure of warbler diet--to study competition and niche partitioning in an evolutionary framework. We find close and kinematically realistic relationships between morphology and foraging behavior, but little connection between warbler ecomorphology and the 2,882 invertebrate taxa detected in their diets. Instead, diet remains phylogenetically conserved--closely related warblers eat similar suites of invertebrates, regardless of where they forage. Finally, we present evidence that these species not only partition niche space in the present day, but that competition has shaped their behaviors over evolutionary time. MacArthur (1958) may have drawn a few incorrect inferences, but his overall conclusion that evolved differences in foraging position, driven by competition among close relatives, does indeed appear to be a key reason these warblers can occur in such close sympatry.

evolutionary biology↗