Immune responses in fruit flies could help us understand and predict the susceptibility of humans to novel viruses. A recent study published in Evolution Letters investigated whether host species within the Drosophilidae family exhibit similar patterns of susceptibility across a diverse range of viruses.
By analyzing infections in 35 species with 11 virus isolates, the researchers from the University of Exeter uncovered a striking pattern — host susceptibility to one virus often correlated positively with susceptibility to others.
These findings provided insights into broader evolutionary trends in host-virus interactions and suggested that phylogenetic relationships could help anticipate how new viral threats may spread.
Study: Positive correlations in susceptibility to a diverse panel of viruses across Drosophilidae host species. Image Credit: Tomasz Klejdysz/Shutterstock.com
Host-Virus Interactions
Viruses frequently cross species barriers, leading to unpredictable disease outbreaks in animals and humans. Past research has shown that closely related species often share similar susceptibilities to certain viruses, but little is known about whether these patterns extend across different viral families.
Most studies focus on single host-virus interactions, overlooking the potential for broader correlations in viral susceptibility.
While some viruses exploit conserved host pathways, others face host-specific resistance mechanisms. Insects, particularly fruit flies (Drosophilidae), provide a valuable model for studying these evolutionary dynamics.
Drosophila species display diverse immune responses influenced by both generalized antiviral defenses and virus-specific adaptations.
However, the dearth of research into phylogenetic correlations across a wide range of viruses leaves a crucial gap in understanding host-virus evolution. Investigating these correlations could help determine whether susceptibility to one virus predicts susceptibility to others and provide insights into how viruses adapt to new hosts.
The Current Study
To examine phylogenetic patterns in viral susceptibility, the researchers infected 35 species of Drosophilidae with 11 virus isolates from seven distinct virus species belonging to six viral families. The study included a mix of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) viruses, ensuring a diverse representation of viral infection strategies.
At two days post-infection, the researchers quantified viral loads using quantitative reverse transcription polymerase chain reaction (qRT-PCR). This time point was chosen based on prior studies, ensuring that sufficient viral replication had occurred without significant infection-related mortality.
To assess phylogenetic correlations, the researchers analyzed the viral load data using Bayesian mixed models, incorporating host phylogenies to measure the degree of correlation in susceptibility between viruses.
The statistical models also accounted for potential confounding factors, including host size and phylogenetic relatedness. The researchers also tested whether the strength of correlations differed between viruses from the same species, family, or different families.
By structuring the analysis across multiple evolutionary scales, they aimed to determine whether generalized host susceptibility indicated positive correlations about other viral infections or whether virus-specific interactions weaken these patterns.
Major Findings
The study found that susceptibility to different viruses was often positively correlated across Drosophilidae host species. Almost all correlation estimates (54 out of 55) were positive, with 30 being statistically significant. No negative correlations were observed, indicating that resistance to one virus did not come at the cost of increased vulnerability to another.
Furthermore, a strong pattern emerged where viruses of the same species showed the highest correlations in host susceptibility, followed by those within the same family. Correlations between viruses from different families were weaker but still generally positive. These results suggested that broad genetic factors influence viral susceptibility, even for distantly related viruses.
Interestingly, some unexpected correlations were also observed between highly diverged viruses, such as between a DNA virus (IIV6) and RNA viruses (Dicistroviruses). This suggested that certain host immune pathways might influence susceptibility to diverse viral types. However, some virus pairs showed no correlation, indicating that species-specific immune adaptations also play a role.
The absence of negative correlations challenges the idea that host evolution involves strict trade-offs between resistance to different viruses. Instead, increased resistance to one virus was generally associated with increased resistance to others.
The findings suggested that host-virus interactions follow predictable evolutionary patterns but also highlighted the complexity of immune defenses.
One limitation of the study was that environmental factors, such as diet and temperature, that could influence viral susceptibility could not be entirely ruled out in the study design. Additionally, the study relied on a single method of viral inoculation, which may not fully capture natural transmission dynamics.
Conclusions
Overall, the study provided strong evidence that viral susceptibility in the fruit fly family Drosophilidae follows predictable evolutionary patterns, with closely related species showing similar responses across diverse viruses.
The findings suggested that phylogenetic relationships can be used to infer potential susceptibility to novel viruses, though individual host adaptations remain important.
Understanding these patterns can improve predictions of virus emergence, offering valuable insights for both evolutionary biology and disease ecology.
Fruit Fly Study Sheds Light on Virus Susceptibility and Host Evolution