Résumé
The geographical distribution and diversity of viruses can differ between cultivated areas and adjacent natural environments, raising questions about the interplay between plant diversity and the species richness and prevalence of the phytoviruses. As both the amplification and the dilution of viral species richness due to increasing host diversity have been theorized and observed, a deeper understanding of how plant-viruses interact in natural environments is needed to explore how host availability conditions viral diversity and distributions. This study explores interactions of viruses from the Mastrevirus genus (family Geminiviridae) with hosts from the Poaceae family across ten sites from three contrasting ecosystems on La Réunion. Among 273 plant pools, representing 61 Poales species, 15 Mastrevirus species were characterized from 22 hosts. We find a strong association of mastreviruses with hosts from agro-ecosystems and the absence of mastreviruses in subalpine areas, dominated by native plants. This suggests that all detected mastreviruses likely originated from viruses introduced through agricultural activities rather than being native to La Réunion. Analyses of the structure of the host plant-mastrevirus interaction network revealed a pattern of increasing viral richness with increasing host richness. Accounting for variations in the diversity of hosts across sites, we observed increasing viral niche occupancies with increasing host species richness. Virus realized richness at any given site is conditioned on the global capacity of the plant populations to host diverse mastreviruses. Whether this tendency is driven by synergy between viruses, or by an interplay between vector population and plant richness, remains to be established.