Abstract
Antarctica, one of the most isolated and extreme regions on Earth, hosts diverse bird species that share breeding and feeding habitats, facilitating interspecies transmission of pathogens. In this study, we investigated penguin siadenoviruses using cloacal swab samples collected from Antarctic penguins between 2017 and 2023 to explore their genetic diversity and evolutionary relationships. The complete hexon gene was obtained from Adélie penguins, while partial hexon and DNA polymerase sequences were detected in Adélie penguin (AP), chinstrap penguin (CP), and gentoo penguin (GP). Phylogenetic and molecular analysis identified multiple siadenoviruses classified into two distinct lineages, indicating ongoing viral evolution in this region. The hexon genes exhibited considerable genetic diversity caused by recombination and mutation, and predicted hypervariable regions (HVRs)-targets of neutralizing antibodies-showed significant structural differences among penguin siadenoviruses. These findings suggest that penguin siadenoviruses are not restricted to a single host species but may circulate among various penguin populations across the Antarctic region. This implies potential cross-infection between local and surrounding penguin populations. Although the predicted structural models showed limited accuracy due to the use of distant templates, the genetic and structural differences observed provide valuable insights into the adaptive evolution of these viruses. Our findings provide an important foundation for understanding viral transmission and evolution in Antarctic avifauna. Furthermore, findings from this study may guide early detection and risk assessment of emerging viral threats in Antarctica.