Rothschild, E. | bioRxiv Science

bioRxiv2025

Rapid Adaptation to Road Salts in a Freshwater Microbial Eukaryote

Humans are changing habitat for wildlife in myriad ways and for populations to persist, they must adapt to this change. In parts of the world that experience snow and ice, road salts are often used to make driving safer in the winter. Runoff from these roads increases the salinity in nearby bodies of water, which has been shown to have detrimental physiological and ecological effects in freshwater ecosystems; however, the evolutionary consequences of salinization remain unclear. Tetrahymena are microbial eukaryotes that live in freshwater habitats and serve as an important link in the microbial food loop. In this study, we test how T. thermophila can evolve in response to increasing concentrations of road salts in their environment. Using experimental evolution, we found that T. thermophila adapt quickly to survive and grow better in increasing salinity. However, populations adapted to the highest salt concentrations experience fitness tradeoffs in salt-free environments. These results demonstrate the rapidity with which microbial populations can respond to anthropogenic changes to their environment, yet highlight the potential costs associated with this adaptation.

evolutionary biology↗

bioRxiv2023

Understanding the Divergent Evolution and Epidemiology of H3N8 Influenza Viruses in Dogs and Horses

Cross-species virus transmission events can lead to dire public health emergencies in the form of epidemics and pandemics. One example in animals is the emergence of the H3N8 equine influenza virus (EIV), first isolated in 1963 in Miami, Florida, USA, after emerging among horses in South America. In the early 21st century the American lineage of EIV diverged into two Florida clades that persist today, while an EIV transferred to dogs around 1999 and gave rise to the H3N8 canine influenza virus (CIV), first reported in 2004. Here, we compare CIV in dogs and EIV in horses to reveal their host-specific evolution, to determine the sources and connections between significant outbreaks, and to gain insight into the factors controlling their different evolutionary fates. H3N8 CIV only circulated in North America, was geographically restricted after the first few years, and went extinct in 2016. Of the two EIV Florida clades, clade 1 circulates widely and shows frequent transfers between the USA and South America, Europe and elsewhere, while clade 2 was globally distributed early after it emerged, but since about 2018 has only been detected in Central Asia. Any potential zoonotic threat of these viruses to humans can only be determined with an understanding of its natural history and evolution. Our comparative analysis of these three viral lineages reveals distinct patterns and rates of sequence variation yet with similar overall evolution between clades, suggesting epidemiological intervention strategies for possible eradication of H3N8 EIV. (242 words) IMPORTANCEThe emergence of viruses in new hosts is a threat to human and animal health. The H3N8 equine influenza virus (EIV) emerged in 1963 by transfer of an avian influenza virus, and the H3N8 canine influenza virus (CIV) subsequently emerged in 1999 when EIV transferred to dogs. H3N8 CIV persistently circulated in only a few locations in the USA, and has not been detected since 2016. In the same period H3N8 EIV has circulated as two separate clades, one in North America and other regions of the world, while the other currently appears to be found only in Central Asia. By comparing the hosts, epidemiology, and evolution of these influenza viruses we explain how these lineages had different evolutionary fates, and show why elucidating these evolutionary processes is key to understanding zoonotic disease and viral emergence. (137 words)

evolutionary biology↗