Pathogen evolution following spillover from a resident to a migrant host population depends on interactions between host pace of life and tolerance to infection

Abstract

Changes to migration routes and phenology create novel contact patterns among hosts and pathogens. These novel contact patterns can lead to pathogens spilling over between resident and migrant populations. Predicting the consequences of such pathogen spillover events requires understanding how pathogen evolution depends on host movement behaviour. Following spillover, pathogens may evolve changes in their transmission rate and virulence phenotypes because different strategies are favoured by resident and migrant host populations. There is conflict in current theoretical predictions about what those differences might be. Some theory predicts lower pathogen virulence and transmission rates in migrant populations because migrants have lower tolerance to infection. Other theoretical work predicts higher pathogen virulence and transmission rates in migrants because migrants have more contacts with susceptible hosts. We aim to understand how differences in tolerance to infection and host pace of life act together to determine the direction of pathogen evolution following pathogen spillover from a resident to a migrant population. We constructed a spatially implicit model in which we investigate how pathogen strategy changes following the addition of a migrant population. We investigate how differences in tolerance to infection and pace of life between residents and migrants determine the effect of spillover on pathogen evolution and host population size. When the paces of life of the migrant and resident hosts are equal, larger costs of infection in the migrants lead to lower pathogen transmission rate and virulence following spillover. When the tolerance to infection in migrant and resident populations is equal, faster migrant paces of life lead to increased transmission rate and virulence following spillover. However, the opposite can also occur: when the migrant population has lower tolerance to infection, faster migrant paces of life can lead to decreases in transmission rate and virulence. Predicting the outcomes of pathogen spillover requires accounting for both differences in tolerance to infection and pace of life between populations. It is also important to consider how movement patterns of populations affect host contact opportunities for pathogens. These results have implications for wildlife conservation, agriculture and human health.

Effect of resistant compartment on pathogen strategy in partially migratory populations

“…In this paper, we found that shorter infection durations can be caused by higher recovery rates. In past work, we have shown that shorter duration caused by higher mortality also leads to a more virulent pathogen strategy [16]. Second, hosts that are better adapted to cope with pathogen infection can lead to higher virulence.…”

“…via hosts maintaining immunity for longer (lower immunity lost µ in our model), or can occur if hosts tolerate infection more (i.e. experience lower mortality) [16]. Third, the abundance of susceptible individuals available to become infected has a stronger effect on virulence than loss of infected individuals.…”

“…experience lower mortality) [16]. Third, the abundance of susceptible individuals available to become infected has a stronger effect on virulence than loss of infected individuals.…”

“…Furthermore, properties of host populations can determine which pathogen strategies lead to the highest pathogen fitness [17]. For example, both the degree of tolerance that hosts have to pathogens as well as host pace of life can shape pathogen strategy [16].…”

“…Although much of the work exploring host-pathogen interactions in migratory species has focused on how pathogens shape host migration [14], we are increasingly learning about how host seasonal migration can shape pathogen virulence [15]. Recent theory shows that sedendary and migratory hosts can favor different pathogen virulence strategies [16]. Furthermore, properties of host populations can determine which pathogen strategies lead to the highest pathogen fitness [17].…”