Human drivers of ecological and evolutionary dynamics in emerging and disappearing infectious disease systems

Abstract

Humans have contributed to the increased frequency and severity of emerging infectious diseases, which pose a significant threat to wild and domestic species, as well as human health. This review examines major pathways by which humans influence parasitism by altering (co)evolutionary interactions between hosts and parasites on ecological timescales. There is still much to learn about these interactions, but a few well-studied cases show that humans influence disease emergence every step of the way. Human actions significantly increase dispersal of host, parasite and vector species, enabling greater frequency of infection in naive host populations and host switches. Very dense host populations resulting from urbanization and agriculture can drive the evolution of more virulent parasites and, in some cases, more resistant host populations. Human activities that reduce host genetic diversity or impose abiotic stress can impair the ability of hosts to adapt to disease threats. Further, evolutionary responses of hosts and parasites can thwart disease management and biocontrol efforts. Finally, in rare cases, humans influence evolution by eradicating an infectious disease. If we hope to fully understand the factors driving disease emergence and potentially control these epidemics we must consider the widespread influence of humans on host and parasite evolutionary trajectories. This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’.

Resistance in persisting bat populations after white-nose syndrome invasion

“…The introduction of species to new regions is one such activity that exerts strong selective pressure [52,53], and the introduction of pathogens to novel host communities is no exception [26]. WNS has caused severe declines in North American bats (more than 90% mortality in several species) and has thereby exerted intense selective pressure on bat populations to evolve traits to persist with this pathogen.…”

“…It has been suggested that populations can undergo shifts in defence systems, either owing to negative frequencydependent selection or as pathogens change in response to host defences [25]. The introduction of pathogens to novel host communities provides an opportunity to understand the development of coevolutionary dynamics between hosts and pathogens [26].…”

Adaptation to fragmentation: evolutionary dynamics driven by human influences

“…These include environmental stochasticity (e.g. pathogen outbreaks [22], prey declines, fire) and demographic stochasticity due to random fluctuations in birth rate, death rate and sex ratios [23]. Fragmentation's ultimate effect on the population dynamics of a given species depends on the degree to which dispersal among fragments is impeded ( figure 1).…”

“…On the one hand, reduced gene flow among patches could maintain among-patch diversity, potentially facilitating local adaptation (see §3a). On the other hand, smaller populations likely have less adaptive variation and will eco-evolutionary feedbacks on other traits and correlated responses joint evolution of dispersal and other traits seed dormancy in non-dispersing morphs in Heterotheca latifolia [22] mating strategies in prairie chickens : larger clutch size and fewer nests [23]; evolution of stress resistance in Tetranychus urticae [24] genetic deterioration fitness loss herb: plants from smaller fragments had lower reproductive success in transplant experiments [25] rstb.royalsocietypublishing.org Phil. Trans.…”

The eco-evolutionary impacts of domestication and agricultural practices on wild species

“…In addition, parasite specialization on livestock can cause a homogenization of genetic structure across large geographical areas that raise the same domesticated species [54]. In addition, the transportation of livestock, feed or equipment can promote gene flow between pest populations among different agricultural areas or between natural and agricultural communities leading to hybridization [13,22,25,55]. On the other hand, long distance transportation can also create genetic bottlenecks in wild species.…”