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’.

No abstract

Many taxa, from plants to zooplankton, produce long-lasting dormant propagules capable of temporal dispersal. In some cases, propagules can persist for decades or even centuries before emerging from seed and egg banks. Despite impressive longevity, relatively little is known about how the chemical environment experienced before or during dormancy affects the fate and performance of individuals. This study examines the hatching rate and developmental success of Daphnia hatched from diapausing eggs isolated from sediments from four lakes that experienced varying levels of metal contamination. Two hundred seventy-three animals were hatched from lake sediments deposited over the past century. Hatching rate was negatively influenced by metal contamination and sediment age. There was a robust positive relationship between sediment metal concentrations and juvenile mortality in Daphnia hatching from those sediments. The negative effect of metals on Daphnia hatching and juvenile survival may stem from metal bioaccumulation, genetic effects, or reduced maternal investment in diapausing embryos. Regardless of the specific mechanism driving this trend, exposure to metals may impose strong selection on Daphnia diapausing egg banks.

BackgroundNonnative Phragmites australis (common reed) is one of the most intensively researched and managed invasive plant species in the United States, yet as with many invasive species, our ability to predict, control or understand the consequences of invasions is limited. Rapid spread of dense Phragmites monocultures has prompted efforts to limit its expansion and remove existing stands. Motivation for large-scale Phragmites eradication programs includes purported negative impacts on native wildlife, a view based primarily on observational results. We took an experimental approach to test this assumption, estimating the effects of nonnative Phragmites australis on a native amphibian.Methodology/Principal FindingsConcurrent common garden and reciprocal transplant field experiments revealed consistently strong positive influences of Phragmites on Rana catesbeiana (North American bullfrog) larval performance. Decomposing Phragmites litter appears to contribute to the effect.Conclusions/SignificancePositive effects of Phragmites merit further research, particularly in regions where both Phragmites and R. catesbeiana are invasive. More broadly, the findings of this study reinforce the importance of experimental evaluations of the effects of biological invasion to make informed conservation and restoration decisions.