Artificial light at night amplifies seasonal relapse of haemosporidian parasites in a widespread songbird

Abstract

14Urban habitats can shape interactions between hosts and parasites by altering within-host 15 processes such as resistance. Artificial light at night is common in urban environments, and 16 chronic exposure can impair host immunity in ways that may increase infection. However, 17 studies of causal links between this stressor, immunity, and infection dynamics are rare, 18 particularly in migratory animals. Here, we experimentally tested how artificial light at night 19 affects cellular immunity and haemosporidian parasite intensity across the annual cycle of 20 migrant and resident subspecies of the dark-eyed junco (Junco hyemalis). We monitored an 21 experimental group exposed to light at night and a control group under nighttime darkness as 22 they passed through short days simulating early spring to longer days simulating the breeding 23 season, followed by fall migration. Using generalized additive models, we show that artificial 24 light at night increased inflammation, and leukocyte counts were greatest in early spring and fall. 25At the start of the experiment, few birds had active infections based on microscopy, but PCR 26 revealed many birds had chronic infections. Artificial light at night increased parasitemia across 27 the annual cycle, with strong peaks in spring and fall that were largely absent in control birds. As 28 birds were kept in indoor aviaries to prevent vector exposure, this increased parasitemia indicates 29 relapse of chronic infection during costly life history stages (i.e., reproduction). Although the 30 immunological and parasitological time series were in phase for control birds, cross-correlation 31 analyses also revealed artificial light at night desynchronized leukocyte profiles and parasitemia, 32 which could suggest a general exaggerated inflammatory response. Our study shows how a 33 common anthropogenic influence can shape within-host processes to affect infection dynamics. 34 35 As suburban and urban habitats expand globally, certain species are attracted to these 36 environments owing to a combination of altered microclimate, predation risk, and resource 37 availability [1,2]. Such changes in biotic and abiotic conditions can have cascading and complex 38 effects on wildlife [3,4]. When considering infectious disease, urban habitats can shape the 39 interactions between hosts and parasites by altering within-host processes such as resistance or 40 tolerance [5]. Understanding how urbanization affects these processes is especially important, as 41 it can facilitate novel cross-species transmission opportunities between various host species [6]. 42 One aspect of urban habitats that could have strong effects on these within-host processes 43 is artificial light at night (ALAN). By altering animal circadian rhythms, ALAN can cause a suite 44 of physiological changes relevant to infection [7]. In particular, chronic exposure to ALAN can 45 suppress various aspects of host immune function, including cellular response and microbial 46killing ability [8,9]. Prolonged ambient lig...

Seasonal associations with light pollution trends for nocturnally migrating bird populations

“…At the individual level, ALAN can disrupt biological rhythm, behavior, and physiology for both migratory and resident species. Examples include adverse effects on body mass and reproductive success (Malek & Haim, 2019), disease tolerance (Kernbach et al, 2021; Malek & Haim, 2019), immunity and parasitism (Becker et al, 2020), intestinal microbiota (Jiang et al, 2020), breeding phenology (Dominoni et al, 2020; Kempenaers et al, 2010), migration phenology (Smith et al, 2021), foraging activity (Amichai & Kronfeld‐Schor, 2019), and sleeping behavior (Aulsebrook et al, 2020; Sun et al, 2017).…”

Exploring the thermal limits of malaria transmission in the western Himalaya

“…infection risk increases with elevation; however, most of these infections were submicroscopic in high elevation in breeding season (April-May). This contrasts with studies on the ecology of haemosporidia in temperate regions where birds with latent infections return to the breeding grounds and experience a relapse, with increase in parasites visible in the blood stages (Applegate, 1970;Becker et al, 2020). In general, We used climate models to interrogate how changing temperature from 2021 to 2040 could potentially lead to an expansion of the temperature range conducive for malaria transmission in highelevation zones.…”

Reactivation of latent infections with migration shapes population-level disease dynamics

“…Such resources could dampen or amplify pathogen relapse at spring departure depending on their nutritional quality or effects on host density and crowding [75]. Other stressors in urban habitats, such as artificial light at night, could further amplify the likelihood of relapse [76]. These consequences of urban habituation could be especially relevant for human health in the context of wildlife reservoirs of relapsing zoonoses, such as flying foxes and henipaviruses [77].…”