Biology subjects

Ketterson, E. D.

Publications and source records attributed to Ketterson, E. D..

9 recordsLinked to original sources

bioRxiv2023

Determinants of spring migration departure dates in a New World sparrow: weather variables reign supreme

Numerous factors influence the timing of spring migration in birds, yet the relative importance of intrinsic and extrinsic variables on migration initiation remains unclear. To test for interactions among weather, migration distance, parasitism, and physiology in determining spring departure date, we used Dark-eyed Juncos (Junco hyemalis hyemalis) as a model migratory species known to harbor diverse and common haemosporidian parasites. Prior to spring migration departure from their wintering grounds in Indiana, USA, we quantified the intrinsic variables of fat, body condition (i.e., mass[~]tarsus residuals), physiological stress (i.e., ratio of heterophils to lymphocytes), cellular immunity (i.e., leukocyte composition and total count), migration distance (i.e., distance to the breeding grounds) using stable isotopes of hydrogen from feathers, and haemosporidian parasite intensity. We then attached nanotags to determine the timing of spring migration departure date using the Motus Wildlife Tracking System. We used additive Cox proportional hazard mixed models to test how risk of spring migratory departure was predicted by the combined intrinsic measures, along with meteorological predictors on the evening of departure (i.e., average wind speed and direction, relative humidity, and temperature). Model comparisons found that the best predictor of spring departure date was average nightly wind direction and a principal component combining relative humidity and temperature. Juncos were more likely to depart for spring migration on nights with largely southwestern winds and on warmer and drier evenings (relative to cooler and more humid evenings). Our results indicate that weather conditions at take-off are more critical to departure decisions than the measured physiological and parasitism variables.

ecology↗

bioRxiv2023

Movement-related drivers of exposure to West Nile virus by American robins (Turdus migratorius)

The ecological processes that determine how individual animals become hosts to zoonotic pathogens is a topic of rapidly growing interest. However, how such exposure is mediated by context (e.g., season, location), host behavior (e.g., migration distance) and host demographics is generally poorly understood. We evaluated seasonal exposure to West Nile Virus of American robins sampled in Indiana and compared our results to those of previous studies. Because robins that breed in Indiana are partial migrants (i.e., only a portion of the population migrates), we evaluated their probability of exposure to WNV as a function of whether they migrated or not and of their movement distance. We also tagged a subset of breeding robins with tracking devices to evaluate their potential to disperse the virus between Indiana and other regions of the continent. We found that robins that breed in Indiana are exposed to WNV at a higher rate than that detected in previous studies, but found no correlation between robin exposure and whether a robin migrated or not, nor with migration distance, season, sex, and breeding latitude (for robins overwintering in Indiana). Our tracking data indicate that robins that breed in Indiana migrate several hundred miles to overwinter in the southeastern US. The mean duration of their return to Indiana in spring is 10.3 days, which is less than the maximum infectious period found for robins in previous studies, suggesting that they have the capacity to move WNV long distances in spring. However, we still know little about the physiological capacity of robins to migrate while being infectious, which could inhibit the dispersal of the virus through robin migration. Future research on the physiological, ecological and behavioral factors mediating the exposure of birds to WNV will lend insight into the role that robins and other birds play in the transmission ecology of the virus.

ecology↗

bioRxiv2022

Novel Rickettsia spp. in two common overwintering North American passerines

American robins and dark-eyed juncos migrate across North America, but their contributions to arthropod-borne disease remain poorly characterized. We identified novel Rickettsia spp. in one wintering migrant per bird species related to bellii, transitional, and spotted fever group rickettsiae and suggest spring migration could disperse these pathogens hundreds-to-thousands of kilometers.

ecology↗

bioRxiv2021

Plasticity in female timing may explain current shifts in breeding phenology of a North American songbird

O_LIClimate change has driven changes in breeding phenology. Identifying the magnitude of phenological shifts and whether selection in response to climate change drives these shifts is key for determining species reproductive success and persistence in a changing world. C_LIO_LIWe investigated reproductive timing in a primarily sedentary population of the dark-eyed junco (Junco hyemalis) over 32 years. We predicted that juncos would breed earlier in warmer springs in response to selection favouring earlier breeding. C_LIO_LITo test this prediction, we compared the annual median date for reproductive onset (i.e., egg one date) to monthly spring temperatures and examined evidence for selection favouring earlier breeding and for plasticity in timing. C_LIO_LIEgg one dates occurred earlier over time, with the timing of breeding advancing up to 24 days over the 32-year period. Breeding timing also strongly covaried with maximum April temperature. We found significant overall selection favouring earlier breeding (i.e., higher relative fitness with earlier egg one dates) that became stronger over time, but strength of selection was not predicted by temperature. Lastly, individual females exhibited plastic responses to temperature across years. C_LIO_LIOur findings provide further evidence that phenotypic plasticity plays a crucial role in driving phenological shifts in response to climate change. For multi-brooded bird populations, a warming climate might extend the breeding season and provide more opportunities to re-nest rather than drive earlier breeding in response to potential phenological mismatches. However, as plasticity will likely be insufficient for long-term survival in the face of climate change, further research in understanding the mechanisms of female reproductive timing will be essential for forecasting the effects of climate change on population persistence. C_LI

ecology↗

bioRxiv2020

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

Urban habitats can shape interactions between hosts and parasites by altering not only exposure rates but also within-host processes. Artificial light at night is common in urban environments, and chronic exposure can impair host immunity in ways that may increase infection. However, studies of causal links between this stressor, immunity, and infection dynamics are rare, particularly in migratory animals. Here, we experimentally tested how artificial light at night affects cellular immunity and haemosporidian parasite intensity across the annual cycle of migrant and resident subspecies of the dark-eyed junco (Junco hyemalis). We monitored an experimental group exposed to light at night and a control group under natural light/dark cycles as they passed through short days simulating early spring to longer days simulating the breeding season, followed by fall migration. Using generalized additive models, we show that artificial light at night increased inflammation, and leukocyte counts were greatest in early spring and fall. At the start of the experiment, few birds had active infections based on microscopy, but PCR revealed many birds had chronic infections. Artificial light at night increased parasitemia across the annual cycle, with strong peaks in spring and fall that were largely absent in control birds. As birds were kept in indoor aviaries to prevent vector exposure, this increased parasitemia indicates relapse of chronic infection during costly life history stages (i.e., reproduction). Although the immunological and parasitological time series were in phase for control birds, cross-correlation analyses also revealed artificial light at night desynchronized leukocyte profiles and parasitemia, which could suggest a general exaggerated inflammatory response. Our study shows how a common anthropogenic influence can shape within-host processes to affect infection dynamics.

ecology↗

bioRxiv2020

Exposure to artificial light at night accelerates but does not override latitude-dependent seasonal reproductive response in dark-eyed juncos

In the modern era of industrialization, illuminated nights have become a common defining feature of human-occupied environments, particularly cities. Artificial light at night (ALAN) imposes several known negative impacts on the neuroendocrine system, metabolism, and seasonal reproduction of species living in the wild. However, we know little about the impact of ALAN on populations of birds that either live year-round in the same location or move to different latitudes across seasons. To test whether ALAN has differing impact on reproductive timing of the bird populations that winter in sympatry but breed at different latitudes, we monitored sedentary and migratory male dark-eyed juncos that were or were not exposed to low intensity (~2.5 {+/-} 0.5 lux) ALAN. All groups were held in common conditions and day length was gradually increased to mimic natural day length changes (NDL). We assessed seasonal reproductive response from initiation to termination of the breeding cycle. As expected based on earlier research, the sedentary birds exhibited earlier gonadal recrudescence and terminated breeding later than the migratory birds. In addition, resident and migrant birds exposed to ALAN initiated gonadal recrudescence earlier and terminated reproduction sooner as compared to their conspecifics experiencing NDL. Importantly, the difference in the reproductive timing of sedentary and migratory populations was maintained even when exposed to ALAN. This variation in the seasonal reproductive timing may likely have a genetic ground or early developmental effects imposed due to different latitude of origin. This study reveals first that latitude-dependent variation in reproductive timing is maintained despite exposure to ALAN, and second that ALAN accelerated reproductive development across both migrants and residents. The results corroborating relationship between latitude, population, and ALAN impact on seasonal reproductive timing, may provide a potential mechanism to test the fitness of a population and its range expansion to exploit urban environment.

ecology↗

bioRxiv2020

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

Annual migration is common across animal taxa and can dramatically shape the spatial and temporal patterns of infectious disease. Although migration can decrease infection prevalence in some contexts, these energetically costly long-distance movements can also have immunosuppressive effects that may interact with transmission processes in complex ways. Here we develop a mechanistic model for the reactivation of latent infections driven by physiological changes or energetic costs associated with migration (i.e., "migratory relapse") and its effects on disease dynamics. We determine conditions under which migratory relapse can amplify or reduce infection prevalence across pathogen and host traits (e.g., infectious periods, virulence, overwinter survival, timing of relapse) and transmission phenologies. We show that relapse at either the start or end of migration can dramatically increase prevalence across the annual cycle and may be crucial for maintaining pathogens with low transmissibility and short infectious periods in migratory populations. Conversely, relapse at the start of migration can reduce the prevalence of highly virulent pathogens by amplifying culling of infected hosts during costly migration, especially for highly transmissible pathogens and those transmitted during migration or the breeding season. Our study provides a mechanistic foundation for understanding the spatiotemporal patterns of relapsing infections in migratory hosts, with implications for zoonotic surveillance and understanding how infection patterns will respond to shifts in migratory propensity associated with environmental change. Further, our work suggests incorporating within-host processes into population-level models of pathogen transmission may be crucial for reconciling the range of migration-infection relationships observed across migratory species.

ecology↗

bioRxiv2019

Breeding at higher latitude as measured by stable isotope is associated with higher photoperiod threshold and delayed reproductive development in a songbird

Many organisms time reproduction to photoperiod, a constant from year to year. Predicting how anthropogenic change will influence future timing demands greater knowledge of the current role of photoperiod. We held two closely related bird populations in a common environment. One population is resident; the other winters in sympatry with the resident population but migrates north prior to reproducing. We increased photoperiod gradually and measured preparation for migration and reproduction, using feather stable isotopes to estimate breeding latitude. We predicted population differences in the minimum stimulatory day length to elicit a response (CPP, critical photoperiod) and co-variation between CPP and distance migrated. We found clear population differences in CPP and greater CPP in longer distance migrants. We conclude that current geographic variation in reproductive timing has a genetic or early developmental basis and recommend that future research focus on how anthropogenic changes will interact with CPP to adjust timing of reproduction and migration.

ecology↗

bioRxiv2019

Urban birdsongs: higher minimum song frequency of an urban colonist persists in a common garden experiment

Environmental changes caused by urbanization and noise pollution can have profound effects on acoustic communication. Many organisms use higher sound frequencies in urban environments with low-frequency noise, but the developmental and evolutionary mechanisms underlying these shifts are less clear. We used a common garden experiment to ask whether changes in minimum song frequency observed 30 years after a songbird colonized an urban environment are a consequence of behavioral flexibility or canalized changes that occur early in development. We captured male juvenile dark-eyed juncos (Junco hyemalis thurberi) from two recently diverged populations (urban and mountain) soon after they reached independence (aged 25-40 days), raised them in identical indoor aviaries, and studied their songs at an age of three years. We found that the large population difference in minimum frequency observed in the field persisted undiminished in the common garden despite the absence of noise. We also found some song sharing between the common garden and natal field populations, indicating that early song memorization before capture could contribute to the persistent song differences in adulthood. These results are the first to show that frequency shifts in urban birdsong are maintained in the absence of noise by genetic evolution and/or early life experiences.

evolutionary biology↗