Emerging infectious diseases have resulted in severe population declines across diverse taxa. In some instances, despite attributes associated with high extinction risk, disease emergence and host declines are followed by host stabilisation for unknown reasons. While host, pathogen, and the environment are recognised as important factors that interact to determine host–pathogen coexistence, they are often considered independently. Here, we use a translocation experiment to disentangle the role of host traits and environmental conditions in driving the persistence of remnant bat populations a decade after they declined 70–99% due to white‐nose syndrome and subsequently stabilised. While survival was significantly higher than during the initial epidemic within all sites, protection from severe disease only existed within a narrow environmental space, suggesting host traits conducive to surviving disease are highly environmentally dependent. Ultimately, population persistence following pathogen invasion is the product of host–pathogen interactions that vary across a patchwork of environments.
For many animals, parental care behavior is an important aspect of their life history that affects both parents and offspring. In birds, one of the most important parental care behaviors is incubation, which is costly to the parent but directly influences embryonic development and fitness of offspring. Some birds exhibit the intriguing behavior of partially incubating their eggs prior to clutch completion for only a portion of each day. This partial incubation is characterized by lower incubation temperatures and constancy than during full‐time incubation, which typically begins at clutch completion. Partial incubation may preserve the viability of eggs laid early in the laying sequence, shorten the length of the full incubation period, and/or provide a favorable microclimate to the incubating parent. It might also reduce the probability of nest predation, nest site takeover by another bird, brood parasitism, and/or predation of the adult. Although there is evidence that partial incubation is an adaptive behavior and that time invested in this behavior varies among individuals of the same species, nothing is known about what may drive this inter‐individual variation. To investigate how environmental and parental characteristics may be related to partial incubation behavior, we studied the partial incubation behavior of wood ducks Aix sponsa using artificial egg temperature loggers within nest boxes. Our results suggest that females with greater mass relative to their structural size invest more time in partial incubation. Additionally, the incubation temperature and length of on‐bouts of partial incubation increased over the course of the partial incubation period, and ambient temperature during on‐bouts was positively related to incubation temperature. Ultimately, our study suggests that characteristics of both the environment and parent may influence the partial incubation behavior of wood ducks, and improves our understanding of an important, but understudied, aspect of avian parental care.
Synopsis Developmental conditions can have consequences for offspring fitness. For example, small changes (<1°C) in average avian incubation temperature have large effects on important post-hatch offspring phenotypes, including growth rate, thermoregulation, and behavior. Furthermore, average incubation temperatures differ among eggs within the same nest, to the extent (i.e., >1°C) that differences in offspring phenotypes within broods should result. A potential consequence of within-nest incubation temperature variation is inequality in behaviors that could cause differences in resource acquisition within broods. To investigate this, we incubated wood duck (Aix sponsa) eggs at one of two ecologically-relevant incubation temperatures (35°C or 36°C), formed mixed-incubation temperature broods after ducklings hatched, and conducted trials to measure duckling behaviors associated with acquisition of heat (one trial) or food (three trials). Contrary to our predictions, we found no effect of incubation temperature on duckling behaviors (e.g., time spent occupying heat source, frequency of feeding bouts). However, we found evidence that ducklings incubated at the higher temperature consumed more food during the 1-h feeding trials, and grew faster in body mass and structural size (culmen and tarsus) throughout the study, than those incubated at the lower temperature. Apparent food consumption during the trials was positively related to culmen length, suggesting that differences in food consumption may be driven by structural size. This could result in positive feedback, which would amplify size differences between offspring incubated at different temperatures. Thus, our study identifies incubation temperature as a mechanism by which fitness-related phenotypic differences can be generated and even amplified within avian broods.
Emerging infectious diseases have resulted in severe population declines across diverse taxa. In some instances, despite attributes associated with high extinction risk, disease emergence and host declines are followed by host stabilization for reasons that are frequently unclear. While host, pathogen, and the environment are recognized as important factors that interact to determine host-pathogen coexistence, they are often considered independently. Here, we use a translocation experiment to disentangle the role of host traits and environmental conditions in driving the persistence of remnant populations a decade after they declined 70-99% and subsequently stabilized with disease. While survival was significantly higher than during the initial epidemic within all sites, protection from severe disease only existed within a narrow environmental space, suggesting host traits conducive to surviving disease are highly environmentally dependent. Ultimately, population persistence following pathogen invasion is the product of host-pathogen interactions that vary across a patchwork of environments.
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