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Demographic factors are fundamental in shaping infectious disease dynamics. Aspects of populations that create structure, like age and sex, can affect patterns of transmission, infection intensity and population outcomes. However, studies rarely link these processes from individual to population-scale effects. Moreover, the mechanisms underlying demographic differences in disease are frequently unclear. Here, we explore sex-biased infections for a multi-host fungal disease of bats, white-nose syndrome, and link disease-associated mortality between sexes, the distortion of sex ratios and the potential mechanisms underlying sex differences in infection. We collected data on host traits, infection intensity and survival of five bat species at 42 sites across seven years. We found females were more infected than males for all five species. Females also had lower apparent survival over winter and accounted for a smaller proportion of populations over time. Notably, female-biased infections were evident by early hibernation and likely driven by sex-based differences in autumn mating behaviour. Male bats were more active during autumn which likely reduced replication of the cool-growing fungus. Higher disease impacts in female bats may have cascading effects on bat populations beyond the hibernation season by limiting recruitment and increasing the risk of Allee effects.
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The landscape of natural selection during early population establishment in an invasive lizard
Abstract Populations during early stages of establishment are sensitive to forms of demographic regulation coinciding with rapid growth, which may also coincide with specific patterns of natural selection due to demographic variation. Understanding how selection varies during the establishment of new populations, however, is complicated by the constraint of knowing the precise age of a population as it grows over time. To address this, we established six brown anole (Anolis sagrei) populations on spoil islands in Florida and manipulated initial sex ratios to understand how natural selection is influenced by the demographic composition of founding populations. We found that initial sex ratios of founding populations led to age-specific patterns of natural selection. Juveniles experienced stronger selection in populations that began with a female-biased sex ratio, and the strength of natural selection on juvenile size strengthened with increasing population density. We also found substantial variation in selection, suggesting that the relationship between phenotypes and fitness across early generations of a population is not consistent over time. As a result, variation in natural selection driven by demographic aspects within populations may provide opportunities for rapid population growth and novel evolutionary trajectories during the earliest stages of establishment.
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- Award ID(s):
- 1942145
- PAR ID:
- 10643194
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Evolution
- ISSN:
- 0014-3820
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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