DOI: 10.5061/dryad.tdz08kq16
title: The probability of being infected with haemosporidian parasites increases with host age

description: In vertebrates, disease susceptibility often varies with age. Older
 individuals may be more susceptible than younger individuals due to
 senescent declines in immune function. Alternatively, disease
 susceptibility may decrease with age if older individuals are more likely
 to have had prior exposures to parasites and acquired adaptive immune
 responses that allowed them to resist future infections. Disease
 susceptibility can also vary with reproductive state, and reproductive
 hormones have been shown to increase infection susceptibility. Here we
 investigated how age and experimentally elevated levels of the
 reproductive hormone testosterone affected haemosporidian
 infections in free-living adult male dark-eyed juncos (Junco hyemalis).
 Samples were collected before and at least one year after experimental
 treatment with either a testosterone implant or empty control implant. The
 probability of being infected with haemosporidians in
 the Plasmodium/Haemoproteus group increased with host
 age but was unaffected by experimental testosterone elevation. Our
 longitudinal sampling design allowed us to determine that the increase in
 infections with host age was driven by variation within individuals, such
 that an individual’s probability of being infected increased with age.
 This suggests that haemosporidian susceptibility increases with host age,
 and/or that haemosporidian-infected juncos sustain long-term
 chronic infections that are rarely completely cleared, and that the
 probability of being infected is higher in older juncos because they have
 experienced higher cumulative exposure risk.
description: Haemosporidian parasite infections in the junco blood samples
 were measured in the Center for the Integrative Study of Animal Behavior
 Laboratory at Indiana University, Bloomington. To determine haemosporidian
 infection status, the haemosporidian parasite cytochrome B
 (<i>cytb</i>) gene was amplified using published nested
 polymerase chain reaction (PCR) protocols (Hellgren et al.
 2004, Waldenström et al. 2004). Each gDNA sample was amplified using the
 external PCR primers HAEMNF and HAEMNR2. Following the first round of
 amplification, PCR product was amplified again using the nested or
 internal primers HAEMF and HAEMR2 (Hellgren et al. 2004), which have been
 shown to very efficiently
 amplify <i>Plasmodium </i>and <i>Haemoproteus
 cytb </i>sequences, and additionally with the nested or internal
 primers HAEMFL and HAEMR2L, for amplification
 of <i>Leucocytozoon </i>sequences (Hellgren et al.
 2004).
description: Slowinski et al. 2021 JAB Dryad data key Data sheets: Plas.Haem: Data sheet for the <i>Plasmodium</i>/<i>Haemoproteus </i>infection status of birds, as determined using the nested or internal primers HAEMF and HAEMR2 (Hellgren et al. 2004). This sheet includes only birds for which the <i>Plasmodium/Haemoproteus </i>infection status could be determined at the time of first implant and in at least one following year. Leucocytozoon: Data sheet for <i>Leucocytozoon </i>infection statust of birds, as determined using the nested or internal primers HAEMFL and HAEMR2L (Hellgren et al. 2004). This sheet includes only birds for which the <i>Leucocytozoon </i>infection status could be determined at the time of first implant and in at least one following year. First.samples: Data sheet for <i>Plasmodium/Haemoproteus </i>and <i>Leucocytozoon </i>infection status of birds at the time of their first implant. This sheet includes only birds for which both the <i>Plasmodium/Haemoproteus </i>infection status and the <i>Leucocytozoon </i>infection status could be determined at the time of first implant Column headings Blood_sample_date: date at which blood sample was collected Implant_in: Closest date to blood sample collection date on which bird was given a testosterone or control implant BloodIDnoletter: Unique ID number associated with each blood sample Ring: Unique ring number associated with each bird Age: age of bird at time blood sample was collected Age_at_first_implant: Age of the focal bird when it received its first testosterone or control implant Mean age: Mean age of the focal bird across all of the ages at which blood samples were collected Age_minus_mean_age: Age of the focal bird at the time the present blood sample was collected, minus the mean age of the focal bird across samples  Implant_number: Number of times the focal bird has been implanted (including the implant associated with the present sample). First_implant_year: Year in which the focal bird was first implanted Years_since_first_implant: Years between the time at which the focal bird was first implanted, and the present sample Treatment_0C_1T: Implant treatment. Control implants represented by zeroes. Testosterone implants represented by ones. Plas.Haem.Infections: <i>Plasmodium/Haemoproteus </i>infection status, as determined by nested PCR and gel electrophoresis. Zeroes represent negative infections. Ones represent positive infections Leuc.0n_1p: <i>Leucocytozoon </i>infection status. Zeroes represent negative infections. Ones represent positive infections.