DOI: 10.5061/dryad.m559kb0
title: Data from: Seasonal differences in baseline innate immune function are better explained by environment than annual cycle stage in a year-round breeding tropical songbird

description: 1. Seasonal variation in innate immunity is often attributed to either
 temporal environmental variation or to life history trade-offs that arise
 from specific annual cycle stages but decoupling them is difficult in
 natural populations. 2. Here, we effectively decouple seasonal
 environmental variation from annual cycle stage effects by exploiting
 cross-seasonal breeding and moult in the tropical Common Bulbul Pycnonotus
 barbatus. We test how annual cycle stage interacts with a key seasonal
 environmental variable, rainfall, to determine immunity at population and
 individual level. If immune challenge varies with precipitation, we might
 expect immune function to be higher in the wet season due to increased
 environmental productivity. If breeding or moult imposes resource
 constraints on birds, depending on or independent of precipitation, we
 might expect lower immune indices during breeding or moult. 3. We sampled
 blood from 818 birds in four annual cycle stage categories: breeding,
 moult, simultaneous breeding and moulting, or neither. We quantified
 indices of innate immunity (haptoglobin, nitric oxide (NOx) and
 ovotransferrin concentrations, and haemagglutination and haemolysis
 titres) over two annual cycles of wet and dry seasons. 4. Environment (but
 not annual cycle stage or interactions between both) explained variation
 in all immune indices, except NOx. NOx concentration differed between
 annual cycle stages but not between seasons. However, within the wet
 season, haptoglobin, NOx, ovotransferrin and haemolysis differed
 significantly between breeding and non-breeding females. Aside from some
 recorded inconsistences, population level results were largely similar to
 results within individuals that were measured repeatedly. Unexpectedly,
 most immune indices were higher in the dry season and during breeding. 5.
 Higher immune indices may be explained if fewer or poorer quality
 resources force birds to increase social contact, thereby exposing
 individuals to novel antigens and increased infection risk, independently
 of environmental productivity. Breeding birds may also show higher
 immunity if less immune-competent and/or infected females omit breeding.
 We conclude that seasonal environmental variation impacts immunity more
 directly in natural animal populations than via resource trade-offs. In
 addition, immune indices were more often variable within than among
 individuals, but some indices are characteristic of individuals, and so
 may offer selective advantages if heritable.
description: Field sampling
 information and measured innate immune indices of Common Bulbuls in
 NigeriaData was collected at
 the Amurum Forest Reserve (09°52’N, 08°58’E) which is located at the A.P.
 Leventis Ornithological Research Institute (APLORI) in Nigeria. Data was
 collected between January 2014 and February 2016. Birds were caught using
 mist nets. Data contains individual information of Common Bulbuls
 Pycnonotus barbatus sampled for blood to quantify indices of innate
 immunity, including haptoglobin, nitric oxide (NOx) and ovotransferrin
 concentrations, and haemagglutination and haemolysis. Worksheet 1 contains
 field information for sampled birds, including, ring number, date, age,
 pectoral muscle score, fat score, brood patch, head moult, body moult,
 wing length, body mass, tarsus length, bill length, capture time, moult
 category, scores of individual primary feathers, cumulative scores of
 primary feathers, colour ring combination and presence or absence of a
 brood patch. Worksheet 2 contains measures of haemagglutination and
 haemolysis titres with ring numbers and capture dates corresponding to
 data in worksheet 1. Worksheet 3 contains measures of haptoglobin
 concentration with ring numbers and capture dates corresponding to data in
 worksheet 1. Worksheet 4 contains measures of nitric oxide concentration
 with ring numbers and capture dates corresponding to data in worksheet 1.
 Worksheet 5 contains measures of ovotransferrin concentration with ring
 numbers and capture dates corresponding to data in worksheet 1. Worksheet
 6 contains assay plate details for nitric oxide concentration assay
 corresponding to data in worksheet 4 - this additional data may be
 required to calculate intra and inter-assay variability. All data include
 notes inserted as comments describing the data columns.JAE_Temporal immune function
 data.xlsx