DOI: 10.5061/dryad.vt4b8gv5k
title: Data from: Dimorphism from an early age: sex differences in size and immune function in great tit nestlings

description: The dataset contains data on great tit nestlings morphometrics (mass,
 wing, and tarsus) and innate immune function (agglutination, lysis,
 haptoglobin concentration, and bacteria killing capability), and was
 collected in a nestbox population in southern Sweden during two
 consecutive breeding seasons (2022 and 2023). In both years, a brood size
 manipulation experiment was carried out. Birds can show patterns of sexual
 size dimorphism as early as during the nestling stage. This raises the
 question of how the faster growing sex might reconcile the energetic and
 nutritional needs of a faster growth rate with resource allocation to
 other important life functions, such as the development of innate immune
 function. Innate immunity represents the main line of defence against
 diseases, and while some innate immune defences are already present at
 hatching, substantial development occurs throughout the nestling stage.
 Hence, this development may compete for resource allocation with growth,
 potentially affecting nestlings in a sex-specific way in species showing
 sexual size dimorphism at early age. However, little is known about how
 sex might shape life-history strategies early in the life cycle. In this
 two-year study, we compared size, mass and immune function
 (Hemolysis-hemagglutination assay, Bacteria Killing Assay and Haptoglobin
 assay) between sexes of great tit (Parus major) nestlings, likely
 reflecting the outcome of relative resource allocation during ontogeny. To
 account for variation in environmental quality, we evaluated
 sex-differences in relation to a brood size manipulation and in relation
 to seasonal progression. We found that male nestlings grew to a larger
 size at day 14 than their female siblings. However, we also found some
 indication that males developed a better immune defense than females
 albeit their faster growth. Thus, males manage to invest more heavily in
 both growth rate and immune defence, probably depending on males being
 dominant to females in the competition for parental feeding, resulting in
 higher resource acquisition.
description: # Data from: Dimorphism from an early age: sex differences in size and
 immune function in great tit nestlings Dataset DOI:
 [10.5061/dryad.vt4b8gv5k](https://doi.org/10.5061/dryad.vt4b8gv5k) ##
 Description of the data and file structure On day 5 (in 2023) or 6 (in
 2022) after hatching, we performed a brood size manipulation experiment by
 moving 4 (in 2022) or 5 nestlings (2023) in-between nestboxes. Thus, our
 experimental set-up included three groups, a reduced and enlarged
 treatment, and some unmanipulated boxes were included as controls. At this
 time, we also ringed most of the nestlings and measured their mass. On day
 14 after hatching, we measured mass, wing and tarsus. We blood sampled a
 subset of the nestlings. We used the blood pellet for molecular sexing and
 the plasma for innate immune function assays (haemolysis-hemagglutination,
 haptoglobin assay, and bacteria killing assay). Agglutination and bacteria
 killing assays are only available for the 2022 breeding season. ### Files
 and variables #### File: 22_23.csv **Description:** This is a dataset on
 great tit nestlings from a nestbox population in southern Sweden. We
 measured morphometrics (mass, wing, tarsus) and innate immunity
 (agglutination, lysis, haptoglobin, bacteria killing), and performed a
 brood size manipulation experiment during the breeding season in 2022 and
 2023. Data on clutch size, hatching dates, and the individual
 nestlings' mass before brood size manipulation were used for
 preliminary analyses. We wanted to check that clutch size, hatching date,
 and mass before brood size manipulation did not differ to validate our
 experimental set-up. * ID=Ring number of the individual * YEAR=Year in
 which the individual was sampled (2022 or 2023) * NB=Nestbox ID (number) *
 NB.YEAR=We added "0.22" or "0.23" to the nestbox ID
 number, to make sure that in the analysis, individuals that occupied the
 same nestbox in different years were not treated as being part of the same
 brood. * TREATMENT=Brood size experimental treatment, R= REDUCED,
 C=CONTROL, E=ENLARGED * AGG= Agglutination scores in titres. N/A means not
 available * SEX= Male (M) or Female (F), according to the results of
 molecular sexing (2 bands assigned " female", 1 band assigned
 "male") * BKA score= Bacteria Killing Assay score, as proportion
 of *E.coli* killed. N/A means not available, assay only done in 2022 * Hp=
 Haptoglobin concentration in mg/ml * 405 nm, 450 nm= Refers to the
 wavelength in nm at which we performed pre-scans to control for redness of
 the samples during the haptoglobin assay * BM= Body mass in grams (g), to
 the nearest 0.1 g * HATCH_DAY= Date on which the individual hatched
 computed as Julian date, starting from May 1st * WNG= Wing length in
 millimeters (mm), only measured in 2023 hence N/A (not available) values
 present * TRS= Tarsus length in millimeters (mm), only measured in 2023
 hence N/A (not available) values present * LYSIS= Lysis scores in titres
 **Files: "broods_22.csv":  and "broods_23.csv": data
 on broods from 2022 and 2023 respectively** * NB= Nestbox ID (number) *
 Clutch_size= number of eggs found in the box at the end of egg laying *
 Hatching_date= Hatching date in the DD/MM/YYYY format * TREATMENT= Brood
 size manipulation experiment treatment: R=reduced, C= control, E=enlarged
 * BS_D5_B and BS_D6 = Brood size on day 5 or day 6 after hatching, i.e.
 before the manipulation was carried out * BS_D5_A and BS_D6_A= Brood size
 after manipulation For broods_23.csv only= "ringed" and
 "unringed" refer to the number of nestlings that were or were
 not ringed prior to manipulation. **Files: "mass_d6_22.csv" and
 "mass_d5_23.csv": data on individual nestlings on day 5 (2023)
 and 6 (2022) after hatching** * RNG= Ring number; non-ringed birds were
 either labeled as N/A or by having e.g. "NR-491-1" where
 "491" is the nestbox number and 1 is used to distinguish the
 individual from other nestlings in the brood. * NB= Nestbox ID (number) *
 TREATMENT= Brood manipulation experimental treatment; R=reduced, C=
 control, E=enlarged * BM= Body mass in grams (g), to the nearest 0.1 g ##
 Code/software Our dataset is in the CVS UTF-8 (Comma delimited
 ".csv") format, we used the Excel version: 2509 Build
 16.0.19231.20138