Data from: Dimorphism from an early age: sex differences in size and immune function in great tit nestlings
Data files
Nov 03, 2025 version files 49.33 KB
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22_23.csv
18.17 KB
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broods_22.csv
1.53 KB
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broods_23.csv
2 KB
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mass_d5_23.csv
11.69 KB
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mass_d6_22.csv
11.69 KB
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README.md
4.24 KB
Abstract
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.
Dataset DOI: 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