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Experimentally impaired female condition does not affect biliverdin-based egg colour

Citation

D'Arpa, Stefania et al. (2022), Experimentally impaired female condition does not affect biliverdin-based egg colour, Dryad, Dataset, https://doi.org/10.5061/dryad.f4qrfj6x7

Abstract

It has been proposed that blue-green egg coloration is a condition-dependent female sexual trait that may modify paternal care in a post-mating sexual selection scenario. This pattern may arise because the pigment responsible for eggshell colouration (biliverdin) may be a costly and limited resource, whose availability is linked to female health state. Thus, it can be predicted that females whose condition is compromised should be constrained in their capacity to deposit biliverdin in the eggshell, thus producing paler clutches. To test this hypothesis, we performed a handicapping experiment by clipping some feathers of female spotless starlings before egg laying and measuring the colour of their clutches. We expected the handicapping treatment to increase flying costs, impairing female overall condition and resulting in paler clutches. Our experiment was successful in lowering the weight gain of handicapped with respect to control females. However, in contrast to our expectations, we found no effect of the treatment on eggshell colouration. Eggshell colour varied along the laying order, with initial eggs of the laying sequence being relatively paler than the rest of the clutch, but this pattern was not different between experimental groups. Despite a very similar methodology, our results differ from a previous study and offers no support to the post mating sexual selected hypothesis, questioning the general applicability of the sexual selection role of eggshell coloration.

Usage Notes

Dataset 1: this is the dataset used for the eggshell coloration analysis.

The dataset presents 145 columns and 197 lines. Each line represents the data relative to a single starlin egg considered for the analysis.

Column 1 is the original ID of the egg in the field noterbook.
Column 2 is the individual code for each breeding attempt (i.d. every time a first egg is found in a nest).
Column 3 is the nest in which each egg has been found.
Col. 4 is the tratment to which the female laying the eggs has been subjected: H, handicap; C, control.
Col. 5 contains the date of measurement of the eggs.
Col. 6 contains the date of laying of each egg (date of April 2020).
Col. 7 the clutch size of each breeding event.
Cols. 8-10 the lenght (mm), widht (mm) and the calculated volume (mm3) of each egg. Please refer to the main text for more information about egg size calculation.
Cols. 11-15 contain the informations about the laying female (IDs and measurements). 
Cols. 16 - 135 contain the repeated measurements of eggshell coloration as stored in the spectrophotometer and the relative values of brightness, BGC, hue and chroma. The x and y are used to distinguish the first from the second spectra values.
Cols. 136-139 contain the values of the mean value of brightness, hue, chroma and blue-green chroma for the repeated measures (x and y).
Cols. 140-142 contain the main, the standard deviation and the maximum values of BGC for each nest.
Cols. 143-145 contain the main, the standard deviation and the maximum values of BGC x100.

Dataset 2: this dataset contains the data of the females recorded before and after the laying.

Col. 1 and 2 contain the ID of the female (ring number and chip code, respectively)
Col.3 the tratment to which the female laying the eggs has been subjected: H, handicap; C, control.
Col. 4 the nest in which the eggs have been laid.
Cols. 5 and 6 contain the dates in which the female has been captured (before and after laying the eggs, respectively).
Cols. 7 and 8 contain the day counts of the corrispective date, starting the day of the laying (April 11th).
Col. 9 and 10 contain the initials of the observer of the first and second capture.
Col. 11 contains the coded age of the oldest nestling: P5, chick of 5 days; P6, chick of 6 days...
Cols. 12 and 13 contain the weights recorded in the first and in the second capture (pre and post laying, respectively).
Cols. 14 and 15 contain the wing (mm) and the tarsus (mm) measurements of the females, recorded in the first capture.

Funding