DOI: 10.5061/dryad.547d7wmb5
title: Maternally-transferred thyroid hormones and life-history variation in birds

description: 1. In vertebrates, thyroid hormones (THs) play an important role in the
 regulation of growth, development, metabolism, photoperiodic responses and
 migration. Maternally transferred THs are important for normal early-phase
 embryonic development when embryos are not able to produce endogenous THs.
 Previous studies have shown that variation in maternal THs within the
 physiological range can influence offspring phenotype. 2. Given the
 essential functions of maternal THs in development and metabolism, THs may
 be a mediator of life-history variation across species. 3. We tested the
 hypothesis that differences in life histories are associated with
 differences in maternal TH transfer across species. Using birds as a
 model, we specifically tested whether maternally transferred yolk THs
 co-vary with migratory status, developmental mode, and traits related to
 pace-of-life (e.g. basal metabolic rate, maximum lifespan). 4. We
 collected un-incubated eggs (n = 1-21 eggs per species, median = 7) from
 34 wild and captive bird species across 17 families and 6 orders to
 measure yolk THs (both triiodothyronine, T3 and thyroxine, T4), compiled
 life-history trait data from the literature, and used Bayesian
 phylogenetic mixed models to test our hypotheses. 5. Our models indicated
 that both concentrations and total amounts of the two main forms of THs
 (T3 and T4) were higher in the eggs of migratory species compared to
 resident species, and total amounts were higher in the eggs of precocial
 species, which have longer prenatal developmental periods, than in those
 of altricial species. However, maternal yolk THs did not show clear
 associations with pace-of-life related traits, such as fecundity, basal
 metabolic rate, or maximum lifespan. 6. We quantified interspecific
 variation in maternal yolk THs in birds and our findings suggest higher
 maternal TH transfer is associated with the precocial mode of development
 and migratory status. Whether maternal THs represent a part of the
 mechanism underlying the evolution of precocial development and migration
 or a consequence of such life histories is currently unclear. We therefore
 encourage further studies to explore the physiological mechanisms and
 evolutionary processes underlying these patterns.
description: The study includes two data sets: yolk thyroid hormones
 ("egg_data_final.csv") and life-history traits
 ("life_histories.csv"). Yolk thyroid hormones
 were extracted and measured by a nano-liquid chromatography tandem mass
 spectrometry protocol from eggs of 34 bird species. Life-history traits
 were collected and compiled from literature at the species
 level.
description: The data package contains four parts: Part I.
 data sets Two data sets are included in this
 study: egg_data.csv: Data set of yolk thyroid hormones
 measured in eggs of 34 bird species life_histories.csv:
 life-history trait values used in the study, collected and compiled from
 the literature info_eggdata.txt: information of
 variables (i.e. all columns) in egg_data.csv
 info_lifehistories.txt: information of variables (i.e. all
 columns) in life_histories.csv Part II.
 phylogeny full_Ericon and full_Hackett: For the 34
 species included in this study, 100 possible phylogenetic trees were
 obtained from two phylogenetic backbones via BirdTree.org.
 Others are the subsets according to data availability. For
 details see the paper and its supplementary materials.
 Part III. model results Our statistical models
 were run across 100 possible trees from the two backbones. The final
 estimates were collected and stored in these files for each
 model. Part IV. R codes All R codes
 used to produce our results are provided.
 data_process_final.R: code to process data before model
 fitting mls_size_corrected.R: code to run size
 correction on maximum lifespan aafr_size_corrected.R:
 code to run size correction on age at sexual maturity
 bmr_size_corrected.R: code to run size correction on
 mass-specific BMR k_size_corrected.R: code to run size
 correction on the logistic growth rate constant k
 models_final.R: code that runs the Bayesian phylogenetic mixed
 models results_final: code that reads, checks and
 collects results from the Bayesian phylogenetic mixed models
 phylogenetic_heritability.R: code that calculate phylogenetic
 heritability associated with our models and results
 model_diagnostics_final.R: code to examine model
 performance ggplot theme setting 2020.R: code that sets
 up the ggplot2 environment to produce the paper figures
 summarySE: a small function to calculate means, SE, etc. for
 graphic purposes phylogeny graph.R: code that produces
 Fig. 1A graphs from raw data.R: code that produces Fig.
 1B-E, 3, and 4B-E in the paper graphs from model
 results.R: code that produces Fig. 2 and 4A in the paper