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This preregistration was written prior to collecting any data.
We may publish the results from each hypothesis separately.
Based on flexibility testing in aviaries, we will develop a flexibility test for individuals in the wild to increase our sample size. Genetic relationships among individuals will be determined using ddRADseq to then investigate this question using the Animal Model. If flexibility is not heritable, this is potentially because behavior is not usually very heritable, and/or we might fail to detect heritability because the A) sample size might not be large enough, and/or B) individuals may not vary enough in flexibility. If we find that flexibility is heritable, this could indicate that there is a stable polymorphism where some individuals have high and others low flexibility, which could give different benefits in a given environment.
Based on flexibility testing in aviaries, we will develop a flexibility test for individuals in the wild to increase our sample size. Genetic variation of individuals will be determined using ddRADseq and gene expression will be determined using RNA sequencing.
R2.1 individual Do the more flexible individuals carry or express genetic variants at specific loci that differ from the less flexible individuals? Genetic variants will be identified using genome wide association studies (GWAS).
R2.2 candidate loci Is one variant of the genetic locus DRD4 (associated with exploratory behavior) primarily present in the more flexible individuals, while the other variant is primarily present in the less flexible individuals?
Genetic variation of individuals will be determined using ddRADseq, and coalescence simulations will be used with the ddRADseq data to determine the common ancestors and timing of divergence of the populations we sample.
No randomization or counterbalancing is involved in this study.
No blinding is involved in this study.
Flexibility 1: Number of trials to reverse a preference in the last reversal an individual experienced (reversal learning; an individual is considered to have a preference if it chose the rewarded option at least 17 out of the most recent 20 trials, with a minimum of 8 or 9 correct choices out of 10 on the two most recent sets of 10 trials). See behavioral flexibility preregistration.
Flexibility 3: If the number of trials to reverse a preference does not positively correlate with the latency to attempt or solve new loci on the multi-access box (an additional measure of behavioral flexibility), then the average latency to solve and the average latency to attempt a new option on the multi-access box will be additional dependent variables. See behavioral flexibility preregistration.
One model will be run per dependent variable.
Model parameters: absolute and change in population size, time, frequency of exchange of individuals/genes between populations. We will then run a simulation and find the combination of values for the parameters that produce the closest fit to the actual data.
Age: adult, juvenile
Body size: tarsus length
Body condition: hematocrit (percentage of red blood cells in the blood)
Number of parasite species hosted
Population: Central America, Arizona, Nebraska
Birth year (random effect)
Pedigree (random effect)
We do not plan to exclude any data. When missing data occur, the existing data for that individual will be included in the analyses for the tests they completed. Analyses will be conducted in R (current version 3.5.2; R Core Team (2017)). We will analyze data for females and males separately because each sex has a distinct natural history (Johnson and Peer (2001)).
NOTE: the analysis plan is still being drafted
Great-tailed grackles (n > 200) will be caught in the wild at three field sites across their geographic range: the center of their original range (Central America), the middle of the northward expanding edge (Tempe, Arizona USA), and on the northern expanding edge (to be determined). Individuals will be identified using colored leg bands in unique combinations, their data collected (blood, feathers, and biometrics), and then they will be released back to the wild. Some individuals (40-100) will be brought temporarily into aviaries for behavioral testing, and then they will be released back to the wild.
Sample size rationale
We will band as many birds as possible throughout the year, and conduct behavioral tests in aviaries (during the non-breeding seasons approximately September through March) and in the wild (year-round) on as many birds as we can at each field site. The minimum sample size will be 200 banded birds and 60 behavior-tested birds in total, however we expect to be able to sample many more.
Data collection stopping rule
We will stop collecting data in April 2023 when the current funding ends, or after data have been collected at all three field sites, whichever date comes first.
This research is carried out in accordance with permits from the:
This research is funded by the Department of Human Behavior, Ecology and Culture at the Max Planck Institute for Evolutionary Anthropology.
We thank the Lab of Ornithology at Cornell University (Irby Lovette and Bronwyn Butcher) for letting us use their lab to process the DNA and for teaching us how; Ben Trumble for providing us with a wet lab at Arizona State University; Melissa Wilson Sayres for sponsoring our affiliations at Arizona State University and lending lab equipment; Kevin Langergraber for serving as local PI on the ASU IACUC; Kristine Johnson for technical advice on great-tailed grackles; Jay Taylor for grackle scouting at Arizona State University; Arizona State University School of Life Sciences Department Animal Care and Technologies for providing space for our aviaries and for their excellent support of our daily activities; Julia Cissewski for tirelessly solving problems involving financial transactions and contracts; Richard McElreath for project support; Erin Vogel, our Recommender at PCI Ecology, and Simon Gingins and two anonymous reviewers for their wonderful feedback; and our research assistants: Aelin Mayer, Nancy Rodriguez, Brianna Thomas, Aldora Messinger, Elysia Mamola, Michael Guillen, Rita Barakat, Adriana Boderash, Olateju Ojekunle, August Sevchik, Justin Huynh, Jennifer Berens, and Amanda Overholt.
Johnson, Kristine, and Brian D Peer. 2001. Great-Tailed Grackle: Quiscalus Mexicanus. Birds of North America, Incorporated.
R Core Team. 2017. R: A Language and Environment for Statistical Computing. Vienna, Austria: R Foundation for Statistical Computing. https://www.R-project.org.