10.5061/DRYAD.K3J9KD559
Wanamaker, Sarah
Indiana University Bloomington
Singh, Devraj
Indiana University Bloomington
Byrd, Allison
Indiana University Bloomington
Smiley, Tara
Indiana University Bloomington
Ketterson, Ellen
0000-0002-7375-6605
Indiana University Bloomington
Local adaptation from afar: migratory bird populations diverge in the
initiation of reproductive timing while wintering in sympatry
Dryad
dataset
2020
Dark-eyed Junco
Breeding latitude
Stable hydrogen isotope
Allochrony
Indiana University’s Grand Challenge Initiative, Prepared for
Environmental Change*
2020-09-17T00:00:00Z
2020-09-17T00:00:00Z
en
29501 bytes
7
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
The initiation of reproduction in many seasonally breeding animals is
controlled by photoperiod and tends to be clinal: populations at higher
latitudes breed later than those at lower latitudes, often reflecting a
higher photoperiodic threshold. Migratory animals presumably time
reproduction to match conditions at their breeding grounds at least in
part by cues perceived on their wintering grounds. We asked how closely
related dark-eyed junco (Junco hyemalis) populations that overwinter in
sympatry but breed in allopatry respond to their shared winter environment
by comparing early spring indices of readiness to migrate and breed
(baseline and elevated testosterone). We measured stable hydrogen isotopes
from feathers grown the preceding year and claws grown during winter to
estimate breeding and wintering latitudes, respectively. We predicted that
if reproductive initiation is adapted to the emergence of resources at
their respective breeding destinations, then birds migrating to higher
latitudes (slate-colored junco; J. h. hyemalis) should delay breeding as
compared to those migrating to lower latitudes (pink-sided junco; J. h.
mearnsi) despite a common overwinter environment. We found higher
testosterone in pink-sided juncos consistent with earlier reproductive
initiation, suggesting local adaptation in reproductive phenology achieved
through differential responses to predictive environmental cues.
From March 18–24, 2019, we captured overwintering PSJU (n = 7) and SCJU (n
= 11) at three field sites: Chatfield State Park in Littleton, CO
(39°31’44”N, 105°05’19”W), Denver Audubon Nature Center in Littleton, CO
(39°29’35”N, 105°05’48”W), and Peyton, CO (39°05’36”N, 104°25’29”W).
Birds were caught using baited potter traps and banded with aluminum
United States Fish and Wildlife Services (USFWS) bands. All standard
morphometric measurements were taken immediately after capture. We
measured Individual tarsus length, wing length, mass, body fat, and
pectoral muscle condition. Blood samples were collected immediately after
capture to measure baseline circulating testosterone (T0) by puncturing
the alar wing vein. Birds then received an intrapectoral injection of
GnRH, (1.25 µg chicken GnRH-I, Sigma L0637; American Peptide 54-8-23,
Sunnyvale, CA), after exactly 30 min, a second blood sample was taken to
measure elevated testosterone (T30) levels. The blood samples were stored
at 4°C, processed for plasma extraction and stored at -20°C until
analyses. See detailed procedure for morphometric measurement,
physiological, and hydrogen isotope data collection in electronic
supplementary methods. Please refer to file named
(BL_PhysiologicalData_Dryad.xlsx) for individual bird data. Feather and
claw hydrogen isotope values were measured to estimate the breeding and
wintering latitude of the birds. See detailed procedure hydrogen isotope
analyses and statistics details in electronic supplementary
methods. Please refer to file named (BL_IsotopeData_Dryad.xlsx) for
individual raw hydrogen isotope values. See ReadMe file for a brief
overview on raw data files, definitions of variables, and other key
information.