DOI: 10.5061/dryad.8gtht76x5
title: Data from: Weak premating reproductive isolation despite divergence in secondary sexual traits in the Variable Seedeater

description: The likelihood of hybridization after secondary contact is reduced when
 assortative mating is strong and fitness of hybrids is low; thus,
 maintaining reproductive isolation. To this end, signals that convey
 population identity may enhance recognition and reduce hybridization by
 promoting assortative mating. Here, we studied visual and acoustic
 signals, plumage colour and song, that commonly mediate species
 recognition in birds to evaluate their role in reproductive isolation in a
 recently diverged clade of Neotropical birds. Subspecies of the Variable
 Seedeater (Sporophila corvina) that differ dramatically in plumage colour
 have established secondary contact at two independent contact zones in
 Costa Rica and Panama. We first evaluated divergence in song in allopatric
 populations close to the most recent contact zone (Costa Rica), where the
 two subspecies do not hybridize, and found significant differences in song
 structure and composition of song elements between subspecies. Then, we
 used an experimental approach to measure a territorial male's
 aggressive response to visual and acoustic signals, as a proxy of the role
 of divergent secondary sexual traits in reproductive isolation. These
 playback experiments did not show clear effects of divergent colour and
 song on aggressive response -- we found no effect of plumage coloration
 and song in one subspecies, and males of the other subspecies were more
 aggressive towards homotypic songs but, unexpectedly, to heterotypic
 plumages. Separately, we also characterized the song structure of hybrid
 individuals from the Panamanian contact zone to evaluate how songs covary
 given evidence for gene flow. These hybrid individuals sang songs of
 different element composition than allopatric subspecies but did not
 differ in most acoustic characteristics. Overall, our experiments suggest
 that reproductive isolation based on secondary sexual signals is weak in
 this group, and after secondary contact, the breeding phenology may
 synchronize, and divergent acoustic signals may homogenize, facilitating
 further hybridization.
description: Song Recording and measurement We evaluated
 variation in song structure and element composition between two<em>
 S. corvina </em>subspecies, <em>S. c. corvina</em> (here
 after named as corvina) and <em>S. c. hoffmanni</em> (here
 after named as hoffmanni). Male songs were recorded in the field at sites
 in the Caribbean (corvina males) and Pacific (hoffmanni males) slopes of
 central and eastern Costa Rica. We also recorded a few hybrid individuals
 from Gamboa, Panama to evaluate how acoustic signals from this black-pied
 hybrid population compares to the allopatric populations. Songs were
 recorded in two consecutive seasons between April and May 2019, and
 between July and August 2020, using a Tascam DR-100MKIII Linear PCM
 Recorder (Tascam Corporation, Japan), coupled with a Sennheiser ME66/K6
 directional microphone system (Sennheiser Electronic Corporation, Germany)
 housed in a Rycote 055208 standard Windshield, at 16 bits and a 48-kHz
 sampling rate in a WAV file. To supplement our field recordings, we
 included recordings available from the Macaulay Library (Cornell Lab of
 Ornithology, Ithaca, NY) and the Laboratorio de Bioacústica (Universidad
 de Costa Rica, San José, Costa Rica), increasing our sample size to a
 total of 89 males (Supplementary Material Table 1). We
 measured three to five songs per male selected randomly (using a random
 number  generator in Excel). In each song, we measured the following eight
 characteristics: 1) duration (s), 2) element richness (number of different
 elements in each song), 3) total number of elements in each song, 4) song
 pace (elements/duration), 5) lowest frequency (Hz), 6) highest frequency
 (Hz), 7) average frequency of maximum amplitude (Hz), and 8) average
 energy entropy (bits). All measurements were obtained using Raven Pro 1.6
 sound analysis software (Cornell Lab of Ornithology, Ithaca, NY), using a
 combination of wave form, sonogram, and power spectrum windows. Our
 spectrograms were built using a frequency resolution of 188 Hz and
 temporal resolution of 5.8 ms, with a Hann window with 50% overlap and 256
 Hz transform size. Song playback and mount presentation
 experiments We performed playback experiments to
 evaluate the aggressive response of local males to different playbacks and
 mounts, simulating intrusions on the focal territory. Playback experiments
 were carried out from July to August 2020, in the Central Pacific and
 Central Caribbean slopes of Costa Rica (Fig.1A, Supplementary Material
 Table 2), along secondary growth habitats. We found territories by finding
 singing males and placed the speaker and mount after a few minutes of
 observation to ensure that males were actively singing and that  the
 target male was the territory owner (i.e., no other males nearby). We
 placed the speaker and mount at 3m height because territorial males
 usually display from high exposed perch (personal observation), and ~10m
 away from the target male close to vegetation. Songs were broadcasted from
 an Anker AK-A3121011 loudspeaker placed just below the taxidermic mount at
 a sound pressure level of 80 dB by a Sper Scientific mini sound level
 meter (model 840014), with a fast response setup, and located 1m away. We
 then moved away 10 m from the speaker and the target male and waited 3
 minutes before starting the acoustic stimuli. Each target individual
 was <br>exposed to just one treatment, which was selected randomly
 from the pool of all possible combinations of stimuli. Treatments
 consisted of eight playback recordings of both subspecies from allopatric
 populations (4 per subspecies), in all possible combinations with four
 mounts of corvina or hoffmanni (2 per subspecies), for a total of 32
 possible combinations. Each experiment consisted of two
 minutes of stimuli, followed by three minutes of silence. For each
 experiment we estimated the initial distance (m), as the distance when
 acoustic stimulus started, and measured the aggressive response as: 1)
 vocal latency (s) or time to first vocal response, 2) song latency (s) or
 time to first song response, 3) number of songs produced in response to
 the first playback, 4) number of calls, 5) flight latency (s) or the time
 to first flight, 6) number of flights, 7) time to approach the mount at
 &lt; 3m (s), 8) total time interacting with the mount at &lt; 3m
 (s), and 9) minimum distance (m) from the mount and speaker. We recorded
 the response behaviours for five minutes, starting when the acoustic
 stimuli were first broadcasted.
description: # Data from: Weak premating reproductive isolation despite divergence in
 secondary sexual traits in the Variable Seedeater
 [https://doi.org/10.5061/dryad.8gtht76x5](https://doi.org/10.5061/dryad.8gtht76x5) The dataset comprises structural measurements of songs from two subspecies and hybrids of *Sporophila corvina*, along with behavioral responses recorded during playback and mount presentations. The song measurements are utilized to estimate song variation between and within subspecies, and to assess how hybrid individuals differ from allopatric populations. Behavioral responses to playback and mount experiments were documented to evaluate how territorial males of *S. corvina* subspecies respond to simulated intrusions from decoys bearing homotypic or heterotypic signals (song and plumage color) in all possible combinations. These behavioral responses are utilized to assess male-male aggression as a proxy for premating reproductive isolation. ## Description of the data and file structure Data is divided in two documents: The first document, 'Scorvina_songs.txt', is a tab-separated file containing various measurements for each song. These measurements include duration (in seconds), element richness (the number of different elements in each song), total number of elements in each song, song pace (elements per duration), lowest frequency (in Hz), highest frequency (in Hz), average frequency of maximum amplitude (in Hz), and average energy entropy (in bits) per song and per individual. All measurements were acquired using Raven Pro 1.6 sound analysis software from the Cornell Lab of Ornithology in Ithaca, NY. The analysis involved utilizing a combination of waveform, sonogram, and power spectrum windows. Spectrograms were constructed with a frequency resolution of 188 Hz and a temporal resolution of 5.8 ms, using a Hann window with 50% overlap and a transform size of 256 Hz. The second document, 'Scorvina_playback.txt', is a tab-separated file containing various measurements related to aggressive responses. These measurements include the initial distance (in meters) at which the acoustic stimulus started and the following recorded responses: vocal latency (time to the first vocal response in seconds), song latency (time to the first song response in seconds), number of songs produced in response to the first playback, number of calls, flight latency (time to the first flight response in seconds), number of flights, time to approach the mount at a distance of less than 3 meters (in seconds), total time interacting with the mount at a distance of less than 3 meters (in seconds), and the minimum distance (in meters) from the mount and speaker. These values were recorded over a period of five minutes, starting from when the acoustic stimuli were first broadcasted.