Speciation is a process in which genetic drift and selection cause divergence over tSpeciation is a process in which genetic drift and selection cause divergence over time. However, there is no rule dictating the time required for speciation, and even low levels of gene flow hinder divergence, so that taxa may be poised at the threshold of speciation for long periods of evolutionary time. We sequenced mitochondrial DNA (mtDNA) and eight nuclear introns (nuDNA) to estimate genomic levels of differentiation and gene flow between the Eurasian common teal (Anas crecca crecca) and the North American green-winged teal (A. c. carolinensis). These ducks come into contact in Beringia (northeastern Asia and northwestern North America) and have likely done so, perhaps cyclically, since the Pliocene-Pleistocene transition, ~2.6 Ma, when they apparently began diverging. They have diagnosable differences in male plumage and are 6.9% divergent in the mtDNA control region, with only 1 of 58 crecca and 2 of 86 carolinensis having haplotypes grouping with the other. Two nuclear loci were likewise strongly structured between these teal (ΦST > 0.35), but six loci were undifferentiated or only weakly structured (ΦST = 0.0–0.06). Gene flow between crecca and carolinensis was ~1 individual per generation in both directions in mtDNA, but was asymmetrical in nuDNA, with ~1 and ~20 individuals per generation immigrating into crecca and carolinensis, respectively. This study illustrates that species delimitation using a single marker oversimplifies the complexity of the speciation process, and it suggests that even with divergent selection, moderate levels of gene flow may stall the speciation process short of completion.
Anas crecca mtDNA control region sequences.fas
FASTA file containing 144 mtDNA control region sequences (987 aligned sites) sampled from Common (Green-winged) Teal (Anas crecca). The first 58 sequences were sampled from Eurasia, and the next 86 sequences were sampled from North America.
TEAL.mtDNA-CR.final.fas
Anas crecca CHD1Z alleles.fas
FASTA file containing 78 resolved alleles from intron 19 of the chromo-helicase DNA binding (CHD1Z) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 45 alleles were sampled from Eurasia, and the next 33 were sampled from North America. Note that CHD1Z is located on the Z-chromosome, and therefore, females only have a single copy.
Teal.CHD1Z.final.fas
Anas crecca CRYAB alleles.fas
FASTA file containing 78 resolved alleles from intron 1 of the alpha-B crystallin (CRYAB) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 50 alleles were sampled from Eurasia, and the next 50 were sampled from North America.
TEAL.CRYAB.final.fas
Anas crecca ENO1 alleles.fas
FASTA file containing 100 resolved alleles from intron 8 of the alpha enolase (ENO1) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 50 alleles were sampled from Eurasia, and the next 50 were sampled from North America.
TEAL.ENO1.final.fas
Anas crecca FGB alleles.fas
FASTA file containing 100 resolved alleles from intron 7 of the beta fibrinogen (FGB) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 50 alleles were sampled from Eurasia, and the next 50 were sampled from North America.
TEAL.FGB.final.fas
Anas crecca GRIN1 alleles.fas
FASTA file containing 100 resolved alleles from intron 11 of the N-methyl D-aspartate 1 glutamate receptor (GRIN1) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 50 alleles were sampled from Eurasia, and the next 50 were sampled from North America.
TEAL.GRIN1.final.fas
Anas crecca LDHB alleles.fas
FASTA file containing 100 resolved alleles from intron 3 of the lactate dehydrogenase B(LDHB) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 50 alleles were sampled from Eurasia, and the next 50 were sampled from North America.
TEAL.LDHB.final.fas
Anas crecca ODC1 alleles.fas
FASTA file containing 100 resolved alleles from intron 5 of the ornithine decarboxylase (ODC1) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 50 alleles were sampled from Eurasia, and the next 50 were sampled from North America.
TEAL.ODC1.final.fas
Anas crecca PCK1 alleles.fas
FASTA file containing 100 resolved alleles from intron 8 of the phosphoenolpyruvate carboxykinase (PCK1) gene sampled from 50 Common (Green-winged) Teal (Anas crecca). The first 50 alleles were sampled from Eurasia, and the next 50 were sampled from North America.
TEAL.PCK1.final.fas
Anas crecca nuDNA for IM.infile
Input file for analysis of population history in the program IM. The input contains 8 loci sampled from 50 individuals of Anas crecca (25 from Eurasia, population 1; 25 from North America, population 2). Note that the data have been filtered for recombination, and therefore, some loci have fewer than 100 alleles sampled. The command line for running IM was: -i infile -q1 25 -m1 20 -m2 20 -t 1 -b 500000 -l 12.0 -a 50 -fg -g1 0.9 -g2 0.85 -k 30 -n 30 -q2 25 -qA 5 -s 105976 -p13 -j1 -e 24.0 -o outfile.txt
infile
Anas crecca mtDNA for IM.infile
Input file for analysis of population history from mtDNA control region (986 aligned nucleotides) in the program IM. The input contains 144 individuals of Anas crecca (58 from Eurasia, population 1; 86 from North America, population 2). The command line for running IM was: -i infile -q1 200 -m1 0.2 -m2 0.2 -t 40 -b 500000 -l 12.0 -fg -g1 0.9 -g2 0.9 -k 10 -n 10 -q2 200 -qA 40 -s 3156714860 -p13 -j1 -e 24.0 -o outfile.txt
infile
Anas crecca LAMARC.menu
Menu file for performing LAMARC analyses using the 8 nuclear introns sampled from Eurasian Common Teal.
TEALow-8loci.menu
Anas crecca Structure infile.txt
File containing genotypic information for 8 nuclear loci sampled from 25 Anas crecca crecca and 25 Anas crecca carolinensis. This file is formatted for STRUCTURE analyses.
Teal_8loci.txt
Anas crecca CRYAB.arp
Resolved alleles for Anas crecca crecca (n = 50)and Anas crecca carolinensis (n = 50) for intron 1 of the CRYAB gene. This file is formatted for analyses in Arlequin and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
TEAL-ABC.arp
TEAL-CHD1Z
Resolved alleles for Anas crecca crecca (n = 42)and Anas crecca carolinensis (n = 36) for intron 19 of the CHD1Z gene. This file is formatted for analyses in Arlequin and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
Anas crecca ENO1.arp
Resolved alleles for Anas crecca crecca (n = 50)and Anas crecca carolinensis (n = 50) for intron 8 of the ENO1 gene. This file is formatted for analyses in Arlequin, and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
TEAL-ENO.arp
Anas crecca FGB.arp
Resolved alleles for Anas crecca crecca (n = 50)and Anas crecca carolinensis (n = 50) for intron 7 of the FGB gene. This file is formatted for analyses in Arlequin, and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
TEAL-BF7.arp
Anas crecca GRIN1.arp
Resolved alleles for Anas crecca crecca (n = 50)and Anas crecca carolinensis (n = 50) for intron 13 of the GRIN1 gene. This file is formatted for analyses in Arlequin, and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
TEAL-MDAR.arp
Anas crecca LDHB.arp
Resolved alleles for Anas crecca crecca (n = 50)and Anas crecca carolinensis (n = 50) for intron 3 of the LDHB gene. This file is formatted for analyses in Arlequin, and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
TEAL-LDH.arp
Anas crecca ODC1.arp
Resolved alleles for Anas crecca crecca (n = 50)and Anas crecca carolinensis (n = 50) for intron 5 of the ODC1 gene. This file is formatted for analyses in Arlequin, and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
TEAL-ODC.arp
Anas crecca PCK1.arp
Resolved alleles for Anas crecca crecca (n = 50)and Anas crecca carolinensis (n = 50) for intron 8 of the PCK1 gene. This file is formatted for analyses in Arlequin, and sequences are sorted between OW (A. c. crecca) and NW (A. c. carolinensis) samples.
TEAL-PCK.arp
Genbank accession numbers.docx
Table of genbank accession numbers for each sample used in this study. Sampling location is provided (Old World, OW, for Eurasian Anas crecca crecca; New World, NW, for North American Anas crecca carolinensis). NA = not applicable (nuclear loci were not sequenced for 94 individuals).
genbank accession numbers.docx