This is a preprint, a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Research
Staffan Bensch
Corresponding Author
ORCiD: https://orcid.org/0000-0002-0082-0899
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Background: Geographic regions, where two close-related taxa with different migration routes come into contact, are known as migratory divides. Hybrids originating from migratory divides are hypothesized to migrate intermediately relative to the parental populations. However, to date and due to technical limitations, few studies testing this hypothesis in wild birds and these have been to hybrids that have completed the migration back to the breeding grounds. Here, we make use of the well-established migration routes of willow warblers ( Phylloscopus trochilus ), for which the subspecies trochilus and acredula have migration-associated genetic markers on chromosomes 1 and 5. This enabled us to analyses the geographic distribution of pure and hybrid genotypes among juvenile birds on their first migration. Methods: Blood and feather samples were collected from wintering birds in eastern and western Africa (n = 69), and from juveniles during autumn migration in Portugal (n = 33), Italy (n = 38) and Bulgaria (n = 32). Genotyping was carried out by qPCR SNP assays, one SNP on chromosome 1 (SNP 65) and one on chromosome 5 (SNP 285). Both these SNPs have alternative alleles that are highly fixed (allele frequency>97%) in each of the subspecies. Results: The observed combined genotypes of the two SNPs were associated with the known migration routes and wintering distributions of trochilus and acredula . We found hybrids (HH) among the juveniles in Italy (5/38) and in Portugal (2/33). The proportion of hybrids in Italy was significantly higher than expected from a background rate of hybrid genotypes (1.5%) in allopatric populations of trochilus and acredula . Conclusions: Our genetic approach to assign individuals to subspecies and hybrids allowed us to investigate migration direction in juvenile birds on their first migration, which should illustrate the innate migratory direction with less of a bias than studies restricted to successful migrants. The excess of hybrid in Italy, suggests that they employ an intermediate route relative to the parental populations. Our qPCR SNP genotyping method is efficient for processing large sample sizes, and therefore powerful in migration research of species with known population genetic structure.
Keywords
Bird migration, genetic migration program, migratory divide, intermediate route, SNP genotyping, hybrid genotype, Phylloscopus trochilus
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This is a preprint, a preliminary version of a manuscript that has not completed peer review at a journal. Research Square does not conduct peer review prior to posting preprints. The posting of a preprint on this server should not be interpreted as an endorsement of its validity or suitability for dissemination as established information or for guiding clinical practice.
Research
Staffan Bensch
Corresponding Author
ORCiD: https://orcid.org/0000-0002-0082-0899
Badges
Prescreen
This manuscript passed our Prescreen assessment
Complete author information
Appropriate declaration statements
Potential risks to human health
Prescreen
History
CURRENT STATUS: Posted
Version 1
Posted 02 Jan, 2020
No community comments so far
Metrics
Comments: 0
PDF Downloads: ...
HTML Views: ...
License:
This work is licensed under a CC BY 4.0 License. Read Full License
Background: Geographic regions, where two close-related taxa with different migration routes come into contact, are known as migratory divides. Hybrids originating from migratory divides are hypothesized to migrate intermediately relative to the parental populations. However, to date and due to technical limitations, few studies testing this hypothesis in wild birds and these have been to hybrids that have completed the migration back to the breeding grounds. Here, we make use of the well-established migration routes of willow warblers ( Phylloscopus trochilus ), for which the subspecies trochilus and acredula have migration-associated genetic markers on chromosomes 1 and 5. This enabled us to analyses the geographic distribution of pure and hybrid genotypes among juvenile birds on their first migration. Methods: Blood and feather samples were collected from wintering birds in eastern and western Africa (n = 69), and from juveniles during autumn migration in Portugal (n = 33), Italy (n = 38) and Bulgaria (n = 32). Genotyping was carried out by qPCR SNP assays, one SNP on chromosome 1 (SNP 65) and one on chromosome 5 (SNP 285). Both these SNPs have alternative alleles that are highly fixed (allele frequency>97%) in each of the subspecies. Results: The observed combined genotypes of the two SNPs were associated with the known migration routes and wintering distributions of trochilus and acredula . We found hybrids (HH) among the juveniles in Italy (5/38) and in Portugal (2/33). The proportion of hybrids in Italy was significantly higher than expected from a background rate of hybrid genotypes (1.5%) in allopatric populations of trochilus and acredula . Conclusions: Our genetic approach to assign individuals to subspecies and hybrids allowed us to investigate migration direction in juvenile birds on their first migration, which should illustrate the innate migratory direction with less of a bias than studies restricted to successful migrants. The excess of hybrid in Italy, suggests that they employ an intermediate route relative to the parental populations. Our qPCR SNP genotyping method is efficient for processing large sample sizes, and therefore powerful in migration research of species with known population genetic structure.
Figure 1
Figure 2
Figure 3
This is a list of supplementary files associated with this preprint. Click to download.
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