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Historic hybridization and persistence of a novel mito-nuclear combination in red-backed voles (genus Myodes).

Runck AM, Matocq MD, Cook JA - BMC Evol. Biol. (2009)

Bottom Line: The introgressant form is characterized by having mitochondrial haplotypes closely related to the northern M. rutilus on a nuclear background and morphological characteristics of southern M. gapperi.Introgression appears to have been historic as pure populations of M. rutilus are now isolated to the north from introgressants or pure M. gapperi by the LeConte Glacier.As we do not find pure M. rutilus or M. gapperi individuals throughout the distribution of the introgressant form, it appears that the introgressants are a self-sustaining entity not requiring continued hybridization between pure parental forms to generate this novel combination of characters.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Idaho State University, Pocatello, Idaho 83209, USA. arunck2@unl.edu

ABSTRACT

Background: The role of hybridization in generating diversity in animals is an active area of discovery and debate. We assess hybridization across a contact zone of northern (Myodes rutilus) and southern (M. gapperi) red-backed voles using variation in skeletal features and both mitochondrial and nuclear loci. This transect extends approximately 550 km along the North Pacific Coast of North America and encompasses 26 populations (n = 485). We establish the history, geographic extent and directionality of hybridization, determine whether hybridization is ongoing, and assess the evolutionary stability of novel genomic combinations.

Results: Identification of M. rutilus and M. gapperi based on the degree of closure of the post-palatal bridge was concordant with the distribution of diagnostic nuclear MYH6 alleles; however, an 80 km zone of introgressed populations was identified. The introgressant form is characterized by having mitochondrial haplotypes closely related to the northern M. rutilus on a nuclear background and morphological characteristics of southern M. gapperi.

Conclusion: Introgression appears to have been historic as pure populations of M. rutilus are now isolated to the north from introgressants or pure M. gapperi by the LeConte Glacier. As we do not find pure M. rutilus or M. gapperi individuals throughout the distribution of the introgressant form, it appears that the introgressants are a self-sustaining entity not requiring continued hybridization between pure parental forms to generate this novel combination of characters.

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Distribution map of Myodes rutilus, M. gapperi, and introgressants in southeast Alaska. Open circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. rutilus. Black shaded circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. gapperi. Grey shaded circles refer to individuals with post-palatal bridge morphology and MYH6 alleles of M. gapperi and cytochrome b haplotypes of M. rutilus. Numbers correspond to population numbers in Table 1. The grey dashed line indicates change in post-palatal bridge morphology. Stippled areas indicate present-day glaciers. Inset of highlighted area is GIS glacial coverage that shows the LeConte Glacier extending to the coast, resulting in a physical barrier between populations 7 and 8.
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Figure 1: Distribution map of Myodes rutilus, M. gapperi, and introgressants in southeast Alaska. Open circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. rutilus. Black shaded circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. gapperi. Grey shaded circles refer to individuals with post-palatal bridge morphology and MYH6 alleles of M. gapperi and cytochrome b haplotypes of M. rutilus. Numbers correspond to population numbers in Table 1. The grey dashed line indicates change in post-palatal bridge morphology. Stippled areas indicate present-day glaciers. Inset of highlighted area is GIS glacial coverage that shows the LeConte Glacier extending to the coast, resulting in a physical barrier between populations 7 and 8.

Mentions: There was a distinct break in character state of the post-palatal bridge near the Stikine River (Table 1). Individuals from Jap Creek (locality 7, Figure 1) and north had incomplete post-palatal bridges, which is the same character state observed in the M. rutilus from the reference sample (interior Alaska), and from throughout its range (Runck in prep). Individuals from Mallard Slough (locality 8, Figure 1) and south had complete bridges, characteristic of the M. gapperi reference sample (Minnesota) and from specimens of M. gapperi throughout its range (Figure 1; Runck in prep). There were, however, two individuals (localities 3 & 4), north of Mallard Slough that possessed complete post-palatal bridges, and two individuals (localities 14 & 23) south of Mallard Slough that had incomplete post-palatal bridges. In interior Alaska, 5 of 46 M. rutilus individuals had complete post-palatal bridges suggesting a low incidence of natural variation within this character in the northern red-backed vole.


Historic hybridization and persistence of a novel mito-nuclear combination in red-backed voles (genus Myodes).

Runck AM, Matocq MD, Cook JA - BMC Evol. Biol. (2009)

Distribution map of Myodes rutilus, M. gapperi, and introgressants in southeast Alaska. Open circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. rutilus. Black shaded circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. gapperi. Grey shaded circles refer to individuals with post-palatal bridge morphology and MYH6 alleles of M. gapperi and cytochrome b haplotypes of M. rutilus. Numbers correspond to population numbers in Table 1. The grey dashed line indicates change in post-palatal bridge morphology. Stippled areas indicate present-day glaciers. Inset of highlighted area is GIS glacial coverage that shows the LeConte Glacier extending to the coast, resulting in a physical barrier between populations 7 and 8.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2697987&req=5

Figure 1: Distribution map of Myodes rutilus, M. gapperi, and introgressants in southeast Alaska. Open circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. rutilus. Black shaded circles refer to individuals with post-palatal bridge morphology, cytochrome b haplotypes, and MYH6 alleles of M. gapperi. Grey shaded circles refer to individuals with post-palatal bridge morphology and MYH6 alleles of M. gapperi and cytochrome b haplotypes of M. rutilus. Numbers correspond to population numbers in Table 1. The grey dashed line indicates change in post-palatal bridge morphology. Stippled areas indicate present-day glaciers. Inset of highlighted area is GIS glacial coverage that shows the LeConte Glacier extending to the coast, resulting in a physical barrier between populations 7 and 8.
Mentions: There was a distinct break in character state of the post-palatal bridge near the Stikine River (Table 1). Individuals from Jap Creek (locality 7, Figure 1) and north had incomplete post-palatal bridges, which is the same character state observed in the M. rutilus from the reference sample (interior Alaska), and from throughout its range (Runck in prep). Individuals from Mallard Slough (locality 8, Figure 1) and south had complete bridges, characteristic of the M. gapperi reference sample (Minnesota) and from specimens of M. gapperi throughout its range (Figure 1; Runck in prep). There were, however, two individuals (localities 3 & 4), north of Mallard Slough that possessed complete post-palatal bridges, and two individuals (localities 14 & 23) south of Mallard Slough that had incomplete post-palatal bridges. In interior Alaska, 5 of 46 M. rutilus individuals had complete post-palatal bridges suggesting a low incidence of natural variation within this character in the northern red-backed vole.

Bottom Line: The introgressant form is characterized by having mitochondrial haplotypes closely related to the northern M. rutilus on a nuclear background and morphological characteristics of southern M. gapperi.Introgression appears to have been historic as pure populations of M. rutilus are now isolated to the north from introgressants or pure M. gapperi by the LeConte Glacier.As we do not find pure M. rutilus or M. gapperi individuals throughout the distribution of the introgressant form, it appears that the introgressants are a self-sustaining entity not requiring continued hybridization between pure parental forms to generate this novel combination of characters.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological Sciences, Idaho State University, Pocatello, Idaho 83209, USA. arunck2@unl.edu

ABSTRACT

Background: The role of hybridization in generating diversity in animals is an active area of discovery and debate. We assess hybridization across a contact zone of northern (Myodes rutilus) and southern (M. gapperi) red-backed voles using variation in skeletal features and both mitochondrial and nuclear loci. This transect extends approximately 550 km along the North Pacific Coast of North America and encompasses 26 populations (n = 485). We establish the history, geographic extent and directionality of hybridization, determine whether hybridization is ongoing, and assess the evolutionary stability of novel genomic combinations.

Results: Identification of M. rutilus and M. gapperi based on the degree of closure of the post-palatal bridge was concordant with the distribution of diagnostic nuclear MYH6 alleles; however, an 80 km zone of introgressed populations was identified. The introgressant form is characterized by having mitochondrial haplotypes closely related to the northern M. rutilus on a nuclear background and morphological characteristics of southern M. gapperi.

Conclusion: Introgression appears to have been historic as pure populations of M. rutilus are now isolated to the north from introgressants or pure M. gapperi by the LeConte Glacier. As we do not find pure M. rutilus or M. gapperi individuals throughout the distribution of the introgressant form, it appears that the introgressants are a self-sustaining entity not requiring continued hybridization between pure parental forms to generate this novel combination of characters.

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