Speciation in Western Scrub-Jays, Haldane's rule, and genetic clines in secondary contact

Speciation in Western Scrub-Jays, Haldane's rule, and genetic clines in secondary contact

Haldane's Rule, the tendency for the heterogametic sex to show reduced fertility in hybrid crosses, can obscure the signal of gene flow in mtDNA between species where females are heterogametic. Therefore, it is important when studying speciation and species limits in female-heterogametic specie...

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Published in:BMC evolutionary biology Vol. 14; no. 1; p. 135
Main Authors: Gowen, Fiona C, Maley, James M, Cicero, Carla, Peterson, A Townsend, Faircloth, Brant C, Warr, T Caleb, McCormack, John E
Format: Journal Article
Language:English
Published: England BioMed Central Ltd 17-06-2014
BioMed Central
Subjects:
Analysis
Animals
Aphelocoma californica
Biodiversity
Birds
Cell Nucleus - genetics
DNA, Mitochondrial - genetics
Evolution
Female
Gene Flow
Genetic aspects
Genetic Speciation
Hybridization
Hybridization, Genetic
Male
Mexico
Microsatellite Repeats
Mitochondrial DNA
Molecular Sequence Data
Museums
Passeriformes - classification
Passeriformes - genetics
Reproductive Isolation
Studies
Zoology
Sierra Nevada Mountain Range
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Summary:Haldane's Rule, the tendency for the heterogametic sex to show reduced fertility in hybrid crosses, can obscure the signal of gene flow in mtDNA between species where females are heterogametic. Therefore, it is important when studying speciation and species limits in female-heterogametic species like birds to assess the signature of gene flow in the nuclear genome as well. We studied introgression of microsatellites and mtDNA across a secondary contact zone between coastal and interior lineages of Western Scrub-Jays (Aphelocoma californica) to test for a signature of Haldane's Rule: a narrower cline of introgression in mtDNA compared to nuclear markers. Our initial phylogeographic analysis revealed that there is only one major area of contact between coastal and interior lineages and identified five genetic clusters with strong spatial structuring: Pacific Slope, Interior US, Edwards Plateau (Texas), Northern Mexico, and Southern Mexico. Consistent with predictions from Haldane's Rule, mtDNA showed a narrower cline than nuclear markers across a transect through the hybrid zone. This result is not being driven by female-biased dispersal because neutral diffusion analysis, which included estimates of sex-specific dispersal rates, also showed less diffusion of mtDNA. Lineage-specific plumage traits were associated with nuclear genetic profiles for individuals in the hybrid zone, indicating that these differences are under genetic control. This study adds to a growing list of studies that support predictions of Haldane's Rule using cline analysis of multiple loci of differing inheritance modes, although alternate hypotheses like selection on different mtDNA types cannot be ruled out. That Haldane's Rule appears to be operating in this system suggests a measure of reproductive isolation between the Pacific Slope and interior lineages. Based on a variety of evidence from the phenotype, ecology, and genetics, we recommend elevating three lineages to species level: A. californica (Pacific Slope); A. woodhouseii (Interior US plus Edwards Plateau plus Northern Mexico); A. sumichrasti (Southern Mexico). The distinctive Edwards Plateau population in Texas, which was monophyletic in mtDNA except for one individual, should be studied in greater detail given habitat threat.
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ISSN:1471-2148
1471-2148
DOI:10.1186/1471-2148-14-135