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Genetic and phenotypic variation across a hybrid zone between ecologically divergent tree squirrels (Tamiasciurus).
Mol Ecol. 2011 Aug; 20(16):3350-66.ME

Abstract

A hybrid zone along an environmental gradient should contain a clinal pattern of genetic and phenotypic variation. This occurs because divergent selection in the two parental habitats is typically strong enough to overcome the homogenizing effects of gene flow across the environmental transition. We studied hybridization between two parapatric tree squirrels (Tamiasciurus spp.) across a forest gradient over which the two species vary in coloration, cranial morphology and body size. We sampled 397 individuals at 29 locations across a 600-km transect to seek genetic evidence for hybridization; upon confirming hybridization, we examined levels of genetic admixture in relation to maintenance of phenotypic divergence despite potentially homogenizing gene flow. Applying population assignment analyses to microsatellite data, we found that Tamiasciurus douglasii and T. hudsonicus form two distinct genetic clusters but also hybridize, mostly within transitional forest habitat. Overall, based on this nuclear analysis, 48% of the specimens were characterized as T. douglasii, 9% as hybrids and 43% as T. hudsonicus. Hybrids appeared to be reproductively viable, as evidenced by the presence of later-generation hybrid genotypes. Observed clines in ecologically important phenotypic traits-fur coloration and cranial morphology-were sharper than the cline of putatively neutral mtDNA, which suggests that divergent selection may maintain phenotypic distinctiveness. The relatively recent divergence of these two species (probably late Pleistocene), apparent lack of prezygotic isolating mechanisms and geographic coincidence of cline centres for both genetic and phenotypic variation suggest that environmental factors play a large role in maintaining the distinctiveness of these two species across the hybrid zone.

Authors+Show Affiliations

Burke Museum and Department of Biology, University of Washington, Seattle, WA 98195, USA. aschavez22@yahoo.comNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

21771139

Citation

Chavez, Andreas S., et al. "Genetic and Phenotypic Variation Across a Hybrid Zone Between Ecologically Divergent Tree Squirrels (Tamiasciurus)." Molecular Ecology, vol. 20, no. 16, 2011, pp. 3350-66.
Chavez AS, Saltzberg CJ, Kenagy GJ. Genetic and phenotypic variation across a hybrid zone between ecologically divergent tree squirrels (Tamiasciurus). Mol Ecol. 2011;20(16):3350-66.
Chavez, A. S., Saltzberg, C. J., & Kenagy, G. J. (2011). Genetic and phenotypic variation across a hybrid zone between ecologically divergent tree squirrels (Tamiasciurus). Molecular Ecology, 20(16), 3350-66. https://doi.org/10.1111/j.1365-294X.2011.05184.x
Chavez AS, Saltzberg CJ, Kenagy GJ. Genetic and Phenotypic Variation Across a Hybrid Zone Between Ecologically Divergent Tree Squirrels (Tamiasciurus). Mol Ecol. 2011;20(16):3350-66. PubMed PMID: 21771139.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Genetic and phenotypic variation across a hybrid zone between ecologically divergent tree squirrels (Tamiasciurus). AU - Chavez,Andreas S, AU - Saltzberg,Carl J, AU - Kenagy,G J, Y1 - 2011/07/19/ PY - 2011/7/21/entrez PY - 2011/7/21/pubmed PY - 2011/10/7/medline SP - 3350 EP - 66 JF - Molecular ecology JO - Mol. Ecol. VL - 20 IS - 16 N2 - A hybrid zone along an environmental gradient should contain a clinal pattern of genetic and phenotypic variation. This occurs because divergent selection in the two parental habitats is typically strong enough to overcome the homogenizing effects of gene flow across the environmental transition. We studied hybridization between two parapatric tree squirrels (Tamiasciurus spp.) across a forest gradient over which the two species vary in coloration, cranial morphology and body size. We sampled 397 individuals at 29 locations across a 600-km transect to seek genetic evidence for hybridization; upon confirming hybridization, we examined levels of genetic admixture in relation to maintenance of phenotypic divergence despite potentially homogenizing gene flow. Applying population assignment analyses to microsatellite data, we found that Tamiasciurus douglasii and T. hudsonicus form two distinct genetic clusters but also hybridize, mostly within transitional forest habitat. Overall, based on this nuclear analysis, 48% of the specimens were characterized as T. douglasii, 9% as hybrids and 43% as T. hudsonicus. Hybrids appeared to be reproductively viable, as evidenced by the presence of later-generation hybrid genotypes. Observed clines in ecologically important phenotypic traits-fur coloration and cranial morphology-were sharper than the cline of putatively neutral mtDNA, which suggests that divergent selection may maintain phenotypic distinctiveness. The relatively recent divergence of these two species (probably late Pleistocene), apparent lack of prezygotic isolating mechanisms and geographic coincidence of cline centres for both genetic and phenotypic variation suggest that environmental factors play a large role in maintaining the distinctiveness of these two species across the hybrid zone. SN - 1365-294X UR - https://www.unboundmedicine.com/medline/citation/21771139/Genetic_and_phenotypic_variation_across_a_hybrid_zone_between_ecologically_divergent_tree_squirrels__Tamiasciurus__ L2 - https://doi.org/10.1111/j.1365-294X.2011.05184.x DB - PRIME DP - Unbound Medicine ER -