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1 October 2005 NO SUPPORT FOR A GENETIC BASIS OF MANDIBLE CROSSING DIRECTION IN CROSSBILLS (LOXIA SPP)
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Abstract

Unusual among birds, the bill tips in crossbills (Loxia spp.) overlap in the vertical plane, with the tip of the lower mandible to either the left or right of the tip of the upper mandible when viewed from above. Patterns observed in wild populations and experimental foraging data suggest that a 1:1 ratio of left- to right-crossing individuals is maintained by frequency-dependent natural selection in some populations, and that genetic drift causes deviation from a 1:1 ratio in other populations. Both processes require a genetic basis for this remarkable polymorphism, yet few data are available that address whether, and how, mandible crossing direction is heritable. To test for a genetic basis of this trait (single or quantitative, autosomal or sex-linked), we analyzed resemblance in mandible crossing direction between related captive-bred individuals of several crossbill taxa with standard statistical techniques as well as modern animal model methodology. Surprisingly, we did not find statistically significant support for a genetic basis of mandible crossing direction. Comparisons of the ratio of left- to right-crossing males and females in wild populations also did not support a sex-linked quantitative genetic basis. We conclude that mandible crossing direction may have uncharacteristically low heritability, but we cannot rule out that it is nongenetically determined.

La Dirección de Cruzamiento de la Mandíbula en las Especies de Loxia no Presenta Base Genética

Pim Edelaar, Erik Postma, Peter Knops, and Ron Phillips "NO SUPPORT FOR A GENETIC BASIS OF MANDIBLE CROSSING DIRECTION IN CROSSBILLS (LOXIA SPP)," The Auk 122(4), 1123-1139, (1 October 2005). https://doi.org/10.1642/0004-8038(2005)122[1123:NSFAGB]2.0.CO;2
Received: 27 August 2004; Accepted: 27 March 2005; Published: 1 October 2005
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