Evolution and inheritance of early embryonic patterning in D. Simulans and D. Sechellia (Evolution, Dec 1 2010)

Evolution. 2010 Dec 1. doi: 10.1111/j.1558-5646.2010.01206.x. [Epub ahead of print]
EVOLUTION AND INHERITANCE OF EARLY EMBRYONIC PATTERNING IN D. SIMULANS AND D. SECHELLIA.

Lott SE, Ludwig MZ, Kreitman M.

Committee on Genetics and the Department of Ecology and Evolution, University of Chicago, 1101 E 57th St., Chicago, IL, 60637, USA Present Address: Department of Molecular and Cell Biology, 387 Stanley Hall #3220, University of California, Berkeley, CA 94720, USA E-mail: slott@uchicago.edu.
Abstract

Pattern formation in Drosophila is a widely studied example of a robust developmental system. Such robust systems pose a challenge to adaptive evolution, as they mask variation which selection may otherwise act upon. Yet we find variation in the localization of expression domains (henceforth ‘stripe allometry’) in the pattern formation pathway. Specifically, we characterize differences in the gap genes giant and Kruppel, and the pair-rule gene even-skipped, which differ between the sibling species D. simulans and D. sechellia. In a double-backcross experiment, stripe allometry is consistent with maternal inheritance of stripe positioning and multiple genetic factors, with a distinct genetic basis from embryo length. Embryos produced by F1 and F2 backcross mothers exhibit novel spatial patterns of gene expression relative to the parental species, with no measurable increase in positional variance among individuals. Buffering of novel spatial patterns in the backcross genotypes suggests that robustness need not be disrupted in order for the trait to evolve, and perhaps the system is incapable of evolving to prevent the expression of all genetic variation. This limitation, and the ability of natural selection to act on minute genetic differences that are within the “margin of error” for the buffering mechanism, indicates that developmentally buffered traits can evolve without disruption of robustness.

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