Evolutionary Genetics of Animal Development

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PROJECT SUMMARY Genes play two different roles in biology, giving shape to phenotypes through developmental processes within individuals, and transmitting traits across generations through Mendelian inheritance. Evolutionary developmental geneticists work at the intersection of these roles, asking how the mechanisms that operate within individuals influence the origin, maintenance, and fate of phenotypic variation in populations. Pleiotropy, dominance, epistasis, polygeny, and linkage are some of the phenomena that unite developmental and population genetics. One further class of phenomenon – early embryonic development – also bridges this divide, involving molecular and cellular contributions from the embryo's own zygotic genome but also from the substance of the egg, a product of its mother's genome. This dual regulation by two genomes creates distinctive transmission genetics properties for early development, properties that alter predictions about patterns of variation and divergence. To better understand how maternal and zygotic genetic effects and their interactions shape variation and evolution of development, this project sets as its goal the characterization of genetic architectures of embryogenesis in multiple experimental model systems, each with unique complementary features. One line of research focuses on Caenorhabditis nematodes, a longstanding experimental model for developmental genetics. Building on the lab's extensive resources for quantitative genetic analysis in these animals, the project will use controlled experimental crosses to reveal genetic variants that act either in the mother's genome or in that of her offspring to influence developmental gene expression. The project will use two experimental panels of C. elegans, one that maximizes detection power and one that maximizes mapping resolution. To address questions about the role of mating system in maternal-zygotic coevolution, the project will also use an experimental panel of C. becei, a closely related species that exhibits obligate outcrossing in contrast to the self-fertilization that characterizes C. elegans. A second line of research focuses on variation in embryonic development an annelid model system, Streblospio benedicti. This species is unique in exhibiting both direct and indirect development as heritable variation, with the alternative modes representing adaptive strategies to different environmental conditions. This system provides a directional selection counterpart to the stabilizing selection that Caenorhabditis embryogenesis experiences. Measurements of embryonic gene expression in a large S. benedicti pedigree will facilitate genetic dissection of both maternal and zygotic contributions to development and tests of the role of maternal-zygotic genetic interactions in driving or preventing adaptive evolution.