The environmental and genetic regulation of obake expressivity: morphogenetic fields as evolvable systems.
The morphogenetic field, a fundamental concept of classical embryology, is once again being invoked to describe developmental processes. Because the evolution of adult structures requires the modification of development, the ways in which morphogenetic fields can change over time may yield insights into evolutionary possibilities. We considered how the duplication/multiplication of a morphogenetic field in fruit flies, caused by the previously described obake (obk) mutation, is regulated by genetic and environmental factors. Mutations of genes in the canonical antenna-producing imaginal disc pathway suppressed duplication as expected, although the results suggested that other pathways might also be involved. Overgrowth mutations, expected to increase duplication, actually suppressed it. Mutations in the heat-shock protein gene Hsp83 did not uniformly enhance obk expressivity as hypothesized. Using third chromosomes extracted from wild-derived lines, natural genetic variation for modifiers of obk function was found to be extensive. Larval crowding suppressed the obk phenotype, but there was no evidence of trade-offs between body or head size and arista number. Our results suggest that a complex interplay of genetic and environmental factors in the regulation of fields may be responsible for ample natural variation in the expressivity of adult phenotypes, affording multiple opportunities for selection and evolutionary modification.
Department of Zoology, University of Toronto, 25 Harbord Street, Toronto, Ontario M5S 3G5, Canada.
Joel
J
Atallah
Ian
I
Dworkin
Una
U
Cheung
Aisha
A
Greene
Bryant
B
Ing
Lisa
L
Leung
Ellen
E
Larsen
D000483:Alleles; D000825:Animal Structures / Q000196:embryology*; D000818:Animals; D001837:Body Weights and Measures; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000196:embryology* / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D005838:Genotype; D006360:Heat-Shock Proteins / Q000378:metabolism; D009024:Morphogenesis; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D011156:Population Density
D029721:Drosophila Proteins; D006360:Heat-Shock Proteins; C089272:Hsp83 protein, Drosophila