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To study how natural allelic variation explains quantitative developmental system variation, we characterized natural differences in germ stem cell niche activity, measured as progenitor zone (PZ) size, between two Caenorhabditis elegans isolates. Linkage mapping yielded candidate loci on chromosomes II and V, and we found that the isolate with a smaller PZ size harbours a 148 bp promoter deletion in the Notch ligand, lag-2/Delta, a central signal promoting germ stem cell fate. As predicted, introducing this deletion into the isolate with a large PZ resulted in a smaller PZ size. Unexpectedly, restoring the deleted ancestral sequence in the isolate with a smaller PZ did not increase—but instead further reduced—PZ size. These seemingly contradictory phenotypic effects are explained by epistatic interactions between the lag-2/Delta promoter, the chromosome II locus, and additional background loci. These results provide first insights into the quantitative genetic architecture regulating an animal stem cell system. Stem cell niches regulate proliferation of stem cells, but variation in this control across natural populations has not been explored. Here they combine quantitative genetics and gene editing to show that natural variation in C. elegans germ stem cell niche activity is shaped by complex gene-gene interactions. [ABSTRACT FROM AUTHOR]

Understanding how the environment impacts development is of central interest in developmental and evolutionary biology. On the one hand, we would like to understand how the environment induces phenotypic changes (the study of phenotypic plasticity). On the other hand, we may ask how a development system maintains a stable and precise phenotypic output despite the presence of environmental variation. We study such developmental robustness to environmental variation using vulval cell fate patterning in the nematode Caenorhabditis elegans as a study system. Here we review both mechanistic and evolutionary aspects of these studies, focusing on recently obtained experimental results. First, we present evidence indicating that vulval formation is under stabilizing selection. Second, we discusss quantitative data on the precision and variability in the output of the vulval developmental system in different environments and different genetic backgrounds. Third, we illustrate how environmental and genetic variation modulate the cellular and molecular processes underlying the formation of the vulva. Fourth, we discuss the evolutionary significance of environmental sensitivity of this developmental system. [ABSTRACT FROM AUTHOR]

Many insect species have evolved a number of antipredator tactics among which the animal can choose when attacked by a natural enemy. While it is known that individuals may differ in how the antipredator tactics are employed, quantitative studies are rare. In the pea aphid, it has been suggested that different clones differ in their propensity to escape from a predator and that this propensity is linked to the body color of the aphid. We tested clonal variation in the escape behavior in red and green clones of the pea aphid. In three experiments the responses of clones to artificial stimuli and a natural predator were quantified. The results indicate that (1) clones differ considerably in their propensity to show escape behavior, (2) red clones are more likely to drop off the host plant when subjected to an artificial stimulus than green clones are, and (3) the patterns of clonal variation in the escape behavior were not consistent through all three experiments, as clones did not differ in their behavior when attacked by a real predator. The differences in the responses of a clone toward different stimuli supposed to mimic predator attack suggest that extrapolating from laboratory experiments to a field situation may be difficult. [ABSTRACT FROM AUTHOR]