Bread and hummus: trait connectance and correlation pleiades in grain crops

Phenotypic integration has been investigated from multiple perspectives. From a developmental perspective, connectance has been defined as the level of linkage between traits. Correlation pleiades, i.e ., correlations between some traits and, simultaneously, lack of correlations between these and other traits have been interpreted as the independence of certain developmental processes with respect to other processes within the organism, and as the outcome from the discrepancy between the agencies participating in the formation of the trait and the selective forces influencing its function. Here, I use two published data sets to test the variation in connectance with both trait and genotype and the existence and meaning of correlation pleiades in wheat and chickpea. Connectance varied from 0.09 to 4.2 in wheat and from 0.06 to 22.8 in chickpea, and cluster analyses revealed correlation pleiades. The frequency distribution of connectance conformed to a power law with similar slopes = −1.665 ± 0.222 for wheat and −1.555 ± 0.126 for chickpea, consistent with developmental self-organisation. Connectance was lower for traits with higher heritability such as seed weight, which together with the negative association between heritability and phenotypic plasticity completes a relational triangle: high connectance ⇔ low heritability ⇔ high phenotypic plasticity.