Arabidopsis thaliana is a plant that underwent a duplication of its entire genome about 20-40 million years ago. Researchers from the University of Texas recently tested the rate of expression divergence between these duplicated genes. [1] What they found was:

The proportion of duplicate genes upregulated under abiotic stress in roots or shoots is significantly greater than that of other genes in the genome.

Furthermore:

We obtained the same conclusion for duplicate genes in response to biotic stress induced by pathogen infections or pathogenic molecules.

And:

The data suggest that duplicate genes are preferentially involved in stress responses, probably through preferential retention or expression divergence of duplicate genes.

The researchers also looked at duplicated genes involved in development:

We found that the frequency of genes displaying differential expression in various developmental stages was greater in gene duplicates than in other genes….The data suggest that duplicate genes increase expression diversity during development, similar to the findings in Drosophila and yeast.

So what happens if we compare the rate of expression divergence between duplicated developmental genes and those genes involved in response to stress?

The expression divergence of duplicate genes under environmental stress is significantly greater than that under developmental process.

So what genes undergo the greatest level of expression divergence?

The levels of expression divergence between gene duplicates were greatest in extracellular transport, signal transduction, stress response and transcription, and lowest in the cellular and developmental processes such as energy pathway, protein metabolism, intracellular transport, DNA and RNA metabolism, and cell organization and biogenesis.

What’s teleological point of all this? For most people focused on evolution, gene duplication is considered as a brute give - something that happens and something that happens to affect evolution. Yet I am becoming increasingly convinced that gene duplication echoes the teleological essence of evolution. In this example, gene duplication functions in the overall context of the cell’s architecture and physiology such that evolution proceeds quite smartly. The genes closest to interfacing with the environment behave almost like “feelers,” helping organisms to find their way across evolutionary time. Yet because of the same cell architecture/physiology, the same process of gene duplication functions more as a buffer in the developmental context, allowing the cell to tweak a constrained process in conjunction to what the “feelers” find. The researchers themselves offer the following conclusion:

We propose a model for different evolutionary fates of duplicate genes in response to external and internal processes. Duplicate genes diverge in expression relatively rapidly in response to abiotic and biotic stresses, which might facilitate subfunctionalization, neofunctionalization and the evolution of an adaptive mechanism to cope with environmental changes. In development, duplicate genes diverge in expression relatively slowly and tend to be coregulated. A relatively slow rate of expression divergence between the duplicates might provide genetic robustness against null mutations and selective advantage by dosage-dependent gene regulation that enables organisms to fine-tune complex regulatory networks through genetic and epigenetic mechanisms. Therefore, duplicate genes could promote an adaptive mechanism for environmental changes or provide genetic robustness and dosage-dependent regulation during organismal development, which might facilitate polyploid evolution.

If this model holds up, what we have here, IMO, is a form of coordinated evolution. And such evolutionary coordination would exist as a function of the original design of the cell.

1. Misook Ha, Wen-Hsiung Li and Z. Jeffrey Chen. 2007. External factors accelerate expression divergence between duplicate genes. TRENDS in Genetics 23: 162-166.