Résumé
Seed plants vary tremendously in size and morphology. However, variation
and covariation between plant traits may at least in part be governed by
universal biophysical laws and biological constants. Metabolic Scaling
Theory (MST) posits that whole-organismal metabolism and growth rate are
under stabilizing selection that minimizes the scaling of hydrodynamic
resistance and maximizes the scaling of resource uptake. This constrains
variation in physiological traits and in the rate of biomass accumulation,
so that they can be expressed as mathematical functions of plant size with
near constant allometric scaling exponents across species. However,
observed variation in scaling exponents questions the evolutionary drivers
and the universality of allometric equations. We have measured growth
scaling and fitness traits of 451 Arabidopsis thaliana accessions with
sequenced genomes. Variation among accessions around the scaling exponent
predicted by MST correlated with relative growth rate, seed production and
stress resistance. Genomic analyses indicate that growth allometry is
affected by many genes associated with local climate and abiotic stress
response. The gene with the strongest effect, PUB4, has molecular
signatures of balancing selection, suggesting that intraspecific variation
in growth scaling is maintained by opposing selection on the trade-off
between seed production and abiotic stress resistance. Our findings
support a core MST prediction and suggest that variation in allometry
contributes to local adaptation to contrasting environments. Our results
help reconcile past debates on the origin of allometric scaling in
biology, and begin to link adaptive variation in allometric scaling to
specific genes.