An experimental test of the Growth Rate Hypothesis as a predictive framework for microevolutionary adaptation

The growth rate hypothesis (GRH), a central concept of ecological
stoichiometry, posits that the relative body phosphorus content of an
organism is positively related to somatic growth rate as protein
synthesis, which is necessary for growth, requires P-rich rRNA and has
strong support at the interspecific level. Here, we explore the use of the
GRH to predict microevolutionary responses in consumer body stoichiometry.
For this, we subjected zooplankton populations to selection for fast
population growth (PGR) in P-rich (HPF) and P-poor (LPF) food
environments. With common garden transplant experiments, we demonstrate
that in HP populations evolution towards increased PGR was concomitant
with an increase in relative phosphorus content. In contrast, LP
populations evolved higher PGR without an increase in relative phosphorus
content. We conclude that the GRH has the potential to predict
microevolutionary change, but that its application is contingent on the
environmental context. Our results highlight the potential of cryptic
evolution in determining the performance response of populations to
elemental limitation of their food resources.