An experimental test of the growth rate hypothesis as a predictive framework for microevolutionary adaptation

Abstract

The growth rate hypothesis (GRH) 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. This hypothesis 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 populations of the rotifer Brachionus calyciflorus to selection for fast population growth rate (PGR) in P-rich (HPF) and P-poor (LPF) food environments. With common garden transplant experiments, we demonstrate that in HP populations evolution toward 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.

Revisiting the growth rate hypothesis: Towards a holistic stoichiometric understanding of growth

“…Organisms can adapt to biogeochemical changes over time through evolved differences in growth rate and nutrient use efficiencies (Frisch et al, 2014 ; Jeyasingh et al, 2009 ; Lemmen et al, 2022a ). For example, the rotifer Brachionus calyciflorus was selected for rapid growth under high P supply and developed faster growth and higher P content, consistent with the GRH (Lemmen et al, 2022b ). However, rotifers selected for faster growth under P‐limitation were able to evolve faster growth rates while keeping their body P content the same.…”

SEED: A framework for integrating ecological stoichiometry and eco‐evolutionary dynamics

“…However, environmental variation can also cause selection on the elemental phenotype in more direct ways. For example, environmental variation in elemental supply can cause stoichiometric mismatches between organisms and their diets, selecting for microevolutionary changes in acquisition, organismal stoichiometry, assimilation or excretion (Declerck et al, 2015; Frisch et al, 2014; Lemmen et al, 2023; Tobler et al, 2016). Such evolutionary responses in the elemental phenotype will likely alter the classical phenotype because the fluxes of elements that constitute the elemental phenotype (Table 1) are realised and controlled by combinations of behavioural, morphological, physiological and biochemical ‘classical’ traits.…”

“…In contrast, when selection arises from a stoichiometric mismatch, organisms are likely to evolve strategies that allow more efficient use of the limiting element. In the latter case, the concentration of that element in the body will either remain constant (Lemmen et al, 2023), or be reduced through elemental sparing (Merchant & Helmann, 2012; Turner et al, 2017) or elemental substitution (Price & Morel, 1990; Van Mooy et al, 2009). More likely than in the case of classic trait evolution, evolutionary responses to stoichiometric mismatch will involve strategies to dispose of excess elements.…”

“…Alternatively, they can test how variation in elemental supply and stoichiometric mismatches alter both elemental and classic phenotypes. Although initial attempts with experimental evolution in a stoichiometric context have yielded encouraging results, they have focused on specific hypotheses and have so far involved an incomplete characterisation of the elemental phenotype (Declerck et al, 2015; Lemmen et al, 2023).…”

“…Furthermore, growth-rate based differences in body P (and body N:P ratios) explain changes observed in zooplankton community composition following alterations in nutrient limitation in lakes (Elser et al, 1988). However, the relationship between intraspecific genetic variation in growth rate and body P appears to be highly variable across taxa and studies (Isanta-Navarro et al, 2022;Lemmen et al, 2023;Liess et al, 2013;Prater et al, 2017;Sherman et al, 2017;Weider et al, 2004). A recent systematic reassessment suggests that the relationship between body P and growth rate is relatively weak (Isanta-Navarro et al, 2022).…”