Genotype-specific relationships among phosphorus use, growth and abundance in Daphnia pulicaria

Abstract

The framework ecological stoichiometry uses elemental composition of species to make predictions about growth and competitive ability in defined elemental supply conditions. Although intraspecific differences in stoichiometry have been observed, we have yet to understand the mechanisms generating and maintaining such variation. We used variation in phosphorus (P) content within a Daphnia species to test the extent to which %P can explain variation in growth and competition. Further, we measured 33P kinetics (acquisition, assimilation, incorporation and retention) to understand the extent to which such variables improved predictions. Genotypes showed significant variation in P content, 33P kinetics and growth rate. P content alone was a poor predictor of growth rate and competitive ability. While most genotypes exhibited the typical growth penalty under P limitation, a few varied little in growth between P diets. These observations indicate that some genotypes can maintain growth under P-limited conditions by altering P use, suggesting that decomposing P content of an individual into physiological components of P kinetics will improve stoichiometric models. More generally, attention to the interplay between nutrient content and nutrient-use is required to make inferences regarding the success of genotypes in defined conditions of nutrient supply.

The Growth Rate Hypothesis as a predictive framework for microevolutionary adaptation to selection for high population growth: an experimental test under phosphorus rich and phosphorus poor conditions

“…2004;Kyle et al 2006), providing support for a phenotypic, but not necessarily genetic association 46 between P-content and growth. Other studies have examined the relationship between SGR and P-47 content across different food quality levels or ontogenetic stages for different genotypes but did not 48 The limited number of studies that do allow for a direct test of GRH predictions at the intraspecific 50 genetic level have reported evidence for considerable heritable variation in SGR but less so for P-51 content, and were inconclusive regarding the genetic relationship between both variables (Arnold et al of association between P-content and SGR could be explained by any (combination) of the following 54 reasons: (1) SGR is predominantly determined by growth efficiency per unit of body P, (2) physiological 55 rates involving mass specific P acquisition and retention are more important determinants of SGR than 56 P-content itself (Sherman et al 2017), and (3) genetic variation in SGR is controlled by traits unrelated to 57 A second prerequisite for the GRH to provide a useful framework for predicting microevolutionary 59 adaptation is that SGR should strongly approximate fitness. While fitness can be estimated in multiple 60 ways (Murray 1990;Metz et al 1992;Benton & Grant 2000), population growth rate (PGR) is a common 61 surrogate for fitness as it integrates all aspects of reproduction and survival Ricklefs 62 1990 may result in evolutionary responses in the latter traits as well, and weaken the association between the 67 evolutionary trajectories of SGR, P-content, and fitness.…”

Stoichiometric Traits Vary Widely Within Species: A Meta-Analysis of Common Garden Experiments

“…Our comparison of the amount of genetic variation in ES traits and the genetic variation in life history traits demonstrated that nearly all types of ES traits showed lower genetic intraspecific variation than life history traits. One clear exception was genetic variation among genotypes in AAA traits, which was influenced by a large amount of variation in one study (Sherman et al, 2017). If this difference in variation between ES and life history traits is genuine, it could be inferred that less genetic variation in ES traits is maintained within populations and that ES trait means evolve slowly across populations, in comparison to life history traits.…”

“…Finally, a "common garden" allows for measurement of the amount of genetic variation in traits in a single environment and the chosen environmental conditions may influence the amount of trait variation displayed. For example, there was more variation in P-acquisition and assimilation under P-limited conditions relative to P-sufficient conditions (Sherman et al, 2017). However, we assumed that the common garden conditions were chosen by the original study authors to reflect ecologically-relevant environments, and that the trait variation we observed is, therefore, a reasonable representation of that found in nature.…”

“…larger than life history traits (with an effect size of 164%) and the magnitude of this effect can be partially attributed to a single study that found substantial genotypic effects, particularly for P retention (Sherman et al, 2017).…”

“…Thus, inherent differences among taxonomic groups may be confounded with the genotypeand population-level comparisons, though the relative amounts of variation were similar among all taxonomic groups. Second, genotype-level variation may be overestimated relative to natural populations, because some studies included genotypes with low ecological fitness (e.g., Sherman et al, 2017) and some collected genotypes from wide geographical areas that covered a range of environments similar to the magnitude of variation we would expect across populations. Third, many of the common gardens were only conducted for a single generation, meaning that maternal and epigenetic effects could represent latent sources of trait variation (Weaver et al, 2004).…”