The temperature‐size rule in Daphnia magna across different genetic lines and ontogenetic stages: Multiple patterns and mechanisms

Abstract

Ectotherms tend to grow faster, but reach a smaller size when reared under warmer conditions. This temperature‐size rule (TSR) is a widespread phenomenon. Despite the generality of this pattern, no general explanation has been found. We therefore tested the relative importance of two proposed mechanisms for the TSR: (1) a stronger increase in development rate relative to growth rate at higher temperatures, which would cause a smaller size at maturity, and (2) resource limitation placing stronger constraints on growth in large individuals at higher temperatures, which would cause problems with attaining a large size in warm conditions. We raised Daphnia magna at eight temperatures to assess their size at maturity, asymptotic size, and size of their offspring. We used three clonal lines that differed in asymptotic size and growth rate. A resource allocation model was developed and fitted to our empirical data to explore the effect of both mechanisms for the TSR. The genetic lines of D. magna showed different temperature dependence of growth and development rates resulting in different responses for size at maturity. Also, at warm temperatures, growth was constrained in large, but not in small individuals. The resource allocation model could fit these empirical data well. Based on our empirical results and model explorations, the TSR of D. magna at maturity is best explained by a stronger increase in development rate relative to growth rate at high temperature, and the TSR at asymptotic size is best explained by a size‐dependent and temperature‐dependent constraint on growth, although resource limitation could also affect size at maturity. In conclusion, the TSR can take different forms for offspring size, size at maturity, and asymptotic size and each form can arise from its own mechanism, which could be an essential step toward finding a solution to this century‐old puzzle.

Linking life‐history theory and metabolic theory explains the offspring size‐temperature relationship

“…Whether the OST and TSR share the same biological drivers is unclear (Efford ; Yampolsky & Scheiner ; Hoefnagel et al . ).…”

Population‐level responses to temperature, density and clonal differences in Daphnia magna as revealed by integral projection modelling

“…From September 2014, we stimulated hatching by exposing the eggs to light and 20°C. The eggs were checked daily, and neonates were placed in individual 100‐ml tubes, held in Dutch Standard Water (DSW; Hoefnagel, de Vries, Jongejans, and Verberk ()) (200 mg/L CaCl 2 .2H 2 O, 180 mg/L MgSO 4 .7H 2 O, 100 mg/L NaHCO 3 , 20 mg/L KHCO 3 ; NEN6503 ()) and fed with instant algae (1.6 × 10 5 cells/ml; Shellfish 1800, Reed Mariculture). Medium, containing new food, was refreshed three times per week.…”

“…Note that lineages L, A3 and A4 are referred to as C, D and E, respectively, by Hoefnagel et al. ().…”

Food availability modulates temperature‐dependent effects on growth, reproduction, and survival in Daphnia magna

“…These individual effects have been shown to scale up to destabilize population dynamics and increase the risk of extinction (Bestion et al, 2015). For example, many studies have shown that body size shrinkage is mediated by genetic background (Cambronero, Beasley, Kissane, & Orsini, 2018;Hoefnagel, Vries, Jongejans, & Verberk, 2018), pesticides (Cambronero et al, 2018), and food availability (Cambronero et al, 2018;Heugens et al, 2001;Orcutt & Porter, 1984). However, the effect of temperature on organismal fitness often depends on several other ecological factors.…”