Density-mediated metabolic rate in Daphnia magna interacting with temperature

ABSTRACT

Zooplankton change metabolic function as a physiological response to crowding. Unclear is whether zooplankton physiological responses also change according to species and measurement conditions, and whether the physiological responses to crowding are also changed by temperature. Further investigation is essential to unravel the intricate interplay between crowding-induced stress, energy allocation strategies, and behavioral adaptations. In this study, we determined the metabolic rates of cladoceran Daphnia magna at 3 different densities (1, 10, and 20 individuals [ind.] per 50 mL) at 2 temperatures (10 and 20 °C) using a highly accurate optical oxygen meter. We aimed to clarify how crowding and temperature together affect metabolic rate. At both temperatures, metabolic rates of D. magna in the 2 crowded treatments were significantly lower than those in a single treatment, and as temperature decreased the rate of metabolic decrease slowed. Q₁₀ values varied from 1.63 for the 20 ind. per 50 mL treatment to 2.29 for the 1 ind. per 50 mL treatment, suggesting that the slowing of metabolic rates due to crowding is slightly less pronounced at lower temperatures and may be linked to reduced food consumption.

KEYWORDS:

• Cladocera
• crowding effect
• population density
• respiration
• temperature

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the China Postdoctoral Science Foundation: [Grant Number: 2023M741994], the China Scholarship Council: [Grant Number: 201908050083], the Japan Society for the Promotion of Science: [Grant Number: 20K15586], the Science and Technology Research Partnership for Sustainable Development (SATREPS): [Grant Number: JPMJSA2005].