Thermal Fluctuations Yield Sex-Specific Differences of Ingestion Rates of the Littoral Mysid Neomysis integer

Abstract

Shallow aquatic environments are characterized by strong environmental variability. For ectotherms, temperature is the main driver of metabolic activity, thus also shaping performance. Ingestion rates in mysids are fast responses, influenced by metabolic and behavioral activity. We examined ingestion rates of the mysid Neomysis integer, collected in the Baltic Sea, after one-week exposure to different constant and fluctuating temperature regimes (5, 10, 15, 20°C and 9 ± 5, 14 ± 5°C, respectively). To investigate possible differences between sexes, thermal performance curves (TPCs) were established for female and male mysids based on ingestion rates measured at constant temperatures. TPCs of ingestion rates at constant temperatures differed between sexes, with female mysids showing a higher total ingestion rate as well as a higher thermal optimum compared to male mysids. Females showed reduced ingestion rates when exposed to fluctuating temperatures around their thermal optimum, whereas ingestion of male mysids was not reduced when exposed to fluctuating temperatures. The observed sex-specific differences might be related to potentially higher lipid and energy demands of the females. We suggest future studies should investigate males and females to improve our understanding about impacts of environmental variability on natural populations.

Ingestion and respiration rates of a common coastal mysid respond differently to diurnal temperature fluctuation

“…S5), suggesting no decreasing effect of fluctuating temperature on ingestion as expected based on the principle of Jensen's inequality. This is in contrast to our hypothesis and to observations of a previous study, where thermal fluctuation caused a decrease in N. integer 's ingestion on a short‐term scale (Hennigs et al 2022). Our results suggest that throughout a whole diurnal fluctuating cycle, mysids might be able to compensate for the potential stress of periodic temperature changes.…”

“…An explanation for these different responses might be that optimal temperatures for the mysids' ingestion could vary from thermal optimums for respiration, as observed for the Baltic blue mussel (Vajedsamiei et al 2021). The TPC for ingestion of N. integer shows an optimum around 10°C for males and around 15°C for females (Hennigs et al 2022) and could be shifted toward colder temperatures for animals used in this study, which were collected at colder in situ temperatures than in the previous study. The TPC for respiration of Baltic N. integer shows increasing respiration for temperatures up to 15°C and higher, or at least equal, respiration rates for temperatures up to 20°C depending on exposure time (Laughlin and Lindén 1983).…”

“…After 24 h in the treatments, replicates were treated as described below for the short‐term measurements. For the 1‐h ingestion measurements, mysids were placed individually in cups containing 50 mL of temperature‐acclimated ASW and 30 freshly hatched A. salina nauplii (following Hennigs et al 2022). After 1 h, mysids were transferred to ASW without A. salina nauplii at 15°C and kept for at least 24 h without food to empty their digestive tract for unbiased dry mass determination.…”

“…Therefore, it can be expected that ingestion shows a less instantaneous response to changing temperature than respiration. Feeding rates of N. integer from the United Kingdom and Germany were found to increase with increasing temperatures up to 15°C (Roast et al 2000; Hennigs et al 2022). It is still largely unexplored whether and how respiration and ingestion of ectotherms are related in variable environments and whether these responses follow thermal signals instantaneously.…”

“…At non‐stressful thermal conditions, ingestion rates were assumed to be positively related to respiration rates, that is, increasing ingestion rate with increasing respiration and vice versa. At higher, more stressful temperatures, we expected the positive relationship between ingestion and respiration rates to disappear, because ingestion rates follow an optimum curve along a temperature gradient with maximal rates at 10–15°C (Hennigs et al 2022).…”