Plastic responses to diel thermal variation in juvenile green sturgeon, Acipenser medirostris

Abstract

Human-induced thermal variability can disrupt energy balance and performance in ectotherms; however, phenotypic plasticity may play a pivotal protective role. Ectotherm performance can be maintained in thermally heterogeneous habitats by reducing the thermal sensitivity of physiological processes and concomitant performance. We examined the capacity of juvenile green sturgeon (Acipenser medirostris) to respond to daily thermal variation. Juveniles (47 days post-hatch) were exposed to either stable (15 ± 0.5 °C) or variable (narrowly variable: 13-17 °C day or widely variable 11-21 °C day) thermoperiod treatments, with equivalent mean temperatures (15 ± 0.5 °C), for 21 days. Growth (relative growth rate, % body mass gain), upper thermal tolerance (critical thermal maxima, CTMax) and the thermal sensitivity of swimming performance (critical swimming speed, U) were assessed in fish from all treatments. Accelerated growth was observed in fish maintained under widely variable temperatures compared to narrowly variable and stable temperatures. No significant variation in CTMax was observed among thermoperiod treatments, suggesting all treatment groups acclimated to the mean temperature rather than daily maximums. The widely variable treatment induced a plastic response in swimming performance, where U was insensitive to temperature and performance was maintained across a widened thermal breadth. Maximum U attained was similar among thermoperiod treatments, but performance was maximised at different test temperatures (stable: 4.62 ± 0.44 BL s at 15 °C; narrowly variable: 4.52 ± 0.23 BL s at 21 °C; widely variable: 3.90 ± 0.24 BL s at 11 °C, mean ± s.e.m.). In combination, these findings suggest juvenile A. medirostris are resilient to daily fluctuations in temperature, within the temperature range tested here.

Consequences of temperature and temperature variability on swimming activity, group structure, and predation of endangered delta smelt

“…Furthermore, swimming performance was insensitive to a wide range of temperatures, suggesting that sturgeon were responding to the mean temperatures and not the daily peaks (Rodgers, Cocherell, Nguyen, Todgham, & Fangue, 2018). Furthermore, swimming performance was insensitive to a wide range of temperatures, suggesting that sturgeon were responding to the mean temperatures and not the daily peaks (Rodgers, Cocherell, Nguyen, Todgham, & Fangue, 2018).…”

“…behaviour, fish species, Hypomesus transpacificus, predator, warming medirostris; Acipenseridae) acclimated to fluctuating temperature conditions (narrow or widely variable) demonstrated no change in upper temperature tolerance. Furthermore, swimming performance was insensitive to a wide range of temperatures, suggesting that sturgeon were responding to the mean temperatures and not the daily peaks (Rodgers, Cocherell, Nguyen, Todgham, & Fangue, 2018). Understanding species-specific responses to increased temperatures as experienced in nature may better inform ecological responses.…”

Physiological responses of the abalone Haliotis discus hannai to daily and seasonal temperature variations

“…tidal flats, tide pools and tidal-mixing fronts, can experience large short-term thermal fluctuations. The responses to short-term cyclic thermal fluctuations vary greatly between ectotherm species and/or physiological processes 10–12 . Such thermally fluctuating conditions can increase the metabolic energy demands of some ectotherms, and even result in a failure to maintain physiological processes and performance traits 10,13,14 .…”

Integrating physiological data with the conservation and management of fishes: a meta-analytical review using the threatened green sturgeon (Acipenser medirostris)

“…However, younger juveniles (155 dph) may be less vulnerable to high temperatures, as Allen et al (2006a) found swimming performance to be greater at 24°C compared to 19°C. Young juveniles (47 dph) have also been shown to respond to daily thermal fluctuations, with fish exposed to wide temperature fluctuations (11–21°C day −1 ) able to maintain swimming performance across a wider range of temperatures and having improved growth compared to fish maintained at stable temperatures (Rodgers et al , 2018).…”

“…Almost all studies (c.f. Allen et al , 2006b; Rodgers et al , 2018) used constant temperatures, but natural river temperatures with daily fluctuations should be mimicked.…”