Behavioural Thermoregulatory Tactics in Lacustrine Brook Charr, Salvelinus fontinalis

Abstract

The need to vary body temperature to optimize physiological processes can lead to thermoregulatory behaviours, particularly in ectotherms. Despite some evidence of within-population phenotypic variation in thermal behaviour, the occurrence of alternative tactics of this behaviour is rarely explicitly considered when studying natural populations. The main objective of this study was to determine whether different thermal tactics exist among individuals of the same population. We studied the behavioural thermoregulation of 33 adult brook charr in a stratified lake using thermo-sensitive radio transmitters that measured hourly individual temperature over one month. The observed behavioural thermoregulatory patterns were consistent between years and suggest the existence of four tactics: two “warm” tactics with both crepuscular and finer periodicities, with or without a diel periodicity, and two “cool” tactics, with or without a diel periodicity. Telemetry data support the above findings by showing that the different tactics are associated with different patterns of diel horizontal movements. Taken together, our results show a clear spatio-temporal segregation of individuals displaying different tactics, suggesting a reduction of niche overlap. To our knowledge, this is the first study showing the presence of behavioural thermoregulatory tactics in a vertebrate.

Heat transfer in fish: are short excursions between habitats a thermoregulatory behaviour to exploit resources in an unfavourable thermal environment?

“…The former behaviour simulated attack rate or feeding bouts in time budget experiments (Marchand et al, 2003) when fish swam rapidly to eat at the surface and then returned to deep water. Previous telemetry studies suggested that the latter behaviour, equivalent to our step change experiments, could be adopted by lacustrine brook trout as a response to summer lake warming (Bertolo et al, 2011;Goyer et al, 2014). Although cyclic oscillations are mainly presented as illustrative examples, we provide quantitative theoretical predictions of the maximum duration of sporadic excursions.…”

“…Brook charr followed with radiotelemetry spent most of their time in the metalimnion, which corresponds to their preferred temperature (i.e. depth <8 m; Bertolo et al, 2011;Goyer et al, 2014), and rarely entered the hypolimnion. Considering a cruising speed of two body lengths per second (Bjornn and Reiser, 1991;Rouleau et al, 2010;Castro-Santos et al, 2013), a brook charr of 300 mm total length could reach the surface within 15 s. Extrapolating our experimental results to natural populations, we can predict excursion times into the epilimnion according to the thermal constraints of the species under study (see Fig.…”

“…These temperature changes were chosen after considering 3 years of empirical data based on observations of wild brook charr in an oligotrophic stratified lake (Bertolo et al, 2011;Goyer et al, 2014). Fish were first transferred from acclimation tanks (10°C) to tanks held at a constant temperature (14, 19 or 23°C; warming experiments).…”

“…The final choice of external or internal tags mainly depends on the goal of the study, the fish species and the habitat type (Bridger and Booth, 2003). For example, the results of Bertolo et al (2011) versus those of Goyer et al (2014) in the same lake system suggest that survival is higher for brook charr (Salvelinus fontinalis) equipped with internal temperature-sensitive transmitters. While external tags are generally well suited to record ambient water temperature, internal tags are preferable if the risk of entanglement is high (e.g.…”

Divergent growth patterns between juveniles of two sympatric Arctic charr morphs with contrasting depth gradient niche preferences

“…Robinson and Parsons 2002). Thus, temperature adaptations have had less focus as the thermal gradient is low along these upper-water resource axes, although thermal microhabitat differences can have significant importance (Bertolo et al 2011). There is an increasing awareness of specifically adapted deep-water morphs of postglacial fishes, both along the benthic zone (e.g.…”