Svendsen, M. B. S. | bioRxiv Science

bioRxiv2021

Evidence that standard metabolic rate and risk-taking to breathe air are linked to boldness, activity level and exploratory behaviour in a catfish.

We used an air-breathing catfish, Clarias gariepinus, to investigate the hypothesis that individual variation in metabolic rate, and the propensity to take risks to obtain a resource (oxygen from air), would be correlated with behavioural tendencies such as boldness, activity level and exploratory behaviour. The standard metabolic rate (SMR) of 58 juvenile catfish was positively correlated with their rates of aerial respiration in daylight when surfacing was inherently risky. SMR was positively correlated with boldness measured in two contexts, namely the time-lag to resume air-breathing in a potentially dangerous environment (T-res, measured in a respirometer), and the timelag to enter the centre of a novel environment (T-centre, measured in an open field test (OFT)). These two measures of boldness were very highly correlated. Thus, these data support the hypothesis that high SMR and an associated tendency to take risks to acquire resources are linked to increased boldness in animals. Individual SMR was positively correlated with the proportion of time the fish spent moving in the OFT, but was negatively correlated with movement speed. The data confirmed previous observations that these catfish may exhibit a bimodal distribution of T-res phenotypes, whereby individuals either resumed air-breathing relatively rapidly (< 85 min, bold n = 26) or more slowly (> 115 min, shy n = 31) after a startle stimulus. Bold T-res phenotypes had significantly higher SMR than shy; breathed more air during the day, and showed greater boldness but less activity and exploration in the OFT. No parallel bold/shy dichotomy was observed, however, in any measure of boldness in the OFT. Therefore, the data support propositions regarding how SMR and risk-taking should relate to boldness, but provide mixed results about how SMR relates to activity and exploration, and whether bold/shy is a dichotomy or spectrum.

animal behavior and cognition↗

bioRxiv2020

Intraspecific variation in thermal tolerance differs between tropical and temperate fishes

How ectothermic animals will cope with global warming, especially more frequent and intense heatwaves, is a critical determinant of the ecological impacts of climate change. There has been extensive study of upper thermal tolerance limits among fish species but how intraspecific variation in tolerance may be affected by habitat characteristics and evolutionary history has not been considered. Intraspecific variation is a primary determinant of species vulnerability to climate change, with implications for global patterns of impacts of ongoing warming. Using published critical thermal maximum (CTmax) data on 203 marine and freshwater fish species, we found that intraspecific vsariation in upper thermal tolerance varies according to a species latitude and evolutionary history. Notably, freshwater tropical species have lower variation in tolerance than temperate species in the northern hemisphere, which implies increased vulnerability to impacts of thermal stress. The extent of variation in CTmax among fish species has a strong phylogenetic signal, which may indicate a constraint on evolvability to rising temperatures in tropical fishes. That is, in addition to living closer to their upper thermal limits, tropical species may have higher sensitivity and lower adaptability to global warming compared to temperate counterparts. This is evidence that tropical fish communities, worldwide, are especially vulnerable to ongoing climate change.

physiology↗