Intraspecific variation in thermal tolerance differs between tropical and temperate fishes

Area of Science:

• Ecology
• Climate Change Biology
• Evolutionary Biology

Background:

• Global warming poses significant threats to ectothermic organisms, particularly fish.
• Understanding intraspecific variation in thermal tolerance is crucial for predicting species' responses to climate change.
• Previous research has focused on species-level thermal limits, neglecting the role of intraspecific variation and its drivers.

Purpose of the Study:

• To investigate how habitat characteristics and evolutionary history influence intraspecific variation in upper thermal tolerance in fish.
• To assess the vulnerability of different fish populations to rising global temperatures.

Main Methods:

• Analysis of published critical thermal maximum (CTmax) data for 203 fish species.
• Examination of the relationship between intraspecific variation in CTmax, latitude, and evolutionary history (phylogenetics).

Main Results:

• Intraspecific variation in upper thermal tolerance is significantly influenced by species' latitude and evolutionary history.
• Tropical fish species, especially freshwater ones, display lower intraspecific variation in thermal tolerance compared to temperate species.
• A strong phylogenetic signal suggests constraints on the evolvability of thermal tolerance in tropical fish.

Conclusions:

• Tropical freshwater fish are particularly vulnerable to climate change due to limited adaptive capacity in thermal tolerance.
• Intraspecific variation is a key factor in determining species' vulnerability to global warming.
• Evolutionary history and geographic location play critical roles in shaping responses to thermal stress.