1. Ectothermic animals depend on external heat sources for pursuing their daily activities. However, reaching sufficiently high temperature can be limiting at high altitudes, where nights are cold and seasons short. We focus on the role of a green-brown color polymorphism in grasshoppers from alpine habitats. The green-brown polymorphism is phylogenetically and spatially widespread among Orthopterans and the eco-evolutionary processes that contribute to its maintenance have not yet been identified.
2. We here test whether green and brown individuals heat up to different temperatures under field conditions. If they do, this would suggest that thermoregulatory capacity might contribute to the maintenance of the green-brown polymorphism.
3. We recorded thorax temperatures of individuals sampled and measured under field conditions. Overall, thorax temperatures ranged 1.7–42.1°C. Heat up during morning hours was particularly rapid, and temperatures stabilized between 31 and 36°C during the warm parts of the day. Female body temperatures were significantly higher than body temperatures of males by an average of 2.4°C. We also found that brown morphs were warmer by 1.5°C on average, a pattern that was particularly supported in the polymorphic club-legged grasshopper Gomphocerus sibiricus and the meadow grasshopper Pseudochorthippus parallelus.
4. The difference in body temperature between morphs might lead to fitness differences that can contribute to the maintenance of the color polymorphism in combination with other components, such as crypsis, that functionally trade-off with the ability to heat up. The data may be of more general relevance to the maintenance of a high prevalence polymorphism in Orthopteran insects.

Thorax temperatures have been measured in the field using thermocouple microprobes and the “grab-and-stab” technique.

The tab separated file contains information on grasshopper body temperatures. Each row represents a single individual. Missing values are indicated by NA.

ID = Arbitrary (running) record identifier
Species = Short species name (first letter of genus, first three letters of species name)
SpeciesFullName = Full scientific namer of the species
Date = Sampling data, DD/MM/YYYY
Time = Daytime of sampling (HH:MM)
Hour = Daytime of sampling (full hour)
TimeCont = Daytime continuous with minutes converted to decimals
Sex = Sex of individual, F = female, M = male
Morph = Morph identity, G = green, B = brown
ThoraxTemp = Thorax temperature in °C
MatchedPairSex = Posthoc matched pairs for testing sex differences in body temperature (arbitrary running numbers with same numbers indicating a pair of records, unique within species)
MatchedPairMorph = Posthoc matched pairs for testing sex differences in body temperature (arbitrary running numbers with same numbers indicating a pair of records, unique within species)