Data from: Morphological and colour morph clines along an altitudinal gradient in the meadow grasshopper Pseudochorthippus parallelus

Many animals show altitudinal clines in size, shape and body colour.
Increases in body size and reduction in the length of body appendices in
colder habitats are usually attributed to improved heat conservation at
lower surface-to-volume ratios (known as Bergmann's and Allen's
rule, respectively). However, the patterns are more variable and sometimes
reversed in small ectotherms that are affected by shortened growing
seasons. Altitude can also affect colouration. The thermal melanism
hypothesis predicts darker colours under cooler conditions because of a
thermoregulatory advantage. Darker colours may also be favoured at high
altitudes for reasons of UV protection or habitat-dependent crypsis. We
studied altitudinal variation in morphology and colour in the
colour-polymorphic meadow grasshopper Pseudochorthippus parallelus based
on 563 individuals from 17 populations sampled between 450 and 2,500 m
asl. Pronotum length did not change with altitude, while postfemur length
decreased significantly in both sexes. Tegmen (forewing) length decreased
in males, but not in females. The results indicate that while body size,
as best quantified by pronotum length, was remarkably constant, extended
appendices were reduced at high altitudes. The pattern thus follows
Allen's rule, but neither Bergmann's nor converse
Bergmann's rule. These results indicate that inference of converse
Bergmann's rule based on measurements from appendices should be
treated with some caution. Colour morph ratios showed significant changes
in both sexes from lowland populations dominated by green individuals to
high-altitude populations dominated by brown ones. The increase of brown
morphs was particularly steep between 1,500 and 2,000 m asl. The results
suggest shared control of colour in males and females and local adaptation
along the altitudinal gradient following the predictions of the thermal
melanism hypothesis. Interestingly, both patterns, the reduction of body
appendices and the higher frequency of brown individuals, may be explained
by a need for efficient thermoregulation under high-altitude conditions.