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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. [ABSTRACT FROM AUTHOR]

Parasitoid host location in nature is facilitated by simultaneously using different information sources. How multisensory orientation on the same spatial scale is influenced by environmental conditions is however poorly understood. Here we test whether changes in reliability of cues can cause parasitoids to alter multisensory orientation and to switch to cues that are more reliable under extreme temperatures. In the ichneumonid wasp Pimpla turionellae, multisensory use of thermally insensitive vision and thermally sensitive mechanosensory host location by vibrational sounding (echolocation on solid substrate) was investigated with choice experiments on plant-stem models under optimum temperature (18°C), at high- (28°C) and low-temperature limits (8°C) of vibrational sounding. Temperature affected relative importance of vibrational sounding whereas visual orientation did not vary. At 18°C, parasitoids used visual and vibrational cues with comparable relative importance. At 8 and 28°C, the role of vibrational sounding in multisensory orientation was significantly reduced in line with decreased reliability. Wasps nearly exclusively chose visual cues at 8°C. The parasitoids switch between cues and sensory systems depending on temperature. As overall precision of ovipositor insertions was not affected by temperature, the parasitoids fully compensate the loss of one cue provided another reliable cue is available on the same spatial scale. [ABSTRACT FROM AUTHOR]

Several parasitic wasps of the Pimplinae (Ichneumonidae) use self-produced vibrations transmitted through plant substrate to locate their concealed immobile hosts (lepidopteran pupae) by reflected signals. This mechanosensory mechanism of host location, called vibrational sounding, depends on the physical characteristics of the plant substrate and the wasp’s body and is postulated to depend on ambient temperature. Adaptations of two parasitoid species to thermal conditions of their habitats and the influence of temperature on the trophic interaction during host location are investigated in the tropical Xanthopimpla stemmator (Thunberg) and compared with the temperate Pimpla turionellae (L.). Plant-stem models with hidden host mimics are offered to individual wasps under defined temperature treatments and scored for the number and location of ovipositor insertions. Significant effects of temperature are found on host-location activity and its success. The tropical species possesses an optimum temperature range for vibrational sounding between 26 and 32 °C, whereas the performance decreases both at low and high temperatures. The temperate species reveals substantial differences with respect to performance at the same thermal conditions. With increasing temperature, P. turionellae shows a reduced response to the host mimic, reduced numbers of ovipositor insertions, and decreased precision of mechanosensory host location. In the tropical X. stemmator, the female wasps are able to locate their host with high precision over a broad range of ambient temperatures, which suggests endothermic thermoregulation during vibrational sounding. Environmental physiology may therefore play a key role in adaptation of the host location mechanism to climatic conditions of the species’ origin. [ABSTRACT FROM AUTHOR]

The thermoregulation behaviour of the codling moth,Cydia pomonella, is investigated in temperature gradient experiments with larvae feeding within apples, and with mature larvae searching for cocooning sites. Feeding larvae appear to prefer the apple hemisphere with a higher temperature (i.e. they build larger cavities in the radiated, warmer part of the fruit). The proportion of larval cavities in the warmer hemisphere is positively related to increasing apple temperature on that side, as well as to the temperature difference between the warm and the cool fruit hemisphere. The mechanism in feeding larvae can be termed as cryptic basking because, during microhabitat selection, the caterpillars exploit temperature differences that are caused explicitly by incident solar radiation. Fifth-instar larvae in search of cocooning sites show no temperature preference within the large gradient offered (9–29 °C), with no difference between males and females. During larval development, the insect changes its thermoregulation behaviour in response to a possible shift in benefits of an elevated body temperature with respect to environmental conditions. Both the thermoregulation behaviour and such a shift of behavioural response should be respected when simulating body temperatures of the species. [ABSTRACT FROM AUTHOR]