Climatic changes can induce geographic expansion and altitudinal shifts in the distribution of invasive species by offering more thermally suitable habitats. At the remote sub-Antarctic Kerguelen Islands, the predatory insect Merizodus soledadinus (Coleoptera: Carabidae), introduced in 1913, rapidly invaded coastal habitats. More recent colonisation of higher elevation habitats by this species could be underlain by their increased thermal suitability as the area has warmed. This study compared the effect of elevational range shift on the morphology and physiology of adult M. soledadinus sampled along two altitudinal transects (from the foreshore to 250 m a.s.l.) and a horizontal lowland transect orthogonal to the seashore (400 m length). Although high inter-individual and inter-transect variations in the traits examined were present, we observed that body mass of males and females tended to decrease with elevation, and that triglyceride contents decreased with distance from the shore. Moreover, protein contents of females as well as those of 26 metabolites were influenced significantly by distance to the foreshore. These results suggest that future climate change at the Kerguelen Islands will further assist the colonisation of lowland inland and higher altitude habitats by this aggressively invasive predator, by making previously sub-optimal habitats progressively more suitable.was only carried out on days with similar weather (no rain, wind below 25 km/h, air temperature at the research station between 9 and 12 °C). Finally, insects were collected in the morning of three consecutive days to average environmentally-induced noise and limit possible effects of any circadian rhythm on the physiology of the insects. Morphological measurements.At each sampling site, 25 individuals (from the 50 sampled beetles) were randomly selected, except for specimens sampled at St. Malo at 0, 50 and 250 m a.s.l. for which only 12, 21 and 6 beetles were available, respectively. Sex of each beetle was determined under a stereo microscope. As often observed for the species at the Kerguelen Islands, sex ratio was biased toward males in 75% of the samples, and it was necessary to include additional females for the Anse des Papous transect (0, 100, 150, 250 and 300 m sampling sites). Pictures of each beetle were taken with a video camera (AxioCam ERc 5 s, ZEISS, Germany) connected to a stereo microscope. Inter-ocular distance, width and length of the thorax, length of the right elytra ( Fig. 7) were measured by vectorial layouts with AxioVison software (repeatability was verified using a set of 20 individuals measured twice for each morphological trait: the mean proportion difference was 0.9, 2.6, 2.4 and 2.9 for inter-ocular distance, width and length of the thorax and right elytra length, respectively. Beetles were subsequently vacuum-dried for 15 h (Speed Vac Concentrator, MiVac, GENEVAC LTD, Ipswich, United Kingdom), before being individually weighed (Balance XP2U METTLER TOLEDO, Columbus, OH, d = 0.1 µg).
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