Effects of elevational range shift on the morphology and physiology of a carabid beetle invading the sub-Antarctic Kerguelen Islands

Abstract

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).

Effects of Thermal Acclimation on the Tolerance of Bactrocera zonata (Diptera: Tephritidae) to Hydric Stress

“…Dispersion of insects to new environments and consequent geographic range expansions implies an evolutionary process in which the organism's inherent phenotypic plasticity is selected by new environmental conditions (Beaman et al, 2016;Tay and Gordon, 2019). Adaptations to the environment usually build up gradually during natural dispersions of insect species to adjacent habitats or previously unoccupied environments (e.g., Ouisse et al, 2020). In other cases though, the process may be abrupt, such as during anthropogenic introductions of insects through long-range trading of commodities, or migration of animals carrying phoretic alien insect species (e.g., Meurisse et al, 2019).…”

Invertebrate monitoring as measure of ecosystem change

“…Increased elevation on SOI is associated with declining environmental favourability (Davies and Melbourne 1999;Chown and Convey 2016;Hugo-Coetzee and Le Roux 2018;Ouisse et al 2020), with temperature decreases and wind speed increases observed along the elevation gradient. However, the ability of some invertebrates to be collected via traps at higher elevations is also compromised by reduced mobility with declining temperature (Chown et al 2004) and interactions between elevation and other variables (e.g.…”

“…Climate change on SOI manifests as increases in temperature, higher mean wind speed, changes to solar radiation, and decrease in mean annual precipitation (Smith 2002;Davies and Melbourne 1999;le Roux and McGeoch 2008a;Adams 2009;Lebouvier et al 2011;Bergstrom et al 2015). The interaction of these variables can have flow on effects on native invertebrates, as they affect altitudinal patterns of native vascular species richness and community composition (le Roux and McGeoch 2008b), drive soil moisture and peat accumulation, (Smith and Steenkamp 1990;Gabriel et al 2001), and can transform habitats at higher elevations that were previously sub-optimal into conditions progressively more suitable to invasive species (Ouisse et al 2020). However, in contrast to other SOI, the precipitation trend on Macquarie Island in the last ~40 years has been one of significant increase (up 35% on annual precipitation), albeit mostly as winter rainfall, and characterised by increased storm events with intermittent dry spells (Adams 2009;Bergstrom et al 2015).…”

“…Endemic high-altitude plant species are already being impacted (Bergstrom et al 2015). Although native invertebrates perform equally to nonnative invertebrates up to certain temperature thresholds, their upper thermal tolerance is generally lower than non-natives (Janion et al 2010;, which out-perform native species through superior reproductive performance and enhanced phenotypic plasticity (Chown et al 2007;Slabber et al 2007;Janion et al 2010;Janion et al 2018;Ouisse et al 2020). Thus, a warmer future climate on SOI will benefit non-native invertebrates and disadvantage native invertebrates.…”

“…Thus, a warmer future climate on SOI will benefit non-native invertebrates and disadvantage native invertebrates. Native species with a preference for cooler conditions in elevated habitats will have no room to expand their range, while non-native species will expand their range attitudinally and also outcompete low-elevation native species with their high reproductive rates in the warmer environment (Janion et al 2010;Ouisse et al 2020). Already, some of the most invasive invertebrates on SOI, reach exceptional abundances in lowland areas, sometimes displacing native species (Convey et al 1999;Gabriel et al 2001;Frenot et al 2005).…”