Physiological responses to temperature in Merizodus soledadinus (Col., Carabidae), a subpolar carabid beetle invading sub-Antarctic islands

Abstract

Recent human activities and rising air temperature have increased the vulnerability of sub-Antarctic islands to alien species. At the Kerguelen Islands, the predaceous ground beetle Merizodus soledadinus is the only invasive insect originating from the southern cold temperate area (native from Patagonia, Tierra del Fuego and Falkland Islands). This austral origin raises the question of the limits of its physiological tolerance and capability to withstand (i) global change and (ii) warmer climates of archipelagos where its accidental transportation could be facilitated from the Kerguelen Islands (namely Amsterdam & Saint Paul). Using GC-MS metabolomics, we compared metabotypes of adults exposed to different temperatures (0, 4, 8, 12, 16, 20° C). All individuals survived after two weeks regardless of the temperature they were exposed to. The physiological changes observed were consistent with increased metabolic rate at increased temperatures, without extreme metabotypes that are characteristic of acute stress. First cues of sub-lethal stress were observed after prolonged exposure to 20° C, a warm regime unrealistic for such duration in sub-Antarctic Islands. Overall, M. soledadinus' thermal tolerance exceeded temperatures currently experienced in nature, suggesting that climate warming may boost its invasion by eliciting its activity and broadening habitat suitability in both invaded and still pristine islands. This thermal tolerance may allow survival aboard ships and development in sub-Antarctic islands with conditions warmer than the Kerguelen Islands, such as Amsterdam & St Paul. Stringent biosecurity measures are thus needed to prevent transfer from Kerguelen to these islands. The native range of this predaceous beetle limited to the Falkland Islands and southernmost South America may be partly constrained by factors other than temperature, such as desiccation, predation or competition.

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

“…This finding could indicate energetic adjustments according to the nature of prey available in horizontal versus altitudinal transects. Consistent with this surmise, diet-related differences have previously been measured in the body composition of adult M. soledadinus 21 .…”

“…must spend a significant part of the year at temperatures around 0-1 °C. These thermal conditions are restricting for an insect whose acute thermal sensitivity in this thermal range has been reported previously: metabolic activity and efficiency of adult M. soledadinus are considerably reduced when temperature falls to around 4 °C 27 , and thermal conditions become increasingly suboptimal for adult M. soledadinus as temperatures approach 0 °C 21,27 . Despite ongoing climatic changes, and as expected, it is therefore very likely that adult M. soledadinus at higher levels in the two altitudinal gradients still experience significant temperature-imposed resource and physiological limitations.…”

“…The main habitat conditions within the natural distribution of M. soledadinus (Falkland Islands, Patagonia) overlap at least partly with the climatic conditions at the Kerguelen Islands 18,26 , which suggests that this wingless beetle was likely physiologically pre-adapted to the chronically cool oceanic climate of the archipelago. Adult beetles perform well at cool temperatures, although the studies of Lalouette et al 27 and Laparie and Renault 21 both suggest that the insects are currently in the lower part of their thermal comfort zone at the Kerguelen Islands.…”

“…The sub-Antarctic Kerguelen archipelago is no exception, with mean air temperatures that have increased by 1.7 °C over the period 1951-2010, while precipitation has decreased drastically since the 1990s 20 . The establishment and geographic spread of aphids, the blowfly Calliphora vicina and the carabid beetle Merizodus soledadinus on the archipelago have likely been assisted by these changing conditions 20,21 .…”

Spotlight on the monitoring of the invasion of a carabid beetle on an oceanic islandover a 100 year period

“…Comparatively, the mean annual temperature is 4.4 °C at Port aux Français, and despite regular snowfalls (circa 15 days per month from June to August, Meteo France source), no permanent snow cover was observed over 1951-1980 at this site. Rising air temperature that occurred during winter months in the early 1990s may have amplified the spreading rate of M. soledadinus at Iles Kerguelen (Lebouvier et al, 2011), including at moderate altitudes (Lalouette et al, 2012;Laparie and Renault, 2016;Ouisse et al 2019). The highest observation in the mid-1990s was 110m a.s.l.…”