New insights into the ecology of Merizodus soledadinus, a predatory carabid beetle invading the sub-Antarctic Kerguelen Islands

Abstract

International audienceOur knowledge of the main determinants of invasion success is still incomplete. Among these factors, the effects of biological traits, including fecundity, longevity and dispersal in newly colonised regions, are pivotal. However, while numerous studies have considered ecological and evolutionary impacts of non-native species, their biology often remains understudied. Despite the continuous geographic expansion of Merizodus soledadinus (Coleoptera: Carabidae) at the Kerguelen Islands over recent decades, the main life-history parameters of this species are unknown. We determined adult longevity under controlled conditions, monitored seasonal activity through pitfall trappings, and analysed temporal variations of egg load and body reserves in field-collected individuals. Themedian adult life span (LT50) was 241 days, with maximum longevity of 710 days (N = 500). Females carriedeggs throughout the year (8.94 ± 3.56 eggs per female), and it was not possible to pinpoint any clear egg-layingperiod. Year-round trappings demonstrated continuous activity of adults over seasons, with a peak during the austral summer that may arguably be associated with higher temperatures. Body stores (glycogen and proteins) did not vary significantly through the year, suggesting that adults feed continuously despite different prey availability between summer and winter, possibly via diet shifts. The amount of triglycerides increased at onset of summer, which may be associated with higher summer locomotor activity and/or more intense predation and reproduction

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

“…Triglyceride amounts of both sexes, and protein amounts of females, decreased with altitude. In a previous study, we did not observe variations in the total number of eggs carried by female M. soledadinus over the year 25 , and they may be capable of multiple egg maturation cycles. At the Kerguelen Islands, trophic resources become more patchy and sporadic at higher altitudes, limiting nutrient availability for the voracious adults of M. soledadinus.…”

“…The predaceous M. soledadinus was introduced from the Falkland Islands to the Kerguelen archipelago in 1913 22,23 . In the archipelago, this insect preferentially feeds on fly larvae 24 , and has year-round activity 25 . 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.…”

Spotlight on the invasion of a carabid beetle on an oceanic island over a 105-year period

“…Thus, even if recent models suggest that it is not possible to make accurate predictions of the duration of lag phases, in particular for introductions occurring in coastal areas 19 as in the case for M. soledadinus, the apparent lag time for this species is consistent with the existing insect invasion literature. The lag time could in part result from Allee effects, which refer to any process whereby any component of individual fitness is correlated with population size ( 76,77 , also see the reviews of 6,78,79 , which describe the different concepts underlying invasion dynamics). Investigations conducted on populations of M. soledadinus support this idea.…”

“…Investigations conducted on populations of M. soledadinus support this idea. For instance, while adult beetles have a relatively long lifespan of 1-2 years 79 , the small (3-12) mature egg load per female, and the long developmental period of the juveniles (at least several months 55,61,79 ), may limit individual opportunities to find a mate. Such life history characteristics may have contributed to restricting population growth in the initial years following the species' introduction at Port-Couvreux.…”

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

“…Furthermore, C. moseleyi appears to be more sensitive to M. soledadinus than A. aptera along seashore. Merizodus soledadinus, year-round active at the Kerguelen Islands (Ouisse et al 2017), acts as a new ecological pressure which could now remove C. moseleyi from a secondary niche. Indeed, algae represent a secondary trophic niche for C. moseleyi whose primary resources are the Kerguelen cabbages (Tréhen et al, 1987) which almost disappeared from most locations invaded by rabbits (Chapuis et al, 1991).…”