DOI: 10.5061/dryad.05qfttfbc
title: Stress resistance as a component of dispersal syndromes in the non-native Merizodus soledadinus on Kerguelen islands

description: Global changes and human activities have increased the likelihood of
 transport of non-native insect species all around the globe. When
 established, the spread of organisms leads to the spatial sorting of the
 populations, progressively contributing to the selection of individuals
 with enhanced dispersal performance at the edges of the invaded range.
 During dispersal, propagules are also subjected to contrasting
 environmental conditions that can be stressful. These include temperature
 extremes and variations, desiccation and the quantity and quality of food,
 which can impose physiological constraints. As a consequence, dispersal
 syndrome may be promoted along invasion gradients with individuals being
 characterized by higher stress tolerance in addition to higher dispersal
 capacities. However, only few studies have examined the differences in
 stress resistance of non-native insect populations along their invasion
 gradient. Merizodus soledadinus (Guérin-Méneville, 1830) is a non-native
 insect species invading the subantarctic Kerguelen Islands, where its
 quick spread highly impacts the native fauna. On the Kerguelen Islands,
 its invasion history is precisely known. This offers a unique opportunity
 to study its stress resistance in relation to the residence time. In this
 study, we investigated the effects of the residence time of populations of
 M. soledadinus on its resistance to heat, desiccation, food deprivation
 and the combination of these three stresses in the laboratory. We found
 that desiccation and multiple stress treatments caused the highest
 mortality rates. Range edge populations showed a longer survival compared
 to core populations. However, the dynamics of survival were different:
 core populations experienced a steady decline in survival, while range
 edge populations initially experienced a slow mortality decline followed
 by a rapid mortality. This suggests greater stress resistance for
 individuals at the invasion front, potentially explaining the intense
 expansion of M. soledadinus on Kerguelen Islands. Further research could
 explore the bioenergetic consequences of these differences in stress
 resistance.
description: <strong><em>Insect
 collection</em></strong> Adults of
 <em>M. soledadinus</em> were hand-collected from six distinct
 localities of the Kerguelen Islands (48°25’ – 50°S; 68°27’ – 70°35’E)
 during the austral summer 2015 - 2016: Port Couvreux (the unique site of
 introduction of the beetle), Cataractes, Anse du Pacha, Pointe Suzanne,
 Isthme Bas and Val Studer (all localities are at least 8 km apart, with
 the furthest being more than 50 km apart, Figure 1). The austral summer
 (from September to April) corresponds to the maximum period of emergence
 for <em>M. soledadinus</em> on the Kerguelen Islands (Ouisse
 et al. 2017). We collected adults in December 2015 - January 2016, to
 maximize the collection of newly emerged individuals. All of the
 localities where specimens of <em>M. soledadinus</em> were
 collected are coastal, except Val Studer which lies around 7.2 km from the
 coastline. All sampling sites host large densities of <em>M.
 soledadinus</em>, for which the year of establishment is known, and
 therefore the time elapsed since colonization (hereafter “residence time”,
 Lebouvier et al. 2020). At the time of collection, populations of
 <em>M. soledadinus</em> were established for 103 years at Port
 Couvreux, 36 years at Cataractes, 21 years at Anse du Pacha and
 Port-aux-Français, 10 years at Pointe Suzanne, five years at Isthme Bas,
 and four years at Val Studer (Figure 1) (Source: project 136 - SUBANTECO,
 French polar institute, also see Lebouvier et al. 2020). Adult longevity
 of <em>M. soledadinus</em> is eight months on average (Ouisse
 et al. 2017). This beetle species can produce up to two generations per
 year. The number of generations since the establishment of the insect in
 each locality is thus expected to vary from a minimum of six (for the
 population with the shortest residence time: Val Studer) to 154 (for the
 population with the longest residence time: Port Couvreux).
 <strong><em>Maintenance of the insect
 populations</em></strong> More than 500
 adults were collected from each locality and directly placed into sealed
 plastic boxes before being brought back to the laboratory of the research
 station (Port-aux-Français, Kerguelen Islands) within 24 - 48 hours after
 sampling. At the laboratory, insects were transferred to plastic boxes (18
 x 12 x 7 cm) at standardized densities of approximately 100 individuals
 per box for each population. The bottom of all plastic boxes was covered
 with filter paper moistened with tap water. Insects were fed <em>ad
 libitum</em> with larvae of the invasive non-native fly
 <em>Fucellia maritima</em> (Haliday 1838) (Diptera:
 Anthomyiidae), and they were provided drinkable water by the addition of 2
 mL microtubes filled with tap water. The microtube caps were kept open,
 and the opening of the tubes was plugged with cotton for a slow diffusion
 of the water. All rearing boxes were maintained during seven days in a
 walk-in climatic chamber at 8 °C, photoperiod 12:12h
 (Light:Dark). <strong><em>Range expansion
 and evolution of stress tolerance</em></strong>
 Transparent Petri dishes (ø 9 x 1.5 cm) were used for all
 survival assays described below. <em>Assessment
 of rearing conditions</em> We used insects from
 the population of Port-aux-Français to monitor the survival of the insects
 under controlled – supposedly non-stressful – conditions. We decided to
 use insects from Port-aux-Français as the longevity of this population was
 formerly assessed by Ouisse et al. (2017) under laboratory conditions,
 thus allowing to determine if lifespan remained in a similar time range.
 Moreover, this population is not used in the stress treatments. In total,
 ten Petri dishes were prepared, each containing 10 individuals of
 <em>M. soledadinus </em>(n = 100 <em>M.
 soledadinus</em> individuals). The Petri dishes
 were maintained at 8 °C in the walk-in climatic chamber (photoperiod
 12:12h (Light:Dark)) corresponding to the mean monthly temperature of the
 austral summer on the Kerguelen Islands (Supplementary information 1,
 Table S1-1; Lebouvier et al. 2011). The bottom of each Petri dish was
 covered with moistened filter paper and a microtube filled with tap water
 was added to provide drinkable water and suitable humidity conditions for
 <em>M. soledadinus</em> individuals. Every 10 days, the filter
 paper and Eppendorf of the Petri dishes were checked to ensure the
 presence of drinkable water and suitable humidity. The filter paper was
 changed every two months. Once a month, adults of <em>M.
 soledadinus</em> were fed with larvae of <em>F.
 maritima</em>. The survival of adult <em>M.
 soledadinus</em> under the rearing conditions was monitored
 fortnightly. The longevity of the individuals of
 <em>M. soledadinus </em>of Port-aux-Français, calculated for
 the 10 replicates, averaged 705 days. Longevity ranged from a minimum of
 190 days and a maximum of 884 days (Supplementary information 2, Figure
 S2). A similar lifespan was reported for this species by Ouisse et al.
 (2017), and is also consistent with former observations in other ground
 beetle species (Lövei and Sunderland 1996), attesting that our laboratory
 conditions did not lead to a reduced survival.
 <em>Abiotic stress</em> The
 tolerance of <em>M. soledadinus</em> individuals from the six
 populations (Port Couvreux, Cataractes, Anse du Pacha, Pointe Suzanne,
 Isthme Bas and Val Studer) to four experimental stress was examined: heat
 (I), desiccation (II), starvation (III) and exposure to multiple stress
 which combined heat, desiccation and starvation (IV). For each
 experimental stress, 10 Petri dishes, each containing 10 insects of one of
 the six populations, were prepared (with few exceptions, 9 - 12 Petri
 dishes replicates, n = 248 Petri dishes in total, see Supplementary
 information 3, Table S3-1 and Figure S3-2). The experimental stress
 started at the end of a 7-day maintenance period following field
 capture. (I) Heat stress treatment: Petri dishes were
 transferred to an incubator (Panasonic, MIR154) that allowed an accurate
 control of the exposure duration at each desired experimental temperature:
 temperature remained at 8 °C for six hours before gradually increasing
 with one-hour increments to 10, 12, 16 °C, and with two-hour increment to
 20 °C, and finally peaking at 28 °C for two hours. Then, the temperature
 gradually decreased on an hourly basis to 20, 16, 12, 10 and finally 8 °C
 which was kept constant for 6h (Supplementary information 3, Figure S3-1).
 This daily variation of the temperature, and the resulting heat stress,
 represented an intense warm event for the insects. So far, the maximum
 mean air temperature measured at 2 m above the ground level on the
 Kerguelen Islands is 25.8 °C (Lebouvier et al. 2011, project 136 -
 SUBANTECO, French polar institute). A 12:12h (Light/Dark) photoperiod was
 applied. To reproduce a diurnal increase in temperature, the periods
 during which the temperature started to increase above 8 °C coincided with
 the sunrise. Humidity conditions and food supply of the insects were
 similar to those used for the assessment of the rearing conditions
 (Supplementary information 1, Table S1-1). (II)
 Desiccation stress treatment: no source of humidity and no drinkable water
 were provided to <em>M. soledadinus</em> individuals. The
 feeding regime, temperature and photoperiod were the same as those used
 for the assessment of the rearing conditions (Supplementary information 1,
 Table S1-1). (III) Starvation stress treatment: for
 this treatment, <em>M. soledadinus</em> individuals were
 deprived from food for three weeks before the start of the experiment to
 ensure that the beetles had empty guts (Laparie et al. 2012) and that the
 food stress started at the beginning of the assay. The insects were then
 starved until death but given drinking water as previously explained
 (moistened filter paper and microtube filled with tap water). Humidity
 level was weekly checked. Temperature and photoperiod were the same to
 those used for the assessment of the rearing conditions (Supplementary
 information 1, Table S1-1). (IV) Multiple stress
 treatment: this treatment corresponded to the combination of heat,
 desiccation and starvation stress treatments. The temperature and
 photoperiod conditions corresponded to those applied to the heat treatment
 (Supplementary information 3, Figure S3-1). Humidity conditions were the
 same as used in the desiccation treatment. The feeding regime was the same
 as the one applied to the starving insects, including the three-week
 deprivation period before the experiment started. During these three
 weeks, water was provided to the individuals with the same set-up as
 previously explained (moistened filter paper and microtube filled with tap
 water), and humidity level was weekly checked (Supplementary information
 1, Table S1-1). <strong><em>Assessment of
 survival</em></strong> The survival of
 adult <em>M. soledadinus</em> was monitored:
 (i) every 12 hours for Petri dishes exposed to the desiccation
 and multiple stress treatments, as they were expected to be the most
 stressful conditions for the beetles (Ouisse et al. 2016),
 (ii) once a day for the heat and starvation stress
 treatments. During these checks, hereafter referred to
 as “experiment time points”, the status of all <em>M.
 soledadinus</em> individuals was determined with a binocular
 magnifier installed in the walk-in climatic chamber (8 °C): individuals
 were classified as alive, comatose, or dead. Alive individuals were moving
 and were standing on their legs. Individuals in a coma were no longer on
 their legs but displayed movements of their appendages (antennas,
 mandibles, legs); individuals in a coma were categorized as alive
 individuals. Dead individuals were on their backs with their legs folded,
 and exhibited no movement of appendages even if stimulated with a
 paintbrush. At each experiment time point, the individuals identified as
 dead, and if necessary, larvae of <em>M. soledadinus</em> were
 removed from the Petri dishes. For each Petri dish, the observations ended
 when all adults had died. Therefore, the duration of the experiment was
 different between each Petri dish. Predation events among <em>M.
 soledadinus</em> conspecifics were observed by individuals found
 dead and which had been partially attacked (e.g., missing or damaged body
 parts). Predation events were observed in low numbers (mostly once per
 Petri Dish), only for the longest stress treatments: starvation and heat
 stress treatments, and for all the studied populations (Supplementary
 information 4, Table S4).   <em>Proportion of
 dead </em>M. soledadinus At each experiment time
 point, the number of dead and alive individuals was counted for each Petri
 dish. We tested the effects of the duration of the experiment (continuous
 covariable), the residence time (continuous) and the stress treatment
 (categorical) on the proportion of dead individuals. These effects were
 first tested across the four stress treatments, then on each stress
 treatment independently. We used a binomial denominator written as a
 vector: number of successes, number of failures (Crawley 2013),
 corresponding respectively to the number of dead individuals and the
 number of living individuals.
description: # Stress resistance as a component of dispersal syndromes in the
 non-native Merizodus soledadinus on Kerguelen islands
 [https://doi.org/10.5061/dryad.05qfttfbc](https://doi.org/10.5061/dryad.05qfttfbc) **Natural range expansion promotes stress resistance as a component of dispersal syndromes in non-native insects** Data for the evaluation of the stress resistance of Merizodus soledadinus on the Kerguelen Islands. Adults of *M. soledadinus* were hand-collected from six distinct localities of the Kerguelen Islands (48°25’ – 50°S; 68°27’ – 70°35’E) during the austral summer 2015 - 2016: Port Couvreux (the unique site of introduction of the beetle), Cataractes, Anse du Pacha, Pointe Suzanne, Isthme Bas and Val Studer. Contact Charly Géron ([charly.geronmailtogmail.com]) with any questions. This manuscript has been accepted for publication (01/20/2025): **Natural range expansion promotes stress resistance as a component of dispersal syndromes in non-native insects** Charly Géron1, Stéphane A. P. Derocles1, Hoël Hotte1, 2, David Renault1 1University of Rennes, CNRS, ECOBIO (Écosystèmes, Biodiversité, Évolution), UMR 6553 Rennes, France 2Nematology Unit, Plant Health Laboratory, ANSES, Le Rheu Cedex, France Data files include: ### Merizodus*StressResistance_StressDataset.csv This file contains data about the stress resistance of M. soledadinus variables | units | description Population  categorical Name of each of the populations used in the study                                              StressTreatment  categorical Stress treatments used in the study Date  date format  Code for each date at which observation on the individuals was made                                  ExperimentTimePoint  Hour format  Hour at which observation on the individuals was made                    Replicate  Categorical Code for replicate : first letter is the first letter of the stress treatment and number is the number of the replicate                                              NumberOfLiveIndividuals  number Number of individuals that were alive at each experimental time point ComaNumber   number Number of individuals in coma at each experimental time point NumberOfDeadIndividuals  number  Number of individuals that were dead at each experimental time point               PredationEvents  number    Number of predation events at each experimental time point ResidenceTimeTears    number  Residence time of each population used in the study in years ### Merizodus*StressResistance_DataAssesmentRearingConditions.csv This file contains data about the stress resistance of M. soledadinus variables | units | description Population  categorical Name of each of the populations used in the study                                          Replicat  categorical Replicate number of each assesment of the rearing conditions BeginDate  date format    Code for each date at which observation on the individuals was made                        Day0LiveIndividuals     date format  Date at which 0 individuals were alive in each replicate                    DayHalfIndividualsLive    date format  Date at which 50% of the individuals were alive in each replicate                SurvivalLengthInDays    number Survival length in days                                              LT50  number day at which 50% of the individuals were dead