Parochlus steinenii, Gerke

Contador, Tamara, Gañan, Melisa, Bizama, Gustavo, Fuentes-Jaque, Guillermo, Morales, Luis, Rendoll, Javier, Simoes, Felipe, Kennedy, James, Rozzi, Ricardo & Convey, Peter, 2020, Assessing distribution shifts and ecophysiological characteristics of the only Antarctic winged midge under climate change scenarios, Scientific Reports 10 (1), pp. 9087-9087 : 9087-

Parochlus steinenii present-day distribution and ecophysiology.

To characterize the present-day distribution of P. steinenii across the South Shetland Islands, we conducted intensive surveys through the ice-free areas accessed ( Fig. 6 , Phase 1) and sourced all available information from the existing literature 30, 35 – 37. All accessible sites were searched for a period of 4 to 6 h, defined by climatic conditions and the availability of logistic support. The fieldwork took place during the active season of the adult flies (austral summer), and we also searched for larvae and pupae in water and around the margins of the lakes accessed. We geo-referenced each location examined with a GPSmap 78sc Garmin© unit. To evaluate the thermal environment in which P. steinenii develops from egg to adult, we installed temperature data loggers (HOBO° U22 Water Temp Pro V2) in three lakes located on King George Island. These were installed on 8 February 2014 and continue to operate to the present day. These lakes were selected as they host a high abundance of P. steinenii and are easily accessible from the Chilean Estación Professor Julio Escudero.

To better understand the present-day distribution, we analyzed the data obtained using spatial point pattern analyses. Spatial point processes are stochastic models that serve as good tools for the analysis of patterns in populations and communities 38. We conducted a large-scale spatial analysis of the distribution of P. steinenii using univariate spatial point process analyses using PAST software 39. To evaluate the spatial distribution of P. steinenii , we used a Complete Spatial Randomness (CSR) model (Ho: P. steinenii has a random spatial distribution in the South Shetland Islands). In this model, spatial points are stochastic and independent, and ‘intensity’ is interpreted as the average density of points per unit area 40. We used Ripley’s K univariate analysis, with the total area of the islands explored. Results were analyzed using the L(r) – r function, which is a transformation of the Poisson K function to a straight line, with a constant value = 0, making it easier to assess the deviation from the theoretical function 41. Monte Carlo tests were conducted (with a 5% probability level) to compare the empirical and the theoretical functions, constructing envelopes under the CSR null hypothesis. The tests reject Ho if the observed function lies outside of the critical envelope at any “r” distance value 42.

Ecophysiology: Critical thermal limits. Lower and upper thermal limits of P. steinenii were examined using the Critical Thermal Method (CTM), which involves changing temperature at a constant rate until a predefined sub-lethal endpoint (used to estimate lethality) is reached 43. Larvae, pupae, and adults were collected with an aspirator from Lakes Kitiesh and Langer on King George Island. Live individuals were transported to the laboratory at Estacion Professor Julio Escudero (King George Island) within 2h of collection. In the laboratory, individuals were acclimated at 8 °C for 24 h in a temperature-controlled cabinet in plastic containers with water, sediment, and small rocks from the collection sites. Larvae (only final instar), pupae and adults were used to conduct experimental assays in the laboratory.

Lower thermal tolerance. Six independent experimental assays for each developmental stage were conducted. Each assay contained 10 individual larvae, pupae, or adults. In the case of larvae and pupae, individuals were placed in plastic vials containing water and were submerged in a programmable, recirculating water bath (Lab Companion RW-0252G, Model AAH57003U, Biotech). Adults were placed in plastic containers, each containing a damp filter paper (to avoid desiccation stress). After a 60 min equilibration period at 0 °C, the specimens were cooled to −1°C at a rate of 0.1 °C/minute. After 1 hour at this temperature, all individuals were removed from the bath and given 24 h to recover at 8 °C in aged tap water, with the exception of adult individuals, which were kept in damp paper towels. After recovery, the target temperature was subsequently lowered by 1 °C and the temperature again reduced at 0.1 °C/min, and the process repeated until the Critical Thermal Endpoints (CTE) was reached (lack of locomotory response to touch with forceps) 44. The removal procedure was repeated during each trial (24h recovery) and each individual was assessed for survival and motor function. Those individuals with full motor function were retained for the subsequent trial. The lower sub-lethal temperature was considered to be the temperature after which survival was consistently less than 100% (see Klok and Chown, 2000) 45.

Upper thermal tolerance. Six experimental trials were conducted, each again containing 10 larvae, pupae, or adults. Individuals were gradually warmed at 0.1 °C min −1 from a starting temperature of 0 °C. This rate of increase needed to be sufficiently rapid to avoid acclimation, but slow enough to ensure that the core temperature reaction to heating was assessed by observing the behavioral response of the test organisms 43. Individuals were checked for survival and locomotor function after each increase of 5°C until reaching 25°C, after which they were checked at every 1°C interval. At each temperature checkpoint, observations of each organism were made. When an organism exhibited behavioral indications (lack of movement, lack of response to physical stimulation) 44 of reaching the critical thermal point, the temperature was recorded, and the organism was removed from the experimental chamber and placed in an aquarium container at 8 °C. Only organisms that recovered from the experimental exposure were included in the subsequent analyses. Successful recovery was defined as the resumption of normal locomotor functions after 24 h recovery time. Differences between the critical thermal limits of each developmental stage (larvae, pupae, and adults), were analyzed using One-Way ANOVAs using PAST software 39. All experiments were conducted under permits issued by the Scientific Ethics Committee from Universidad de Magallanes and the Bioethics Committee of the Instituto Antártico Chileno (INACH), for INACH project RT_48_16.

Figures

Figure 6. Methodological framework for this study.Phase 1 included assessment of occurrences of Parochlus steinenii in its Antarctic distribution, analysis of spatial distribution patterns and thermal ecophysiology of each developmental instar. Phase 2 consisted of the creation of climate layers for the Antarctic, through statistical downscaling, at a spatial resolution of 0.01 (1km). Phase 3 represents the generation of Ecological Niche Models for each time period and scenario.Photographs of larvae, pupae, and adult Gonzalo Arriagada (CC-BY-4.0). The maps in this figure were created using software ArcGIS°software by Esri. ArcGIS°and ArcMap̿, ArcGis v.10.1. Base layers:Seamask_high_res_polygon, coastline_high_res_polygon and Rock_outcrop_high_res_ polygon available from the Scientific Committee for Antarctic Research (SCAR) Antarctic Digital Database (ADD Version 7; http://www.add.scar.org). These data are licensed according to Creative Commons CC-By – data are free to use, modify and redistribute.