DOI: 10.5061/dryad.73n5tb31j
title: A polar insect’s tale: observations on the life cycle of Parochlus steinenii, the only winged midge native to Antarctica

description: Antarctica and the sub-Antarctic islands are considered natural
 laboratories to study and understand the influence of environmental
 variable and patterns of variation therein on the biota, including the
 influences of climate change.  The Antarctic terrestrial fauna
 consists only of small invertebrates, with just two native species of
 holometabolous insects, Parochlus steinenii and Belgica antarctica, and
 two established non-native species, Eretmoptera murphyi and Trichocera
 maculipennis. Studies of the life history, phenology and stress tolerances
 of insects are critical to better understand adaptations to natural
 environmental stress and the ecological consequences of recent and ongoing
 climate change. In this context, we characterized the habitat preferences,
 life cycle and phenology of P. steinenii, the winged Antarctic midge, in a
 lake on King George Island, South Shetland Islands, maritime
 Antarctic.  Based on the data obtained, we hypothesize that P.
 steinenii has a multi-year life cycle that may span as much as four years.
 The species is very restricted in terms of its preferred microhabitat
 distribution, being highly abundant only at shallow depths close to the
 edge of the lakes in which it is found. A combination of further field and
 laboratory studies are now required to assess how the length of P.
 steinenii life cycle is influenced by the scale of temperature variation
 typically experienced in its natural habitat, and as predicted under
 different climate change scenarios, as well investigating the ability and
 timing of larval movement to take advantage of the conditions of specific
 microhabitats at different times of year.
description: Habitat preferences of
 Parochlus steinenii: We studied the habitat preferences and the life
 history of P. steinenii in Lake Kitiesh, Fildes Peninsula, King George
 Island (62°S, Maritime Antarctica) over the austral summer seasons from
 2014-2019, during short (several week) field expeditions organized by the
 Chilean Antarctic Institute (INACH); longer duration, including
 year-round, field sampling is not possible at this location due to
 logistic limitations, as is commonly the case in Antarctic field research.
 This lake hosts an abundant population of P. steinenii and is easily
 accessible from Professor Julio Escudero Station (INACH, Chile), allowing
 for continuous site monitoring during the expeditions and the deployment
 of year-round environmental monitoring equipment.  Antarctic populations of P. steinenii are
 restricted to permanent deeper lakes, which are ice-covered 9-10 months
 each year. To characterize
 the terrestrial habitat in which adults are found, we established five
 line transects around the perimeter of Lake Kitiesh. Two transects were
 located parallel to the main inflow and outflow streams, while the other
 three were oriented approximately in N, NE and S directions, in each case
 perpendicular to the lake and starting at the lake edge. Along each
 transect, we quantified adult densities using 50 × 50 cm quadrats
 (subdivided into 10 × 10 cm grids) at 0, 2, 4 and 6 m from the lake shore.
 Adults of P. steinenii were not observed beyond 6 m from the lake edge.
 Numbers of adult flies in each 10 × 10 cm grid were recorded, and a
 digital photograph of each entire quadrat was taken to allow assessment of
 habitat preferences (Canon PowerShot D20). We recorded rock, snow, mud,
 moss and water proportions within each quadrat. We assessed differences in
 P. steinenii adult density around the lake shore using Permutational
 Multivariate Analysis of Variance (PERMANOVA), based on a Bray-Curtis
 similarity matrix. We also investigated the relationship between P.
 steinenii density (individuals/m2) and habitat type (rock, snow, mud, moss
 and water) using Distance Based Linear Models (DistLM). Both analyses were
 run in PRIMER-E v7 with Permanova+add-on (Anderson
 2005). Thermal
 environment and growing degree-days: To assess the thermal characteristics
 of the aquatic environment in which P. steinenii develops from egg to
 adult, we anchored one temperature data logger (HOBO® U22 Water Temp Pro
 V2) at a depth of 50 cm in Lake Kitiesh, corresponding to the depth at
 which high densities of larvae are commonly found during the austral
 summer. Minimum, maximum and average daily water temperature
 (°C) were recorded from January 2014 to January
 2019. Using these data, we calculated growing degree-days (GDD), using the
 pollen package in R (Nowosad 2019, R Core Team.
 2021), which calculates
 GDDs available for development as the accumulated product of time and
 temperature above 0°C (noting that lake water temperatures are not likely
 to exceed the upper developmental temperature of P. steinenii, although
 this has not been formally assessed) and that the larvae do not survive
 freezing) using daily maximum and minimum temperature data
 (Nufio and Buckley
 2019).
 To describe the life cycle of
 P. steinenii, we collected reproductive adults (n = 200) from rocks along
 the lake shore. Small rearing chambers (10 containers of 250 mL) were set
 up under controlled temperature conditions (4°C) in the laboratory of Prof. Escudero Station
 as described by Harada et
 al. (2014). Each rearing
 chamber contained lake sediment, rocks, and water from the midge’s
 habitat. Groups of ~ 20 reproductive adults were placed in each container,
 where mating occurred followed by oviposition on the surface of the rocks.
 The egg masses were then transported in the rearing chambers to the
 Wankara Laboratory (Universidad de Magallanes) in Puerto Williams,
 Navarino Island, Chile. At the Wankara Laboratory, the chambers were
 maintained in an incubator with a 16 h light and 8 h dark cycle (LD = 16:8
 h) at ~ 4°C (range achieved 4-4.5°C), monitored by a temperature logger (Hobo ®
 U22 Water Temp Pro V2) recording from the first day of observation until
 the hatching of the adults. Weekly observations of larval development were
 made until they reached the adult stage. Larval instar was assigned based
 on size, initially by eye and then followed by detailed measurements of
 head width and length (mm) using a microscope with built-in camera (Leica
 DM750), calibrated for each image. Head capsule length (mm) was measured
 from the anterior margin of the frons to the posterior margin of the
 head’s sclerites, while the width (mm) was measured as the distance across
 the eyes on the head capsule. This enabled larval development to be
 followed through four distinct developmental instars (L1, L2, L3, L4).
 Growing Degree
 Days (GDDs, thermal units) needed to complete a cycle
 from egg to adult were then calculated. We obtained the GDDs required for
 each developmental stage and compared these with the GDD accumulation
 curve obtained from the water temperature recorded at 50 cm depth in Lake
 Kitiesh between 2014 and
 2019.