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Knowledge of the life cycles of non-native species in Antarctica is key to understanding their ability to establish and spread to new regions. Through laboratory studies and field observations on Signy Island (South Orkney Islands, maritime Antarctic), we detail the life stages and phenology of Eretmoptera murphyi (Schaeffer 1914), a brachypterous chironomid midge introduced to Signy in the 1960s from sub-Antarctic South Georgia where it is endemic. We confirm that the species is parthenogenetic and suggest that this enables E. murphyi to have an adult emergence period that extends across the entire maritime Antarctic summer season, unlike its sexually reproducing sister species Belgica antarctica which is itself endemic to the Antarctic Peninsula and South Shetland Islands. We report details of previously undescribed life stages, including verification of four larval instars, pupal development, egg gestation and development, reproductive viability and discuss potential environmental cues for transitioning between these developmental stages. Whilst reproductive success is limited to an extent by high mortality at eclosion, failure to oviposit and low egg-hatching rate, the population is still able to potentially double in size with every life cycle. Electronic supplementary material The online version of this article (doi:10.1007/s00300-018-2403-5) contains supplementary material, which is available to authorized users.
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Polar Biology (2019) 42:115–130
https://doi.org/10.1007/s00300-018-2403-5
ORIGINAL PAPER
Life cycle andphenology ofanAntarctic invader: theightless
chironomid midge, Eretmoptera murphyi
Jesamine C.Bartlett1· PeterConvey2· ScottA.L.Hayward1
Received: 18 January 2018 / Revised: 12 September 2018 / Accepted: 14 September 2018 / Published online: 29 September 2018
© The Author(s) 2018
Abstract
Knowledge of the life cycles of non-native species in Antarctica is key to understanding their ability to establish and spread
to new regions. Through laboratory studies and field observations on Signy Island (South Orkney Islands, maritime Antarc-
tic), we detail the life stages and phenology of Eretmoptera murphyi (Schaeffer 1914), a brachypterous chironomid midge
introduced to Signy in the 1960s from sub-Antarctic South Georgia where it is endemic. We confirm that the species is
parthenogenetic and suggest that this enables E. murphyi to have an adult emergence period that extends across the entire
maritime Antarctic summer season, unlike its sexually reproducing sister species Belgica antarctica which is itself endemic
to the Antarctic Peninsula and South Shetland Islands. We report details of previously undescribed life stages, including
verification of four larval instars, pupal development, egg gestation and development, reproductive viability and discuss
potential environmental cues for transitioning between these developmental stages. Whilst reproductive success is limited to
an extent by high mortality at eclosion, failure to oviposit and low egg-hatching rate, the population is still able to potentially
double in size with every life cycle.
Keywords Chironomidae· Signy Island· Embryogenesis· Pupal development· Population growth
Introduction
The sub-Antarctic islands, with a longer history and greater
level of human influence than any other part of the Antarctic
(Convey 2013), have a greater number of non-native species
than the more extreme maritime and continental Antarctic
regions further south (Convey and Lebouvier 2009; Frenot
etal. 2005). However, in recent years and decades, there
have been increasing records of species establishing in the
maritime Antarctic with anthropogenic assistance, particu-
larly in the South Shetland Islands and northern Antarc-
tic Peninsula (e.g. Greenslade etal. 2012; Volonterio etal.
2013; Hughes etal. 2015; Molina-Montenegro etal. 2012).
With synergy between high and increasing levels of human
activity in this region of the Antarctic, and recent rapid rates
of regional climate change, further establishment of non-
native species is predicted, presenting fundamental chal-
lenges to the protection and conservation of Antarctic ter-
restrial biodiversity, and to the management and governance
processes in the Antarctic (Chown etal. 2012; Chown and
Convey 2016; Hughes and Worland 2010; Tin etal. 2009).
The brachypterous midge Eretmoptera murphyi (Chi-
ronomidae, Orthocladiinae) is a non-native species on Signy
Island (South Orkney Islands, maritime Antarctic), to which
it is thought to have been inadvertently introduced in the
1960s, in association with plant transplant experiments
(Block etal. 1984; Convey and Block 1996). Its larvae have
the capacity to rapidly cold harden, cryoprotectively dehy-
drate (Everatt etal. 2012, 2015; Worland 2010), respire in
water and withstand ice entrapment (Everatt etal. 2014).
These traits have allowed it to succeed in the maritime
Antarctic, which is more extreme in comparison with the
species’ native sub-Antarctic South Georgia. The sub-Ant-
arctic has a relatively stable and chronically cool oceanic-
influenced climate year-round. This presents fundamentally
Electronic supplementary material The online version of this
article (doi:https ://doi.org/10.1007/s0030 0-018-2403-5) contains
supplementary material, which is available to authorized users.
* Scott A. L. Hayward
s.a.hayward@bham.ac.uk
1 School ofBiosciences, University ofBirmingham,
EdgbastonB152TT, UK
2 British Antarctic Survey, NERC, High Cross, Madingley
Road, CambridgeCB30ET, UK
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116 Polar Biology (2019) 42:115–130
1 3
different pressures for terrestrial invertebrates to that of
the much more extreme seasonality of the maritime Ant-
arctic, where overwintering microhabitat temperatures can
regularly fall below −10°C, contrasting with minima only
marginally below zero on South Georgia (Convey 1996a;
Convey and Block 1996). To date, studies of E. murphyi
have primarily focussed on the ecophysiology of late instar
larvae (Everatt etal. 2012, 2015; Worland 2010; Hughes
etal. 2013). However, a much more detailed characterisa-
tion of all life stages is required to determine how current
and predicted future climate changes may affect this species
development and phenology.
Life history strategies ofpolar arthropods
Driven by the short growing seasons and environmental
extremes, polar invertebrates often exhibit ‘adversity-
selected’ life history strategies in comparison with their
temperate counterparts (Convey 1996b). They have slow
growth rates (Convey 1996b), extended and free-running
life cycles with reduction of obligate overwintering stages
(Fogg etal. 2008), considerable investment in stress tol-
erance mechanisms (Convey 1996b; Hayward etal. 2003;
Everatt etal. 2015) and the ability to opportunistically take
advantage of even short periods of conditions suitable for
growth and activity; for instance, the Antarctic oribatid mite,
Alaskozetes antarcticus, has a life cycle duration of around
5years, whilst comparable temperate species are typically
annual or biennial (Convey 1994; Block and Convey 1995).
Consequently, multi-year life cycles are common in polar
arthropods and many lack a true diapause, instead entering a
state of temporary quiescence during winter or other shorter
periods of unsuitable conditions. Thus, the most commonly
shared life history feature across polar arthropods is the flex-
ibility which enables the challenges of adverse conditions to
be overcome, although some ‘programmed’ elements may
remain so that key life stages can take advantage of regu-
lar environmental triggers each season (Convey 1996a, b;
Danks 1999; Worland and Convey 2008).
Chironomid midges are a group of higher insects that are
particularly well represented at high latitudes in both hemi-
spheres relative to other insect groups (Chown and Convey
2016; Convey and Block 1996; Coulson etal. 2014). Polar
representatives typically conform to the normative polar life
history strategy as defined by Danks (1999), having a fixed
and synchronous spring emergence after overwintering in
a late larval stage, and a brief adult reproductive stage dur-
ing summer, but an otherwise flexible life history. Asexual
reproduction is prevalent in all major polar arthropod and
microinvertebrate groups (Chown and Convey 2016; Convey
1996a) and especially so in sub-Antarctic Psychodidae, a
family of biting midges (Duckhouse 1985). However, asex-
ual reproduction has not yet been definitively proved in any
maritime Antarctic insect species (Convey 1996a) despite
being strongly suspected in E. murphyi (Convey 1992; Cran-
ston 1985).
Life histories ofAntarctic chironomids
The life histories and biology of the native Antarctic chi-
ronomids Parochlus steinenii (Gercke 1889) (Podonomi-
nae) and Belgica antarctica (Jacobs 1900) (Orthocladiinae)
have been well studied (e.g. Allegrucci etal. Allegruci
etal., 2006, 2012; Convey and Block 1996; Harada etal.
2014; Hahn and Reinhardt 2006; Sugg etal. 1983; Usher
and Edwards 1984). These are typically characterised by
larval development taking place over 2years, overwintering
as either early or late instars, followed by synchronised mass
emergence of adults in summer (Convey and Block 1996;
Harada etal. 2014; Sugg etal. 1983). Belgica antarctica
occurs along the Antarctic Peninsula and is the only higher
insect endemic to the Antarctic continent (Convey and Block
1996; Kelley etal. 2014). It experiences environmental con-
ditions similar to those of E. murphyi on Signy Island, and
the assumption is that both species have similar ecologi-
cal niches. Recent molecular evidence also suggests that E.
murphyi should be assigned to the genus Belgica (Allegrucci
etal. 2012), further supporting likely common life history
strategies. However, questions remain as to whether the long
evolutionary history of E. murphyi on sub-Antarctic South
Georgia has provided the opportunity for the evolution of
a temperate-style life history pattern that would show less
flexibility than that of a more typical polar insect.
In the field on Signy Island E. murphyi is thought to emerge
en masse, possibly in response to abiotic factors such as
increased spring daylength, the seasonal melt of basal snow
(Block etal. 1984; Gardiner etal. 1998) or as a heritage trait
from related chironomids (Armitage etal. 1995). Convey
(1992) showed that rates of egg development decrease with
an increase in temperature (2–12°C) and that the females
invest greatly in reproduction with ca. 85 eggs being laid in a
single hydrosensitive egg sac—representing a dry mass twice
that of the female post-oviposition. Once larvae hatch they
are thought to overwinter twice (Hughes etal. 2013; Worland
2010), once in an early larval stage and later in the fourth
instar, although this has not been explicitly demonstrated.
It is assumed that E. murphyi has four larval instars like B.
antarctica, although previous size class distribution analyses
and taxonomic studies have identified only two distinct classes
via assessments of larval mass or field observations (Cranston
1985; Hughes etal. 2013). One reason underlying the current
lack of explicit knowledge of E. murphyis life history has
been the challenge of establishing a long-term laboratory cul-
ture, with all data obtained to date derived from short periods
of field observations combined with laboratory experiments
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117Polar Biology (2019) 42:115–130
1 3
relying on field-collected material (Convey 1992; Everatt etal.
2014; Hughes etal. 2013).
Patterns ofclimate change inthewestern Antarctic
Peninsula andScotia Arc
In recent decades, rapid regional warming and other physi-
cal environmental changes have been documented in parts of
Antarctica, in particular in the region of the western Antarctic
Peninsula and Scotia Arc (Turner etal. 2009, 2014), including
Signy Island (Cannone etal. 2016; Royles etal. 2012; Smith
1990). Signy Island was recognised early on as a paradigmatic
location at which to study terrestrial biological processes in
the maritime Antarctic, and how these might change under
the influence of changing environmental drivers (Smith 1990).
Within terrestrial ecosystems, the primary consequences of
these environmental changes are longer active seasons (ear-
lier spring thaw combined with later autumn freeze), greater
integrated thermal energy availability (increased temperatures)
and greater availability of liquid water to terrestrial organisms.
Thus, and unlike the general consequences in many regions of
the world, regional warming in parts of the Antarctic relaxes
the current extreme environmental constraints on biological
processes, and recent syntheses recognise that many of the
native biota in these regions, including polar terrestrial inver-
tebrates, are likely to benefit from the changes being observed
(Bale and Hayward 2010; Convey 2011; Convey etal. 2014).
It is also increasingly recognised that this relaxation of envi-
ronmental constraints, with or without the direct influence of
human assistance in transporting propagules, will lower the
barriers to new species arriving and establishing in Antarctica
(Frenot etal. 2005; Hughes etal. 2006).
Aims ofthis study
Against this background, the primary aims of this study are to
provide the first detailed characterisation of different devel-
opmental stages within the life cycle of E. murphyi, and to
investigate the potential role of abiotic triggers in the timing of
major life history transitions on Signy Island, such as pupation,
adult eclosion or oviposition. These are then considered in the
context of the implications of climate change for this species’
life history and distribution on the island and, potentially, more
widely in the maritime Antarctic.
Materials andmethods
Sample collection andprocessing
All samples were either obtained from, or observed
insitu, on the Backslope and in the immediate vicinity
of the British Antarctic Survey (BAS) research station
on Signy Island (South Orkney Islands, maritime Ant-
arctic, 60°430S, 45°360W; Fig.1a, b). Samples col-
lected during the 2014/2015 austral summer by BAS staff
were returned to the United Kingdom by ship in + 4°C
cold storage (10weeks), and then maintained at + 4°C
at the University of Birmingham until use. Studies were
conducted in the field on Signy Island between December
2016 and March 2017. All laboratory cultures and experi-
ments, both at the University of Birmingham and on Signy
Island, were maintained on local Signy peat soil substrate,
which is both the species’ habitat and food source on the
island. The substrate was kept moist with a soil solution
comprising 3:1 deionised water to Signy soil (hereafter
termed ‘field water’) to ensure that conditions deviated as
little as possible from the natural environment.
Eretmoptera murphyi’s current distribution on Signy
Island is centered around the research station and adja-
cent Backslope, and therefore all monitoring and sam-
pling occurred within a few hundred metres of the station
(Fig.1b). All images and morphological measurements
were obtained using a Leica EZ4 digital microscope and
associated software. Individual larvae or adults were
extracted from the soil/moss substrate by washing through
stacked sieves (2-mm, 0.5-mm mesh sizes) and handpicked
from the remaining soil solution. Moss and peat substrate
was broken apart with fine tweezers prior to washing to
ensure individuals were not trapped amongst the fibres.
Weather conditions were noted in association with all field
experiments and collection days, with particular attention
to recording strong sunshine and significant precipitation
events.
Measurement oflarvae
Larvae were assigned to instars based on size. They were
initially separated into approximate size classes by eye,
followed by detailed width and length measurements using
images taken with a digital microscope with in-built cam-
era (Leica EZ4). The microscope software was calibrated
for each image using a micrometre stage graticule. Width
measurements were taken by measuring the length of the
intersegmental groove between segment IV (SIV) and seg-
ment V (SV)—the intersection of the cephalothorax and
abdomen. Length measurements were taken from head to
anus, but did not include mandibles or posterior parapods
(the latter only in the case of L1). This information on dis-
tinct size classes then informed the selection of L4 larvae
for studies of pupal development and larval instar occur-
rence in phenological surveys, described below.
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118 Polar Biology (2019) 42:115–130
1 3
Fig. 1 Maps showing the
Location of the South Orkney
Islands and Signy Island in the
Southern Ocean. Inset—Map
of Signy Island, with Research
Station (and thus current area
of E. murphyi distribution)
highlighted. Created using Arc-
Map®10.4.1 software by Esri.
Copyright © Esri
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119Polar Biology (2019) 42:115–130
1 3
Environmental triggers forpupation
In laboratory samples maintained at 4°C under constant
darkness, progression to pupae from the L4 instar is infre-
quent and unpredictable (PC, JB, pers. obs.). We therefore
hypothesised that other environmental signals might be
required to trigger pupation. In a simple test of this, batches
of L4 larvae (n = 20) were placed under the following con-
ditions representing different temperature, light and water
availability scenarios on Signy Island during the transi-
tions from winter to spring and summer (Table1). Control
conditions were constant darkness at 5°C. To determine if
light was a trigger for pupation, samples were transferred to
19L:5D (5°C), which approximates summer photoperiods
on Signy. A fluctuating temperature regime of 5°C dur-
ing illumination and 0°C during darkness was also used, to
approximate typical Signy summer diurnal conditions. To
determine if spring melt/access to water was a trigger for
pupation, larvae were maintained either under “wet” condi-
tions (1:1 soil mass-to-‘field water’ volume ratio) or “dry”
conditions (no additional water was added to the substrate)
in petri dishes.
Larvae were maintained under these experimental con-
ditions for 60days from 18 December 2015 to 18 Febru-
ary 2016, and cumulative pupation recorded. Any pupae
obtained were maintained under the same temperature and
light conditions, but with saturated soil, until either death or
eclosion to imago.
Pupal development
Initial observations suggested morphologically distinct
phases of pupal development, so n = 31 individual pupae
were observed and imaged as they occurred in laboratory
stocks throughout the study (i.e. from both the 2014/2015
BAS collection and 2016/2017 collections). To clearly docu-
ment the discreet phases, digital images were taken of all
pupae under the different treatments applied, with width and
length data recorded as well as other key morphological and
physiological changes including development of gonads,
development from stemmata to compound eyes and changes
to cuticle pigmentation (Table2). This definition of pupal
phases informed the experimental design for field monitor-
ing of pupal and imago development during the 2016/2017
season.
Pupal andimago development intheeld
Field monitoring of pupal development took place during
January 2017 adjacent to Signy Research Station. Individual
pupae (n = 20) were placed in open petri dishes containing
local substrate within a larger arena placed on the ground,
and temperature data were recorded for the duration of the
observations. The arena was constructed using 2-L plastic
tubs with modified lids of nylon mesh, in order to keep the
arena open to the environment whilst preventing damage by
local wildlife, predominantly the Brown Skua (Stercorarius
antarcticus). Pupae were assessed daily from 20 December
2016 to 6 January 2017. Temperature readings inside the
arena were taken each day at the time of surveying using
a soil temperature probe and digital thermometer (RS Pro-
206-3738 with Type K thermocouple probe) and ambient
readings collected with an adjacent temperature logger
external to the arena (Tinytag Transit TG-0050). Pupae were
followed through their development via assessment with a
hand lens and allocated to the developmental stages as noted
Table 1 Environmental treatments used to assess influence of temper-
ature, light and soil saturation on pupation
Dominant light
condition
Temperature
(°C )
Light regime
(L:D)
Soil moisture
Light 5 19:5 Wet
Dry
Light 2 19:5 Wet
Dry
Dark 5 0:24 Wet
Dry
Dark 5–0 19:5 Wet
Dry
Table 2 Description of pupal phases and classification guide for development tracking
Average development time within each phase ± SEM. n = 31 pupae assessed in laboratory conditions (5°C, saturated soil, dark). Eye type: S =
stemmata; C = compound eye. Size is total body length
Pupal Phase Size (mm) Physically mobile Eye type Pigmentation Legs Gonapophysis Repro-
ductively
viable
Development
time in phase
(days)
1 1–1.5 Ver y S None Sheathed None No 3.00 ± 0.82
2 1.5 Somewhat S&C Cephalothorax & legs Sheathed Yes No 4.67 ± 2.75
3 2 Sessile C Full, opaque Sheathed Yes No 2.14 ± 2.59
4> 2 Somewhat C Full, opaque Free Yes Yes 1.00 ± 1.31
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120 Polar Biology (2019) 42:115–130
1 3
above and in Table2, followed by recording their eclosion
date and any subsequent oviposition by adults.
Adult emergence
Three 0.5-m2 quadrats were set out on a moss bank adjacent
to the research station and all were monitored twice daily for
5min at 1000 and 1600 local time, noting the presence of
adults active on the surface, between 20 December 2016 and
6 January 2017. Ground surface temperature readings were
taken each day during the observation periods, as described
above.
Egg maintenance andlarval development
Laboratory cultures established from the 2014/2015
stocks enabled the rearing of larvae to pupation and sub-
sequent emergence with successful oviposition. From
these laboratory eggs, an initial four-phase classification
system of embryonic development was established to aid
development stage identification (Table3). All laboratory
adults that emerged and then oviposited under one of the
experimental environmental conditions described above
were subsequently maintained with their egg sacs at 5°C
on saturated substrate to maintain sac structure. Hydrated
egg sac diameters were measured, and numbers of eggs
were recorded. Eggs were assessed every 48h, and devel-
opmental stage recorded.
Monitoring ofegg development intheeld
Recently laid egg sacs (n = 11) collected from field sam-
ples were placed in open 2-cm petri dishes with saturated
substrate in an external arena and monitored every 48h
until development ceased, or the eggs hatched (a maxi-
mum of 39days), and then again on day 45 to confirm that
Table 3 Description of egg development stages and classification guide for development tracking
Typical duration of each stage given and mean success rate/progression to next phase ± SEM. Success rate = % that successfully complete each
development stage
Egg stage Image Description Develop-
ment
(days)
Success rate (%)
1—Opal
1mm
Opaque white eggs granulated and slightly iridescent in appearance.
No pigmentation
10–14 66 ± 2.72
2—Yellow
1mm
Outer-casing turning yellow/brown. Still granulated and no sign yet of
embryonic form.
5–7 100
3—Early embryo
200µm
Shape of embryo becomes clearer and red stemmata eyes become
evident.
7–10 92.2 ± 0.97
4—Late embryo
100µm
Pharate larva visible with some evidence of internal organs, eyes and
mandibles clearly visible.
7–10 82 ± 2.29
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121Polar Biology (2019) 42:115–130
1 3
no further delayed development had occurred. Tempera-
ture readings inside the arena were noted daily as above.
The development stage of each egg (Table3) within each
egg sac was recorded using a dissecting microscope. On
day 45, all egg sacs were dissected, and any remaining
unhatched eggs individually inspected. A total of n = 740
eggs were assessed.
Phenology ofsummer‑occurring life stages
Weekly soil cores (n = 5) were taken from a site adjacent to
the research station where E. murphyi was abundant, using a
steel 5-cm × 10-cm corer. This took place between 23 Janu-
ary and 6 March 2017 (= late summer season). Soil cores
were returned to the Signy laboratory in a sterile sealed bag
and processed within 24h. Cores were divided into vegeta-
tion and soil/peat substratum and weighed using a Sartorius
precision balance (E6202) before being carefully washed
separately through stacked sieves as described above. All life
stages were extracted, sorted into groups (adults; pupae; L4
larvae; L3 larvae; L2 larvae; eggs unhatched, eggs hatched)
and counted. L1 larvae were not included as their small size
would have resulted in sample processing being too time
consuming. All sieved substrate was dried for 24h at 60°C
and re-weighed to obtain constant dry mass, against which
all counts were normalised. An additional core was collected
each week, divided into vegetation and soil components and
used to make pH and salinity measurements with a Hanna
combo water reader (HI-98129). Throughout the field period
in 2016/2017, the presence of pupae or adults on the surface
were recorded, from which the final dates of sighting of both
pupae and adults were established.
Results
Environmental description
The Signy field site was generally very stable through-
out the 2016/2017 season. The mean pH in the vegeta-
tion layer was 5.3 ± 0.13 SE, n = 7, and underlying soil pH
was 5.5 ± 0.11 SE, n = 7. Salinity was also largely stable,
with only one spike during a week of high storm activity
detected in the vegetation layer, when it rose to 425µS
from an average of 174 ± 45µS SE, n = 7. Salinity in the
soil layer remained close to 70 ± 10µS SE, n = 7.
Larval classication
Size class analysis proved to be suitable for separating the
four larval instars, with each size class being significantly
different from each other in both width at SIV and length
(Fig.2), and no overlap between instar size classes.
Fig. 2 Classification of the four larval instars by a total body length
and b width at segment four/five intersection; n = 10 individuals for
each of L1, 3 and 4, n = 12 individuals for L2. All instars signifi-
cantly different from each other for length: ANOVA F(3,31) = 372.2,
p < 0.0001; width: ANOVA F(3,34) = 780.7, p < 0.0001. c Larval
instars side by side: Top to bottom, L1 to L4
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122 Polar Biology (2019) 42:115–130
1 3
Larval survival andenvironmental triggers
forpupation
Larval survival (Fig.3) was greatest in the control/dark
5°C conditions (70% survival after 60days), and was
significantly different from the light treatments (two-way
ANOVA with Tukey’s multiple comparisons column fac-
tor, F(3,20) = 9.71: Light 2 °C—32.5% survival after
60days, p = 0.008; Light 5°C—30% survival after 60days,
p < 0.001). Overall survival dropped significantly over time
across all treatments (two-way ANOVA with Tukey’s multi-
ple comparisons, F(4,20) = 11, p < 0.0001) and soil moisture
only had a small effect on survival in the warmest lit condi-
tions of Light 5°C (Mann–Whitney U = 3, p = 0.046,). Of all
environmental conditions tested, the fluctuating freeze/thaw
cycle of + 5°C/0°C with corresponding 19:5/L:D, which is
the condition most reflective of Signy summer conditions,
led to the greatest level of pupation, although this was not
significantly different from other treatments (Kruskal–Wal-
lis, H = 13.7, p = 0.6).
Pupal classication anddevelopment
Pupae exhibited four distinct phases of development before
completing the molt to imago (Table2). Broadly, the first
and second phases were differentiated by an increased level
of pigmentation and development of the gonads. The third
phase was quite sessile, deeply pigmented and with the legs
still encased in leg sheaths. There was a thickening of the
cuticle in this stage. The final fourth phase was a partial
eclosion, where the legs were free of the sheath but the
imago not fully eclosed from the exuvia. Mean develop-
ment time in the field from initial pupation to eclosion was
14days (± 5 days, n = 12), with the longest period spent
in the seconnd phase of pupation (Table2). There was no
difference in development rates of pupae incubated at con-
stant or fluctuating temperature in laboratories in the UK,
compared with those in the field conditions with a fluctuat-
ing temperature on Signy Island (Kruskal–Wallis, H = 1.3,
p = 0.54).
Eclosion, imago development andphenology
Only 45% of pupae (n = 20) placed within the external field
arenas successfully eclosed, and 55% of these adults ovipos-
ited. There was no correlation between numbers of individu-
als eclosing and either ambient temperature on the ground
surface over the preceding 24h or within the pupation arena
at the time of sampling (surface temperature: rs =0.21,
p = 0.4; arena temperature: rs =0.31, p = 0.2). There was,
however, a strong correlation between the temperature out-
side the arena and the spot temperature taken within it at the
time of surveying, verifying that the arena did not increase
temperature artificially (rs =0.88, p < 0.0001). Monitoring
of quadrats for the presence of adults showed no correlation
with daily ambient mean temperatures (r2 = 0.07), although
anecdotally adult presence was associated with calm clear
days (Online Resource 1).
Egg classication andmonitoring
Egg sacs (n = 30) had a mean dry mass of 0.14 mg
0.06mg) and water content of 96% (± 1.29%) fresh
mass. Egg sacs contained a mean of 48 (± 12.48 n = 30)
individual eggs and had a diameter of 1.78 (± 0.4 n = 30)
mm, with size not being significantly correlated to either
number of eggs or water content (r2 = 0.08 and 0.009,
respectively). Changes in the proportion of different egg
stages within egg sacs (Table3) until hatching are pre-
sented in Fig.4a. Stage 1 (opal) spanned c. 14days across
all samples, although very consistently across all egg
sacs approximately 40% of eggs did not develop beyond
this stage (Fig.4b). The eggs then turned yellow, before
the early embryo with stemmata evident become visible
around day 19. Late embryos, with visible mandibles and
pharate larvae, appeared around day 25 and eggs hatched
by day 31. Development within an individual egg sac was
not tightly synchronised. After 45days of field observa-
tions of n = 740 eggs, 40% (± 2.72%) did not progress
past the first ‘opal’ stage (Fig.4b). Nearly all remaining
eggs progressed through the yellowing phase, but 7.6%
0.97%) did not progress beyond the early embryo and
16% (± 2.29%) beyond the late embryo, with only 35% of
all eggs (± 2.44%) going on to hatch. There was no differ-
ence in development rates of eggs incubated at constant
temperature compared with those under field conditions
Fig. 3 a Larvae survival over 60days after exposure to varied light,
temperature and substrate saturation levels (n = 20 for each condi-
tion). Survival over time across all treatments (2-way ANOVA Tuk-
ey’s post hoc comparisons, F(4,20) = 11, p = < 0.0001). Soil moisture
effect the only significant variable in Light 5°C (Mann–Whitney U,
p = 0.046). b Total pupations from larvae during experimental condi-
tions (Kruskal–Wallis, H = 13.7; p = 0.6)
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
123Polar Biology (2019) 42:115–130
1 3
with fluctuating temperature (Mann–Whitney U = 17,
p = 0.62) (Fig.5). Phenology andenvironmental factors
Seasonal life-stage monitoring in the field over the late sum-
mer showed that the E. murphyi population had progressed
Fig. 4 a Egg development in field conditions on Signy Island. Stages of individual egg (n = 740) development within each egg sac (n = 11)
recorded over time, shown with CI of 95%. b Maximum stage reached after 45days of monitoring (Tukey’s plot) with outliers
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124 Polar Biology (2019) 42:115–130
1 3
through pupal and adult stages before the end of January
(Fig.6a). The last pupae were found on 3 January 2017 and
the last adult was seen on 19 January 2017 (Fig.6b). By
13 February 2017, no further viable unhatched eggs were
found in the samples (determined by the presence of hatched
eggs alongside those that had stalled development at a much
earlier stage), with only hatched eggs collected thereafter.
Unhatched eggs that were considered undeveloped/unviable
appeared to decompose, becoming opaque, soft and bloated,
often combined with visible fungal development. The phe-
nological soil core surveys did not include any counts of
adults or pupae (Fig.6b), so these were discounted from
analysis. There was no significant difference in the appear-
ance of the larval instars or trend over time (Kruskal–Wallis,
H = 1.3, p = 0.53; r2 = 0.1). The appearance of unhatched and
then hatched eggs did show a visible difference (Fig.6b),
with a distinct increase in the number of hatched eggs over
time compared to a decline in unhatched (Mann–Whitney
U = 202, p = 0.008).
Population success
Analysis of reproductive output (Table4) suggests that the
E. murphyi population can potentially double with each life
cycle. Considering the percentage of larvae that survive over
60 days, pupae that successfully eclose, adults that success-
fully oviposit and the viability of eggs laid, this will amount
to an average 50,000 additional L1 added to the population
every two years, based on the most recent distribution data
reported by Hughes and Worland (2010) (Table4).
Discussion
Larval andpupal development
The developmental stages described here for larval instars
are consistent with the only taxonomic study of E. murphyi
(Cranston 1985) and provide a first description of the L1
and L2 instars. Like the sister species B. antarctica (Sugg
etal. 1983), and typical for chironomids, there are four lar-
val instars, which in our data do not overlap in size classes
for either width or length and provide a clearer assessment
Fig. 5 Mean (± SE) time (days) taken to complete egg or pupal stage
under different temperature conditions. Also shown, the mean period
from eclosion to oviposition and adult longevity post eclosion. Field
conditions are shown as the mean temperature experienced (F: x̄)
over the relevant period. Pupae and adult development periods over-
lapped and thus were subject to the same average field temperatures.
Lab temperatures were either static 5°C or 12h 5/12h 0°C. Sam-
ple sizes—Egg development: “F: x̄ 3.5, n = 6 egg sacs; “+ 5 n = 7.
Pupae development: “F: x̄ 4.2 n = 5; “+ 5 n = 4. Oviposition F: x̄
4.2 n = 5; “+ 5 n = 4. AdultsF: x̄ 4.2 n = 5; + 5 n = 4
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125Polar Biology (2019) 42:115–130
1 3
of all instars than the use of body mass classes (cf. Hughes
etal. 2013). Our observations of pupae indicate that meta-
morphosis takes around 14 d, and can be divided into four
morphologically distinct phases, providing a new level of
detail for E. murphyi and for chironomids in general, whose
pupal stage is understudied (Armitage etal. 1995). Appar-
ent obligate parthenogenesis in E. murphyi enables oviposi-
tion to occur prior to the completion of eclosion. Whilst this
alone is not unique among asexual chironomids (Armitage
etal. 1995; Langton etal. 1988), it does offer E. murphyi a
Fig. 6 a Mean (weekly) hours
of daylight and darkness as well
as high and low air temperatures
on Signy Island, annotated with
key points in the development
of E. murphyi life stages: SM
basal snow melt, mid Nov 2016;
LP last pupae seen 3 Jan 2017;
LA last adult seen 19 Jan 2017;
LE last unhatched eggs seen
30 Jan 2017; SR snow returned
27 Feb 2017. b Abundance of
different E. murphyi life stages
found in soil cores from a single
site collected from late Janu-
ary to the beginning of March
2017, shown as mean percent-
age of total population (±SE).
A adults, P pupae; L2, L3 and
L4 larval instars; EU egg sacs
where majority (> 50%) of eggs
were unhatched, EH egg sacs
where the majority (> 50%) of
eggs had hatched
Table 4 Life stage success table using population densities of larvae reported by Hughes and Worland (2010)
Average larval densities are taken from the whole sample site. ~70% of L4 larvae survive; 45% of larvae successfully eclose, 55% then oviposit,
with a mean of 48 eggs per oviposition and 35% go on to hatch
Population density Larvae density (m2) Approximate lar-
vae survival (m2)
Successfully
eclose (m2)
Successfully
oviposit (m2)
Total Eggs laid (m2) Total Hatched (m2)
High 150,000 105,000 47,250 25,987 1,247,400 361,746
Average 21,000 14,700 6,615 3,638 174,636 50,644
Low 500 350 157 87 4,158 1,205
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126 Polar Biology (2019) 42:115–130
1 3
distinct advantage in a polar habitat such as on Signy Island,
enabling it to reproduce even if conditions or physiology do
not permit eclosion. Our data do not provide evidence for
a temperature or moisture/spring thaw trigger for pupation.
Fluctuating temperatures of the spring season (+ 5/0°C),
did result in more pupae; however, this was not statisti-
cally different from other treatments. Block etal. (1984)
reported that pupae of E. murphyi appeared shortly after
spring thaws, and a similar observation has been reported in
an aquatic Antarctic midge, Parochlus steinenii (Hahn and
Reinhardt 2006; Rauschert 1985), but further early season
sampling will be required to clarify the cues required to initi-
ate pupation.
Adult emergence andparthenogenesis
The emergence of E. murphyi adults does not take place in a
synchronous mass event as reported in B. antarctica (Sugg
etal. 1983) but continues over a 2–3-month period (Online
Resource 1). In the 2016/2017 summer season, adults were
already noted to be active when Signy station was opened
in mid-November (Station Leader M. Jobson, pers. comm.),
coinciding with an early spring thaw. Hatched eggs were
already present in the soil in late December 2016 which,
based on the egg development times recorded in this study,
means they would have been laid in late November at the
earliest. This could give E. murphyi a distinct advantage
over sexual reproducers, such as B. antarctica, the only
chironomid that successfully completes its life cycle on the
Antarctic Peninsula. Whilst B. antarctica is limited by the
need to have males and females emerge synchronously to
reproduce sexually, E. murphyi is not even limited by the
need to complete eclosion. Staggering the emergence period
means that any adverse weather encountered in the summer
months would not necessarily impede the species’ continued
survival on the island, as posited by Hughes etal. (2013).
The lack of mass emergence also suggests that E. murphyi
has a more flexible life history, and emergence may be trig-
gered by significant environmental cues for favourable con-
ditions rather than any obligate physiology.
Parthenogenetic reproduction is a common feature within
the Chironomidae, and in the Orthocladiinae usually takes
the complete form of parthenogenesis known as thelytoky
(Moller Pillot 2014; Scholl 1956; Thienemann 1954). In
thelytoky, genetic fertilisation is absent and so females
only produce female progeny, as is seen in E. murphyi
(Convey 1992; Cranston 1985). It is likely that E. murphyi
exhibits apomictic thelytoky, the most widespread from of
thelytoky in Orthocladiinae (Scholl 1956, 1960) and that
the lack of progression of a significant proportion of eggs
beyond the initial development stage seen here is the result
of a mechanical failing at an early maturation stage of mito-
sis (Porter and Martin 2011), possibly as the result of an
environmental stressor. It is thought that the adoption of
thelytoky by arthropods is an advantageous strategy. It may
particularly benefit polar species, through the elimination of
males, which have been shown to be more susceptible to the
cold and extremes in temperature (Oliver and Danks 1972;
Rinehart etal. 2000; David etal. 2005; Colinet and Hance
2009). Thus, the need for synchronous mass emergence is
redundant. (Downes 1962; Porter and Martin 2011).
Egg development
A total of 740 individual eggs were studied to document
embryogenesis and hatching. Unusually for the sub-family
Orthocladiinae, eggs are laid in an almost uniform spherical
mass rather than in a rope-like mass or bale, a trait that is
otherwise used to define the group (Nolte 1993) and that is
also exhibited by B. antarctica. Individual egg morphology
is consistent with previous descriptions of Orthocladiinae
(Armitage etal. 1995; Nolte 1993; Thienemann and Stren-
zke 1940), and particularly that of B. antarctica (Harada
etal. 2014). Eretmoptera murphyi individuals produced an
average clutch size of 48 eggs in this study, of which only
29% hatched successfully. This is a small clutch size for a
chironomid midge, which typically produce hundreds if not
thousands of eggs, but not unusual for terrestrial Orthocladi-
inae which have been recorded to lay eggs in numerous small
batches or even individually (Nolte 1993). Another Antarc-
tic chironomid, P. steinenii lays an average of 191 eggs per
batch, sometimes over multiple batches (Hahn and Reinhardt
2006), whilst Harada etal. (2014) describe a mean batch size
of 41 eggs per string for B. antarctica with a gestation of just
16days. Neither of these studies documented the percentage
of eggs that go on to hatch.
With ground surface temperature variation of as much as
24.8°C (see Online Resource 2) in a 12-h period on Signy
Island, temperature stress may account for the long egg
development time and high mortality observed. Despite the
low clutch size and hatching success, our data indicate that
at least 13 eggs will hatch for every E. murphyi adult. With
population densities as high as 150,000 ind.m2 (Hughes
and Worland 2010), this could result in as many as 1.2 mil-
lion eggs being laid per m2 in parts of the species’ current
distribution and, consequently, further local dispersal if no
checks are held on the population at other points in the life
cycle. However, as nearly half of all pupae failed to eclose
to adult under field conditions, and 55% of adults failed to
successfully oviposit, these two life stages appear to repre-
sent a major limitation. Whether this indicates lower stress
tolerance in these life stages requires further study, given
that only larval stages have been studied in detail to date.
Even taking this into account, with an average density of E.
murphyi within its distribution on Signy Island of 21,000
ind. m2 (Hughes and Worland 2010), we estimate that the
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127Polar Biology (2019) 42:115–130
1 3
species could have the potential to double its population over
every life cycle of two years. If so, a simple back-calculation
would suggest an introduction date of a single individual
in the early 1970s, which is generally consistent with the
assumed introduction event with plant transplants in the lat-
ter part of the 1960s (Burn 1982; Block etal. 1984).
Phenology
Although all larval instars were present throughout the study
period (Fig.6b), their relative densities were highly vari-
able over time. These data appear to reflect more the patchi-
ness of larval distribution than the sequential occurrence
of particular instars over time. Whilst eggs are immobile
and thus easier to represent through repeated sampling in a
fixed location, larvae are mobile. Patchiness in larval distri-
bution, including aggregations of larvae, was also reported
by Hughes and Worland (2010), and is a characteristic of
Antarctic terrestrial invertebrate communities (Usher and
Booth 1984). Any increase in hatched eggs naturally infers
an increase in the number of L1 in the soil but, due to the
very small size of this instar, it was not practicable to include
them in this survey. Unhatched eggs do not overwinter. Bel-
gica antarctica is also thought to overwinter only in the
larval stage and in all four instars (Sugg etal. 1983). How-
ever, during soil core analyses, L1 and L3 E. murphyi larvae
were noted to be molting towards the end of the season,
indicating that L2 and L4 are likely to be the primary over-
wintering larval instars, as suggested by Convey (1996a) and
Hughes etal. (2013).
A mid-range climate forecast for the Antarctic Peninsula
and South Orkney Islands suggests that mean annual air
temperatures are expected to increase by 1.5–2°C by 2100
(Larsen etal. 2014). Temperature warming is thought to
benefit polar terrestrial invertebrates by reducing the stress
of low-temperature extremes and giving greater liquid water
availability (Bale and Hayward 2010; Convey 2006, 2011;
Convey etal. 2014) and, in the case of non-native species,
making available locations that were previously uninhab-
itable. By increasing our knowledge of E. murphyis life
cycle, we can better understand any threat it may pose to
Signy Island terrestrial ecosystems, and its potential as an
invasive invertebrate at other at-risk areas, such as along the
Antarctic Peninsula (Fig.7).
Fig. 7 Summary of Eretmoptera murphyis life cycle
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128 Polar Biology (2019) 42:115–130
1 3
Conclusions
This study provides the first comprehensive documentation
of the life cycle of E. murphyi, a flightless chironomid midge
that is currently expanding its distribution following anthro-
pogenic introduction to Signy Island. The species’ reliance
on parthenogenesis is confirmed and new information pro-
vided on the characteristics of all life stages, their develop-
ment rates, the phenology of previously undescribed eggs
and pupae and the emergence of adults. Adults do not show
synchronised emergence, rather appearing throughout the
first half of the summer season, which suggests a flexible
life history strategy where emergence is not dependent on
any discrete environmental cue. Ground temperature vari-
ability and spikes in field temperature may explain the long
development time of eggs compared to previous laboratory
studies, and their low percentage of successful maturation.
Despite the limitations on survival at each of the life stages,
the population is potentially able to double in size every life
cycle/2years, highlighting the ability of this species to fur-
ther expand its population and distribution on Signy Island.
This study provides a springboard for further description
and physiological studies of all life stages of this species,
which will increase our understanding of the risks it poses
as a non-native species on Signy Island, and the potential to
colonise new areas, if given opportunity.
Acknowledgements J Bartlett is funded by a Natural Environment
Research Council (NERC) through The Central England NERC
Training Alliance (CENTA) Doctoral Training Partnership (DTP)
(RRBN19276). Her PhD studentship is supported by the University
of Birmingham and the British Antarctic Survey (BAS). P. Convey
is supported by NERC core funding to the BAS ‘Biodiversity, Evolu-
tion and Adaptation’ Team. Fieldwork in this study was supported by
BAS through a NERC–CASS grant (CASS-121) and permitted by the
British Foreign and Commonwealth Office through Specialist Activi-
ties in Antarctica (No 22/2016). The authors also thank staff at Signy
Research Station for their practical and moral support, and thank the
reviewers for their helpful comments. This study contributes to the
SCAR ‘State of the Antarctic Ecosystem’ (AntEco) programme.
Compliance with ethical standards
Conflict of interest We confirm that no part of this study has been pub-
lished before or is under consideration for any other journal by either
myself or my co-authors. None of the authors have any conflicts of
interest to disclose and all authors have approved this manuscript and
its submission to Polar Biology.
Ethical approval We confirm that the use of invertebrates complied
with all relevant ethical standards and that field work in Antarctica
was conducted with permissions from the UK Foreign Office and that
returned samples were permitted by the Department for the Environ-
ment, Farming and Rural Affairs (DEFRA).
Open Access This article is distributed under the terms of the Crea-
tive Commons Attribution 4.0 International License (http://creat
iveco mmons .org/licen ses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give appro-
priate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made.
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... First, E. murphyi has subsequently been shown in a detailed potential distribution modelling study to be highly likely to survive and establish even under current climatic conditions throughout the west coast of the Antarctic Peninsula at least as far as this more southern location. Second, the species reproduces parthenogenetically, which means only a single individual is required to achieve successful colonization, magnifying the risk of assisted transfer (Bartlett et al. 2019a(Bartlett et al. , 2019b, as may well have happened in the species' initial transfer to Signy Island. The observed high densities of H. viatica (Convey et al. 1999, Enríquez et al. 2019, with its wide though spatially separated invaded range in Antarctica from South Georgia to Adelaide Island (Convey et al. 1999, Hughes et al. 2015b; although it has not proved possible to confirm its continued presence at the latter southern location -see Hughes et al. 2017), highlight the potential risk of onwards 'stepping stone' transfer of such species from already colonized locations in Antarctica. ...
... Similarly, the recently documented very high larval population densities of E. murphyi close to the research station on Signy Island increase the risk of its inadvertent entrainment with human movement (Bartlett et al. 2019b). Locations of known high density or diversity of established non-native species, such as Signy Island (Bartlett et al. 2019a), Fildes Peninsula and Point Thomas (King George Island;Volonterio et al. 2013, Galera et al. 2019, Remedios-de León et al. 2021, Deception Island , Enríquez et al. 2019) and other parts of the western Antarctic Peninsula (Molina-Montenegro et al. 2012, Russell et al. 2014, require particular focus on effective biosecurity procedures to prevent the transfer of these potentially propagule-rich species along the well-used standard logistical and tourist traffic routes in this region (Hughes et al. 2019). Nevertheless, more data documenting propagule pressures for non-native taxa are clearly required in order to allow further evaluation of the introduction risk within the various gateways to Antarctica and to strengthen related biosecurity management strategies , Hughes et al. 2019. ...
... In turn, P. pratensis, while managed to acclimatize to the harsh conditions of Cierva Point, was not able to adapt towards reproducing effectively in such conditions. Most of the non-native invertebrates (Diptera and Collembola) introduced to the continent also possess good cold-tolerance capabilities (Bahrndorff et al. 2009, Bartlett et al. 2019a, Liu et al. 2020) that make them readily adaptable to their Antarctic environments (Worland 2010). In the case of the dipteran T. maculipennis, representing the latest threat, recent studies have confirmed the capacity of its larvae to withstand temperatures down to -5°C for short periods , while the northern boreal parts of its native distribution expose it to similar or more severe thermal stresses than characterize its establishment locations on King George Island (Remedios-de León et al. 2021). ...
Article
Understanding the success factors underlying each step in the process of biological invasion provides a robust foundation upon which to develop appropriate biosecurity measures. Insights into the processes occurring can be gained through clarifying the circumstances applying to non-native species that have arrived, established and, in some cases, successfully spread in terrestrial Antarctica. To date, examples include a small number of vascular plants and a greater diversity of invertebrates (including Diptera, Collembola, Acari and Oligochaeta), which share features of pre-adaptation to the environmental stresses experienced in Antarctica. In this synthesis, we examine multiple classic invasion science hypotheses that are widely considered to have relevance in invasion ecology and assess their utility in understanding the different invasion histories so far documented in the continent. All of these existing hypotheses appear relevant to some degree in explaining invasion processes in Antarctica. They are also relevant in understanding failed invasions and identifying barriers to invasion. However, the limited number of cases currently available constrains the possibility of establishing patterns and processes. To conclude, we discuss several new and emerging confirmatory methods as relevant tools to test and compare these hypotheses given the availability of appropriate sample sizes in the future.
... Egg development takes 16 days at 4°С (Harada et al., 2014). The larval stage is the longest, lasting almost 2 years, and includes four instars (Usher & Edwards, 1984), as is typical of other Chironomidae (Bartlett et al., 2019b;Finch et al., 2020). Wirth and Gressitt (1967) suggested that the pupae can survive the winter, while other studies have reported that larvae pupate early in the austral summer in late November and that the adults emerge approximately 1 month later and can be observed from late December through to late January (Martin, 1962), as is also the case in E. murphyi (Bartlett et al., 2019b). ...
... The larval stage is the longest, lasting almost 2 years, and includes four instars (Usher & Edwards, 1984), as is typical of other Chironomidae (Bartlett et al., 2019b;Finch et al., 2020). Wirth and Gressitt (1967) suggested that the pupae can survive the winter, while other studies have reported that larvae pupate early in the austral summer in late November and that the adults emerge approximately 1 month later and can be observed from late December through to late January (Martin, 1962), as is also the case in E. murphyi (Bartlett et al., 2019b). The nonfeeding adults survive only 1-2 weeks after their summer emergence (they are found from late December to March) (Sugg et al., 1983;Usher & Edwards, 1984;Rinehart et al., 2006;Finch et al., 2020). ...
... At 6-7°С, virgin females will lay unfertilized eggs 5-7 days after hatching. These eggs do not develop, suggesting the species lacks parthenogenesis, unlike E. murphyi (Edwards & Baust, 1981;Cranston, 1985;Convey & Block, 1996;Bartlett et al., 2019b). ...
Article
Full-text available
Belgica antarctica (Diptera: Chironomidae), a brachypterous midge endemic to the maritime Antarctic, was first described in 1900. Over more than a century of study, a vast amount of information has been compiled on the species (3 750 000 Google search results as of January 10, 2021), encompassing its ecology and biology, life cycle and reproduction, polytene chromosomes, physiology, biochemistry and, increasingly, omics. In 2014, B. antarctica’s genome was sequenced, further boosting research. Certain developmental stages can be cultured successfully in the laboratory. Taken together, this wealth of information allows the species to be viewed as a natural model organism for studies of adaptation and function in extreme environments.
... Samples were kept on soil substrate from their local habitat and returned to the United Kingdom by ship (+ 4 °C, 10 weeks), where they were maintained under the same 'control' conditions at the University of Birmingham. Larvae were maintained, extracted and classified to instar following Bartlett et al. (2018). Larval submersion experiments used seawater from stocks at the British Antarctic Survey, Cambridge. ...
... Egg sacs were removed from the substrate as described by Bartlett et al. (2018). All eggs within the egg sacs were confirmed to be at the first (opal) developmental stage prior to the start of experiments and were then used for the entire egg development period of 35 days (Bartlett et al. 2018). ...
... Egg sacs were removed from the substrate as described by Bartlett et al. (2018). All eggs within the egg sacs were confirmed to be at the first (opal) developmental stage prior to the start of experiments and were then used for the entire egg development period of 35 days (Bartlett et al. 2018). If any eggs showed signs of yellowing or embryonic development the entire egg sac was discarded and not used for experimentation. ...
Article
Full-text available
The non-native midge Eretmoptera murphyi is Antarctica’s most persistent non-native insect and is known to impact the terrestrial ecosystems. It inhabits by considerably increasing litter turnover and availability of soil nutrients. The midge was introduced to Signy Island, South Orkney Islands, from its native South Georgia, and routes of dispersal to date have been aided by human activities, with little known about non-human-assisted methods of dispersal. This study is the first to determine the potential for dispersal of a terrestrial invertebrate species in Antarctica by combining physiological sea water tolerance data with quantitative assessments of ocean current journey times. Fourth instar larvae tolerated sea water submergence for up to 21 days, but submerged egg sacs had significantly reduced hatching success. Using near-surface drifter data, we conclude that ocean current dispersal from Signy Island would not present a risk of species transfer beyond the South Orkney Islands on the tested timescales. However, if E. murphyi were to be introduced to the South Shetlands Islands or Adelaide Island, which are located offshore of the Antarctic Peninsula, there would be a risk of successful oceanic dispersal to neighbouring islands and the Antarctic Peninsula mainland. This study emphasises the need for effective biosecurity measures and demonstrates the role that currently undocumented pathways may have in dispersing non-native species.
... (boiemicus) Lindeberg 1971 Micropsectra silvesterae (Langton, 1999) Langton 1998 Micropsectra sp. (nigripila) Armitage et al. 1995Micropsectra sedna (Oliver, 1976 Porter Orthocladiinae there are 12 species from 9 genera (Edwards 1919;Thienemann 1954;Edward and Colless 1968;Forsyth 1971;Armitage et al. 1995;Siri and Donato 2014;Andersen et al. 2016;Bartlett et al. 2018); and in the Telmatogetoninae there are two species from the type genus Telmatogeton (Crafford 1971;Delettre et al. 2003). ...
... This allows for rapid population growth and productivity. Sexually reproducing species tend to require more individuals for population establishment to be successful, because future generations may be unlikely to find mates if founding numbers are low (Suomalainen 1962;Lynch 1984;Bartlett et al. 2018;. ...
... The species may simply have gone undetected during the 1970s because their habitat type was not as frequently sampled as it was in the 2010s. It is also possible that this parthenogenetic species is a recent invader of this polar extreme, similar to the parthenogenetic chironomid Eretmoptera murphyi that recently invaded Antarctica (Bartlett et al. 2018;, but this remains unknown. ...
Article
Full-text available
Parthenogenesis, reproduction without fertilization, is not common in the Chironomidae (Diptera), a family of insects with more than 6,000 described species. Nonetheless, parthenogenetic species and strains have been documented in at least three subfamilies (the Chironominae, Orthocladiinae, and Telmatogoninae), spanning 17 genera and ~30 species. One such species, Paratanytarsus laccophilus Edwards 1929, is known to be parthenogenetic in a small portion of its range in Finland, with most other European populations of this species showing evidence of sexual reproduction. We present evidence of parthenogenetic populations from the Paratanytarsus laccophilus species group in the Nearctic, specifically a High Arctic site near Utqiaġvik (formerly Barrow), Alaska. During May-July of 2015 and 2016, we sampled emerging adult chironomids and pupal exuviae daily to document insect emergence phenologies. Across 15 local populations, all 623 pupal exuviae collected from the P. laccophilus species group were female. Larvae reared from two populations under controlled temperature treatments emerged as female adults (N=37). When isolated, these reared female adults oviposited, and eggs hatched successfully. These progeny were reared for another 12-13 days, reaching second instar larvae when they were preserved at the end of our field season. Taken together, this evidence strongly indicates parthenogenesis from the P. laccophilus species group at this location. This species was not previously documented at Utqiaġvik. Although parthenogenetic, their emergence at this location was highly synchronized. In the harsh environment of arctic Alaska, the fitness rewards of parthenogenesis are likely great. Indeed, chironomid parthenogenesis in the northern hemisphere is most commonly documented from far-northern extremes and in extreme habitats.
... However, importantly, these previous assessments were conducted using tap water, and the species' ability to survive an entire winter entrapped in ice under more field-realistic conditions, where temperatures will not rise above freezing for months [22,23], remains unknown. As with studies of the related Belgica antarctica [24][25][26], most physiological examinations of E. murphyi have been conducted on mature larvae-with the exception of two studies that examined desiccation and heat tolerance in eggs [27,28]. Thus, knowledge of the cold-tolerance abilities of different life stages remains limited. ...
... For each temperature exposure, four replicates of five individual larvae (n = 20), and ten replicates of a single egg sac, were placed in a sealed Eppendorf tube with a thermocouple wire threaded through a small hole in the lid. The 10 egg sacs contained c. 630 eggs between them (based on Bartlett et al. [27]). After each treatment, individuals were removed and placed in a petri dish containing moist Signy soil substrate and kept at control conditions in a dark refrigerator. ...
... In order to first ascertain the experimental impact of using different water types in freezing experiments [21], we measured the freezing point of 18 MΩcm deionized water (DIW) and Signy field water (FW). Signy field water was prepared as described by Bartlett et al. [17,27]. Seven 1.5 mL Eppendorf tubes containing each water type were placed in an alcohol bath (as above) and taken from +5 °C to −10°C at a rate of 0.2 °C min -1 , and the freezing point was recorded. ...
Article
Full-text available
An insect’s ability to tolerate winter conditions is a critical determinant of its success. This is true for both native and invasive species, and especially so in harsh polar environments. The midge Eretmoptera murphyi (Diptera, Chironomidae) is invasive to maritime Antarctic Signy Island, and the ability of fourth instar larvae to tolerate freezing is hypothesized to allow the species to extend its range further south. However, no detailed assessment of stress tolerance in any other life stage has yet been conducted. Here, we report that, although larvae, pupae and adults all have supercooling points (SCPs) of around −5 °C, only the larvae are freeze-tolerant, and that cold-hardiness increases with larval maturity. Eggs are freeze-avoiding and have an SCP of around −17 °C. At −3.34 °C, the CTmin activity thresholds of adults are close to their SCP of −5 °C, and they are likely chill-susceptible. Larvae could not withstand the anoxic conditions of ice entrapment or submergence in water beyond 28 d. The data obtained here indicate that the cold-tolerance characteristics of this invasive midge would permit it to colonize areas further south, including much of the western coast of the Antarctic Peninsula.
... In contrast, following its introduction to Signy I., the E. murphyi population, which has a dominant larval life stage spanning almost 2 years, has expanded locally in the vicinity of the original introduction site close to Signy Research Station. In particular, this species has expanded along well-used path routes suggesting an important element of human-assisted dispersal (Bartlett, Convey, & Hayward, 2018a;2018b;Bartlett, Convey, Pertierra, & Haiward, 2019;Hughes & Worland, 2010). This is a concern as Hughes, Worland, Thorne, and Convey (2013) calculated that in the area where the species occurs on Signy I., it is responsible for increasing litter turnover by up to almost an order of magnitude compared to that achieved by the entire native invertebrate community (see also Bridge & Denton, 2007;Montiel, 1998). ...
... From these sources a total of 15 records, set in a 5 arc-min grid-cell resolution, were assigned at icefree coastal bays where the species was historically observed (see Supporting Information S1). One additional record was added to indicate the species' presence on Signy I. following Bartlett et al. (2018a). ...
... To ensure that environmental conditions deviated as little as possible from the natural environment, the substrate was kept moist with a soil solution comprising 3:1 deionized water to Signy soil. Only L4 larvae were used in experiments, selected according to instar class size categories (Bartlett et al., 2018a). Ten individual larvae were placed in each Petri dish containing moistened substrate, with three and seven replicate dishes alternated for each consecutive experimental temperature exposure (according to larvae availability). ...
Article
Correlative species distribution models (SDMs) are subject to substantial spatio‐temporal limitations when historical occurrence records of data‐poor species provide incomplete and outdated information for niche modelling. Complementary mechanistic modelling techniques can, therefore, offer a valuable contribution to underpin more physiologically informed predictions of biological invasions, the risk of which is often exacerbated by climate change. In this study we integrate physiological and human pressure data to address the uncertainties and limitations of correlative SDMs and to better understand, predict and manage biological invasions. Western archipelagos of the Southern Ocean and martime Antarctica. Eretmoptera murphyi (Chironomidae), invertebrates. Mahalanobis Distances were used for correlative SDM construction for a species with few records. A mechanistic SDM was built around different fitness components (larval survival and life stage progression) as a function of temperature. SDM predictions were combined with human activity levels in Antarctica to generate a site vulnerability index to the assess colonization risk of E. murphyi. Future scenarios of ecophysiological suitability were built around the warming trends in the region. Both SDMs converge to predict high environmental suitability in the species' native and introduced ranges. However, the mechanistic model indicates a slightly larger invasive potential based on larval performance at different temperatures. Human activity levels across the Antarctic Peninsula play a key role in discerning site vulnerabilities. Niche suitability in Antarctica grows considerably under long‐term climate scenarios, leading to a substantially higher invasive threat to the Antarctic ecosystems. In turn changing conditions result in growing physiological mismatches with the environment in the native range in South Georgia. Long‐term studies of invasion potential under climate benefit from integrating correlative predictions with physiological experiments, as the invasion potential varies depending on the area and the timescale examined. This study also highlights a conservation paradox whereby the accidental introduction of an insect represents a threat to the Antarctic ecoystems that contrasts with its endangered status at the native range.
... In the latter instance, all larvae were rested in control conditions for 48 h to ensure that the extraction process was not an additional stressor prior to treatment. All larvae were subsequently assigned to instars based on size (Bartlett et al. 2018a). Experiments using eggs were conducted in laboratories at Signy Research Station during January 2017, using recently laid egg sacs collected from moss banks surrounding the research station. ...
... For experiments on eggs, conducted on Signy Island, seawater was collected locally. All eggs within the egg sacs were confirmed to be at the first (opal) developmental stage prior to the start of experiments and were then used for the entire gestation period of 35 days (Bartlett et al. 2018a). If any eggs showed signs of yellowing or embryonic development, the whole egg sac was discarded and not used in this study. ...
Article
Full-text available
The flightless midge Eretmoptera murphyi is thought to be continuing its invasion of Signy Island via the treads of personnel boots. Current boot-wash biosecurity protocols in the Antarctic region rely on microbial biocides, primarily Virkon® S. As pesticides have limited approval for use in the Antarctic Treaty area, we investigated the efficacy of Virkon® S in controlling the spread of E. murphyi using boot-wash simulations and maximum threshold exposures. We found that E. murphyi tolerates over 8 h of submergence in 1% Virkon® S. Higher concentrations increased effectiveness, but larvae still exhibited > 50% survival after 5 h in 10% Virkon® S. Salt and hot water treatments (without Virkon® S) were explored as possible alternatives. Salt water proved ineffective, with mortality only in first-instar larvae across multi-day exposures. Larvae experienced 100% mortality when exposed for 10 s to 50°C water, but they showed complete survival at 45°C. Given that current boot-wash protocols alone are an ineffective control of this invasive insect, we advocate hot water (> 50°C) to remove soil, followed by Virkon® S as a microbial biocide on ‘clean’ boots. Implications for the spread of invasive invertebrates as a result of increased human activity in the Antarctic region are discussed.
... B. Frenot et al., 2005;Russell et al., 2013;Hughes et al., 2015b;United Kingdom, 2015). So wurde die für Südgeorgien endemische flügellose Zuckmücke (Familie: Chironomidae) in den 1960er Jahren auf Signy Islands eingeschleppt Bartlett et al., 2019). Während die Mehrzahl der nicht-heimischen Arten in natürlicher Umgebung, jedoch an Orten verstärkter menschlicher Aktivität, gefunden wurde Chown et al., 2012), konnten sich einige Arten auch innerhalb von Gebäuden oder Abwassersystemen von Antarktis-Stationen etablieren . ...
... Invertebrates living in these habitats often display adaptations that allow them to tolerate extreme conditions. Therefore, understanding the physiology of resident invertebrate species provides the basis for comparisons across species or environments [16][17][18][19][20][21][22][23]. ...
Article
Full-text available
The habitat of the intertidal flightless midge Telmatogeton magellanicus (Jacobs, 1900) is described for the first time from the northern coast of Navarino Island, Tierra del Fuego, Chile. Additionally, we report the first observations of adult behaviour in the wild. We delineate the species’ distribution across three tidal zones (high, mid and low), and identify substrate characteristics that favour the presence of the midge. The mid-tide zone was the key habitat utilized by T. magellanicus, with lower densities in the low-tide zone and no presence in the high-tide zone. There was a strong association between the presence of larvae and filamentous algae, especially Bostrychia spp. and, to a lesser extent, Ulva spp., as well as between larvae and the presence of larger, more stable boulders. As a result, the species’ overall distribution was widespread but patchy. We suggest that the main limiting factor is the relative humidity experienced in different habitats. One of the most striking features of the behavioural observations during data collection was the extremely active adults, which suggests high energy expenditure over a very short period of time. This may be due to the limited time available to find mates in a single low-tide period, when adults have about three hours after emerging from the pupa to complete mating and oviposition before inundation by the tide. The data presented here provide a baseline for future studies on this species’ ecology, phenology, physiology and general biology.
... For much of Antarctica's history of human contact, the ice-free areas of the Antarctic Peninsula and McMurdo Valleys have attracted considerable interest from scientists eager either to understand their paleoclimates or, more lately, to work with NASA to develop and plan for Moon and Mars landings (Salazar 2017). Now other areas such as Signy Island are hotspots for research as scientists discover new species such as the flightless midge, which feeds on organic matter and has been responsible for affecting peat decomposition and soil structure (Bartlett et al. 2019). ...
Chapter
This book presents a novel and systematic social theory of soil, and is representative of the rising interest in ‘the material’ in social sciences. Bringing together new modes of ‘critical description’ with speculative practices and methods of inquiry, it contributes to the exploration of current transformations in socioecologies, as well as in political and artistic practices, in order to address global ecological change. The chapters in this edited volume challenge scholars to attend more carefully to the ways in which they think about soil, both materially and theoretically. Contributors address a range of topics, including new ways of thinking about the politics of caring for soils; the ecological and symbiotic relations between soils; how the productive capacities and contested governance of soils are deployed as matters of political concern; and indigenous ways of knowing and being with soil.
Article
Full-text available
The rediscovery of the species as a suspected introduction to Signy Island (South Orkney Islands) allows description of the immature stages and redescription of the female, the only sex known. E. murphyi larvae are terrestrial, living in damp moss and peat, and the brachypterous adult is probably parthenogenetic. Eretmoptera appears to have an isolated position amongst the terrestrial Orthocladiinae.-from Author
Book
The dipteran family Chironomidae is the most widely distributed and frequently the most abundant group of insects in freshwater, with rep­ resentatives in both terrestrial and marine environments. A very wide range of gradients of temperature, pH, oxygen concentration, salinity, current velocity, depth, productivity, altitude and latitude have been exploited, by at least some chironomid species, and in grossly polluted environments chironomids may be the only insects present. The ability to exist in such a wide range of conditions has been achieved largely by behavioural and physiological adaptations with relatively slight morphological changes. It has been estimated that the number of species world-wide may be as high as 15000. This high species diversity has been attributed to the antiquity of the family, relatively low vagility leading to isolation, and evolutionary plasticity. In many aquatic ecosystems the number of chironomid species present may account for at least 50% of the total macroinvertebrate species recorded. This species richness, wide distribution and tolerance to adverse conditions has meant that the group is frequently recorded in ecological studies but taxonomic difficulties have in the past prevented non-specialist identification beyond family or subfamily level. Recent works, including genetic studies, have meant that the family is receiving much more attention globally.
Article
The ability of the Utah energy-balance and snowmelt model (UEB) to simulate decline in snow water equivalent (SWE) at an extreme location was assessed. Field data were collected at Paternoster Valley, Signy Island, South Orkney Islands (60°43′S) during the austral summer of 1996–97. This is the first application of UEB in a maritime Antarctic site. UEB is a physically based snow melt model using a lumped snow-pack representation with primary state variables SWE and snow pack-energy content (U). Meteorological inputs are air temperature, wind speed, humidity, precipitation and total incoming solar and longwave radiation. The Paternoster Valley catchment was subdivided into eight non-contiguous terrain classes for sampling and modelling using a geographical information system (GIS). Simulations of SWE in each of these classes were compared พ with field observations. It is shown that initial U and snow-surface thermal conductance (Ks) affect model simulations. Good approximations of SWE depletion are obtained using measured incoming solar radiation to drive the model but there are shortcomings in the characterization of long wave radiation and sensible-heat fluxes.
Article
About 50% of individuals survived for the duration of the stuidy, with best survival being at 2°C and poorest at 12°C. Growth rates were rapid over short periods (eg nymphs could double their fresh weight in 4-6 wks), although individuals then spent much longer periods at a more stable weight in a resting or premoult stage. Mean and maximum growth rates were most rapid at 7°C, and moulting occurred predominantly in the 7 and 12°C cultures. Individuals may achieve a single moult each year in the field, at microhabitat mean temperatures approaching 7°C. At low (2°C) temperatures survival is maximised, but at higher temperatures there is a trade-off between increased growth rate and moulting frequency, and increasing mortality with lower weight at moulting. In the field Alaskozetes may take full advantage of the abundant food resources available in summer, in order to achieve maximum growth rates and moult once each season. -from Author
Article
The Antarctic region comprises the continent, the Maritime Antarctic, the sub-Antarctic islands, and the southern cold temperate islands. Continental Antarctica is devoid of insects, but elsewhere diversity varies from 2 to more than 200 species, of which flies and beetles constitute the majority. Much is known about the drivers of this diversity at local and regional scales; current climate and glacial history play important roles. Investigations of responses to low temperatures, dry conditions, and varying salinity have spanned the ecological to the genomic, revealing new insights into how insects respond to stressful conditions. Biological invasions are common across much of the region and are expected to increase as climates become warmer. The drivers of invasion are reasonably well understood, although less is known about the impacts of invasion. Antarctic entomology has advanced considerably over the past 50 years, but key areas, such as interspecific interactions, remain underexplored.