Not so free range? Oviposition microhabitat and egg clustering affects Eretmoptera murphyi (Diptera: Chironomidae) reproductive success

Abstract

Understanding the physiology of non-native species in Antarctica is key to elucidating their ability to colonise an area, and how they may respond to changes in climate. Eretmoptera murphyi is a chironomid midge introduced to Signy Island (Maritime Antarctic) from South Georgia (Sub-Antarctic) where it is endemic. Here, we explore the tolerance of this species’ egg masses to heat and desiccation stress encountered within two different oviposition microhabitats (ground surface vegetation and underlying soil layer). Our data show that, whilst oviposition takes place in both substrates, egg sacs laid individually in soil are at the greatest risk of failing to hatch, whilst those aggregated in the surface vegetation have the lowest risk. The two microhabitats are characterised by significantly different environmental conditions, with greater temperature fluctuations in the surface vegetation, but lower humidity (%RH) and available water content in the soil. Egg sacs were not desiccation resistant and lost water rapidly, with prolonged exposure to 75% RH affecting survival for eggs in singly oviposited egg sacs. In contrast, aggregated egg sacs ( n = 10) experienced much lower desiccation rates and survival of eggs remained above 50% in all treatments. Eggs had high heat tolerance in the context of the current microhabitat conditions on Signy. We suggest that the atypical (for this family) use of egg sac aggregation in E. murphyi has developed as a response to environmental stress. Current temperature patterns and extremes on Signy Island are unlikely to affect egg survival, but changes in the frequency and duration of extreme events could be a greater challenge. Electronic supplementary material The online version of this article (10.1007/s00300-018-2420-4) contains supplementary material, which is available to authorized users.

Combining correlative and mechanistic niche models with human activity data to elucidate the invasive potential of a sub‐Antarctic insect

“…For example, ground and vegetation surfaces both in the laboratory and in the field are typically warmer than the air temperatures obtained from weather stations used in our projections (Bartlett et al, 2018b;Convey, Coulson, Worland, & Sjöblom, 2018). This means that the resulting maps from these projections should be interpreted as relative rather than absolute values, while keeping in mind that the magnitude of the associated uncertainty should be directly related with the heterogeneity within each grid cell.…”

“…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).…”

Surviving the Antarctic Winter—Life Stage Cold Tolerance and Ice Entrapment Survival in The Invasive Chironomid Midge Eretmoptera murphyi

“…All experiments, apart from those on ice-entrapment and water submergence, were conducted in laboratories at the British Antarctic Survey's Signy Island Research Station, South Orkney Islands, maritime Antarctic (Figure 1), during the 2016/2017 austral summer season. Samples were collected as described by Bartlett et al [17]. All eggs used were confirmed to be at the first (opal) developmental stage [17] using a dissecting microscope (Leica EZ4).…”

“…Samples were collected as described by Bartlett et al [17]. All eggs used were confirmed to be at the first (opal) developmental stage [17] using a dissecting microscope (Leica EZ4). If any eggs showed signs of yellowing or embryonic development, the entire egg sac was discarded.…”

“…The midge is native to sub-Antarctic South Georgia (55 • S, 45 • W) ( Figure 1), where it is paleoendemic [15,16]. It has a life cycle of two years, spending most of that as one of four larval instars [17]. In addition to being freeze-tolerant, this species has several other pre-adaptations, enabling survival of conditions experienced in the maritime Antarctic, including desiccation tolerance [18], and the ability to rapidly cold-harden [19].…”