Abstract
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.
Highlights
Survival in the polar regions requires the ability to tolerate conditions that regularly fall below freezing, sometimes for months at a time
We report that, 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
Other live E. murphyi samples used in the ice-entrapment and water submergence experiments were collected during the 2014/15 austral summer by British Antarctic Survey (BAS) station staff on Signy Island and were returned to the United Kingdom by ship in refrigerated (+4—5 ◦ C) cold storage (10 weeks) and maintained on their native substrate at
Summary
Survival in the polar regions requires the ability to tolerate conditions that regularly fall below freezing, sometimes for months at a time. Antarctic winters are long and harsh, and even in the warmer maritime Antarctic where two species of insects are native, temperatures remain below freezing for several months of the year [1] These insects, like any terrestrial invertebrate that lives in the polar regions, are at risk of their body fluids freezing, causing potentially fatal injury [2]. To survive such conditions, invertebrates have developed physiological and behavioral cold-tolerance strategies that allow them to either tolerate freezing or avoid it [3]. Understanding how an invasive species survives polar winter conditions is crucial in understanding its potential to establish and spread
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