The Scotia Arc, comprising southern South America, South Georgia and the South Orkney Islands and the Antarctic Peninsula, is home to a range of understudied insect species which are constantly exposed to extreme environmental conditions. To help reduce the amount of uncertainty surrounding insect taxa evolution in the region, we aimed to elucidate the evolutionary relationships and divergence times of non-biting midges (Diptera) and beetles (Coleoptera) naturally occurring in the lands around the Scotia Arc. The main objectives here were to learn how the evolution of select species of these two orders of insects is linked to the region’s geographical history, through the use of phylogeography, and what kind of adaptations (morphological and physiological) they have developed to deal with the environmental conditions and changes, such as osmotic stress and desiccation tolerance. There was also an intrinsic objective to ascertain the taxonomy of the midge Telmatogeton magellanicus, which potentially belongs to the genera Belgica or Halirytus. The individual studies in this thesis were carried out in the British Antarctic Survey (BAS) and in field stations in Navarino Island (Chile) and the South Shetland Islands (Antarctica), with additional field work in South Georgia Island.

Habitat Characterisation and Ecophysiology: As a first step to enable the understanding of the physiological adaptations of the brachypterous midge T. magellanicus we first had to describe, in detail, its habitat. To that end, we made use of Permutational MANOVA and Similarity Percentages, through which we were able to identify the mid-tidal zone of the intertidal as its favoured habitat, while also providing details on their abundance and the fact they mostly need filamentous algae to thrive. Subsequentially, we exposed larvae of T. magellanicus to different physiological treatments and showed that they are very resistant to osmotic stress and temperature extremes, but that exposure to desiccation are one of the main dangers to their survival. In the meantime, larvae of Eretmoptera murphyi were also exposed to osmotic stress treatments, but were shown to struggle much more to deal with saline water.

Morphology: We hypothesised that the South Georgian isolate of the diving beetle Lancetes angusticollis, could have changes to its hind wing morphology, potentially causing a loss of the ability to fly. However, the wings bear only minute changes that did not enable us to correlate that to specific environmental conditions.

Phylogeography: By means of two genetic markers (COX1 and 28S) we were able to assess the phylogeographic structure of the winged Antarctic midge Parochlus steinenii, who is spread out across the Scotia Arc, with a clear split of its South American population.

This thesis shows how insects can help us understand the development of a specific region in the globe, but also shows us how much more there is left to explore in terms of the biology and evolution of insect taxa in the Scotia Arc, specially in light of the current international debates on climate change, as these are among the organisms that are the most susceptible to sudden alteration of their habitat composition.