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Title: Herbivory in Antarctic fossil forests and comparisons with modern analogues in Chile
Author: McDonald, Claire Margaret
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2009
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During the Tertiary (~ 50 million years ago) forests were present in Antarctica, but fossil evidence of insect life in the forests is rare. Extensive fossil floras from Antarctica contain evidence of insect herbivory on the leaves; these provide indirect evidence of past insect life. Such preservation of the behaviour of insects (insect trace fossil) can be used to examine the diversity of insects that lived in the forests of Antarctica in the past. Palaeogene (65 Ma - 35 Ma) fossil floras from two localities on the Antarctic Peninsula (King George Island and Seymour Island) were examined for the presence ofinsect trace fossils. Fossil leaves were preserved as impressions and compressions within siltstones and sandstones and represent leaves that were preserved within a quiet lake environment (King George Island) or shallow marine setting (Seymour Island). The floras were dominated by leaf morphotypes that resemble modem Nothofagaceae (Southern beeches), but leaves similar to other Southern Hemisphere families were also present, including the Cunoniaceae, Proteaceae and Lauraceae. Over 2,000 fossil leaves were examined for traces of past insect activity. Over 150 fossil leaves (6.9%) contained evidence of feeding traces on the leaves (54 trace types from King George Island and 19 from Seymour Island). The trace fossils were grouped into four functional feeding types: general leaf chewing, skeleton feeding, leaf mines and leaf galls. General leaf chewing was the most common trace type at both localities and leaf mines the least common. The nearest living analogues of the Antarctic Palaeogene forests are the Valdivian and Magellanic forests of Chile and so insect activity in these forests was studied in order to understand past insect activity in Antarctica. The diversity of insect traces in the Chilean forests was investigated at six sites within National Parks, covering alatitudinal range between 37°S and 55°S. Insects associated with two deciduous species, Nothofagus pumilio and Nothofagus antarctica, were of particular focus. The factors that affected the level of insect damage and the proportion ofleafmines and galls included height within the tree,orientation ofleaf within the tree, altitude, season, leaf age, latitude, plant species and insect species. Insects which created similar general leaf chewing traces in the modem forests in Chile siinilar to those on the fossil leaves were larvae of Lepidoptera (Geometridae), Hymenoptera (Symphyta) and the larvae and adults of Coleoptera (Chrysomelidae, Curculionidae, Cerambycidae). Leaf mines were created by species of Coleoptera and Hymenoptera. Species of Diptera (Cecidomyiidae) and Hymenoptera (Cynipidae) created leaf galls. Other invertebrates (Acari (Eriophyidae) and Nematoda (Tylenchida)) also created leaf galls in Chile, similar to fossil leaf galls from Antarctica. Herbivory types on the fossil flora from King George Island were most similar to modem types in Puyehue (a northern study site, Chile) and those from Seymour Island were most similar to Torres in the south, indicating a possible climatic control on their distribution. Based on this relationship, estimates of palaeoclimate of Antarctica suggest that the climate of King George Island to the west of the Peninsula was warmer and wetter (3.5°C - lO.4°C mean annual temperature, 3.5°C 24.3°C maximum and minimum mean monthly temperature and 1500 mm annual precipitation) than the cooler and more stable environment at Seymour Island to the east (3.5°C - 10AoC mean annual temperature, -O.4°C - 16°C maximum and minimum mean monthly temperature, and 570 mm annual precipitation). The studies of fossil and modern insect traces in Antarctica and Chile have provided a unique opportunity to reconstruct past insect life of Antarctica during the Palaeogene. This is the first documented evidence of insect life during the Palaeogene on Antarctica and highlights the value of modern analogue comparisons to obtain a greater insight into past insect ecology.
Supervisor: Francis, Jane ; Compton, Steve Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available