The Evolution of the Australian Amitermes group
by Bastian Heimburger
Date of Examination:2022-03-18
Date of issue:2022-04-05
Advisor:Dr. Tamara R. Hartke
Referee:Prof. Dr. Stefan Scheu
Referee:PD Dr. Christian Roos
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EnglishAlthough the Australian Amitermes Group (AAG) is the most diverse and speciose group of higher termites (Termitidae) in Australia, relatively little is known about the origin and evolution of the group. Recent phylogenetic studies of the major termite groups suggest that the AAG and other derived subfamilies arrived in Australia from Southeast Asia in the mid-to-late Miocene (Bourguignon et al. 2017), after the Australian and Southeast Asian plates collided (Zachos et al. 2001). Today, the group is distributed across the continent (Watson and Abbey 1993) and has an unparalleled rate of endemism (Calaby and Gay 1959): only two Australian taxa (A. arboreus and A. laurensis) are known to also occur in Papua New Guinea (Miller 1994, see also Krishna et al. 2013). Currently, the group is split into five genera broadly based on nesting/feeding habits: subterranean or protected foraging (Amitermes), foraging in the open (Drepanotermes), or living exclusively within the nests of other termite species (Ahamitermes, Incolitermes, and Invasitermes) (Krishna et al. 2013). In this thesis, I reconstructed a robust “backbone” phylogeny to recapitulate the diversification and biogeographical history of the AAG, which coincides with the aridification of the continent over the last 15 million years (Byrne et al. 2008, 2018). The results are consistent with migratory patterns in other insects that followed a northern route from Southeast Asia (Yeates and Cassis 2017), suggesting that the ancestor of the AAG likely arrived in Australia by rafting in logs. The favorable conditions in the late Miocene, with extensive woodlands and open forests, presumably facilitated the rapid range expansion of early lineages across Australia. The evolutionary trajectory of the AAG shows a diversity-dependent pattern in which a steady increase in the diversification rate from the late Miocene onwards is followed by a period of accelerated diversification in the Pliocene. At the boundary of the Plio-Pleistocene, the diversification rate decelerated. Diversification analyses showed that declining species accumulation is likely due to progressive niche saturation. Finally, by combining both barcoding sequences and whole mitochondrial genomes, I reconstructed the ancestral nesting habit of Drepanotermes, related nesting habits to past climatic conditions, and predicted current and future habitat suitability of selected taxa. It is the first time that both abiotic and biotic factors were used to predict habitat suitability in Australian termites. Results show that mound-building evolved multiple times within Drepanotermes and likely facilitated its spread into regions characterized by high temperature and precipitation. Indeed, mound-builders are more common in hot and wet regions of Australia, in contrast to subterranean species, which are generally found in more arid conditions. Generally, mound-building appears to be an adaptation to extreme weather events (e.g. floods and bushfires). Evidence of strong phylogenetic signal of bioclimatic variables linked to seasonality (e.g. precipitation of warmest quarter) supports my hypothesis that mounds are selectively favored over subterranean nests in habitats experiencing occasional, unpredictable extreme events.
Keywords: Australia; Amitermes group; biogeography; climate change; diversification; phylogenetics; niche modelling; habitat suitability; evolutionary adaptations