Spatial correspondence between the specialist galling insect genus Kladothrips (Thysanoptera: Tubulifera: Phlaeothripidae) and its Acacia host: ecological and evolutionary constraints on host use.

Specialised insect-plant associations, and the presence of other organisms that specifically target this interaction, represent relatively ancient ecological interactions. These types of associations are characterised by non-random geographical range correspondence, especially in the presence of narrow resource use. However, empirical studies rarely investigate how spatial relationships between insects and their host plants contribute to phenotypic interactions resulting from host shifting. This is important because geographic range discontinuities highlight biotic or abiotic conditions that might interfere with ecological interactions and how species diversify. In this study, we test the null hypothesis that the geographic range of the galling genus Kladothrips corresponds with their Acacia hosts. We then evaluate whether ecological characteristics of Acacia are related to evolutionary constraints on Kladothrips host use. The results indicated discontinuities between spatial distribution models of Acacia and the hosts that support Kladothrips. Temperature, precipitation and edaphic variables contributed strongly to these differences and reveal Kladothrips gall Acacia hosts present in harsh, arid environments. However, Acacia are distributed throughout all Australia's diverse biomes including mesic, arid and monsoonal regions. Discontinuities in spatial correspondence between Acacia and Kladothrips suggest biotic and abiotic pressures limiting ecological interactions are present in mesic and hydric climates. Acacia hosts observed to support Kladothrips share strong spatial model equivalency, but not necessarily close phylogenetic relatedness. Co-phylogenetic analyses indicated contrasting host use conservatism between Acacia sections. The results of this study support the hypothesis that specialised associations between insects and plants are a function of varying climatic and evolutionary constraints over the geographic range of the host lineage. These findings agree with the premise that ecological constraints underlie evolutionary patterns of host use. [ABSTRACT FROM AUTHOR]