Systematics and biogeography of hard ticks, a total evidence approach

Systematic relationships among the basal Ixodidae are examined using one morphological and three molecular data sets, 18S and 28S nuclear and 16S mitochondrial rDNA. Although different combinations of partitions are incompatible in a partition homogeneity test, combining them produces similar or better support for most major lineages through both additive and complementary effects. The different data sets are not complete for all taxa, but inclusion or exclusion of taxa with missing data for one or more data sets (8 of 29 ingroup taxa) does not influence overall tree topology and only weakly affects support levels. The only notable effect was based on gap treatment in the 28S data set. Gap treatment completely changes the arrangement and support levels for one basal node. The combined analyses show strong support for the Metastriata, a lineage including most endemic Australian Ixodes, and a lineage including the remaining Ix-odes, but not for the Prostriata (= Ixodes s.l.). The distribution pattern of endemic Australian taxa (nearly all included in three exclusively Australian basal lineages) suggests that these lineages, and by extension the Ixodidae, originated after the isolation of Australia in the late Cretaceous, much more recently than previously indicated. (C) 2000 The Willi Hennig Society.