Systematic Research on the Millipede Assassin Bugs (Hemiptera: Reduviidae: Ectrichodiinae)
- Author(s): Forthman, Michael
- Advisor(s): Weirauch, Christiane
- et al.
The predominantly circumtropical millipede assassin bugs (Ectrichodiinae) comprise the fifth largest subfamily of Reduviidae with 736 described species in 121 genera. Ectrichodiinae appear to be specialized millipede predators and stand out among other Reduviidae in the high proportions of aposematically colored and sexually dimorphic species. These phenomena make Ectrichodiinae an attractive group for ecological, behavioral, and evolutionary research, but is hindered by a lack of thorough taxonomic treatments and phylogenetic hypotheses. This dissertation improves our knowledge of Ectrichodiinae life history, diversity, and phylogeny by: 1) reviewing Ectrichodiinae predatory behaviors and supplementing this with field observations; 2) revising the Madagascan fauna; 3) investigating historical biogeographic patterns of Madagascan Ectrichodiinae; and 4) constructing the most comprehensive Ectrichodiinae+ Tribelocephalinae phylogeny to study the evolution of aposematic coloration and sexual dimorphism. (1) About 2% of Ectrichodiinae species are documented to prey on juliform and, to a lesser extent, polydesmid millipedes. The majority of observations suggest that immatures typically exhibit communal predation, while adults usually engage in solitary predation. (2) The taxonomic monograph includes description of 63 new species and three new genera of endemic Madagascan Ectrichodiinae, as well as redescriptions and synonymies of previously described taxa. (3) Madagascan Ectrichodiinae do not form a monophyletic group, with lineages exhibiting close relationships with Oriental or Afrotropical taxa. Ectrichodiinae colonized Madagascar in the last 68 my via transoceanic dispersal at least twice from the Oriental region and once from the Afrotropical region; a single out-of-Madagascar dispersal event to the Afrotropical region is recovered in some analyses. Dispersal between these regions were likely facilitated by islands and/or ocean currents. (4) Ectrichodiinae are not monophyletic with respect to Tribelocephalinae. Aposematic coloration evolved from a cryptic ancestor early in the evolutionary history of Ectrichodiinae+Tribelocephalinae, with subsequent reversals and regains. A positive association between the prevalence of aposematic coloration and body length is recovered when phylogenetic logistic regressions are conducted on ultrametric trees, but is not supported when phylograms are used. Extreme sexual dimorphism is shown to evolve multiple times from a more limited condition. Based on phylogenetic results, a new Ectrichodiinae classification is proposed.