Halteria is the name for a group of insects defined by a severe modification of flight wings into gyroscopic stabilizing structures called halteres. The group includes all the true flies plus Strepsiptera, an oddball lineage of parasites. This taxonomic scheme is a pleasing arrangement by some counts, as it requires but a single evolutionary origin of a complex structure.
Halteria was named 15 years ago when the first DNA sequences were applied to reconstruct insect evolution. A 1994 paper by Michael Whiting & Ward Wheeler discovered an unexpected relationship of flies to Strepsiptera using a fragment of ribosomal DNA. Previously, Strepsiptera had been considered by morphologists as relatives of beetles.
The new find was exciting. It not only suggested that molecular data would yield novel evolutionary relationships, but also that extensive body rearrangements might be possible via developmental mutations. The halteres of Strepsiptera are fashioned from forewings, while those of the flies from hindwings, implicating a rare segment swap.
There’s one problem with Halteria, though. Beyond the original papers, there’s no evidence it exists.
First came a study by John Huelsenbeck suggesting Halteria might be a statistical artifact. Then came the observation that the fine structure of the appendages did not match, followed by a finding that Strepsiptera lacked the expected sort of hormonal receptor for a fly relative. Last year saw an avalanche of molecular phylogenetic studies (here, here and here), each with considerably more data than the early genetic work. These unanimously concluded that the morphologists- as crusty and out-of-date as they may be- had been correct. Strepsiptera are related to beetles, not flies.
I bring all this up because a new paper by Ishiwata et al adds yet more genetic data in favor of the old Beetle-Strepsiptera connection:
It’s only 3 genes, but they are big ones, and the tree is eminently sensible. The Neoptera (insects that can fold their wings over their backs) and Holometabola (insects with complete metamorphosis) are both supported, and the overall tree topology agrees with that of the larger genomic studies. And Strepsiptera do not group with the flies in any scenario.
I’m not sure how many nails the Halteria coffin needs. But surely that lid is now shut so tight that not even flies can get in.
source: Ishiwata, K. et al 2010. Phylogenetic relationships among insect orders based on three nuclear protein-coding gene sequences. Molecular Phylogenetics and Evolution, online early.