BASE-COMPOSITIONAL BIASES AND THE BAT PROBLEM - II - DNA-HYBRIDIZATION TREES BASED ON AT- AND GC-ENRICHED TRACERS

We conducted a series of parallel DNA-hybridization experiments on a s mall group of bats (species of Pteropus, Rhinolophus, Noctilio and Pte ronotus) and outgroups (Lemur, Cynocephalus, Didelphis), using whole-g enome labels and tracers made from extracts enriched with AT and two l evels of GC content. FITCH (additive phylogenetic trees) topologies we re constructed from the four sets of comparisons, indexed as both Delt a T-mode and Delta NPHs (normalized percentage of hybridization). Base d on our previous work showing that the shared AT bias of pteropodids and some microchiropterans may affect the rank-ordering of taxa based on either AT-or GC-rich labels, our expectation was that the resulting trees would show differing topologies when generated from tracers mad e with the variously enriched DNA extracts. Whereas there was some var iation among the trees, most of them grouped the bats together, and al most all paired the representative megachiropteran and rhinolophoid mi crochiropteran as sister-taxa in contrast to the other microchiroptera ns. As the pteropodid-rhinolophoid relationship is an unexpected and u nlikely one, we attribute this association to an AT bias that was not obviated even by our most GC-rich labels, and suggest that such a bias may compromise the truth of some molecular trees. Accordingly, we bel ieve the broader issue of bat monophyly remains unresolved by DNA-hybr idization and probably also by gene-sequencing studies.