Jhg. Van Der Schulenburg et al., Molecular evolution and phylogenetic utility of Wolbachia ftsZ and wsp gene sequences with special reference to the origin of male-killing, MOL BIOL EV, 17(4), 2000, pp. 584-600
A detailed assessment of the evolution and phylogenetic utility of two gene
s, ftsZ and wsp, was used to investigate the origin of male-killing Wolbach
ia, previously isolated from the ladybird Adalia bipunctata and the butterf
ly Acraea encedon. The analysis included almost all available sequences of
B-group Wolbachia and two outgroup ta,:a and showed that (1) the two gene r
egions differ in phylogenetic utility, (2) sequence variation is hen correl
ated with phylogenetic information content, (3) both genes show significant
rate heterogeneity between lineages, (4) increased substitution rates are
associated with homoplasy in the data, (5) wsp sequences of some taxa appea
r to be subject to positive selection, and (6) only a limited number of cla
des can be inferred with confidence due to either lack of phylogenetic info
rmation or the presence of homoplasy. With respect to the evolution of male
-killing, the two genes nevertheless seemed to provide unbiased information
. However, they consistently produce contradictory results. Current data th
erefore do not permit clarification of the origin of this behavior. In addi
tion, A. bipunctata was found to be a host to two recently diverged strains
of male-killing Wolbachia that showed increased substitution rates for bot
h genes. Moreover, the wsp gene, which codes for an outer membrane protein,
was found to be subject to positive selection in these taxa. These finding
s were postulated to be the product of high selection pressures due to anta
gonistic host-symbiont interactions in this ladybird species. In conclusion
, our study demonstrates that the results of a detailed phylogenetic analys
is, including characterization of the limitations of such an approach, can
serve as a valuable basis for an understanding of the evolution of Wolbachi
a bacteria. Moreover, particular features of gene evolution, such as elevat
ed substitution rates or the presence of positive selection, may provide in
formation about the dynamics of Wolbachia-host associations.