Molecular Biology and Evolution, Vol 15, 1288-1297, Copyright © 1998 by Society for Molecular Biology and Evolution
B Mantovani
In the genus Bacillus (Insecta, Phasmatodea) the Bag320 satellite DNA
family is present in the bisexual B. grandii and in the related automictic
nonhybrid B. atticus; it is lacking in the other bisexual taxon of the
genus, B. rossius. This family of highly repeated sequences was analyzed
for 11 populations of the apomictic triploid hybrid B. lynceorum. In the
neighbor-joining dendrogram, B. lynceorum nucleotide sequences distribute,
regardless of geographical origin, among two clusters, one also including
all clones of the three B. atticus races, and the other including sequences
of the B. grandii grandii subspecies. Thus, B. lynceorum is a trihybrid
taxon: as the molecular approach definitively demonstrates, it embodies one
haploid complement each of both B. grandii grandii and B. atticus, which
must be added to that of B. rossius. The contribution of the latter species
has already been assessed on karyological and allozymic grounds. A
statistical analysis performed on p-distances shows that for the parental
taxa, nucleotide substitution values are of comparable magnitudes at the
population level but differ at the subspecific level, being higher for the
bisexual taxon. In the apomictic hybrid, atticus- and grandii grandii- like
sequences coexist with significantly different p-distance values. For three
clones, the nucleotide compositions at the diagnostic loci suggest that
gene conversion can occur between atticus- and grandii grandii-like
monomers. On the whole, this supports bisexuality as a driving force in
variant fixation and suggests that in Bacillus, different gametogenetic
processes and different origins of the unisexuals are mirrored in genomic
turnover rates of satellite DNA.
ORIGINAL ARTICLE
Satellite sequence turnover in parthenogenetic systems: the apomictic triploid hybrid Bacillus lynceorum (Insecta, Phasmatodea)
Dipartimento Biologia Evoluzionistica Sperimentale, Universita di Bologna, Italy. barman@alma.unibo.it
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