Data from 1238 fishes from 19 sturgeon species and 1 paddlefish were used t
o analyze heteroplasmy in sturgeon. Lengths of central repeat units ranged
from 74 to 83 bp among sturgeon species. No repeat sequence was found in th
e paddlefish, Polyodon spathula. A general feature of the repeat units was
the presence of termination associated sequence (TAS) motifs. About 50% of
138 interspecific mutations observed among the D-loop sequences are located
10 bp down- and upstream from these TAS motifs. Interestingly, most homopl
asmic species showed deletions upstream to the TAS motifs, whereas deletion
s downstream to the TAS motifs: observed in two species do not seem to prec
lude heteroplasmy. Calculations of secondary structures and thermal stabili
ties of repeat units showed DeltaG values for all heteroplasmic species to
be <-8 and for most homoplasmic species <Delta>G value to be >-8. Most hete
roplasmic fishes had two and/or three repeat units. No homoplasmic sturgeon
with >2 repeat units were observed. Molecular phylogeny based on the entir
e cytochrome b showed that heteroplasmy probably resulted fr om a single ev
olutionary event. Our data demonstrate that heteroplasmy is present in most
sturgeon species and suggest that the thermal stability of the secondary s
tructure of the repeat unit in combination with mutations downstream of the
TAS sequences influences heteroplasmy.