1993, 1997): Huso dauricus was a sister-species to
the genus Acipenserinstead of being basal to all aci-
penseriforms, and ScaphirhynchusandPseudosca-
phirhynchusdid not form a monophyletic group.
(6) A partial sequence of the cytochromebgene
(270 bp) was used to examine relationships within
the genus Acipenser. Seven additional species of
Acipenser were included in this part of the study
(A. brevirostrum, A. gueldenstaedtii, A. mikadoi, A.
naccarii, A. nudiventris, A. oxyrinchus, andA. stel-
latus). The data support the hypothesis that octo-
ploid species appeared at least three times within
theAcipenser.Also they show close relationships
between the Eurasian A. ruthenus and the Pacific A.
mikadoi-A. medirostris-A. transmontanus, between
the European A. gueldenstaedtii, SiberianA. baerii,
and American A. brevirostrum, between two Eu-
ropean species, A. stellatus andA. naccarii, as well
as a possible trans-Atlantic relationship between
the Eurasian A. nudiventris and American A. oxy-
rinchussuggesting limited utility of geographic lo-
cality as an indicator of relationship.this group), as considered before. We hope that fu-
ture analyses involving longer regions of the cyto-
chromebgene and, possibly, some other protein
coding genes will help to establish mono-or pol-
yphyly of this genus.
Conclusions
(1) Little cytogenetic change has occured during the
evolution of Acipenseriformes. Polyodontidae and
Acipenseridae presumably originated from a tetra-
ploid ancestor whose karyotype consisted of 120
macro-and microchromosomes with a DNA con-
tent about 3.2–3.8 pg per nucleus. Tetraploidization
of the 60-chromosome ancestor possibly occurred
at the early times of evolution of the Acipenseri-
formes, probably, during the origin of this group in
the Mesozoic.
(2) No conclusions regarding interrelationships
within Acipenseridae among Huso, Acipenser, Sca-
phirhynchus, and Pseudoscaphirhynchus can be
made based on cytogenetic data. Divergence of
these lineages of sturgeons occurred without pol-
yploidization. Acknowledgements
(3) Diversification withinAcipenserwas accom-
panied by appearence of octoploids (according to We are very grateful to all colleagues who helped us
karyotypic and DNA content data) and 16n-ploids to collect blood and tissue samples: Serge Gamalei
(according to DNA content data). The octoploid (Moscow Aquarium, Moscow), Boris Goncharov
240 - chromosome sturgeon species have about 240 (Institute of Developmental Biology, Russian
chromosomes and may have originated independ- Academy of Sciences, Moscow), Evgenii Artyuk-
ently in different geographic areas. The two 16n- hin (Central Laboratory of Regeneration of Fish
ploid species,A. mikadoiandA. brevirostrum,may Resources, St. Petersburg), Francesco Fontana
be the youngest species within the genus. (University of Ferrara), Herb Bollig (US Fish and
(4) A study of partial sequences of genes from mi- Wildlife Service, South Dakota), Boyd Kynard (Na-
tochondrial DNA (16S rDNA, 315 bp; 12S rDNA, tional Biological Survey, Massachusetts), John
189 bp, and cytochrome b,270 bp) and of one nucle- North (Department of Fish and Wildlife, Oregon),
ar gene region (18S rDNA, 230 bp) demonstrated and John Waldman (The Hudson River Founda-
very low levels of variability in the eight acipenseri- tion, New York). We are also indebted to Paul Vra-
form species surveyed (Polyodon spathula, Huso na for his kind permission to use his collection of
dauricus,four species of Acipenser, Scaphirhynchus tissue samples. We are extremely thankful to Willy
albus,andPseudoscaphirhynchus kaufmanni).This Bemis for his patient reading of the manuscript and
low variability is unusual for these genes, which are his important notes which allowed us to improve
commonly used as phylogenetic tools. the manuscript immensely.
(5)The molecular tree based on combined data
from all four genes had two major departures from
the existing morphological hypothesis (Findeis,