thesetechniques may be applied. Additionally, we Moreover,variation in thesize of mtDNAwithin
present agenetic comparison between two ambig- individuals (heteroplasmy) wasseen inA. trans-
uouslydifferentiated, putative sturgeon species, montanus,but not A. oxyrinchus (Stabile et al.
Acipenser oxyrinchus (American Atlantic stur- 1996). Athoroughreview of theacipenseriform ge-
geon) andA. sturio(EuropeanAtlantic sturgeon). nomeappears inBirstein et al.(1997thisvolume).Characteristics of the acipenseriform genome Molecular studies of acipenseriforms directed
toward management and conservation
All acipenseriforms arepolyploids andtheirchro-
mosomes can bearranged as aseries4n–8n–16n ldenitification and discrimination of taxa
(Birstein et al.1993,Blacklidge & Bidwell1993, Bir-
stein et al. 1997 thisvolume).Chromosomenum- In theU.S., thetaxonomicstatus of threatened or
bers arevery high:120, 240, and possibly,500. Two endangeredpopulations ofvertebrates is important
forms of chromosomes are found:normal-sized indetermining thedegree ofprotection they may
‘macrochromosomes’ and very small‘microchro- receive under the Endangered Species Act
mosomes’. Anumber ofstudieshaveindicated slow (O’Brien &Mayr1991). ForAcipenseroxyrinchus
rates of DNA andprotein evolution ofsturgeons the Altantic (A. o. oxyrinchus) and Gulfforms (A.
and paddlefishes (Birstein1993): webelievethat ex- o. desotoi) were designated subspecies based on dif-
tended generationtimes in comparisonwithmost ferentiation ofmorphologicalfeatures, although
otherfishes maydecelerate theirmolecular evolu- only two Gulfspecimens were examined (Vladykov
tion.Acipenseriformshybridize readily in the lab- 1955). Wooley(1985)reanalyzed thesemorpholog-
oratory and in nature, at even the intergenericlevel icalfeatures of alargersample ofGulfsturgeon and
(Birstein et al. 1997 thisvolume). concludedthatonlyone.relative spleenlength, was
In most respects, thestructure andevolutionary diagnostic.However,values for relative spleen
change of theacipenseriformmitochondrial DNA length of the two forms were not discrete and it may
(mtDNA)genome istypical ofvertebrates.Esti- be thatdifferences inthesevalues areecophenotyp-
mates of thesize of mtDNA inAcipenser transmon- ic in nature. Ong et al.(1996)useddirectsequencing
tanus(whitesturgeon,16.1–16.7kilobases,Brown et of a hypervariablearea(203base pairs) of the con-
al. 1992) andAcipenserfulvescens(lake sturgeon, trolregion ofmtDNA toquantify theextent of ge-
16.6-16.9kb,Guenette et al.1993) are within the netic differentiation between the twoputative sub-
range of mostothervertebratetaxa(16.5 ± 0.5 kb, species.Representatives of eachsubspecies from
Meyer1993).Genecomposition andgeneorder of populations across their distributions were sur-
acipenseriform mtDNAhave notbeendirectly in- veyed and three fixed differences were found
vestigated; however, themtDNAcontrolregion of among 15polymorphicsites. A nadditional two nu-
A. transmontanusis organizedsimilarly toother cleotides werenearly fixed. Although polymor-
vertebrates(Buroker et al.1993). plisms also were detected within populations
Differences in thesize of the mtDNAmolecule across thedistribution of each subspecies, nofixed
have been observed amongacipenserids. In A. differencesamong populationswerefound. Ong et
transmontanus(Buroker et al.1990) andA. fulves- al. (1996)concludedthat thesedatastrongly sup-
cens(Ferguson et al.1993), theoverall size of the ported thedesignation of subspecies ofA. oxyrin-
mtDNAmoleculediffersamongindividual speci- chus.
mens(bothwithin andamong populations)because The relationshipbetweenA. oxyrinchusandA.
of variablenumbers of tandemrepeatunitswithin sturiohas longbeendebated.Thesefish arefound
the controlregion. In contrast, noevidence of on oppositesides of theNorthAtlantic and are phe-
mtDNAlength variation was observedamong spec- notypically very similar.Aciperiser oxyrinchusoc-
imens ofA. oxyrinchus(Waldman et al.1996b). curs widely along the Atlantic coast of North Amer-