shusandS. albus (pallid sturgeon) was compared
using PCRproducts(amiplicons)(GeneticAnalys-
es^1 ).Acipenser fulvescens and the two subspecies of
A. oxyrinchuswere analyzed to provide additional
points of reference. PCR primers were designed Analyses of hybridization and introgression
based on conservedsequences (amongmammals)
for eightnDNAgenes and these wereshown to am- Scaphirhynchus albus andS. platorynchus have
plifysturgeon DNA and to produceamplicons. been recognized as similar, but distinct species of
Theseaniplicons werethendigestedwith abattery river sturgeonwithin theMississippiRiver drainage
of differentrestriction enzymes and DNA band (Forbes &Richardson1905).Significantdifferenc-
sharing wascomparedbetween two putative taxa. es in meristic,morphometric, andlifehistorychar-
The level of genetic differentiation between S. sutt- acteristiessupportthistaxonomicdivision. In re-
kusiand the other twospecies ofScaphirhynchus cent years, a small but increasing number of fish col-
was greaterthanthatbetween subspecies ofA. ox- lectedfrom theMissouri andMississippirivers ex-
yrinchusbut lessthan thatbetween the twospecies hibited intermediacy in the expression ofthese
ofAcipenser.The authorsalso concludedthat dis- discriminatorycharacters,suggesting theexistence
tinct species designation for S. albus andS. plato- of inerspecifichybrids (Carlson et al.1985). Pop-
rynchusmay not be valid, butinstead.that the two ulations of both species, but particularly of S. albus,
forms mayrepresentmorphologicalvariants of a currently areseverelydepleted,probably due to
singlespecies. habitatalterations, andS. albusis listed asendan-
A later,expandedmtDNAstudy(Campton et gered by theU.S.Fish and WildlifeService(Dryer
al^2 ) alsofoundvery low levels ofdivergence be- & Sandoval^3 ). Hybridization betwcen twosturgeon
tweenS. suttkusi(N = 3) and the other twoScaphir- speciesunderthese circumstanceswould not be un-
hynchusspecies. Auniquehaplotypedistinguished expected; Hubbs(1955)concludedthat anthropo-
the threespecimens ofS. suttkusifrom all individu- genicimpacts andsharpimbalances in theabun-
als of the other twospecies ofScaphirhynchuscol- dances of potentiallyhybridizingspecies signifi-
lectedfrom the upperMissouriRiver, butthis ha- cantly increase the frequency of hybridization
plotypedifferedfrom themost commonhaplotype events infishes.
found among S. albus andS. platorynchus by only a Geneticstudies wereconducted toquantify the
singlenucleotide substitution.Campton et al.^2 con- relatedness ofS. albusandS. platorynchusand to
cludedthat the mtDNAdata support the morph- identifymarkerswhichcould be used to identify F 1
ological andbiogeographicarguments forrecogniz- and later generationhybrids.Protein electrophore-
ingS. suttkusias an endangered‘species’ of‘distinct sisstudies revealed only lowlevels ofpolymor-
population segment’ asdefined by theU.S.Endan- phismwithin andbetween thesetaxa andthoseloci
gered Species Act.Analysis ofadditionalspeci- (3 of 37) whichwere polymorphic did notdisplay
mens of S. albus andS. platorynchus from the lower significant interspecific allelicdifferences(Phelps
Mississippi River (nearer the range of S. suttkusi is & Allendorf1983).Thus, proteinelectrophoresis
provedinsensitive indistinguishingthesespecies,
perhaps due to itsfocus ongeneproductsthat are
essential for survival andthattend to beconserva-
trict:U.S.Fish andWildlifeService, Bismarck,NorthDakota; fiveacross taxa.
U.S.Army Corps ofEngineers, Mobile District. 41 pp. Recently, direct analyses of nuclear DNA
(^2) Campton,D.E.,A.I.Garcia.B.W.Bowen & F.A.Chapman. (nDNA) andmtDNAwereused tofurtherdiscrimi-
1995.Geneticevaluation ofpallid,shovelnose, andAlabama
sturgeon(Scaphirhynchus albus, S. platorynchus andS. suttkusi)
based on control region (D-loop)sequences of mitochondrial
DNA.FinalReport to theU.S. Fish andWildlifeService,Bis-
marckNorthDakota. 35 pp.
needed toconfirm the genetic discreteness ofS.
suttkusifrom itscongeners.
(^1) Genetic Analyses, lnc. 1994. Genetic studies of Scaphirhynchus
spp.Report to theU.S.ArmyCorps ofEngineers,Omaha Dis-
(^3) Dryer,V.P. &A.J.Sandoval.1993.Recoveryplan for thepallid
sturgeon(Scaphirhynchus albus).U.S. Fish and Wildlife Service,
Denver. 55 pp.