(Apalachicola,Ochlockonee, andSuwannnee riv- Conclusions and recommendations
ers).GeneflowestimatesderivedFromRFLPanal-
ysiswereevenlower onaverage, and rangedfrom Thecomparatively few molecular analysesdirected
0.09between the western and Choctawhatchee Riv- to conservation of acipenseriforms have yielded
er stocks to0.66between thewestern andEscambia unique andimportantinformation.Some ofthese
River-YellowRiver stock. studieshave refinednotions concerningspecies and
Thesegeneflowvalues arevery low incompari- subspecies status; ouranalysis ofmtDNAcontrol
son withestimates forotheranadromousfishes. Es- regiondifferencesbetween theAmerican and Eu-
timatedannualstrayingratesamongpopulations of ropeanAtlanticsturgeonsshowsthatshouldrelict
Pacificsalmonshaverangedbetween about 1 % and populations of thelatterbecomeextinct, restocking
27% (reviewed inAdkindson1996).Laughlin & withA. oxyrinchuswouldconstituteintroduction of
Turner(1996)used twostatisticalmethods toesti- aforeignspecies.Likewise, thestudy by Ong et al.
mate Nmof Moronesaxatilis(striped bass)among (1996)supportingsubspeciesdesignationsforAt-
threeVirginiatributaries of ChesapeakeBay: the lantic andGulf forms ofA. oxyrinchusreinforces
privatealleleapproach of Barton &Slatkin(1986) thecurrentstatus of thelatter as athreatened sub-
yielded anestimate of Nm= 14.2,whereas the Fstap- speciesunder theU.S.EndangeredSpeciesAct.
proachyielded anestimate of Nm= 2.7. In acapture- Unfortunately, to date, conservation directed
mark-recapturestudy, Melvin et al.(1986)estimat- molecular studies ofacipenseriforms at thespecies
ed an annual strayingrate of 3% amongCanadian level andbelowhavealmostexclusively been re-
populations ofAlosasapidissima(Americanshad). stricted toNorth Americanspecies.Highlysensi-
Moreover, the low geneflowestimates forA. o. tive determination of the genetic relationships
desotoiwere obtainedacrosspopulationsthatoccur amongextantspecies.stocks, andbetweenextinct
in eightrivers, themouths ofwhich arearrayed andcloselyrelatedextanttaxa arepossible.Much
across littlemorethan 500 km of coastline.Sturgeon of thelatter analyseswill usearchivedmuseum
from theserivers have theopportunity to mix in the samples as sources ofDNA.Birstein(1993)provid-
Gulf ofMexicoduringwinter.ThesemtDNA data edmany examples ofEurasian sturgeons that are
showthatdespite the geographicproximity of these phenotypicallydifferentiated (i.e.,large and small
rivers, stocks ofA. o. oxyrinchusgenerally exchange ‘forms’) below the species level but that have not
lessthan onefemale pergeneration, alevel sufficient received geneticanalysis. Even if financial re-
to permitdifferentiation at thestocklevel (Adkin- sources are currently notavailable:samples can be
son 1996).Geneflowestimatesalso weregenerally collected andarchived forFutureanalyses.
higheramongproximal stocks.suggestingthatwhat Population surveys alsohavebeenlimitedlargely
straying occurs does so in ‘stepping stone’ fashion toNorth America. Geneticanalyses ofP. spathula
(Kimura &Weiss 1964) inwhichmigrantsamong andA. fulvescens-paddlefish and sturgeon species
semi-isolated populations are exchanged chiefly withsimilar andbroadNorth Americandistribu-
withneighboringpopulations. Ifthis istrue forA. o. tions –have revealedrelativelylittle genetic varia-
desotoi,thensuchspatiallyrestricted strayingshould tion andonlyminorsubstructingamongpopula-
have contributed to the geographic structuring ob- tions. Incomparison,coastalspecies such asA. ox-
servedamongthese populations (Adkinson1996). .yrinchusandA. transmontanousexhibit higherlevels
Stabile et al.(1996)hypothesizedthat thehoming ofpolymorphism andgreatergeographic popula-
imperative ofA. o. desotoifor spawningpurposes is tionstructuring. The reasons forthisdisparity are
strong, butthat it may bereinforced bymetabolic notapparent, and arecontrary to comparisons
constraints.Acipenseroxyrinchusdesotoireturns to amongother freshwater andanadromousfishes
rivers from theGulf of Mexico to summernearcold (Waldman&Wirgin 1994). Wecannot besure if
watersprings;tagging hasshownthatindividuals arc presentlevels ofgeneticdiversityamongthesefour
recaptured at the samecoolwaterrefuges inwhich species reflects prebottleneck levels, given the
they werefirst tagged(Clugston et al.1995). widespread anthtopogenically-imposed bottle-
martin jones
(Martin Jones)
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