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<br />~~22
<br />
<br />Hubbs and Miller
<br />
<br />personal observations). It is now common in impoundments, par-
<br />ticularly in Sahuaro I,ake and in other reservoirs in the Salt River
<br />.'lystem below Roosevelt Lake.", Ike Dowell, local commercial fisher-
<br />man, testified that h~ caughtJ'~~~~.\~~~i~~~~i~~~o.f~hu~pb~ck.s"~;kers:,.
<br />mSahuaro<L~ke,durmg, the,~spa~n.~n?seas,~e..~~f,19~9 '~I.In l=to~se~el t!;~~
<br />Lake, ,..to"1Yhlch.Tonto Creek IS "trlbutary.{and ;,l~ the ,Salt; Rlyer!i
<br />"lystem,' above' tlia i reservoir i;th:=Sp~etil:ji~~xtirpated:';a(:cbra"'l
<br />,'",- " .....&.' , ,,',,,, ,""" t,;,""'~ ':,_ ""., ,", " __" '
<br />,ing to T. T. Frazier, informed local residertti..(thelake'wentcom-
<br />pletely dry in July, 1930). He said it was common there in 1905,
<br />and Hubbs and Schultz collected an adult in the lake at the time
<br />they took the hybrids in Tonto Creek (September, 1926). Decreased
<br />
<br />TABLE VI
<br />
<br />RELATrVE NUMBERS OF CATOSTOMUS INSIGNIS, HYBRIDS, AND XYRAUCHEN
<br />TEXANUS
<br />The data are limited to catalogued material in the Museum of Zoology in the
<br />University of Michigan, since the profuse freshwater-fish collection or that museum
<br />j j largely composed of un selected mass samples. All specimens have been identified
<br />by one or both authors. See text for discussion of ratios.
<br />
<br /> Catoatomus Hybrids
<br />Specimens in 17niversity or ins ignis
<br />Michigan Museum of Zoology Per- Per-
<br /> No. No.
<br /> centage centagE
<br /> - - -
<br />'n collection containing hybrid. . . . 13 40.6 6 18.7
<br />,'rom entire Gila River system . . . . 4,595 99.4 6 0.1
<br />
<br />Xyrauclten
<br />
<br />texanus
<br />
<br />No. Per-.
<br />centage
<br />
<br />18 40.6
<br />20 0.4
<br />
<br />l,umbers of Xyrauchen may have contributed to the hybridization
<br />in that stream. Only a short section of the creek was seined, and
<br />t he six young hJ'brids may have stemmed from a single mating.
<br />Xyrauchen has taken to spawning in the impounded waters of
<br />the lower Colorado River basin (Douglas, 1952, and local. testimony,
<br />particularly for Sahuarb Lake). Sahuaro Lake has no tributaries,
<br />and all spawning there must take place in the reseJ'voir. Since
<br />other species of the sucker family are absent or very rare in such
<br />waters, the incidence of hybridization in the Gila River system and
<br />in the lower Colorado River is nowpresumablyverYlow., ,..' '.
<br />In former years the hurnpb~ck.su?kerpr()bablyoften bre'd;inp?ol~
<br />and-riffle tributaries. Jorda:n(1891;p: '~5)"'i!eported Io~::al te~H~nony,
<br />~- " -,~- ..)',.:,~,.. ..u";';'"""-,-,,, _"..c ,.._ .
<br />
<br />Hybridization between Catostomus and Xyrauchen 223
<br />
<br />,~,"::'-":', :' :,:: ",',' , "',' _< ',,', _" ;_,:~f,~)!tJ~"1(~':,1-V'!','-'P!~ .r..':t-',,' r,
<br />to .theeff~c~1<th~t~this;andthe~;otherjlarge%~~~i!~:~~~~~S.l' . .
<br />trado I River .,ascended,~the" medlUm-slzed:,:aI?i:t.~~~a.
<br />tgoihg .'. back to'. deep ,. water, after" spa wIIlllg,;"Ill!W
<br />~attcity;,otY6u'ii.i(in~alI,collectiorl's"ho~e~et~~~~f, "";, ~ ,J
<br />hliefrY:lhti f.ha,t,ched :in;,the.' small:stre~ms,~so2n.1fol~~,.e! " "' ; ~. ,,~~,f"
<br />~:iIlt6' 1 the'la~ger'and " deeper, ',wa ters"whICh:~ha ye~t b~en;jJneg ~ctedL,bY.z!
<br />t:, ,"',,1 :;"i,., ',A~":', -~,:,,;>o\.(,jf-rJ;'i-,c~"'J."'''~:--'' ,.,,".~ ... "1..""
<br />t'!I~conect6rs:<;",'."f .
<br />\1;ii:t~i'""Whethei'th~ hybrids react in intermediate fashion or like one or
<br />the other parental species cannot be said. They may act distinc~
<br />tively. Like certain centrarchid hybrid~ and lik~the goldfish-carp
<br />combination (Carassius auratus X Cyprmus carpw), as observed by
<br />the senior author in the GreatLakes region, they may display hetero-
<br />sis by stemming swift currents with more vigor than either p~rental
<br />species (a reaction that sometimes leads to large concentratIOns of
<br />sterile hybrids).
<br />It is not safe to iIifer, therefore, that the relative numbers of
<br />hybrids and of the parental species indicated in Table VI are clos~ly
<br />representative of the actual populations. We may conclude With
<br />some confidence however, that at least under certain conditions
<br />Catostomus insig~is and Xyrauchen texanus occasionally hybridize.
<br />
<br />
<br />INTERMEDIACY OF HYBRIDS
<br />
<br />The Catostomus insignis X Xyrauchentexa~us .hybrids are also
<br />intermediate between the parental species. They closely resemble.
<br />the C. latipinnis X X. texanus crossbreeds, differing c~iefly in re-
<br />spects attributable to the differences between the specIes of Cato-
<br />stomu.q involved in the cross-matings (p. 208).
<br />These hybrids exhibit distinctive intermediacy in scale number
<br />(Table II) ; in the number of dorsal rays, again with a ~lose approach
<br />to the Catostomus parental species (Table III); and III the number
<br />of gillrakers (Table IV). The hybrids of this combination are not
<br />exceptionally variable in scale number. .
<br />In most measurable characters by which the parental specIes
<br />differ at such small size (between 50 and 80 mm. standard length),
<br />the hybrids are intermediate (Table VII). ~or this combi~ation it
<br />was possible to compare the six young hybrids, on the baSIS of t~e
<br />proportional measurements, with specimens of the parental s~ectes
<br />of about the same size. For Xyrauchen texanus we used the thirteen
<br />specimens that were seined with the hybrids. Since only one Cato-
<br />
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