THE WA S M . NN JO URNAL OF BIO L OGY
VoL. 34, C\o. 1 SPRING, 19i6
Cyprinid Fishes of the Genus Gila from the Lower Colorado River Basin
J OHN N . R I C\ N E, Department of Z oology, Ari=ona Stat e University, T empe, Arizona 85281.
I NTRODUCTION Western cyprinid fishes of the genus Gila Baird and Girard have had a long, tortuous, taxonomic history, which has resulted largely from a lack of understanding of their individual and geographic variation, or from erroneous in terpretations of it. Geographi c or ecologic allopatry, so characteristic of western fi shes, prevails, and local differentiation is paramoun t. Interpreta tion of the vari ous forms of ch ubs has ranged from a prolifera ti on of generi c names, to synonymization of diverse mor photypes as subspecies or "ecotypes" of a single polymorphic species. In the Gil a River basin alone ( fi g. 1) , the forms here recogni zed have been placed und er six generi c names and have accumulated more than a dozen speci fi e synonyms. Gila elegan s Baird and Girard, the bony-tail, perhaps has been subject to least taxonomic confusion. It was co nsidered a valid species until Ellis ( 1914) synonymized it with C. ro busta. About 30 years ago _ Iiller ( 1946b) placed this fo rm as a subspeci es of C . robusta Baird and Girard in the " Gila robusta co mplex -" l\Iore recent studies of it ecology (Vanicek and Kramer, 1969) and tax onomy (H olden and Stalnaker, 1970), however, sugaest specific status for this chu b. l t was considered ex tinct in the lower Colo rado Rive r basin (::.liller and Lowe, 1967), but more recent col lections by the Arizona Game and Fish Department suggest it is
1 Current address: Rocky 2\lountai n Fores t and Range Experiment Stati on, Forest Hy drology Labora tory, :\ SL , Tempe, Ari zona 8528 1 ]65] 66 THE WASMANN J OURNAL OF BIOLOGY, VoL. 34 , No. I , 1976
F1c URE 1. Map of rivers and streams in the lower Colorado River basin a nd in surrounding basins. 1. Phoenix; 2. Buckeye; 3. F lorence; 4. Safford; 5. Prescott ; 6. Roosevelt Lake ; 7. Sulli van Lake; 8. Lake .Mead ; 9. Salton Sea ; 10. Guzman Basin ; II. Gi la River; 12. Salt Rive r ; 13 . White Rive r ; 14. Black Rive r; 15. San Francisco River; 16. San Simon River; 17. San Pedro River ; 18. San Carl os River ; 19. Santa Cruz River; 20. Verde Rive r ; 2 1. Agua Fria River ; 22. Bill W illiams River ; 23. Virgin R ive r ; 24. Little Colorado R iver ; 25. Zuni River ; 26. Pluvial White River; 27. Colorado Ri,·e r ; 28 . Rio Grande; 29 . Pecos Ri,·er ; 30. Rio Conchas; 3 1. Rio Yaqui ; 32 . Rio Sonora; 33 . Rio de Ia Concepcion ; 34. Monkey Springs; 35 . Aravaipa Creek; 36. Queen Creek; 37. Fish Creek; 38. Cave Cree k; 39. East Verde River ; 40. Wet Beaver Cree k ; 4 1. Oak Creek ; 42. Sycamore Creek ; 43. Bi g Ch ino Wash ; 44. Tonto Creek ; 45. Carizzo Creek; 46. Fossil Creek ; 47. Wesl Clear Creek ; 48. Gulf of Cali fornia. extant in thi s portion of the ri ver. H owever, it is rare at present in the lower basin and is not specificall y in volved in the problems di scussed here. The other forms of Gila in the lower Colorado River basin are not as easil y interpreted. CYPRINID FISHES-RI::\fNE 6i
The purpose of this stud y was to examine and compare speci mens of the genus Gila fo und throughout the lower Colorado River basin in order to define their di stribution. Emphasis is therefore placed upon temporal and spatial stability of morphometri es and meristics and of habitat co nditions. In addition, it was deemed important that ecological information of the different forms of Gila be compared to determine if the ecotypic concept of inter pretation of these chubs was acceptable and appli cable. Synon ymies, distribution maps, rationale for taxonomic decision and a key to the species of Gila in the lower basin are provided . Present distribution and abundance of chubs in this portion of the Colorado River basin reflect the radical changes in surface water that have occurred in the last 100 years. Arroyo cutting has lowered water tables and drained many marshy habitats (Hastings, 1959 ; :\Iiller, 196 1b ; Hastings and Turner, 1965 ; :\Iinckley and D eacon, 1969) . Pumping of underground waters and placement of major and minor clams have dried streams. These phenomena necessitated examination and comparison of observed patterns of variation in fish population characteristics to both recent changes in aquatic habitats and to more ancient (geologic) drainage histori es.
l\IATERIALS AND l\IETHODS Approximately 1,8 00 specimens of chubs from the lower and middle Colorado River basins and northern l\Iexico ( fi g. 1) were examined. Samples included both coll ections made by the author and museum records from the institutions cited in the acknowl edgements. Counts and measurements (the latter taken with a fin e-pointed dividers) were made following Hubbs and Lagler ( 1958). Tn ad clition to body length, six morphometric measurements (interor bital width, head width, head length, caudal peduncle depth, caudal peduncle length, length of anal fin-base) and one ratio (head length/ caudal peduncle depth) were employed in analyses. Counts of dorsal, anal, and pelvic fin-rays and scales in the lateral line series were also made and used for comparisons. Raw data were punched on computer cards, converted to thou sandths of standard length, and subjected to tests of analyses of variance at the Arizona State University Computer Center. 68 THE \\"ASMA);:\ ]0 R:\_-\L OF BIOLOGY, YoL 34, No. I, 1976
The contribution of allometries to vari abili ty in morphometries was examined first. ~ext , all morphometric data from available samples of GiLa fr om the two major drainages, the Bi ll \\-illiams and Gila ri ve rs, we re ubjected to a standard tes t of analysis of variance to determine if significant differences ( P < 0.05) ·were present. Variati on in morphology between samples in these two drainages \vas quite high. In order to identify sources of variation and finally to determine their geographic relati ons a number of arbitrary groupings were then tested, both with analyses of va ri ance and empiricall y. Co nsequently, fi shes were stratified ac cording to sub-basins within the Gil a and Bill \\"illi am drainages and into mainstream versus tributary waters, hi gh versus low alti tude reaches of streams and year versus year (o f collec ti on ). Sam ples from the middle Colorado Ri ve r were subsequently analyzed owing to their apparent similarities to problematic populations in northern porti ons of the study area along the l\Iogollon Rim (fig. 9) . Fishes of the genus GiLa from ri ver basins in northern l\Iexico were also examined and compared principall y to samples from the Gi la River basin in so uthern Arizona .
p ATTER S OF VARIATION Possible influences of allometric growth on vali dity of measure ments were examined using specimens of G. intermedia fr om ~I o n key Springs, a southern tri butary of the Santa Cruz River ( fi g. 1), and of G. r . 1·obusta fro m the mainstream of the Salt Rive r (figs. 2-3 ) . The Salt Ri ve r form reaches a far greater size than do fi shes in the popula ti on from Monkey Springs a the upper ra nge of data indicates. ote also that no pecimen less than 40 mm standard length (SL ) were available from the Salt Ri ver. Within the size range of specimens used for morphometric com parisons, usually between 70 and 200 mm SL, si mnar all ometric trends are evident in the two populations (although actual values differ markedly) . T he popul ation from l\Ionkey Springs is remark ably vari able in the length of head and of caudal peduncle (fig. 2), more so than in other populations studied . Simn arly, vari ation in length of caudal peduncle in the Salt RiYer populati on was high. The possibility that meri stic features varied with size also was exami ned, but no such trend were evident. CYPRINID FISHES-RINNE 69
.. ~ ·. :: . i: •. .· .:[. . \·· · :.... ··;.: \. : ·~\- ·~··. .· ·:·· :1:: ...... I )- ~lOO w -' 0 "' I "'~ 160 <1 )- "l · [/) 14 0 . ·=r· · . - ;· : . 0 ~: t ·~. . .. • I • i . THOUSANDTHS OF STANDARD LENGTH Frc UJu: 2. Allometric growth in Gila inter media from Monkey Springs. Further definition of intrapopulation vari ability was made by meristic and morphological comparison of samples from the same place, but from different years. In seri es of samples where ade quate material is avajlable over a relatively long period of time (e.g . East Verde River, ~I o nkey Springs, Cave Creek, \Ve t Beaver Creek, and the Gila River headwaters; table 1 )' marked stability through time is indicated. Further, a sketch by J ohn Mix Stanley ::3 Data on mcri stics and morphometries of samples of Gila from specific loca lit ies in the lower Co lorado River basin too extensi\·e to publish are obtainable from the ed itor, \\"asmann Journal of Biology. 72 THE \V ASM A:-.JN ]OU R'.JAL OF BlOLOGY, VoL . 3+, :-.Jo. 1, 1976 TABT. E 2 . R esult s of Analysis of t'ariance comparisons of morphometries of all chubs examin ed ( circa 100 ; fro m Monkey Springs with other s pecimens of G. inte rmcdia from selected localities throughout the Gila R iver basin. !Y S denotes uon-significcwce ( P > 0.05 ) ; iudicates significance at I he same COII fidence level. Caudal Caudal Head H ead peduncle peduncle Drainage; locality Interorbita l wi dth length depth length Santa C ruz drainage ::\S ,, Sabino Creek ::\ S * _? .)' Binglnmpton * :\IS * * * _,r P ond Mexico, tributa ry 21 to the Santa Cruz Shee hy Springs ::\ S ::\S * 25 San P edro drainage 13abacomari River * 4 1 Turkey C reek ::\ S :\IS ::\S 8 O'Donnel Creek ::\S ::\S ::\S ::\ S 6 Middle Gil :1. RiH r drainage San Carlos Ri,·er * * 25 Salt Ri,·er drainage Fish Creek ::\S ::\S 32 \ ·c rdc R ive r d ra in age Big Chino \Vash NS * NS 25 others in the Gil a basin shoul d perhaps be described as a new taxon (table 2) . With that exception, lateral line scales are in vari ably between 60 and 80, dorsal and anal fin-rays both 8 (very rarely 7 or 9) . All fi sh are thi ck bodied and darkl y pigmented (fig. 4) . In all respects, they correspond to the original description of T igo ma ( = Gila) intermedia Girard ( 1856) , and to all previous and later descri ptions of chubs from the Santa Cruz basin (see synonymy fo r G. intennedia). Va riation in populations of Gila from the \'erde River system was exceedingly high in almost all proportional and meristic fea tures. H owever, samples from throughout the Verde River main stream are morphometricall y uniform. In tributaries a mosaic CYPRH\ID FISHES-RINNE 73 A 8 c 0 FIGURE 4. Gila inlermedia: (A) Monkey Sprin gs, ASU uncataloged, 22 0 mm SL ; (B) O'Donnel Creek , ASU 2720, 126 mm SL; (C) Ba bacomari River, ASU uncataloged, 150 mm SL; (D ) San Carlos River, ASU uncataloged, 125 mm SL. pattern of variation occu rs with no apparent geographic coherence. Samples from tributary streams were therefore systematically ex amined relative to the di stance of each collection site from the Verde itself. l\Ieristics and morphology in samples from the lower ends of tributaries below any barrier fall s or rapids (namely West Clear, Wet Beaver, and Sycamore creeks) with the exception of Wet Beaver Creek (discussed later) were the same as that of fi sh from the Verde River mainstream (fig. 6C). All correspond 70 THE \VASMA:--.J:\ J OUR:\.-\L OF BlOLOGY, \ .01. ..H , :\o. 1, 1976 .. .· ·...... ·. . " "[_ . \". : .::~~ .. . .':; l.; : .... \ .:": ·. . ·. ... :.c ·. ·:.: ..\ ~:·.. :r::;: ..·. '\ · . . ·. ! ::. ··.· .. ··::::·:I : ·.. [r· . • j • . : ~ :. . i .. ..J·. ·!.::;::.. :. :. "J .. _...... I· ·: ·. :·_::-,. : . . _I .. · ·.; _ J~> . ...j· .... ; .":i· ...... • • 0 0 0 •••• : f::·: 0 ... • • • . .. ·,. . 0 • ..•• THOUSANDTHS OF STANDARD LENGTH FrG\: RE 3. Allometric growth in Gila robusta robust a from the Salt Ri,·er mainstream. CYPRlN lD FISHES-RINNE 71 T ABLE 1. M orphom et,ric stability /,hrough time of chubs, g e JIUS Gila, from selected localities i11 lower Colorado River basiu. Da/,a are e ~· pressed as thou- sand/ hs of standard length ± 95% confidence li·mits. Wi d th of Depth of l.c ngt h of Length of int er- \\'idth of Length of cauchtl caudal anal Locali ty ( n) orbital head head peduncle pedunc le fin-ba!'ie Monkey Springs 1954 (25) 82 ± 5 162 ± 10 28 7 ± 11 102 ± 6 196 ± 14 104 ± 7 1964 ( SO) 87 ± 1 158 ± 5 309 ± 4 100 ± 1 205 ± 4 108± 3 Gil a Rive r headwaters 1938 (25) 84 ± 2 147 ± 299 ± 4 96 ± .l 209 ± + 11 5± 5 1949 (23) 84 ± 2 146 ± 3 293 ± 5 85 ± 3 210 ± 5 134± 6 195.3 (22) 79 ± 4 135 ± 5 2 79 ± 85 ± 5 212 ± 8 11 6 ± 10 Upper East Verde Rive r 1926 (25 ) 8 7 ± 2 157 ± 306 ± + 96 ± .) 205 ± 6 107 ± 3 1965 (33) 84 ± 2 153 ± 29 7 ± 3 97 ± 2 209 ± 111 ± Lower Wet Beaver Creek 193 i (4) 93 ± 4 151 ± 5 292 ± 9 97 ± .'l 226 ± 13 108 ± 6 1956 ( 10) 80 ± 3 150 ± 3 304 ± 6 89 ± 3 208 ± 8 106 ± 4 1964- 66 (5) 78 ± 1 134 ± 5 280 ± 8 86 ± 4 2 11 ± 10 111± Cave Creek 1950 (25) 89 ± 1 150± 3 294 ± 6 117 ± 2 211 ± 109 ± 3 1963 ( 7) 84 ± 3 160 ± 4 304 ± 12 121 ± .) 208 ± 8 123 ± 6 (Emory, 1848) of the " Gila trout"= G. robusta, the first known record of a fi sh from the upper Gila River, even resembles the form inhabiting that area until recently. It is now thought to be extinct in that reach of stream (LaBounty and i\ Iinckley, 1972 ). Since allometric problems seemed minimal and temporal sta bility in morphology and meristics was apparent, grouping data according to major sub-basins was used to test for intra-stream variation. Significant differences (P < 0.05) were present within the Santa Cruz, Verde, San Pedro and upper Gila River samples, and further analyses were undertaken. Populations from the Santa Cruz Ri ve r system are modally quite similar, despite hi gh individual variations. Isolated popu lations from Monkey Springs, which are uniformly di stinctive over a number of years from all other sa mples in this drainage a.ncl 74 THE WASMA:--I),T J OUR:\.-\L OF BIOLOGY, VuL. 3-t, l'\o. I , 197 6 well to the ori ginal and subsequent descriptions of G. robusta Baird and Girard ( 1853a ) . Fish from Bi g Chin o \\"ash, an extreme upper tributary of the Ve rde system, above a seri es of fa ll s and rapids now partiall y inundated by Sulli va n Lake, are G. intermedia , sim ilar in most respects to samples from the Santa Cru z system. A small sample of juvenile fish from upper Oak Creek also has counts and qualitative features suggestive of C . 'intennedia . However, there is high probabil ity that the last population results from intro duction in this inten sively managed, heavily fished stream. Fishes from a reas above rapids or barrier falls in tributaries of the Verde River usually have lateral-line scales ranging between 70 and 90, with 7 5 to 85 being most common. Dorsal fin-rays are usually 9, except in the Fossil Creek population which has 8 or 9. Anal fin-rays are predominantly 8, and pelvic fin-rays are most com monl y 9 on each side. All these fi shes are relatively thick bodied ( fi g. SA- B ), though not as extreme as G. intennedia ( fi g. 4 ) . A thorough search of all the synony m.i es o f chubs from the Gil a basin, examinati on of ori ginal descri ptions, and comparison of Verde River tributary sa mples (and others) with cotypes of G. gralzami (table 4 ) revealed the most likely applicability of the name G. grahami Bai rd and Girard ( 1853c), type locali ty " R.io San Pedro, Arizo na. " This name is applied through the remainder of this paper as C . robusta grahami. Temporal stability of morphology is manifest in both mainstream and tributary forms of Gila in the Ve rd e River basin (table 1) . The onl y marked exception is in \Vet Beaver Creek, where populations appeared stable (G. r. grahami) between 193 7 and 1956 but changed in 1964- 66. Wet Beaver Creek was treated with rotenone in 1962 (Bassett, 1962) and the change may refl ect invasion of the lower part of the creek by Verde R.i ver G. r. robusta and intergraclation of that form with renmants of the original popul ation. Some of the indigenous fi sh must have survived since Bassett indicated ..., FIG URE 5. Gila robusta gra.hami : (A) Upper Sycamore Creek, ASU 1833, 140 mm SL ; (B ) East Verde River, ASU 407 , 170 mm SL ; (C ) Ara,·a ipa Cree k, ASU 3093, 200 mm SL ; (D ) Taylo r Creek, UMMZ 110434, 160 mm SL. Gila 1·. robusta X Gila r. gralta.mi: (E ) Tonto Creek, ASU 3255 , 155 mm SL ; (F ) Ca rizzo Cree k, ASU 3175, 150 mm SL . 75 CYPRlN lD FISHES-Rl:-i:-.JE A c F 76 THI:: \VASMANN J OUR)JAL OF BIOLOGY, VoL. 34, No. l , 1976 that limited areas in the canyon were not treated, and Kruck enberg ( 1968) found individuals of Gila abundant in the upper part of the stream in the mid-1 960s. Samples from the Salt River basin, upstream from Roosevelt Lake belong to C. r. robusta ( fi g. 6) except for fishes from Tonto Creek (discussed below). Specimens from the ex treme upper reaches of the Black River are sli ghtly thicker bodied than those down stream, and this also may be noted in several of the smaller tributary populations. H eavier bodied specimens a re especially evident in Carizzo Creek (fig. SF ): however, the tendency toward thi ck heavy bodies does not approach the overall morphology of G. r. graha·mi. Chubs from Tonto Creek (fig. SE ) , a major tributa ry of the Salt River that heads near the eastern margin of the Verde River basin, differ from other populations of the upper Salt River. They resemble fi sh from the East Verde River in external appearance (fig. SB), and meri stic fea tures of upstream populations (Uni versity of l\Iichi gan l\Iuseum of Zoology 131102 ) are very sim.ilar to G. r. grahami. Meristics of downstrea m populations reflect intergradati on with Gila robusta robusta. Sim.ilarity of the pop ulations in the upper portions of Tonto Creek and those of the East Verde River may be explained by recent geological evidence : basin fill of the same origin and age combin ed with the nature of stream gravel deposits are firm evidence for a. previous con nection of these adjacent (although presently separated with almost completely opposed fl ow patterns) stream channels (Pederso n and Royse, 1970). In Fish and Cave creeks that enter the Salt River downstream from its major canyon, the chubs belong to C . intermedia. l\laterial from the headwaters of the San Pedro River presented no problem of interpretation. It is identical to C. intennedia from the adjacent Santa Cruz (when Monkey Sprinas is exclud ed ), as are 17 extant specimens from the extreme upper San Simo n River. ~ FrGURE 6. Gila. robusta. robusta.: (A) Bill Willi ams River, ASU 2774 , 170 mm SL ; (B) \Ves tcrn Canal, ASU 15U , 11 4 mm SL ; (C) Verde River, ASU 24 75 , 145 mm SL ; (D ) Salt Ri,·cr, ASU 1373, 160 mm SL ; ( E ) Salt Ri,·er, ASU 3 118, 195 mm SL ; (F ) Lowe r Sycamore Creek, ASU 3284, 116 mm SL. CYPRINID FISHES-RINNE 8 c D E F 78 THE WA SMA"'N J OURNAL OF 1310LOGV, VoL. 34, No. 1, 1976 Addi ti ona! populations referable to G. inter media inhabit the San Carl os River and Queen Creek. The last population is most likely ex tinct, and was possibly introduced from "Salt River" according to notes on fil e at the Uni ve rsity of ::\1ichigan . The remainder of the upper Gi la River basin , and Aravaipa Creek ( fi gs. SC-D ), a tributary to the extreme lower San Pedro Rive r, is inhabited by C. r . grahami. W . ]. Koster (perso nal communi cati on to W. L . M inckley) has likewise found only one fo rm of C. ro busta in the upper Gi la River, and co mmented on its general uniformity. A t rend toward thinner bodies and sli ghtly higher meristi c fea tures (9 dorsal , anal and pelvic fin-rays) is, however, evident in C. r. grahami in the lower main stream of the Gila Ri ver. This trend parall els, in general, that seen in C. r. robusta in the Salt drainage, and may re fl ect in both instances in tergra dation of C. r. 1·obusta and C. r. graham.i in the larger waters. A blotched color pattern, characteristic of many populations of C. r. g1·ahami, also occurs in frequently in the Black River, and in the Gila mainstream. Specimens of C. robusta from the Bill Williams Ri ver system, an independent tributary of the Colorado River that has derived much of its fa una from the Gila basin (Miller, 1946b; ::\I iller and Lowe, 1967; Smi th, 1966), have higher lateral-line and fi n ray co unts and are referable to G. r. robusta. Th ey have a high incidence of blotching (see fi g. 6A); however, this may refl ect the influence o f C. r. grahami or other highl y blotched popu lations to the north (especially C. r. jordani Tanner, from the Pluvial \~ 'b it e River, Nevada). Few specimens of Gila from the Little Colorado R iver were examined ; they are presently rare in thi s drainage. D ata indicate that t hi s form is similar in most all respects to G. r. grahami (tables 3-4 ). E coTYPY AN D C H UBS OF THE LowER CoLORADO Miller ( 1946b) referred to chubs of the Colorado R ive r basin as " ecological subspecies " because of a. general trend fr om thick bodies in the "small tributary and brook" form (C . intermedia ) to the attenuate, "swift river-channel" form (C. elegans). These same concepts were outlined by Hubbs ( 1940 ; 1941 ) and have appeared subsequently in a number of wo rks (L a. Ri vers, 1962 : T t\BLE 3. Meristic variations m ch11.b s, genus Gi la, from river systems SO I/.th a.nd east of the lower Colorado River basin, a.nd () sfr eams tributary to t.he middle Colorado River. >< "0 B Sea lcs in th e Latera 1 'Lin e z Dorsal fin -rays Anal fi n-rays Pelvic fin-rays 50- 55- 60- 65- 70- 75- a >-rj Localilies and Catalog N umbers 54 59 64 69 74 79 II 8 9 II 8 9 II 8 9 ..... "' (f) :r: Gila ditacn ia- Rio de Ia Con cepc iOn, Arizona r:i and So nora. ASU 2729 and 2749 16 13 - 30 - 29 30 29 - 30 29 - 30 (f) Gila purpurea- Rio Yaqu i ba.:; in. Ari zo na and I Sonora. ASU 1649, 2233 , 2284, Uncataloged. 2 1 - 30 29 - 30 26 - 30 - 30 - 30 ~ Gila nigrescens- Guzma n basin , Chihu ahu a, z Rio Casas Grand es. ASU 816 14 25 25 25 25 25 15 r:i Rio Pi edras Verd es. ASU 82 1 10 25 24 25 25 25 25 25 Rio del Carm en. ASU 709 8 - 19 2·1 25 - 25 - 25 23 25 Ri o Santa ~~1ar i a. ASU 838 6 6 6 6 6 6 Gila. pa11dora- Ri o Grand e basin, New ~ l ex i c a, H ondo Creek. AS 1323 12 - 17 - 22 - 22 20 - 22 - 20 22 jemez Ri ver, New ~ l ex i c a. ASU 2362 10 - 18 18 - 18 16 - 18 4 14 18 65- 70- iS- 80- 85- 90- 69 74 79 84 89 94 II 9 10 II 10 II 10 II G. r. grahami Littl e Co lorado Ri ve r, Ar izo na. U~ i:II Z 117834, 11 7835, 124752 , 137080 13 23 - 23 - 23 22 - 23 20 - 23 East Clear Cree k, Arizo na. · ~ L\ I Z 17869 1 I I I Chcv al on Creek, Arizona. ASU 2 185 I I I I I I G. r. jorda ni- Ash Sprin gs, ~c·•ada. ASU 3757 10 19 18 19 19 19 - 19 19 G. r. seminuda- !\ loapa Ri ver , Nc,·ad a. ASU 64 -6547,3775,3849,3850, 3853, 4055,4057, 4058, 4059' 4060, 406 1' 4062' 4063' 4064' 4065, ·107 I, 4072 17 41 30 12 103 90 10 103 83 IJ 103 II 92 - 103 \ "irgin Ri ve r, Arizona. ASG 37 15. ...., 40i5, 4076 II - 15 - 21 25 - 23 25 23 - 25 _, 80 THE WASMAI'\:'\T JOU R:'\ .-\L OF BIOLOGY, VoL. 34, No. 1, 19i6 T ABLE 4. R esults of analysis of varia11 ce com parisons ( morphometries) of 2 co types of Gi la grahami wit h the subspecies of Gi la robusta from I he Gila, Little Colorado, and m.iddle Colorado river basi11s . NS indicates 1/.011-sigllificall ce ( P > 0.05 ) ; ,., depicts sig11ificant comparisons at. t he same confide/i ce level. Caudal Caudal H ead H ead peduncle peduncle Subspecies; Locali ty Interorbital width length depth length GILA RIVER BASIN G. r. grahmni Aravaipa Creek NS NS NS NS East Verde R i,·e r 1\ S 1\S 1\S NS 87 Fossil Creek NS 1\S ="'S 29 Tonto Cree k l'\S :'\S :'\S NS * 29 Bea,·e r, T aylor creeks and West Fork Gila Ri'-er :'\S :'\S :'\S :'\ S * 32 Gila River at C li ff, l'\ew Mex ico l'\S :'\TS :.IS NS 79 Sa n Francisco RiYer :'\S :'\S :.IS :'\ S * 17 Eagle Cree k :'\S :'\S :'\S :'\S :'\S 28 Sycamore Creek :--: s :'\S :'\S :'\ S :'\S 10 G. r. robusla Salt Ri,·er :'\S :'\S 104 Verde Ri,·er :'\ S :'\S 44 Wh ite Ri,·e r :.IS i1 Black Ri ,·e r :'\S :'\S 42 Bill Williams Ri'u 1\S :'\S :'\S :'\S 45 TRIBUTARIES TO THE MIDDLE CO LORADO RIVER BAST:'\ G. r. jordani White Rive r (Nevada) :'\S :--i S NS NS :\S 15 G. r. seminuda Moapa Rh·c r :'\ S :\S :\S 16 Virgin Rive r "'S ="'S 25 LITTLE COLORADO Rl\'ER BA SI:\' G. r. graha:mi E ast Clear and Chevalon creeks :'\TS :'\S :'\S 21 CYPRII'\ ID FI S HE S- RI ~l\E 8 1 Beckman, l 963; Sigler and Miller, 1953; Miller and Lowe, 196 7) . Ecotype, a term proposed by Turesson ( 1922) fo r plants, as " the product a ri sing as a result of genotypi cal response of an eco species to a particular habitat," is generall y equivalent to M iller's use of the term " ecological subspecies." The " ecospecies, " also coined by Turesson, is equivalent to the "Linnaean species from a n ecological point of view [Mayr, 1963 :35 1J." May r et al . ( 1953 : 3 13) define ecospecies (modifi ed from Turesson ) as "a group of populations so related that they are able to exchange genes freely without loss of ferti lity or vigo r in offspring, " and ecotype as "a descriptive term applied to plant races of varying degrees o f di s tin ctness whi ch owe their most conspicuous characteristi cs to the selecti ve eff ects of local environments." Earli er, Hubbs ( 1943) stated that " in increasing numbers, subspeci es are being shown to be ecological or microgeographical races" (see also Hubbs, 196 1) . Another term that may be pertinent is "ecotypic va ri ati on ," as defin ed by l\Iayr ( 1963 :4 15 ), " the formati on within each geo graphic area of numerous locali zed populations that speciali ze in ecologically eli ff erent subareas, and are not obliterated by gene exchange with adjacent, differently speciali zed populations." I n appli cation of such co ncepts to the fishes presently under con sid eration (excluding C . elega11s), the ecospecies wo uld be Gila rob usta, with three ecotypes or ecosubspecies, C . 1' . 1·obusta, C . 1'. gmha·m.i, and C. r. inten ncdia. The " va rying deg rees of distinct ness" would be their external morphology, in a graded series from C . r. i11t ennedia. through C. r. gm hami to C . robusta, as described befor e. H abitats from whi ch chubs have been collected by me and other personnel from Arizo na State Uni versity are generall y inco nsis te nt with an " ecotype" interpreta ti on. For example specimens of C. r. J!. mhami have been taken in small , wa rm, desert streams like Aravaipa Creek (mean gradi ent 7.0 m/ km ) , which co nsists prin cipally of riffles and few pools (Barber and l\Iinckl ey, 1966) and in Fossil Creek which is h rge a nd swift with a constant-temperature spring a t its so urce and a drop of almost 500 m in its 18 km de cent to the Verde River. This subspecies also is relatively uniform in the upper Gil a Ri ver basin , from the large ma instream to the hi gh mountain (2 ,500 to 3,000 m) tributa ri es. 82 THE WASMANN JOURNAL OF BIOLOGY, VoL. 34, :'\o. 1, 1976 Great stability in body form also exists in C. r. robusta. This subspecies li ves in habitats ranging from the large, warm, strongly fl owing Phoeni x Canal system ( 300 m above mean sea level ) through the turbulent Salt River to the cold hi gh-gradient White and Black rivers (2 ,500 m ) . lt also is present in small, pool-riffle, low-gradient tributary creeks. Jn the Bill Williams drainage specimens of C . T . robusta have been taken from marshy creeks of the headwaters and in pool-riff les further downst ream. The p redominantly southern C. intennedia is ra re in the Gila R iver system. Jn the so uthern portion of its range the habitats of this fish are principall y lentic, in marshes, brooks, or in impound me nts. T o the north it is fo und in the relatively large San Carlos Ri ver, in rock pools of F ish Creek Canyon, and in pool- riffles in Cave Creek. One population li ves in an a rtificial habitat, the Buckeye Canal. Each of the three forms of chu bs lives in a diff erent place and hence they a re essentiall y allopatric. Yet the habitats of each com pri se a spectrum from la rge ri vers to small streams, from low to hi gh elevation, and from relative swift and turbulent to semi lentic conditions. Populations of C. interm edia prefer quiet water, although they li ve successfull y and retain their identity in the large San Carl os River and in the Buckeye Canal. The forms of C . robusta, on the other ha nd, inhabit almost all kinds of habitats, and remain fai rly uniform in morphology over broad geographic areas. No habitat preference is apparent fo r these animals. A sli ght trend toward thicker bodies and reduction of meristic fea tures in popula ti ons of the upper tributaries of the Salt R iver (C. r. 1·obusta) and of the Gila Rive r (C. 1'. grahami) , may be an eco typic response, or intergradation between the subspecies ; it is not of a magnitude that obscu res distinctness of the taxa. I t is hi ghly unli kely that morphological stability of ecotypes would prevail if the animals we re as plastic as ecotypic responses presumably require. A c COU N TS OF SPECIES AN D SUBSPECIES All literature on the " Gila robusta complex" that was avail able is cited in the fo ll owing accounts. Recent publi cations are included only if they refer to fi sh from the lower Colorado Rive r basin below Lake l\Jeac\ ( fi g . 1). Comparisons of critical cha racters a re given in the key. 84 THE WASMAN:\T J OUR:\TAL OF BIOLOGY, VoL. 34, :\To. 1, 1976 : . • {O ,• - ~:_ ... :. ... B -· ..... ,-- FJGURE 7. Distribution of Gila elegans ( A) a nd Gila int ermedia (B ) in the lower Colorado Ri,·er basin. Solid circles arc localities from which specimens were examined , small open circles represent literature records, and the la rge open circle is the type locality. CYPRTNID FISHES-RINNE 85 sucker (Xyrauchen texanus Abbott) formerly moved to even hi gher elevations Ofinckley and Alger, 1968; :\linckl ey and D eacon, 1968). Large specimens of Gila reported from T empe (Gilbert and Scofield, 1898), undoubtedly belong to C. elegans. Gila elegans BAIRD and GIRARD, 1853a:369 (original description, "Zuni Ri,·er, New M exico"), 1853b: 150-51 (characters, figures) ; GmARD , 1858 :286, 1859: 61 (cha racters); CoPE, 1871 :441 (listed ) ; J onDAK and GILBERT, 1883 :22 7 ( listed ); J ORDAN, 1885 : 8 18 ( listed ), 1891:22 (distribution); J oRDAN and EVERMANN, 1896 :226-2 7 (s ~ ' non y m y, cha racters); GILBERT and ScoFIELD, 1898 :492 (cha racters); MEEK , 1904:53-54 ( range, characters); ELLIS , 1914 : 56 (synonvmized with C. robusta); SNYDER, 1915:580-81 (comparisons); J o RD AN et al., 1930: 114 (synonym y); MOFFETT , 1942:82, 1943 : 182 (" L ake Mead a rea"); DILL, 1945: 153-54 (distribution, a bundance); MINCKLEY and D EACO:<, 1968: 1427 (listed ) ; Rlli: Gila intermedia (Girard ). Gila. chub. This speci es is endemic to the Gi la. River basin and is most abundant and wid espread in the southeastern part (fig. 7B). It co mmonly inhabits small creeks and ciengas. Its northernmost rep resentation in the upper Verde system below the Mogollon Rim (e .g. , Bi g Chino \Vash and perhaps Oak Creek) may best be explajned by way of stream capture from headwaters of the Agua Fria River (see discussion ). The specific identity of C . intennedia is proposed on the basis of a co mbination of characters. For example, 97% of 390 specimens of C . intermedia have fewe r than 80 scales CYPRI:\'ID FlSHES-RIN="iE 83 KEY TO SPECIES OF GILA 1a . Body streamlined; skull depressed on dorsum, a rching smoothly into a predorsal hump in large adults. Total number of vertebrae (including one urostylar vertebrae and four in the Weberian a pparatus) 47-50. Caudal peduncle thin, pencil -like, length of caudal peduncle/ length of head 1.0 or greater, length of bead/ depth of caudal peduncle usua lly 5.0 or greater. Squamation often in complete, with sca les absent or high ly embedded on predorsum, venter, an d caudal peduncle. Fins la rge and fa lcate, origin of dorsal fin nea rer to tip of snout th an to caudal fin -base. Dorsal fin -rays almost always 10 or more; anal fin rays usua ll y 10 ---·--··--··· ------····--· ----· Gila elegans Baird and Girard b. Body t hick, not ob,·iously streamlined ; skull sli ghtly depressed or rounded on dorsum, predorsal hump absent, or if prese nt, fatty and rising abruptly at the nape. T otal number of vertebrae 38-49. Caudal pe duncle short, thick, and wide, length of caudal peduncle/ length of head less tha n 1.0 ; length of head/ depth of ca udal peduncle 5.0 or less (usua ll y less than 4.0). Squamation complete. Fins small , rounded ; origin of dorsal fin nearer to caudal fin-base than tip of snout. Dorsal and anal fin -rays 9 or fewer (very rarely 10) ·------···----·------·------·------2a. Body chubby, clark in coloration. Scales large, thick, and broadly im bricate; basal radii usually present. Lateral-line scales almost always fewer than 80. Dorsal fin-rays usually 8 (rarely 7 or 9); anal fin rays 8 (rarely 7); pelvic fin-rays 8 or 9. Length of head/ depth of caudal peduncle usually 3.0 or less. An abrupt, fatty, nuchal hump develops in large females of some populations. Total number of ve r tebrae 38-45 ·--·------·------·-·-···---·------····------Gila intermedia Girard b. Body t hick, but not chubby, Li ght to mottled co loration. Scales sma ll , thin , and slightly imbricate; basal radii absent to weakly de,·eloped. Lateral-line scales usuall y more than 80 (C. r. grahami ranges as low as 75) . Dorsal fin-rays 9, anal fin-rays mostly 9 (C. r. gra.ha.m.i bas 8 or 9), pelvic fin-rays usua ll y 9. Length of head/ depth of caudal peduncle usually 3.0 or more. Fatty nuchal hump rarely developed, and if prese nt, sca rcely discernible. Total number of \"Crteb rae, 43-49 ----·-··-·------·-·-···----··-·---·---·-····--··------·-···------Gila robusta. Baird a nd Girard Gila elegans Baird and Girard. Bonytail chub. Though once widespread in the Colorado River basin , thi s spe cies is now essentially restricted to that portion of the drainage above Lake l\Iohave (Holden and Stalnaker, 1975 ) . It is extinct in the Gila River system ( fi g. 7A ). Literature records are from the mouth of the Gila River to Fort Thomas on the mainstream (Kirsch, 1889) . This record may be questionable, especially if based on small specimens. Nevertheless, other " big-river fi shes" such as the squawfish (Pt·ychocheilus lucius Gi rard) and humpback 86 THE WASMAl\ N j OURl\AL OF BIOLOGY, VoL. 34, l\o. t , 1976 in the lateral series ( 7 7% have fewer than 7 5), whereas, 80% of the 670 specimens of C . robusta (both subspecies) have 80 or more lateral line scales, and 96 o/o have more than 7 5. Strongly-in scribed basal radii were present in 63 o/o of about 70 C. intermedia from throughout its range, but basal radii were present in onl y 14.6% of 13 7 specimens of C. 1·obusta, and then were onl y weakly de veloped. Dorsal fi n-rays in C . intennedia were 7 or 8 in 94o/o of the specimens examined, and were 9 or more in 83o/o of the C . robusta. N umbers of anal fin -rays are less reliable for separating the species because of the high incidence of 8 rays in C. r. grahami individuals (about 50% ): 98% of the C . -intermedia examined had 7 or 8 anal fin-rays and only 13% of the C. r. robusta specimens had 8 or fewer. Pelvic fin-rays are almost always 9 in this sub species of C. robusta (greater than 95 o/o ), a nd are 8 or 9 in C. intennedia (about 50:50). Length of head/ depth of caudal pe duncle is more than 3.0 in 8 7% of C. robusta, and below 3.0 in 83 % of C. interm.edia.. Gila r. robusta. is more di stinct (greater than 95 % above 3 .0) from C. inter-media. than is C. r. gmha.mi ( 77 % more than 3 .0 ) . Breeding colora tion of specimens o f C. intermedia. from 1\Ionkey Springs has been recorded by ::\IinciJey ( 1969): " The axial and inguinal regions become deep orange-red, whi ch may develop fur ther in to a broken, orange-red band along the lower sides and caudal peduncle, and extend forward to include the branchioestegal rays and cheeks. The eyes of males become yellow to yellow orange and the body is blue-black dorsall y. Fins of so me indi viduals, especially the larger ones may be washed with lemon yell ow." Breeding colors in C. intennedia. recorded by myself from specimens from the San Carlos River were similar. Gila gibbosa B AIRD and GmARD , 1854:28 (o rigina l descri ption , "Rio Santa Cruz, Ari zona"). Tigo m.a intermedia. GIRARD, 1856:206 ( original description, " Rio San P edro of t he Gila [Arizona]" ). Tigo ma gi bbosa, G IRARD , 1856:207, 1859 :64 (ch a racters, fi gures) ; J ORDAX et al. , 1930: 119 ("Rio Gila, .-\rizona"). Gila 11igra Cope, in COPE and YARROW , 18 76:663 (origina l description , ".-\ sh Creek , Arizona," and "San Carlos, Arizona" ). Squalius intermedius J OHDAN a nd GILBE RT , 1883:238 (listed ). Squalius niger J onDAK a nd GILBERT , 1883:238 (li sted ) . CYPRl NID F ISHES-RINN E 87 Squalius lemmoni SllllTH, 1884 : 111 (origina l description, "Rillito Creek, near T ucson , Arizona") . L eucisws intermedius EVERJ\'IA NN and R uTTER , 1895 :484 (" Rio San Pedro, tributary of R io Gi la") ; GILBERT and SconELD, 1898:493-94 (in part ; characters, synony my, "Tempe and Chino, Arizona"); MEEK , 1904 :56 (char acters, synonymy). Leuciscus niger, ] ORDAN and EVERMA NN, 1896:235 (" Rio Gila," characters, synony my) . R ichardso 11ius gibbosus, SNY DER , 1915:581-82 (in pa rt; characters, synonymy , "Rio Santa Cruz"). Gila robusta i11termedia, MILLER , 1945: 108-09 (compari sons), 1946b :414 (characters) , 196 1b :377- 79 (habitat , ra nge, "ecotypy") ; LA R IVER S, 1963 : 392 (comparisons) ; MrLLER a nd LowE, 1964 :140, 1967 : 140 ( habitat, range); UYENO and M ILLER, 1965: 39 (comparisons); BARBER and MINCKLEY , 1966: 3 17-19 (comparisons) ; MIKCKLEY and ALGER , 1968:94 (comparisons) ; CoLE , 1968:4 71-72 (habitat, figure). Gila inter-media, MmCKLEY and DEACON, 196 8 : 1427 (listed ) ; STOUT et al. , 1970: 109 (ecology); R IN NE a nd MINCKLEY , 1970:13,16,18 ( range, figure, ecology) ; Mwcr:LEY, 1971 : 185 ( key); MrNC KL EY, 1973 : 104 (synonymy, characters, ecology); RINNE , 1975:186, 193 (ecology . dist ri bution). The name "Gil a gibbosa" has obvious pri ority for this fish, but is unavailable since it was synonymized with Leuciscus niger (Cope) by Jordan and Evermann ( 1896) . The name " gibbosu s" was twice preoccu pied in Leuciscus, and Article 59 of the International Code of Zoological Nomenclature ( 196 1) di ctates continued sup pression of a name that was once a homonym, even if the homonymy is inco rrect. The next available name, Tigoma inter-media, is there fore applied. Gila robusta Baird and Girard . Colorado Rive r chub. This species is presently the most widely distri buted in the Colorado Ri ver basin where it is represented by fo ur forms : G. r. robusta, throughout the basin in the larger streams ; G. 1· . grahami, Gila River basin (fig. 8B ); G. t . seminuda (Cope) , Vi rgin River, and G. r. jordani, the Pluvial White River, Nevada. Gila r. gra hami is restricted to the Verde River tributaries, upper Gila Rive r, and Aravaipa Creek. R ecords of G. gmhami fro m Utah (Evermann and R utter, 1895) were based on misidentifications of G. r. robusta. Gila 1· . robusta inhabits the Verde R iver mainstream and the Salt River ystem above Roosevelt D am. Intergrading populations seem present in lower \Ve t Beaver Creek, Tonto Creek, Salt and upper Gila rivers, and possibly in the Bill vVill iams River (fig. SA). SS TBE \\1:\ SMA:\TN JOUIU\AL OF BIOLOGY, VoL. 34, 1\o. 1, 1976 ' ( ,• r I ~ ) )r: - /< I . ~ A · ·;::J 0 B <.::r · FIGURE 8. Distribution of Gila robusta. robusta. (.'\ ) and Gila robust a gra hami ( B ) in th e lo wer Colorado Ri,·e r basi n. Solid circles are localities from which specimens were examined, small open ci rcles represent literature rec ords, and the large open circle is the type locality . CYP R IN ID FISH ES-R I NN E 89 Gila r. gralzami has between 70 and 90 scales in the lateral series in 98% of the specimens, with most (82%) falling between 75 and 85 ( range of means 77.0 to 82.4 ) . Gila r. robusta has 80 or more lateral-line scales in 97 % o f specimens examined ( range of means 83 .8 to 91.3) . D orsal fin-rays are 9 in 99% of G. T. robusta, whereas 18% of G. r. gm lz ami had 8 do rsal fin-rays and the remainder 9. An al fin- rays are 9 in 87% of G . r. robusta while G. r. grahami has an approximate 50:50 ratio of 8 and 9 anal fin-rays. The pelvic fin-rays are almost always 9 in both sub species (9 1% in G. r. g1·ahami and 97 % in G. r. robusta) . R ecal culati on of data accumula ted gives the rati o of mean length of caudal peduncle/ length of head usually less than 0. 74 in G. r . gm lz ami (44%) , and in G. T. robusta 84% of the total sample had a rati o greater than 0. 74. Population mea ns of length of head/ depth of caudal peduncle fa ll s between 3.00 and 3.30 in 99% of G. r. gmhami, as compared to 81% of G. r. 1·obusta that fall above 3 .30 ( range of means 2.78 to 3.27 and 3.2 8 to 3.62, respectively ) . Blotching is co mmonly p resent in G. r. gralzami (similar to that of G. r. j01·dani in the P lu vial vVhite River (T anner, 19 50 ; La Ri vers, 1962 ) , but is ra rely developed in G. r. robusta. Breeding colors that have been noted in both G . 1·. robusta and G. r. grahami resemble those of G. intermcdia ; however, great vari ati on in in tensity exists. For example, specim ens of G. r. robusta collected thro ughout the year fr om the Salt River mainstream fail to display even the slightest development of nup tial colors, even in ripe males. In contrast, colors of mature male specimens of G. r. grahami from Aravaipa Creek we re well developed. The foll owing synony mi es for the subspecies of G. robusta from the Gila River basin summari ze my findings. Gila robusta BAJR D a nd GIIV\R D, 1853a :369 ( o r i ~,oi. n a l desc ri ption , "Zuni R ive r, )lew M exico") , 18.13 b: I48-49 (cha racters, figures); GIRARD, 1856:205 ( listed ) ; E VER]I[ANN and R UTTE R, 1895:483 ( ra nge, characters, synony my , " Ba bacoma ri Cree k, .'\rizona " ) ; J o RDA N and EvmJ\IANN , 1896 :22 7-28 (cha r acters, synonym y); GILBERT and SCOFIELD , 1898 :493 (synonym y, characters, compa ri sons) ; SxYDER , 19 15:581 (characters, compa risons) ; J ORDA N et al ., 1930: 11 4 (synony my ) ; M ILLER, 1945 :104 ( in part; cha racters, range); LA R I VERS, 1962 :392 (cha racters, comparisons); Mwc KLEY a nd D EACON , 1968 : 1427 (in pa rt ; listed ). 90 THE WASMANN JOURNAL OF BIOLOGY, VoL. 34, No. 1, 1976 Gila gracilis BAIRD a nd G LR ARD , 1853a : 369 (origin al description, "Zuni Ri,·er, ~ew Mex'co") ; GuvH DiscussiON AND CoNCLUSIONS T axonomic conclusions in preceding sections are based largely on the lack of " ecotypy" in chubs of the lower Colorado River basin, and on their di stributions that are inconsistent with any conceivable pattern of species intergradation. Interpretation of patterns of variation necessitates exa mination of the hi story of inte gration in the drain age basin , and of age, origins, and a ffinities of its fauna. Since chubs referable to Gila are known from rnid-Miocene to present (Mill er, 1965), and species near, if not identical to, G. robusta are present in late Pliocene (Uyeno and Miller, 1963, 196 5), it will be necessary to review much of the kn own Cenozoic history of the lower Colorado River basin . As an orientation to the se quence of differentiation of Gila in this area , the following events are proposed as mos t probable and wi ll be justified and expanded later: ( 1) The lower basin was inhabited by a fo rm of G. robusta derived from the north in early stages of drainage integration with the Colorado Plateau and began to differenti ate ; (2) a second form of GiLa (G. intermedia or its ancestor ) invaded from the south, and inhabited waters south and west of the l\Iogollon Highl ands; ( 3) completion of internal integration of the Gila basin allowed another invasion of the aggressive, large-ri ver populati on of G. robusta into areas inhabited by both the other chubs: ( 4) eco logical adjustments and displacements occurred, plus intergradation of the two forms of G. robusta, until presen t distributions were attain ed. Interpretation of changes in drainage in thi s vast region center principall y on the relationships of the Colorado Plateau to areas to the so uth and west (fig. 9). In n1.id to late Cenozoic ( 18 million years ago; Lucchi tta, 197 2) , the Colorado Plateau most likely consisted of a low, alluvial plain near sea level with drainage to the east and northeast toward receding seas (Wilson, 1962; McKee et aL. , 196 7) . In Laramide times uplift along the western margin and in so me areas on the plateau was gentle; directions of drainage remained relatively unchanged. Extensive erosion of Mesozoic de posits was accompanied and fo llowed by deposition of ex tensive northern and eastern beds during the Eocene in the area that now is Utah . According to l\IcKee et al. (196 7), two drainage systems appeared on the Colorado Plateau by ea rly M iocene, or sooner: the 92 THE W.'\ SM.-\::\::\ J OUR:\.'\L OF BIO LOGY, VoL. 3-l , :'-J o. 1, 1976 3 7 ~ 29..__ I 103" FIGURE 9. Geological index map of Arizona and surrounding states with place names where appropriate. 1. Phoeni x; 2. Florence; 3. Globe ; 4. Safford ; 5. Prescott ; 6. Chin o Valley ; 7. Colorado RiHr ; 8. Gi la River ; 9. Salt Ri ve r ; 10. San Pedro River ; 11. Sa nta Cruz River; 12. Verde River; lJ. Agua Fria Ri,·er ; 14. Bill vVilliams RiY er ; 15. Little Colorado Rive r; 16. Vi rgin Ri,·c r; 17. Pluvial White Ri,·er; 18. Salton Se a ; 19. Lake M ead ; 20. Gulf of Cali fornia ; 21. Rio de Ia Concepcion; 22 . Rio Sonora ; 23 . R io Yaqui; 24 . Guzman Ba sin ; 2 5. Rio Conchos; 26 . P ecos Ri,·cr ; 27. Rio Grande; 28 . Mogol lon Rim ; 29 . Area of Colorado P lateau ; 30. Area of Mogollon High lands ; .1 1. Area of Basin and Range Pro,·ince; 32 . Area of Mohavia L andmass; 33 . .'\rea of Kai ba b Upwarp ; 34. Area of Defiance Upli ft ; 35. Area of Zuni Uplift ; 36 . .-\re a of H opi Buttes Volcanic Field ; 37. Area of \\'bite Mts. Volcanic Field ; 38. San Francisco Ri,·e r ; 39. Area of Bl ack Hills ; 40. :\rca oi Upper .-\n ccstral Colo rado Ri,·er ; 41. Area of Hualapai Drainage; 42 . Area of Bouse EmbaY ment ; 43. Approximate limits of Pleistocene la ke beds; 44. Area of lo wer extent of Bidahochi Formation. CYPRINID FISHES-RINNE 93 small Hualapai system west of the Kaibab upli ft ; and another larger system to the east (fig. 9). The Hualapai apparently flowed southwest or possibl y west. The other system ultimately drained toward the east or so utheast, perh aps near the present course of the Little Colorado River. Continuing upli ft so uth of the southern border of the Colorado Plateau in a posi ti ve (upthrusted ) area called the Mogoll on Highlands (H a rshbarger et al. , 195 7) and Central Ari zo na i\f ou ntai ns ( i\IcKee et at. , 196 7) provided from its northern exposures extensive gravels to the southern plateau margin (l\Ic};.ee, 195 I ). Changes on the plateau in Pliocene times (:\fcKee et at. , 1967 ), or pe rhaps in the ::vliocene (Cooley, in l\lcKee, 1967; Cooley and Akers, 196 1; Cooley and Davidson, 1963) , co nsisted of deposition of the ex tensive Bid ahochi Formation (fig. 9) in the so utheastern part (Repenning and Irwin, 1954; Repenning et at ., 1958), and of integrati on of the eastern and western drainages of the Colorado Plateau into the through-flowi ng Colorado River. The question persists as to the course of the Colorado River west of the plateau. It may have fl owed westward, as indicated by extensive Pliocene siltstones west of the Salton Sea (Woodring, 193 2; Reed , 1933 ), and perh aps substantiated by fis h distributions (Hubbs and i\Iiller, 1948 ; Smith 1966) , or it may have flowed southward, in or near its present channel (Lucchitta, 1972). There is little doubt, how ever, that the ri ve r fl owed through the area now occupied by Lake Mead in late Pli ocene ( l\IcKee et at. , 1967) , between 18 and 10 mi lli on years ago (Lucchitta, 1972), and on to the Gulf of Cali fornia (i\Ietzger, 1968) . The lands formi ng part of the present Gi la River segment of the Colorado River basin, sou th of the l\logollon Highlands, were drained by southwesterly-fl owing streams in post-Laramide times. The i\Iogoll on Highl ands were co ntinuous with a landmass, in what is now southern Nevada and eastern California (fig. 9) , formi ng during much of the Cenozoic a divid e between the Colorado Pla teau and the Basin and Range Province (Cooley and Davidso n, 1963) . Southwesterl y drainage through the highlands, from the edge of the uplifted plateau, was disrupted in the Miocene by ad ditional uplift of the highlands as a unit (Lance, 1960). Gorges were cu t in the ri sing mountains, and drainages developed trans verse to the superimposed systems along zones of weakness, or 94 THE WASMANN JOURNA L OF BIOLOGY, VoL. 34, No. 1, 1976 under structural control (Melton, 1960, 1965; Cooley and David son, 1963). By this time, much of the southern edge of the pla teau had been captured by so uth-flowing streams, and the Mogollon Rim (fig. 9) was well established as the di vide between the Gi la and the Little Colorado rivers (McKee and McKee, 1972). The Bi ll Williams R iver area has been li ttle studied, but it lies south west of the Mogollon Highlands in an area of relative stability, and may long have occupied its present position. Gila robusta, or its progenitor, mu st have li ved in the lower basin at least by the Pliocene and perhaps prior to the cutting of the Grand Canyon. Early access was possible through massive headward erosion and capture of the southern part of the Colo rado Plateau by the ancestral Salt and Gi la ri vers in late Miocene or more likely in the Pliocene (Cooley and Davidson, 1963; McKee and McKee, 1972). Establishment of a sharp drainage divide with uplift on the Mogollon Rim in mid-Pliocene may have provided effective isolation, and the upper Verde basin was diverted south by uplift of the Black Hills (fig. 9) at about this time (Lehner, 1958 ; Cooley and D avidson, 1963). Access from the west obvi ously could not have occurred prior to cutting of the lower Colorado River and may have been blocked for a time by the Pliocene Bouse Embayment (Hamilton, 1960 ; Metzger, 1968; Lucchi tta, 1972). M iller ( 1961a) suggested that the distinctive fauna of the Gila River indicated a rather recent connection with the Colo rado River. However, for part of the Pliocene, the lower basin must have been accessible to chubs from that direction. Events in later Pliocene agai n cut off much of the upper part of the ancestral Gila Ri ve r basin from the Colorado mainstream, and provided isolation for differentiation of the chubs. Lacustrine and fluvial material were deposited to depths exceeding 600 m in the extensive structural trough, partially a graben, that bounds the Colorado Plateau from the mouth of the Grand Canyon to northern Chihuahua, Mexico ( Brand, 193 7; Feth and Hem, 1963 ; Feth, 1964). Surface elevations of these deposits are remarkably similar throughout the a rea, and fo ssil s included in a number of them correlate well (Taylor, 1963; Feth and Hem, 1963) suggesting their synchrony. Paneling of the ri vers was ef fected by extrusion of volcani c materials and uplift in the lower Salt R iver area (fig. 9) east of the present city of P hoenix (Melton, 1960, 1965) . At 98 THE \VA SMANI'\ J OURNAL OF BIOLOGY, VoL. 34, No. I, 1976 SUMMARY D ata on more than 1,500 speci mens of ch ubs from the lower Colorado River basin, and several hundred from northern M exico and several tributaries of the middle Colorado River were analyzed. Complex , enigmatic patterns of vari ation in morphometries and meristics of chubs in the first basin dictated co mparison with ri ve rs of the other two regions and correlation of these data to habitat conditions, ecological information, changes in recent and ancient drainages, and the " ecotypic" concept of so me members of this genus in the lower Colorado basin. An a rti ficial key and synonymies to the species of Gila in the lower Colorado River basin are con structed. A rationale for taxonomic decisions of each species or subspecies and distributional maps are provided. Four forms of the genus Gila appear to be indigenous to the lower Colorado basin (five, if an archaeological record of G. cypha M ill er from Catclaw Cave, iVIohave County, Arizona [Miller, 1955] is included ). Gila elegans, although once widespread in the Colo rado River basin, is restricted to that portion of the drainage above Lake Mohave. Both this species and G. cypha were not considered pertinent to this study . Gila 1·. Tobusta is ·widespread throughout the Colorado basin and li ves in the Bill Willia ms drainage, the mainstream of the Verde, and the Salt River system. Problematic populations, formerly considered intergrades between G. intermedia and G. r. Tobusta are interpreted as a di stinct subspecies of G. ro busta on the basis of morphometric and meristic data, character combinations, lack of " ecotypy," and co rrelation of vari ations with drainage hi story. This resurrected form , inhabits the Verde Ri ver tributaries and the upper Gi la River system . G . intennedia, a Gi la River endemic, is elevated to specific status and is known onl y from isolated habitats in central and southern Ari zo na. A CK NOWLE DGMENTS This is, in part, a study presented to the Graduate School at Ari zo na State University in partial fulfi lment of the requirements of Master of Science in zoology. I wish to express my indebtedness to Robert R. Miller, \Y illiam ]. Koster, and Charl es H. Lowe of the Universities of Michigan, New M exico, and Arizo na, respec tively, for pe rmitting me to bo rrow speci mens or enter thei r mu seums. Funds to \V. L. l\1inckley from the U ni ve rsity Grants CYPRINJD FISHES-RINNE 95 this time the upper Gila River (not including the reach east of Safford ) may have joined the Salt R iver north of the present town of Globe. An extension of the extru sives to the north along the Verd e impounded that stream (Jenkins, 1923) and to the east of Florence, the San Pedro segment of the basin was similarly isolated. The Santa Cruz and other lesser rivers entering the lower Gila valley vvere scarcely affected and flowed far wes t to enter the drain age. The upper Gila River, above Safford, was not ap parently integrated to the west until mid-Pleistocene, after the onset of incision of the volcani c dams, and prior to that time presum ably fl owed south into a closed basin ; or perhaps into lVl ex ico (Morri so n, 1964 ; Cooley and D avidso n, 1963; i\Ielton, 1965; Kottlowski et al. , 1965 ) . The ancestor of Gila intermedia co uld have di spersed into north fl owi ng tributari es of the ancestral Gil a basin at almost any time in the Pliocene or Pleistocene and remained in relatively small headwater situations to the south and west of the l\Iogollon High lands moving into that region as dissecti on (down-cutting) pro gressed. General distribution of this fish in recent times in the southern tributaries of the Gila ( fi g. 1), perhaps refl ects movement over lowered di vides resulting from all uviation of valleys between the Sa nta Cruz and San Pedro rivers in the Pleistocene (Melton, 1965) or co nceivably, actual riding of land masses themselves (An derson, 1970 ; Elders et al ., 1972). The occurrence of C. inter·m.edia in the ex treme upper Verde may result from a diversion of part of the Agua Fria River to the Ve rde in the area east-northeast of Prescott (Chino Va ll ey) . Little preserved material of Gila (two uncataloged specimens available to me) is known from the Agua Fria. These two fi shes are unmi stakably C . inten nedia. They are identical with specimens seen and id entified by W. L. Mi nckley (personal communication ) in 1966. Recently they have been re ported by Forest Service personnel (personal communication to lVI inckley) in that same stream. Cutting of dams that blocked the rivers was initiated in earl y mid-Pleistocene with cessation of vulcani sm and upli ft at points of damming. Breaching of dams reinteg rated much of the system ; base levels in the alluviated vall eys we re high above that of the lower part of the system and further down-cutting p rogressed fairl y rapidly . This deg radation left remn ant populations of fi shes, 96 THE WASMANN JOURNAL OF BIOLOGY, VoL. 34, No. 1, 19i6 including C. r. grahami, above fall s of small tributaries. ::vlovement of downstream populations, presumably C. r. robusta by this time, al so was possible and they invaded upstream and largely displaced the former isolate, C. 1·. gmhami. An obvious alternative to the interpretations given so far is sec ondary contact and hybridization ( Mayr, 1963: 502 ) between a Gila River endemic (C. intermedia), and an upper basin form (C. robusta). This cannot be completely rej ected. If true, however, the hybridization must predate cutting of the lake beds (m.i d earl y Pleistocene) since C. r. graha-rni now persists in hanging tribu taries (viz., above barrier falls) of the Verde system (i .e., Fossil Creek) and shows remarkable homogeneity in morphology and me ristics over a di verse spectrum of habitats, and in re lation to time. Present intergraclation between two subspecies (C. T. Tobusta and C . r. intennedia) also may generally be rejected on the same bases. No current zones of sympatry between C. robusta and C . intermedia are known but some old er records (e.g., Gilbert and Scofield, 1898), indicate local sympatry in complex habitats. The intermediate form, C. grahami, may show differentiation fr om place to place, a possible indication of isolation above clams of the different rivers during Plio-Pleistocene impoundment. These variations seem inde pendent of the proximity of C. intennedia. Variation within C. intennedia is highly localized ('i.e. , Monkey Sp rings), and in the case of C. T. robusta, seems attributable to intergraclation from C. r. grahami populations, or phenotypic response to local environ men tal conditions. The proposed origin of C. ·intermedia from the south is sub stantiated by its apparent relati onships to chubs of the l\ Iex ican Plateau. Related species of the adjacent, so uthern and eastern basins include C. ditaenia Miller from the basin of the Rio de Ia Concepcion, Arizona and Sonora, and the R.i o Sonora, Sonora; C. nigrescens (Girard ) from the co mplex Guzman basin, New :\Iex.ico and Chihuahua; and C. pandora (Cope) from the R.i o Grande and Pecos basins, New Mexico and Texas. All are large-scaled , thick bodied, darldy pigmented fi shes with relatively low scale and fin-ray counts (table 3), quite unlike C. robusta and its relatives, and very simi lar to C. intennedia. All of these, plus C. orcutti (Eigen mann and Eigenmann ) of coastal streams of so uthern Cali fo rn ia, CYPRll'\ ID FISHES-RINNE 97 we re consid ered by Uyeno ( 196 1) to have originated from the " ancestral form that gave ri se to C. 1·. intennedia in the Gila Rive r. " If populations of C. ·intermedia are more cl osely related to those of the south, as proposed here, then they are most likely derived from captures in volving north-flowing tributaries of the Gila River, or perhaps earlier as part of an ancient fauna of the original south west trending stream systems. H owever, shifting of land masses along coastal areas of western Mexico and Baja Cali forn ia cannot be ruled out completely as a means of dispersal. Connections of the upper Gila River segment to the Guzman basin of northern Chihuahua (Cooley and D avidson, 1963; Weber, in Kottlowski et al., 1965; Melton, 1965) is not supported by evidence from the ichthyofauna. Gila 11igrescens of the Guzman basin is quite simn ar to C. intermedia, differing mostly in having 9 dorsal fin-rays rather than 8. Yet, no species and few genera are in common between the Gila and Guzman systems, the latter having principally a Rio Grande assemblage of native fi shes, whereas the Gila River basin is occupied by a disti nctive, highly endemic fauna (Miller, 1958) . One aquatic organi sm, a unionid clam, Anodonta californiensis Lea, known from a number of western drainages as fo ssil or living material (Taylor, 1963), is present in both the Gi la and Guzman basins. Its absence from adjacent southern systems may, however, reflect a lack of collecting (D. \V. T aylor, personal communication ) . T he Rio Yaqui system and other minor coastal drainages of Sonora, Mexico, share a number of ichthyofaunal elements with the Gila (Meek, 1904; Miller, 1958) . These are Agosia cj. chryso gaster (Girard) , Poeciliopsis occidentalis (Baird and Girard) , and other pairs of species tha t are cl osely related : Catostom.us insignis Baird and Girard and C. bemardini Girard; C. robusta and C . minacae Meek ( = C. robusta? ; Miller 1958) , and another Gila that may be near G. interm edia ("C. nigrescens" of Meek 1904, in part; dorsal and anal fin-rays 8, scales in the lateral seri es 60- 7 5). Also , a number of Rio Grande fi shes have penetrated the Rio Yaqui (e .g., iVotropis, Campostorna, Pimephales, l ctalU1·us ), presumably from the Gu zman basin and/ or from the Rio Co nchos. T he absence of these in the Gi la River, es pecially some of the more aggressive, upland minnows, indicates an invasion of the Yaqui that postd ates any large faunal exchange between that drainage and the lowe r Colorado basin . 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