8238

• UCREFRP Catalog Number: 8238
• Author: Douglas, M. E., W. L. Minckley and B. D. DeMarais
• Title: Did Vicariance Mold Phenotypes of Western North American Fishes? Evidence From Gila River Cyprinids
• USFW Year: 1999
• USFW - Doc Type: Evolution
• Copyright Material: YES

VICARIANCE AND WESTERN NORTH AMERICAN FISHES

239

.

ARIZONA

SONORA

o 50 100
1l"".....""lIj..........1
scale, km

N

I

~!
If!
j1 : NEW MEXICO
.
R.{{ /.~ .1' \
~upper !
Ii .\..-~:."en ~~dro ! _.._......._._.

--...------- --;l~~-----------?-...---.i~~-;~~::A

FIG. 1. Sketch map showing the distributions of collecting locales for roundtail (Gila robusta, dots); Gila (G. intermedia, squares); and
headwater (G. nigra, diamonds) chubs in the Gila River basin of southwestern North America; for locality data see Rinne (1969) and
DeMarais (1986).

MATERIALS AND METHODS

Study Region

The southern part of the Gila River Basin (Fig. 2) includes
streams flowing north from highlands associated with the
Sierra Madre Occidental of Mexico. This area is dominated
by basin-and-range topography, a series of northwest-to-
southeast-trending mountain ranges separated by parallel val-
leys through which rivers flow. Isolated peaks rise higher
than 3000 m, whereas valley floors rise from a few meters
above mean sea level (MSL) in the west to ~ 1000 m in the
east. Northern (south-flowing) tributaries of the Gila River
originate on the southern escarpment of the Colorado Plateau,
dissecting a zone of highly variable relief. The southern edge
of the transition zone from plateau to basin-and-range ap-
proximates the former plateau margin migrating northward

through erosion and faulting (Elston 1984). The present es-
carpment, termed the Mogollon Rim in Arizona, lies -1700
m above MSL, with higher peaks of volcanic origin (Kottlow-
ski et al. 1965). Geologic events shaping the region were
reviewed relative to fish biogeography by Minckley et al.
(1986).

Specimens and Data Collection

Data were compiled from 1106 adult Gila (standard length
[SL] > 50 mm) from 33 sampling sites; at least 25 fish were
examined from each locale (DeMarais 1986). For present
purposes we partitioned the Gila River Basin into seven sub-
basins (Fig. 2A; numbers of localities in parentheses): Santa
Cruz (4); upper San Pedro (4); lower San Pedro (2); Gila (4);
Verde (7); Salt (6); and Agua Fria (3).