9327

• UCREFRP Catalog Number: 9327
• Author: Starnes, W. C.
• USFW Year: 1995.
• Copyright Material: NO

in the Gila Basin, and, indeed, the Colorado Basin overall,
renders it impossible to unequivicobally reject the hypothesis
that they constitute a single, ecophenotycally diverse species,
the amount and patterns of allelic variation reduce that
liklihood.
The lack of homogeneity is not consistent either with
expectations among populations which have responded to their
respective environments agenetically, such as through adjustments
along developmental pathways as might be expected of an
ecophenotype. Under an ecophenotypic concept, without the
piecemeal amalgamation of separately evolved allozyme alleles,
one might predict only gentle geographic clinal variation in
frequencies rather than the complex pattern observed. Rinne
(1976) and DeMarais (1986) have pointed out numerous
inconsistencies among phenotypes that would be predicted under
this concept, as well as for ecotypy, for given habitat types and
those that actually exist.
Data presented herein are consistent with hypotheses of
widespread introgression among Gila populations inhabiting the
lower Gila Basin and possibly the Bill Williams system but do not
corroborate these beyond a shadow of a doubt. This is so because
marker alleles cannot be identified in populations outside the
zone of sympatry (in the broad sense) for the individual taxa
(i.e., robusta, intermedia) involved; allopatric populations of
robusta-like chubs in extralimital (e.g., upper Colorado) areas
generally contain all alleles which occur in samples from
throughout the area of sympatry where putatively introgressed
populations occur; intermedia, as presently construed, does not
occur outside that area, so no comparisons are possible. One
possible marker for intermedia does occur at the LDH-B locus
(Fig. 9), also mentioned by DeMarais (1992) as having a high
association with that form in the only habitat where both forms
are parapatric (Eagle Cr. of upper Gila). The 11111 allele occurs
only in the Gila portion of the Colorado Basin and occurs only in
populations classified on morphology by recent workers (Rinne,
1976, DeMarais, 1986; Douglas, herewith) as intermedia except for
the lower Eagle Creek population. However that allele is
confined to the southeastern headwaters portion of the Gila. If
it was formerly unique to the intermedia morphotype, then it has
been completely swamped and displaced by the 11211 allele in some
populations of that area and in all Gila populations in more
westerly portions of the Gila Basin, which are comprised of
either intermedia or robusta morphotypes or intermediates.
Alternately, this allele might be construed as a relatively
recent regional mutant which has achieved somewhat limited
dispersal among populations or a novel allele which has arisen in
the course of hybridization though a simple base substitution in
the DNA sequence coding for the allele (sensu Bradley et al.,
1993).
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