9613

• UCREFRP Catalog Number: 9613
• Author: Desert Fishes Council.
• Title: Proceedings of the Desert Fishes Council Volume XXVII 1995 Annual Symposium.
• USFW Year: 1995.
• USFW - Doc Type: Ingram, Texas.
• Copyright Material: NO

DFC PROCEEDINGS - CONTRIBUTED PAPER
Traditionally, reports on biological problems
emphasize the species studied. Some reports,
mostly recent, have demonstrated intraspecific
variation of life history traits. The classic lizard
studies by Tinkle (1969) have shown that
variation correlated with environmental factors
such as the latitude at which the stocks lived. A
few fish studies (Haskins et al., 1961; Houde,
1988; Foster, 1994; Endler and Houde, 1995;
Reznick et al., 1996; Reznick and Bryga, 1996)
have shown variation in reproductive or
predatory activities. Previously, I have shown
that populations of Gambusia affinis vary in
predation on congeneric newborns (Hubbs, 1992)
that can be called cannibalism (Hubbs, 1991). In
this report I expand on those data by using two
other life history traits: birth weight of young and
time between broods from females isolated from
males. I also expand the number of species used
for interpopulation comparisons to include
Gambusia geiseri and G. nobilis. This report also
includes comparable data on one population of G.
speciosa, G. senilis, G. longispinis, G. sp., G.
heterochir, and G. gaigei. The last three species
have (or had) limited geographic ranges and
consequently only one population could be used.
Six of the species (G. nobilis, G. speciosa, G.
longispinis, G. senilis, G. gaigei, and G. sp.) are
native to the Chihuahuan Desert and five are
listed as endangered by the appropriate federal
government (all but the extinct G. sp.).
Gambusia minis is widely distributed in the
south-central North America. It is used
extensively by public health agencies as a
biological control for mosquitos. It is possible
that some of my populations may have been
introduced (one certainly has), but the
intraspecific variation in three life history traits
suggests limited replacement of native
populations by introduced stocks.
Gambusia nobilis occurred in several spring-
fed waters in the Pecos valley of West Texas and
eastern New Mexico. Presently it occupies two
New Mexico areas: Blue Spring and the Bitter
Lakes National Wildlife Refuge. It also occurs in
two areas in Texas: Diamond-Y Spring and the
spring complexes around Balmorhea (Hubbs and
Springer, 1957). I have samples from all of these
regions except Blue Spring. Two, Bitter Lakes
and the Balmorhea complex, have two or more
separate populations studied.
G. geiseri occurred in two spring areas in
Central Texas: Comal and San Marcos springs.
Some time about 1930, stocks were widely
released elsewhere in Texas, presumably by public
health agencies (Hubbs and Springer, 1957).
Consequently, I have data on native
populations of two species (G. affiinis and G.
nobilis) and data on two native populations and
six introduced sixty years ago of a third species
(G. geiseri).
Materials and Methods
Stocks were obtained from 48 populations of
Gambusia af"inis, 7 of G. nobilis, 10 of G. geiseri,
and one each of the other six species (Table 1).
Five populations had only adults used.
Additionally, predation studies were also
performed using Poecilia young. Most of the
samples were from widely-distributed localities in
Arizona, New Mexico, Texas, and Arkansas (Map
1). Several localities were relatively close
together (Map 1, Insets). The fish were brought
into the Austin laboratory and fed heavily with
Tetra Min and Drosophila larvae and adults.
Predation studies: Three to twenty newborn
young were randomly isolated in aquaria with one
adult that had been in the laboratory at least one
week. Each aquarium (49 by 15 by 17 cm
(deep)) had an airstone and a series of snails
(Physa) that could consume excess food and
provide supplemental food for the fish (Hubbs,
1990). Each experiment was fed ca. 20% of total
fish biomass daily with flake food and with
Drosophila larvae. The surviving young were
counted 31 days later. About 7% of the
experiments had no adult at the end of the 31-
day interval; those experiments were excluded
from the predation data presentations (Table 2).
Gambusia seldom live more than two years, and it
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