7998

• UCREFRP Catalog Number: 7998
• Author: Desert Fishes Council, G. a. S., ed.)‎.
• Title: Proceedings of the Desert Fishes Council Volume XXVII, 1995 Annual Symposium.
• USFW Year: 1996.
• USFW - Doc Type: November, 16-19.
• Copyright Material: NO

DFC PROCEEDINGS - CONnuBurm PAPER
for G. gaigei, 47 days for G. heterodiir, and 52 days
for G. nobihs.
Numerous interbrood intervals were
recorded for G. of j5?nis and G. geiseri. The
maximum number of broods for an isolated G.
affinis female was 5 (4 interbrood intervals) and 4
(3 interbrood intervals) for isolated G. geiseri
females. A larger fraction of the isolated G. affinis
females attained 5 broods than isolated G. geiseri
females attained 4 broods. Commonly, the last
G. geiseri brood had one young while the last G.
affinis brood had a normal number of young.
Females of both species have been held in
isolation for more than three additional months
without producing more broods.
Discussion
Populations of Gambusia affinis vary widely
in predation on newborn, birth weight, and
interbrood intervals. Populations of G. geiseri also
vary in each factor but at a reduced rate.
Populations of G. nobilis vary in predation and
birth weight. The degree of variation is
substantially greater for G. of finis than for most
introduced populations of G. geiseri. The amount
of variation for G. nobilis is less certain, primarily
due to relatively small sample sizes. Several
locations have samples of two or three species.
The variations of life history traits are not
concordant, thus demonstrating that the variation
is internal to the species (genetic) and not
controlled by the habitat (environmental). For
example, I have data on populations from
Phantom Cave and Diamond-Y Refugium for all
three species and all three traits: Birth weight: G.
afflnis heavy at Diamond-Y, G. nobilis and G.
geiseri heavy at Phantom Cave. Interbrood
interval: G. geiseri long at Phantom Cave, G. affinis
and G. nobilis long at Diamond-Y. Cannibalism:
G. of j"inis extensive at Phantom Cave, G. geiseri
extensive at Diamond-Y, G. nobilis virtually the
same.
This report includes comparisons of
variation in life history traits for three factors for
two species and two factors for one species. All
eight vary sufficiently to provide unusual data if
one population were to represent the species. For
example, G. affinis female conspecific predation is
about 30% survival, G. geiseri predation on G.
affinis is about 20% survival, and G. nobilis
predation on G. affinis has about 9% survival. In
contrast, however, if G. affinis were to be
represented exclusively by Falcon females, G.
geised and G. nobilis by Balmorhea females, the
survival rates would be 0% (versus 30%), 12%
(versus 2096), and 14% (versus 9%), a reversal of
the relative predation rates for the three species
as a whole. Similarly, birth weights of newborn
Poecilia can vary by species depending upon the
population used.
Predation rate is associated with birth weight
and interbrood interval by species. The most
predaceous species, G. nobilis, has the heaviest
young and takes longer between broods.
Conversely, most populations of G. afrnis have
low predation, lighter young and shorter
interbrood intervals. The interspecies
correlations do not extend to population studies.
Contrasts look like a shot gun blast.
Similarly, the birth weight and interbrood
intervals for the species as a whole can be
reversed by the use of selected populations of G.
affinis and G. geiseri.
Stockwell (1995) showed that introduced
populations of G. affinis in Nevada varied in
minimum size of female maturity and fat content.
His populations were introduced about 55 years
ago from central Texas. They were initially
introduced into one location and then transferred
to four others. Two populations were from
thermally stable environments, one from a warm
spring, and one from a thermally unstable
environment. The two from thermally stable
environments were similar to each other and
differed substantially from those from the
unstable environment; the warm spring
population was intermediate. He found other
differences in field samples that did not recur in
laboratory experiments.
These results resemble those reported by
Stearns (1983) who showed that introduced
populations of Gambusia of finis in Hawaii varied
in fecundity and in the dry weight of females and
of embryos. All of the stocks he analyzed had
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