7986

• UCREFRP Catalog Number: 7986
• Author: Allendorf, F. W.
• Title: Conservation Biology of Fishes
• USFW Year: 1988
• USFW - Doc Type: Conservation Biology
• Copyright Material: YES

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Notes

Delay of Adaptation to Captive Breeding
by Equalizing Family Size

FRED W. ALLENDORF

Division of Biological Sciences
University of Montana
Missoula, MT 59812, U.s.A.

Introduction

Captive breeding programs have been initiated with
many species that are threatened in the wild. One ob-
jective of these programs is to maintain the genetic
characteristics of the population in order to maximize
the probability of success when the population is intro-
duced back into the wild (Frankham et al. 1986).
Two major types of harmful genetic c~~~S. aulpCCUC
during ca. Ptivity.1..2!l-. e. ~;=~~e~uen=.
d'~. .' """"'.. '-'--"-LU'''.~.-.'lh . Pti~Ai
andtheI'!~~c~ti~n., 0' "'~h"
The seco~d ',is" . tion to captivity through natural
selection; that is, those genotypes best suited for sur-
vival and reproduction in captivity will tend to increase
in frequency. Darwin (1868) pointed out that natural
selection for tameness and other adaptations to the cap-
tive environment is inevitable. Characteristics selected
for under captivity generally are disadvantageous in the
natural environment (Spurway 1952; Kohane & Parsons
1988 ).
Most recommendations on the genetic management
of captive populations have been concerned with the
effects of genetic drift. Genetic drift can be minimized *
by increasing effective population size. This is the size of
an ideal population that has the same rate of increase in
homozygosity or gene-frequency drift as the actual pop-
ulation under investigation (Crow & Denniston 1988).
ffistimates of effective population size assume that the
.'genetic variation under consideration is selectively neu-
l. (tral--does not affect survival or reproductive success.
Differences in reproductive success among individu-

Paper submitted August 1, 1991; revised manuscript acceptedAugust
27, 1992.

416

Conservation Biology
Volume 7, No. 2,June 1993

als have an important effect on effective population size.
In general, for a population of constant size,

4N- 2
Ne = 2 + Vk

where N is the variance effective population size, N is
e . .
the census population size, and Vk is the variance 10
progeny number (Crow & Denniston 1988). Under cap- ,..
tivity, where differences in reproductive success aul
sometimes be controlled, the effective population size
can actually surpass the census size of a population. For
example, if reproduction is restricted to equal-sized full-
sib families with each male and female parenting a single
family, then Vk will be zero and the effective population
size will be nearly double the census population size

(Equation 1).
Reducing differences in family size will also diminish .*
the effects of selection in captivity. There will be no
reproductive differences between individuals if all ind.i-
viduals produce the same number of progeny. Ut'this *
situation, natural selection will operateQI1lY~:~~fP1
differences in relative survi~f different genotypes
within fainilies of full- or half-sibs.
TIlls ~ectmay be especially important for organisms
th.at have~large family sizes. ,Rapid adaptive changes to
captivity have been documented in many species of fish
(see Moyle 1969; Verspoor 1988; Swain & Riddell 1 99(f;
Johnsson & Abrahams 1991). As expected, hatchery fish
generally do not fare well in natural conditions in com-
parison with wild fish when environmental differences
are eliminated (Fraser 1981; Chilcote et al. 1986;
Lachance & Magnan 1990). There is evidence for rapid
adaptation to captivity in insects as well. Myers and Sa-
bath (1980) have shown that minimum time in captivity

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