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166 Conservation Genetlcs of Desert Fishcc
<br />tionists," attempting to develop and implement a policy
<br />that would restore a system to an approximation of its
<br />former self. In a stream hierarchical system that has un-
<br />dergone radical changes to the point that some natural
<br />populations are extinct and others are artificially iso-
<br />lated, we favor restoration of gene flow and diversity to
<br />mimic the natural situation, rather than maintaining an
<br />unnatural and zoogeographically perverse "status quo."
<br />Estimates of effective migration rates from genetic struc-
<br />ture statistics can give us a rough guideline for the ex-
<br />tent of gene flow that should be considered.
<br />3. Test the relative roles of genetic adaptation and
<br />developmental plasticity in local phenotypic differert-
<br />tiation, Desert fishes are notorious for phenotypic dif-
<br />ferentiation among localities (Miller 1948; Minckley
<br />1973). This differentiation may be the result of genetic
<br />differences or plastic developmental processes influ-
<br />enced by the local environment. Identification of the
<br />causes of phenotypic differentiation is important to
<br />management of individual populations. If differentiation
<br />is genetic, it is critical to maintain the diversity repre-
<br />sented by differences among colonies (D~). If differen-
<br />tiation is simply a plastic response to local conditions,
<br />then a particular phenotype may be induced from a
<br />broad range of genotypes by creating the proper envi-
<br />ronment. The latter may occur in a goodeid fish in Mex-
<br />ico (Turner et al. 1983), a cichlid in Cuatro Cienegas,
<br />Mexico (Kornfield et al. 1982; Liem and Kaufman
<br />1984), several African cichlids (Greenwood 1965), and
<br />Artic charr (Vrijenhoek, Marteinsdottir, and Schenck
<br />1987). Thus, we need critical experiments that separate
<br />true genetic differentiation (local evolutionary change)
<br />from simple environmental induction of unique morphs.
<br />A Final Question
<br />We conclude by raising a question, one that we cannot
<br />definitively answer but one that is critical to all conser-
<br />vation programs. What are our objectives in conserva-
<br />tion biology? Specifically, what should we conserve?
<br />Species? Subspecies? Individual populations? Unique al-
<br />leles? This is a difficult question, and perhaps the most
<br />important philosophical issue facing us, for we cannot
<br />design effective conservation programs until we identify
<br />specific goals.
<br />The answer may depend upon the organism of con-
<br />cern, and economic constraints. For a tiger or rhinoc-
<br />eros, we may have to settle for a representative type of
<br />the species, for it may be difficult to do otherwise, since
<br />natural and financial resources are limiting. It is also
<br />unrealistic to expect to conduct experimental work on
<br />the genetic structure of such taxa. However, we can do
<br />much more with desert fishes. It is far less costly to
<br />maintain regional, local, or even allelic diversity in these
<br />fishes-they can be easily manipulated, local habitats
<br />McBe and Vdje~iltcek
<br />are available or can be made available, and fish can be
<br />kept in small refugia such as hatcheries or even aquaria.
<br />!n particular, the Sonoran topminnow is a model or-
<br />ganism with which to develop a conservation program
<br />with a sound genetic basis. The topminnow is more
<br />abundant than many endangered species, and much is
<br />known about its ecology, physiology, and genetics
<br />(Constantz 1975; Minckley, Rinne, & Johnson 1977;
<br />Schoenherr 1977; Bulger & Schultz 1982; Meffe 1984,
<br />1985; Vrijenhcek, Douglas, &Meffe 1985). It is easy to
<br />raise in captivity and hardy under field and experimen-
<br />tal conditions. Concerted efforts in recovery of this spe-
<br />cies, currently underway by several groups, could ben-
<br />efit other endangered species programs by developing
<br />sound management schemes, including application of
<br />genetic principles and field and laboratory experimen-
<br />tation of fitness responses to management prograns.
<br />With this species at the forefront, we have an excellent
<br />opportunity to restore an entire endangered fauna to
<br />some semblance of its historical condition; as conserva-
<br />tion biologists, this should be our goal.
<br />Acknowledgments
<br />We thank M. E. Douglas for his efforts in fieldwork and
<br />analysis of original P. occidentalis samples and J. B.
<br />Coleman and L. Orebaugh for assistance with figures.
<br />Two anonymous reviewers raised important points for
<br />clarification. GKM was supported by contract DE-
<br />AC09-76SR00-819 between the U.S. Department of En-
<br />ergy and the University of Georgia. RCV was supported
<br />by National Science Foundation grant BSR86-00661.
<br />Liter~ttrre Cited
<br />Allendorf, F. W. 1983. Isolation, gene Ilow, and genetic differ-
<br />entiation among populations. Pages 515 in C. M. Schone-
<br />wald-Cox, S. M. Chambers, B- MacBryde, and L Thomas, edi-
<br />tors. Genetics and Conservation: A Reference for Managing
<br />Wild Animal and Plant Populations. Benjamin/Cummings,
<br />Menlo Park, California.
<br />Brooks, J. E. 1986. Status of natural and introduced Sonoran
<br />topminnow (Poeciliopsls o occrdentalss) populations in Ari-
<br />zona through 1985. Report to Offices of Endangered Species
<br />and Fishery Resources, U.S. Fish & Wildlife Service, Albuquer-
<br />que, New Mexico.
<br />Bulger, A. )., and R J. Schultz. 1.982. Origin of thermal adapta-
<br />tions in northern versus southern populations of a unisexual
<br />hybrid fish. Evolution 36:1041-1050.
<br />Cokendolpher, J. C. 1980. Hybridization experiments with the
<br />genus Cyprinodon (Teleostei: Cyprinodontidae). Copeia
<br />1980:173-176.
<br />Constantz, G. D. 1975. Behavioral ecology of mating in the
<br />male Gila topminnow, Poeclliopsis occiderttalis (Cyprinodon-
<br />tiformes: Pceciliidae). Ecology 56:966-973.
<br />Conservation Biology
<br />Volume 2, No. 2, June 1988
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