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We discuss the roles of gene flow, genetic drift, and selection in determining the distribution of genetic variation in complex, real-world landscapes. A metapopulation is a group of populations that experience some degree of gene flow among them. Metapopulation structure can have complex effects on patterns of genetic variation within and among populations. For species that do not naturally occur in discrete habitat patches, a landscape genetics framework is more appropriate. Landscape genetics combines population genetics, landscape ecology, and spatial statistics to understand how environmental heterogeneity affects gene flow and genetic variation. Habitat loss and fragmentation have severed connectivity among populations of many formerly continuous species, isolating populations that then lose genetic variation due to reduced gene flow. Genetic rescue, the supplementation of small inbred populations with immigrants from larger more genetically diverse populations, can be used to increase genetic diversity and reduce extinction probabilities of populations isolated by habitat fragmentation.

The risks of inbreeding and outbreeding depression, and the prospects for genetic rescue are often different in species with alternative mating systems and mode of inheritance (compared to outbreeding diploids), such as self-incompatible, self-fertilizing, mixed mating, non-diploid (haploid, haplodiploid and polyploid) and asexual.

Having identified small geographically and genetically isolated populations, we need to determine whether they are suffering genetic erosion, and if so, whether there are any other populations to which they could be crossed. We should next ask whether crossing is expected to be harmful or beneficial, and if beneficial, whether the benefits would be large enough to justify a genetic rescue attempt. Here, we address these questions based on the principles established in the preceding chapters.

Evidence of population structure and limited gene flow often leads to the questionable conclusion that populations should be managed as separate unit. A paradigm shift is needed where evidence of genetic differentiation among populations is followed by an assessment of whether populations are suffering genetic erosion, whether there are other populations to which they could be crossed, and whether the crosses would be beneficial, or harmful, and if beneficial, whether the benefits would be large enough to justify a genetic rescue attempt. Here we address these questions based on the principles established in the preceding chapters.

The growing commitment of zoos to address accelerated rates of extinction and losses of biodiversity utilizing the populations they manage has led to the exploration of options to rescue species from extinction, including advanced genetic and reproductive technologies. The availability of banked viable cell cultures, such as those held in collections like San Diego Zoo Global’s Frozen Zoo® and other facilities, may ultimately provide resources to reduce extinction risk of species for which appropriate samples have been collected. This resource may provide options for genetic rescue, restoration of lost genetic variation to contribute to population sustainability, and for some species, may be the only means of preventing their extinction. In an era of declining biodiversity and expanding scientific capabilities, a new relationship with nature stands to emerge. Genetic techniques such as whole genome sequencing and genetic engineering, and alliances of these technologies with advances in cell and developmental biology, especially stem cell biology, now portend a new form of husbandry that may enrich and sustain some species. It is timely to evaluate and apply advances in animal biosciences to endangered species conservation in the fight against extinction.

Genetic management of fragmented populations is one of the major, largely unaddressed issues in biodiversity conservation. Many species across the planet have fragmented distributions with small isolated populations that are potentially suffering from inbreeding and loss of genetic diversity (genetic erosion), leading to elevated extinction risk. Fortunately, genetic deterioration can usually be remedied by augmenting gene flow (crossing between populations within species), yet this is rarely done, in part because of fears that crossing may be harmful (but it is possible to predict when this will occur). Benefits and risks of genetic problems are sometimes altered in species with diverse mating systems and modes of inheritance. Adequate genetic management depends on appropriate delineation of species. We address management of gene flow between previously isolated populations and genetic management under global climate change.

Genetic management of fragmented populations is one of the major, largely unaddressed issues in biodiversity conservation. Many species across the planet have fragmented distributions with small isolated populations that are potentially suffering from inbreeding and loss of genetic diversity (genetic erosion), leading to elevated extinction risk. Fortunately, genetic deterioration can usually be remedied by gene flow from another population (crossing between populations within species), yet this is rarely done, in part because of fears that crossing may be harmful (but we can predict when this will occur). We address management of gene flow between previously isolated populations and genetic management under global climate change.