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Habitual self-fertilization by hermaphroditic individuals is a sexual route by which genetically identical individuals can arise. The phenomenon occurs in various plants and invertebrates but is known in only one vertebrate species: the mangrove killifish. Selfing is an extreme form of inbreeding (even less severe cases of which often result in inbreeding depression), and for this and other reasons constitutive self-fertilization is rare in the biological world. Instead, most selfing species also outcross occasionally, and thus have a mixed mating system. Habitual selfers nevertheless have some special adaptive advantages not shared by their sexual counterparts. This chapter compares population-genetic and ecological features of mangrove killifish with those of analogous plants and invertebrate animals that likewise have mixed-mating systems. Such species probably gain the best of two worlds by capitalizing jointly on the short-term advantages of selfing (fertilization assurance, and the propagation of fit “clonal” genoypes) and also the long-term as well as short-term advantages of outcrossing (genetic health and adaptability).

This chapter focuses on Allee effects in relation to genetics and evolution. These topics intersect in four different ways. First, genetics creates its own set of Allee effect mechanisms (e.g., via inbreeding depression). Second, there may be genetic differences among members of a population in their susceptibility to ecological Allee effects. Third, Allee effects are considered in the light of evolution — have populations evolved mechanisms to avoid Allee effects, and if so, how is it possible to find anything other than the ‘ghosts of Allee effects past’ in modern populations? Finally, Allee effects themselves may act as a selection pressure, and members of populations subject to Allee effects may thus evolve different characteristics as compared with those bounded only by negative density dependence. The chapter considers all these four issues in turn.

Although much is known about the consequences of sexual abuse and the characteristics of the individuals and families involved, these pieces of information have yet to be arranged to form a clear picture of why sexual abuse occurs. This chapter provides an account of how an evolutionary computational framework can help organize what is currently known about sexual abuse and provide a set of answers to the question of why it happens. It focuses specifically on one component of our evolved psychology hypothesized to play a significant role in explaining why sexual abuse occurs: inbreeding avoidance mechanisms. Identifying the cues our evolved psychology uses to detect kin and generate sexual aversions towards them can help illuminate why sexual aversions fail to develop, leading, in some circumstances, to an increased risk of incest or sexual abuse within the family.

The guppy raises three different classes of conservation issues. First, the species is a useful model for freshwater fish species — one of the most endangered vertebrate groups. Second, although guppy populations are generally large and the species is widely distributed across Trinidad, some of the diversity that has provided such rich material for evolutionary biology is under threat from pollution, habitat loss, exotic introductions, and so on. Guppy populations are also potentially at risk from scientists who observe, collect, and manipulate guppy populations. Artificial introductions have proved very informative but may lead to irreversible changes in a river. Finally, introductions of guppies to countries outside their range, either for the control of malaria vectors, or through escapes of ornamental fish, can adversely affect vulnerable faunas. This chapter discusses these issues.

This chapter begins with a brief introduction to the focus of this book, which is the idea that extinction of species is somehow related to loss of genetic variation. Theoretical considerations suggest that small — that is, endangered — populations are different from large ones in two important aspects. The level of inbreeding is increased and likewise the importance of genetic drift, the stochastic loss of alleles, in shaping a population's genetic architecture is increased. Both these processes ultimately lead to loss of genetic variation. The chapter examines each of these arguments. It considers experimental studies that tested whether inbreeding and/or reduced levels of genetic variation leads to greater extinction risk. It shows that many studies of genetic causes for extinction seem to suggest that inbreeding depression is the main genetic problem in conservation biology. On the other hand, hardly any study has convincingly shown that reduced adaptability or fixation of mildly deleterious alleles have contributed to extinction. Thus, it seems prudent for conservation geneticists to focus on inbreeding and inbreeding depression.

This chapter outlines the theory of inbreeding including a brief account on the theory of population subdivision and gene flow. This is of relevance to conservation issues because habitat loss and fragmentation induces elevated levels of population structure in endangered species through reduced migration between remaining habitat fragments. Population structure is a major cause of inbreeding. The relationship between genetic diversity and fitness is discussed, covering the issues of inbreeding depression and heterosis.

In this chapter, Corey J. A. Bradshaw and Barry W. Brook, discuss measures of biodiversity patterns followed by an overview of experimental design and associated statistical paradigms. Conservation biology is a highly multidisciplinary science employing methods from ecology, Earth systems science, genetics, physiology, veterinary science, medicine, mathematics, climatology, anthropology, psychology, sociology, environmental policy, geography, political science, and resource management. Here we focus primarily on ecological methods and experimental design. It is impossible to census all species in an ecosystem, so many different measures exist to compare biodiversity: these include indices such as species richness, Simpson's diversity, Shannon's index and Brouillin's index. Many variants of these indices exist. The scale of biodiversity patterns is important to consider for biodiversity comparisons: α (local), β (between‐site), and γ (regional or continental) diversity. Often surrogate species ‐ the number, distribution or pattern of species in a particular taxon in a particular area thought to indicate a much wider array of taxa ‐ are required to simplify biodiversity assessments. Many similarity, dissimilarity, clustering, and multivariate techniques are available to compare biodiversity indices among sites. Conservation biology rarely uses completely manipulative experimental designs (although there are exceptions), with mensurative (based on existing environmental gradients) and observational studies dominating. Two main statistical paradigms exist for comparing biodiversity: null hypothesis testing and multiple working hypotheses – the latter paradigm is more consistent with the constraints typical of conservation data and so should be invoked when possible. Bayesian inferential methods generally provide more certainty when prior data exist. Large sample sizes, appropriate replication and randomization are cornerstone concepts in all conservation experiments. Simple relative abundance time series (sequential counts of individuals) can be used to infer more complex ecological mechanisms that permit the estimation of extinction risk, population trends, and intrinsic feedbacks. The risk of a species going extinct or becoming invasive can be predicted using cross‐taxonomic comparisons of life history traits. Population viability analyses are essential tools to estimate extinction risk over defined periods and under particular management interventions. Many methods exist to implement these, including count‐based, demographic, metapopulation, and genetic. Many tools exist to examine how genetics affects extinction risk, of which perhaps the measurement of inbreeding depression, gene flow among populations, and the loss of genetic diversity with habitat degradation are the most important.

Inbreeding and its consequences are the main subject of Chapter 3, beginning with the concepts of identity by descent versus identity by state, the inbreeding coefficient F, genotype frequencies with inbreeding, and calculation of the inbreeding coefficient from pedigrees. Inbreeding and heterosis are discussed along with the effects of inbreeding in humans and other organisms, regular systems of mating (selfing and partial selfing, sib mating), and the utility of recombinant inbred lines. The chapter emphasizes the intimate connection between inbreeding and hierarchical population structure as measured by the F-statistics.

This chapter presents an overview of the development of medieval incest law, in relation to biblical teaching and Greco-Roman law. It raises questions about the rationale for a system of taboos that had become so complex by the early 13th century that to avoid hardship the number of prohibited degrees of relationship were drastically reduced by the Fourth Lateran Council in 1215. Various modern hypotheses about the medieval taboo are reviewed. Fear of inbreeding and deformity is rarely mentioned. What justified the inclusion of such distant relatives, and why the ban on in-laws and ‘spiritual incest’? How seriously did medieval people take these laws? Among the aristocracy, at least, they seem often to have been honoured in the breach. The practice of selling of dispensations to marry within the prohibited degrees was condemned by Luther, among others.

Incest seems an ever-present danger in medieval literature, although it can be absolved by repentance and grace. The genetic consequences of inbreeding are ignored: children of incest are usually heroic and beautiful (Adonis), with a few exceptions (Mordred). Medieval incest narratives are compared with Renaissance drama, where incest leads to many deaths and represents corruption in society, not individual sinfulness. The one exception to the taboo is the Virgin Mary, regularly described in medieval texts as the mother/sister/daughter/bride of Christ. Her ‘incest’ is necessary for Christian salvation; it happens only once, and is spiritual not sexual, a victory rather than a moral defeat. It is suggested that this trope may have developed as a response to the carnality of the pagan gods, and to the frequent accusations of sexual misbehaviour aimed at the early Christians. Medieval incest stories reflect a strong sense of human sinfulness, but incest is also a productive literary theme.

Populations may respond to environmental changes through phenotypic plasticity, adaptation, migration, or suffer demographic declines if they are unable to respond. Climate change is already causing shifts in species ranges, changes in phenotypes, and altered life history traits and interspecific interactions. The capacity for a population to adapt to new conditions is a function of the amount of genetic and phenotypic variation for traits under selection, fecundity, and the rate of environmental change per generation. Several genomic approaches are available for predicting the extent of maladaptation of populations resulting from climate change based on the mismatch between genotypes and new climates. The conservation of populations that are threatened by rapid climate change may in some cases require management tools including assisted gene flow to facilitate adaptation, and greater connectivity of habitats to facilitate range shifts and migration (i.e., gene flow).

Contemplate the descent of a piece of DNA (or RNA in organisms using this as their genetic material). The DNA is copied, and copies are passed to descendants. If the copies were error-free we could rightly think of them as perfect clones that pass down indefinitely through the eons. This logic led Richard Dawkins to speak of immortal coils in his book on selfish genes; here, it instead brings up issues of the common ancestry of genes and of individuals, and of the definition and consequences of inbreeding and outbreeding, the subjects of this chapter. When two individuals share one or more ancestor, they are relatives, both in common parlance and by technical definition in biology. The consequence of their mating is inbreeding, that is, the production of offspring receiving copies of a given gene through both mother and father that can be traced to the common ancestor(s). These gene copies are identical by descent (IBD; not to be confused with an acronym for inbreeding depression, see below), a shorthand for “identical by the fact of descending as copies of the same original piece of DNA”. The probability that two gene copies are IBD in a diploid individual, or its inbreeding coefficient, symbolized by f, is a simple function of the genetic relatedness of its parents and the segregation of genes during meiosis and gametogenesis. Because the probability is one-half that two gametes from the same individual carry identical gene copies, fertilization by self produces f of one-half, a brother-sister mating or parent-offspring mating produces f of one-quarter, a first-cousin mating produces f of one-sixteenth, and so on (see “Measurement of Inbreeding and Outbreeding,” below). In these examples, we assume that neither common ancestor(s) nor parents themselves are inbred; such inbreeding reflects additional common ancestry and so inflates f. From all of this, a definition of outbreeding as “mating of nonrelatives” follows automatically. As just defined, inbreeding and outbreeding rely on an absolute measure of relatedness. An alternative definition that may be of more value in real, finite populations (as opposed to ideal, infinite ones) is that inbreeding is mating with relatives more often than expected by chance, and outbreeding the opposite.

We recommend augmentation of gene flow for isolated population fragments that are suffering inbreeding and low genetic diversity, provided that proposed population crosses have low risks of outbreeding depression, and the predicted benefits justify the financial costs.

This chapter provides an overview of beaver dispersal. There are a number of reasons why beavers have to disperse from their native family. As a relatively long-lived species, beavers produce 3–4 newborns every year. If the young stay with their parents and siblings, the colony would grow huge in a few years and soon outstrip its food resources. More importantly, grown-up offpring must find mates to start reproducing themselves. Mating with close relatives would often result in disastrous genetic defects, a phenomenon called inbreeding depression. This chapter discusses the risks that come with dispersal and explains how natural dispersal differs from translocation and homing. It also considers the age at which beavers usually leave their family, along with the timing, direction, distance, and duration of dispersal.

It is assumed that dominance genetic variance contributes little to the prediction of evolutionary change in polygenic traits. This is based on the assumption that populations are large, panmictic, and randomly mating. However, the ecological contexts of most wild populations studied to date violate one, if not several, of these assumptions, and the widespread occurrence of inbreeding and inbreeding depression of phenotypic traits and fitness suggests dominance genetic effects are ubiquitous. This chapter reviews what genetic dominance represents at the level of a single locus and how this contributes to phenotypic variation and discusses how to estimate dominance variance with emphasis on the complications arising in wild populations and with inbreeding. Next, empirical estimates of dominance variance are reviewed. Since no estimates exist of dominance variance in the wild (except for humans), laboratory and agricultural populations are examined, and it is shown that dominance variance is a major contributor to phenotypic variation and in some cases contributes as much as additive genetic variance. This chapter also discusses how inbreeding and dominance affect predictions of evolutionary change, and ends with a review of some of the empirical questions for which genetic dominance is an important quantity in its own right. In this chapter, it is argued that dominance variance has been ignored for too long, may hamper the ability to predict evolutionary change, can be a major contributor to phenotypic variance, is interesting to study in its own right, and provides many avenues of research to be addressed by empirical study.

All populations are finite in size so that genetic drift will occur in all natural and managed populations. Genetic drift causes both changes in allele frequencies and the loss of genetic variation. Loss of heterozygosity and loss of alleles are t^ghe two primary measures of the loss of genetic variation in populations. Matings between related individuals (i.e., inbreeding) is more common in small populations, and this will lead to inbreeding depression in small populations. Understanding the effects of genetic drift is especially important for conservation because loss of genetic variation and inbreeding depression can reduce the probability of population persistence.

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.