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Organisms move, and their movement can take place by walking, swimming, or flying; via transport by another organism (phoresy); or by a vehicle such as wind or current (Dingle 1996). The functions of movement include finding food or mates, escaping from predators or deteriorating habitats, the avoidance of inbreeding, and the invasion and colonization of new areas. Virtually all life functions require at least some movement, so it is hardly surprising that organisms have evolved a number of structures, devices, and behaviors to facilitate it. The behavior of individuals while moving and the way this behavior is incorporated into life histories form one part of this chapter. This discussion focuses on the action of selection on the evolution of individual behavior, on how specific kinds of movement can be identified from the underlying behavior and physiology, and on the functions of the various movement behaviors. The other major part of our discussion focuses on the consequences of movement behaviors for the ecology and dynamics of populations. The pathways of the moving individuals within it can result in quite different outcomes for a population. First, movements may disperse the members of the population and increase the mean distances among them. The separation may be a result of paths more-or-less randomly chosen by organisms as they seek resources, or it may be a consequence of organisms avoiding one another. In contrast to dispersing them, movement may also bring individuals together either because they clump or congregate in the same habitat patch or because they actively aggregate through mutual attraction. Clumping can also lead to aggregation and mutually attracting social interactions. A classic example is the gregarious (aggregating) phase of the desert locust (Schistocerca gregaria), in which huge swarms of many millions of individuals first congregate in suitable habitats and then develop and retain cohesion based on mutual attraction. The foraging swarms make the locust a devastating agricultural pest over much of Africa and the Middle East (Farrow 1990; Dingle 1996). It is the aggregation of locusts that makes them such destructive pests; they would be far less harmful if the populations dispersed.

Conservation biology as a discipline focused on endangered species is young and dates only from the late 1970s. Although conservation of endangered species encompasses many different biological disciplines, including behavior, ecology, and genetics, evolutionary considerations always have been emphasized (e.g., Frankel and Soule 1981). Many of the applications of evolutionary concepts to conservation are ones related to genetic variation in small or subdivided populations. However, the critical status of many endangered species makes both more precision and more caution necessary than the general findings for evolutionary considerations. On the other hand, the dire situations of many endangered species often require recommendations to be made on less than adequate data. Overall, one can think of the evolutionary aspects of conservation biology as an applied aspect of the evolution of small populations with the important constraint that any conclusions or recommendations may influence the actual extinction of the populations or species under consideration. From this perspective, all of the factors that influence continuing evolution (i.e., selection, inbreeding, genetic drift, gene flow, and mutation; e.g., Hedrick 2000) are potentially important in conservation. The evolutionary issues of widest concern in conservation biology’”inbreeding depression and maintenance of genetic variation’” can be seen in their simplest form as the joint effects of inbreeding and selection, and of genetic drift and mutation, respectively. However, even in model organisms such as Drosophila, the basis of inbreeding depression and the maintenance of genetic variation are not clearly understood. In addition, findings from model laboratory organisms may not provide good insight into problems in many endangered species, the most visible of which are generally slowly reproducing, large vertebrates with small populations. Here we will first focus on introductions to two important evolutionary aspects of conservation biology: the units of conservation and inbreeding depression. Then, we will discuss studies in two organisms as illustrations of these and related principles’”an endangered fish species, the Gila topminnow, and desert bighorn sheep’”to illustrate some evolutionary aspects of conservation. In the discussion, we will mention some of the other evolutionary topics that are relevant to conservation biology.

An introduction to randomness and the neutral theory of molecular evolution and how it contributes to levels of genetic diversity in populations. The estimation of random shifts in allele frequencies over time is discussed using the binomial probability distribution. This chapter visualizes how different initial allele frequencies relate to their probability of being fixed in a population when only drift is acting. The outputs of multiple simulations of a population undergoing random increase and decrease in allele frequencies per generation are built, run, and visualized. The fixation index (F) is introduced to quantify the loss of genetic variance over time.

Genetics affects host–parasite interactions in various ways, e.g. by additive genetic variance and epistasis. Various models, such as gene-for-gene or matching alleles, describe the interactions. Heterozygous individuals and genetically more variable populations often have lower parasite loads, but specific gene variants are critical. Variation in gene expression adds plasticity to host defences and parasite characteristics. Horizontally transferred pathogenicity islands are important for bacterial virulence: in viruses, genomic organization matters. Host and parasite characteristics are heritable and evolve; genetics is also important for the microbiota. In populations, signs of selection point to directional or balancing selection in different parts of the immune defences, or in parasites due to medical interventions. Parasite population genetic structure, furthermore, is affected by genetic exchange during co-infections. Modern genomic tools allow studying genotypes and entire genomes at a massive scale. This is also used for genome-wide association studies.

The sexes (male, female) differ in parasite load and immune defences. In general, males are more frequently infected and often have lower defences. The differences are one consequence of sexual selection, where females invest more in maintenance. Females can choose males based on signs (e.g. ornaments) of higher resistance to parasites. Several theoretical scenarios can explain part of this variation. Advantages also result from genetic heterozygosity. Sex-specific hormones affect immune defences in many ways.