Chapter 20 bio

Selection imposed by host immune systems influences large-scale pathogen evolution. Some viral pathogens, like the human influenza A virus, readily evolve in a way that allows them to reinfect hosts, which is why flu vaccines change from year to year and need to be administered annually. The pattern of diversification for such a virus generates a(n) _______________ phylogeny in which most lineages are lost in any given year, and the few strains that persist represent ______________ that have evolved means of evading the immunological memory of previously infected hosts. In contrast, viruses like measles trigger a stronger immune response than influenza A, and hosts are immune for life after recovering from the infection. The phylogeny of such a virus is more _________ than the flu phylogeny, since clones are less likely to evade host immunity and outcompete the others in the population. Multiple lineages can thus coexist in the population for an extended period of time.

- cactus-shaped -escape variants -deep-branching

evolutionary

-The adaptive significance of fever may derive partly from its ability to trigger the expression of heat shock proteins that help cells deal with the stress of infection. -The temperature increase associated with fever may boost the host's immune response, increasing the probability of surviving an infection

Niko Tinbergen distinguished among four types of explanation relevant to "why" questions about behavior. These explanatory categories also apply to other areas of biology, including medicine. Explanations at the ____________ level invoke the immediate mechanisms underlying a trait and can directly guide __________ medicine, which is characterized by clinical attempts to correct existing pathologies. Explanations at the ___________ level address the course of trait acquisition over an individual's lifetime. The practice of ____________medicine, which attempts to intervene before a pathology appears, draws extensively on this class of explanation. Understanding how mechanisms like natural selection have shaped human vulnerability to certain pathologies requires ______________ explanations, and questions about the history of traits related to vulnerability in humans and related lineages calls for _____________ explanations. These last two levels of explanation can suggest new hypotheses that drive medical research and clinical practice.

-proximate -reactive -developmental -preventative -evolutionary -phylogenetic

Experimental evidence supports the hypothesis that fever is an adaptive response that helps the body clear infections. The principle of asymmetric harm likely applies to the evolution of fever, since the fitness consequences of developing a fever when ___________, are less severe than the consequences of not developing a fever when _______________, Under these conditions, a false ________________, is more dangerous than a false ________, which explains why fevers often occur even when they aren't crucial for successful recovery and are thus safe to treat with antipyretic drugs.

-there is no infection -there is an infection -negative -positive

Evolution can explain a variety of human vulnerabilities to disease and other health hazards. Humans are prone to choking because the _____________ , the tube through which air flows to the lungs, crosses paths with the _______________________ , the tube through which food travels to the stomach. All tetrapods share this unfortunate anatomical arrangement, which reflects the origin of the lungs as an outpocketing of the gut in ancestral fish and thus provides an example of how ____________________ can prevent natural selection from generating adaptations that perfectly match form and function. Among the mammals, humans are particularly prone to choking because the larynx has descended as an adaptation to human vocalizations. A higher larynx, as seen in mammals like dogs, allows the epiglottis to effectively seal off the mouth when the opening to the air passage is exposed, but it also limits the ability to control airflow through the mouth cavity and into the larynx, which is necessary for speech. Human vulnerability to choking thus reflects a _____________________ between communication ability and choking risk.

-trachea -esophagus -phylogenetic constraint -trade-off

proximate

A patient with hypothyroidism takes a daily pill containing synthetic thyroid hormones and experiences relief from symptoms like lethargy and dry skin.

developmental

A physician recommends exercise and weight loss to reduce a patient's chances of getting type 2 diabetes.

Drag each feature below to the correct box to indicate whether or not it would give a bacterial pathogen an advantage in a coevolutionary arms race with its human host.

Advantageous to Bacterial Pathogen: large bacterial population size shorter generation time than the host

disposable-soma hypothesis

All species are subject to extrinsic mortality, so selection will favor genotypes that prioritize reproduction over repair processes that would eliminate senescence.

evolutionary

An allele that causes sickle cell anemia is common in human populations from regions with a high prevalence of malaria. Heterozygotes carrying this allele are resistant to malaria, so natural selection based on heterozygote advantage is likely responsible for the unfortunate susceptibility of certain human populations to sickle cell anemia.

phylogenetic

As shown in this figure, both endothermic and ectothermic vertebrate taxa show elevated body temperatures when infected.

As shown in the graph, bats live longer than nonflying mammals of comparable body size, which suggests that flight increases their ability to evade predation. Which of the following conclusions can you draw from this observation?

Bats have lower extrinsic mortality than nonflying mammals, which should be associated with stronger selection against deleterious late-acting alleles and thus with slower senescence.

Drag each statement to the correct box to indicate whether or not it is a cost associated with fever as a physiological response to infection in endotherms.

Correct Answer(s) -Fever raises the metabolic rate and thus imposes an energetic cost. -Fever enhances the immune response, which can cause tissue damage even as it fights off infection.

The figure depicts several ___________ of Gram-positive bacteria that can be recognized by receptors on host immune cells.

Correct choicepathogen associated molecular patterns (PAMPs)

Drag each piece of evidence to the correct box to indicate whether it provides evidence for or against the rate-of-living hypothesis for the evolution of senescence.

Evidence for -inverse relationship between metabolic rate and life span across many species of mammals and birds

Drag each statement to the correct box to indicate whether or not it exemplifies one of Williams and Nesse's six explanations for vulnerability to disease.

Exemplifies One of the Six Explanations -Genotypes that are associated with nearsightedness in modern human populations probably conferred no disadvantage in ancestral environments. -Some diseases strike humans primarily in old age.

This graph depicts patterns of behavioral thermoregulation in a healthy desert iguana. How do you expect this graph to change if it were to depict thermoregulatory patterns in a lizard exhibiting behavioral fever in response to infection? Drag each statement to the correct box to indicate whether or not it is a change you would expect to see under these conditions.

Expected Change -upward shift in dotted line -increase in pink shading relative to blue shading

Williams and Nesse provided six evolutionary explanations for human vulnerability to disease. Which of these explanations best addresses why natural selection has not eliminated traits like the fever and nausea associated with certain human illnesses?

Fever and nausea are associated with beneficial responses to disease that were favored by natural selection.

phylogenetic

Humans can choke because the vertebrate lung first appeared as an outpocketing of the esophagus in early fish.

proximate

Immune cells responding to a pathogen release cytokines that stimulate the brain to raise the body's thermal set point.

antagonistic pleiotropy hypothesis

Mutations that are beneficial early in life are deleterious late in life.

Drag each of the following statements to the correct box to indicate whether or not it is a prediction of the smoke detector principle as applied to the evolution of fever in humans.

Prediction -Even though fever is an adaptive response to infection, physicians can usually administer fever-reducing medications to their sick patients with little risk. -The principle of asymmetric harm applies to fever as an evolved response to infection.

mutation accumulation hypothesis.

Selection against late-life mutations is so weak that drift predominates over selection, whereas natural selection can more efficiently remove deleterious late-life mutations from a population.

In a laboratory experiment, Vaughn et al. (1974) injected healthy desert iguanas (Dipsosaurus dorsalis) with killed bacteria to elicit an immune response. Lizards injected with bacteria showed thermoregulatory behaviors that raised their body temperatures above the species optimum, but uninjected lizards and lizards injected with saline maintained their usual preferred temperature.Drag each statement below to the correct box to indicate whether or not this experiment supports the conclusion.

Supports the Conclusion -Since lizards injected with saline behaved like uninjected lizards, it is likely that lizards injected with killed bacteria changed their thermoregulatory behavior in response to the bacteria and not as a consequence of experimental handling. -Fever is an adaptive response to infection in ectotherms as well as in endotherms.

Drag each statement to the correct box to indicate whether or not it is a conclusion you can draw from the figure about optimal investment in heart and lung function.

The model depicted in the graph predicts that organisms should evolve to invest in heart and lung function so as to balance the gain in longevity per unit cost. At the optimal level of investment in heart and lung function, there is a higher probability of lung failure than of heart failure.

Which of the following conclusions can you draw from the results shown in the graphs, which depict the results of Austad's (1993) study comparing island and mainland populations of the Virginia opossum (Didelphis virginiana)?

There is a positive association between extrinsic mortality and senescence in these opossums, as predicted by the mutation accumulation and antagonistic pleiotropy hypotheses.

Drag each statement to the correct box to indicate whether it is true or false regarding the adaptive significance of fever in vertebrates.

True -Fever imposes substantial costs but nonetheless has a wide phylogenetic distribution. -Experimental evidence suggests that elevated body temperature is associated with quicker recovery from infection.

Drag each statement to the correct box to indicate whether it is true or false of human senescence based on the information in the graphs.

True -The mortality rate in females begins to increase around the age at which fertility falls but does not rise sharply until well after reproduction has ceased. -Many human females live well beyond their reproductive years.

Drag each statement to the correct box to indicate whether it is true or false of the rate-of-living hypothesis of senescence.

True -The rate-of-living hypothesis posits that senescence is a consequence of physical wear and tear that the body experiences over a lifetime. -The rate-of-living hypothesis predicts that there should be nearly no genetic variation associated with the rate of senescence in humans. -The rate-of-living hypothesis predicts an inverse correlation between metabolic rate and life span.

Clonal selection acts on existing variation in antigen-binding specificity among antibody proteins during maturation of a lineage of B lymphocytes. What is the primary source of variation in the antigen-binding region of antibodies within an individual?

V(D)J recombination

Which of the following statements is true regarding V(D)J recombination?

V(D)J recombination is a form of somatic recombination that generates antibodies capable of binding a diverse array of antigens.

The ____________ hypothesis explains senescence as the outcome of selection that favors "senescence alleles" because they confer a fitness advantage early in life. Even in the absence of senescence, extrinsic mortality makes selection _________ against late-effect deleterious mutations than against early-effect mutations. When senescence exacerbates late-life mortality, it further weakens selection against late-effect mutations and thus creates positive feedback. The fitness effects of late-effect deleterious mutations may be so small that these alleles behave neutrally and increase in frequency via __________ as posited by the ______________ hypothesis

antagonistic pleiotropy weaker genetic drift mutation accumulation

Pathogen and host species engage in ____________ n which they impose reciprocal selection pressures on each other. The pathogen selects for host defenses, and these defenses in turn select for pathogens that can evade them. A microbial pathogen has a larger ____________ and shorter _____________ than a vertebrate host and can thus rapidly evolve evasive mechanisms. We might expect these pathogen traits to give microbes a major evolutionary advantage over multicellular vertebrate hosts. However, the _______________ generates populations of immune cells that recognize a wide array of pathogen-associated antigens before an infection even happens. At the onset of an infection, the immune cells with receptors that bind antigens specific to that pathogen proliferate preferentially. This process, known as _________________ , allows for rapid responses to both initial and future infections.

coevolutionary arms races population size generation time adaptive immune system clonal selection

pattern recognition receptor

component of human innate immune system that binds highly conserved molecules found in pathogens

Preventative medicine draws on an understanding of how pathologies originate and progress over the course of a person's life. This clinical approach depends most directly on Tinbergen's _______ level of explanation.

developmental

What is the proximate cause of choking in humans?

food or another object that enters and blocks the trachea

Bipedal locomotion presumably conferred a selective advantage in ancestral hominids, but the prevalence of lower-back pain in humans suggests that the vertebral column is imperfectly adapted to withstand the stresses of an upright posture. We can attribute this suboptimal anatomical arrangement to ___________, since adaptations to walking evolved in a skeleton that was already adapted to ancestral quadrupedal locomotion.

phylogenetic constraint

Traits evolve as natural selection "tinkers" with existing forms, which can bias adaptive evolution in directions that don't necessarily generate an optimal match between form and function. When a trait seems maladaptive because of such an ancestral legacy, what do we say that trait has been subject to?

phylogenetic constraint

clonal selection

process whereby adaptive immune cells that recognize host antigens are eliminated and those that bind foreign antigens proliferate after initial exposure

affinity maturation

selective process whereby a population of B-cells comes to bind more effectively to its target antigen during clonal expansion

Ackerman's (2003) experimental demonstration of senescence in stalked cells of the asymmetrically dividing bacterium Caulobacter crescentus indicates which of the following?

the disposable soma hypothesis can explain the evolution of senescence even in organisms without a germ-soma distinction

Which of the following tactics is least likely to allow a pathogen to successfully evade the immune system of a vertebrate host?

upregulating expression of MHC proteins