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Chapter 11 Evolution - Coggle Diagram

- - - - Evolution toward similar characteristics in unrelated species is called convergent evolution.
      - Analogous structures, such as wings on birds and insects, are common examples of convergent evolution.
      - Another example is the tail fin of fish and marine mammals, Sharks, which are fish, and dolphins, which are mammals, are separated by about 300 million years of evolution.
      - they have both evolved similar tail fins to propel themselves through the water. However, the tail fins of sharks and other fish are vertical, while those of dolphins are horizontal.
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  - - - The evolution of the
        red fox and the kit fox is an example of this trend.
        
        Though closely related, the two species have different appearances that are the result of adapting
        to different environments.
        
        The red fox lives in temperate regions, usually
        in forests.
        
        Its dark reddish coat helps it to hide from predators.
        
        The sandy-colored coat of the kit fox allows it to blend in with its desert surroundings. Kit foxes also have large ears relative to their body size. This adaptation helps them to keep cool in the desert heat.
  - - - For example, they may compete for the same food source or be involved in a predator prey relationship. Most of these interactions do not involve evolutionary changes. However, sometimes the evolutionary paths of two species become connected.
    - - The bull-thorn acacia is a plant species with branches covered in hollow thorns.
      - Although the thorns protect the plant from being eaten by large animals, small herbivores such as caterpillars can fit between them.
      - this relationship may seem to be a simple cooperation
        between two species, it is much more than that. The acacia and the ants share an evolutionary history.
      - Coevolution is the process in which two or more species evolve in response to changes in each other.
      - Close relatives of these species that are not involved in this type of relationship do not have these traits. Such specialized relationships form through coevolution.
    - - Coevolution can also occur in competitive relationships. These interactions can lead to “evolutionary arms races,” in which each species responds to pressure from the other through better adaptations over many generations.
        
        For example, many plants produce defense chemicals to discourage herbivores from eating them.
        
        Natural selection then favors herbivores that can overcome the effects of the chemicals. After many generations, most herbivores have some level of resistance and are again able to safely eat the plant.
        
        Natural selection then favors plants that have evolved even more potent chemicals.
        
        In another case, the thick shells and spines of murex snails are an adaptive response to predation by crabs. In turn, crabs have evolved powerful claws strong enough to crack the snails’ shells.
  - - - Just as birth and death are natural events in the life of an individual, the rise and fall of species are natural processes of evolution.
      - Extinction often occurs when a species as a whole is unable to adapt to a change in its environment.
      - Background Extinctions
        
        Extinctions that occur continuously but at a very low rate are called background extinctions.
        
        They are part of the cycle of life on Earth. Background extinctions occur at roughly the same rate as speciation.
        
        Unlike catastrophic mass extinctions, background extinction events usually affect only one or a few species in a relatively small area, such as a rain forest or a mountain range.
        
        They can be caused by local changes in the environment, such as the introduction of a new predator species or a decrease in food supply. From a human perspective, such extinctions seem to occur randomly but at a fairly constant rate.
      - Mass Extinctions
        
        Mass extinctions are much more rare than background extinctions.
        
        These events often occur at the global level. Therefore, they destroy many species even entire orders or families. Mass extinctions are thought to occur suddenly in geologic time, usually because of a catastrophic event such as an ice age or asteroid impact. The fossil record confirms that there have been at least five mass extinctions in the past 600 million years.
    - - Paleontologists have long noticed a repeating pattern in the history of life, reflected in the fossil record. Bursts of evolutionary activity are followed
        by long periods of stability. This pattern is described by the theory of punctuated equilibrium, which states that episodes of speciation occur suddenly in geologic time and are followed by long periods of little evolutionary change.
        
        The diversification of one ancestral species into many descendent species is called adaptive radiation.
        
        These descendent species are usually adapted to a wide range of environments. One example of adaptive radiation is the radiation of mammals following the mass extinction at the end of the Cretaceous period 65 million
        years ago.
        
        Early mammals were able to coexist with dinosaurs because mammals and dinosaurs had different niches, or roles in the ecosystem. You will learn more about the concept of niches in Interactions in Ecosystems.
        
        ECOLOGY
        
        Although mammals had evolved for about 150 million years before the end of the Cretaceous period, they barely resembled the mammals we know today. The earliest mammals were tiny, usually insect eaters, and mostly nocturnal. These characteristics allowed them to coexist with the dinosaurs. The extinction of the dinosaurs left environments full of opportunities for other types of animals. In the first 10 million years following the dinosaurs’ extinction, more than 4000 mammal species had evolved, including whales, bats, rodents, and primates.
- - - - At the
        same time, these alleles are removed from the gene pool of its former population.
  - - - The bottleneck effect is genetic drift that occurs after an event greatly reduces the size of a population.
        
        One example of the bottleneck effect is the overhunting of northern elephant seals during the 1800s.
  - - - In many species, this difference in reproductive cost makes females choosy about mates. Sexual selection occurs when certain traits increase mating success. There are two types of sexual selection:
      - • Intrasexual selection involves competition among males, such as the head-butting of bighorn sheep. The winner of the competition mates with the female.
      - • Intersexual selection occurs when males display certain traits that attract the female, such as peacocks fanning out their tails.
  - - - The gene pools of these populations are often very different from those of the larger populations.
        
        The founder effect can be studied in human populations, such as Old Order Amish communities.
        
        These communities were founded in North America by small numbers of migrants from Europe.
        
        For example, the Amish of Lancaster County, Pennsylvania, have a high rate of Ellis–van Creveld syndrome.
        
        Geneticists have traced this syndrome back to one of the community’s founding couples.
        
        Form of dwarfism is rare in other human populations, it has become common in this Amish population through genetic drift.
  - - - Problems
- - - - Phenotype is a trait produced by one or more genes. Various forms of expression appear in a population, for example, some are short and round, and others are tall and slim.
      - The allele frequency is a measure of how common an allele is in a population.
  - - - If the mutation happens in a cell that makes gametes sperm or eggs then the mutation can be passed on to offspring. Mutations increase the genetic variation in a gene pool.
  - - - Hybridization is a cross between two species that share a common gene.
      - Studies have shown that this process occurs within many animal groups, including birds and mammals, when similar species live in the same area and individuals cannot easily find a mate for their species.
- - - - If gene flow between two populations stops for any reason, the populations are said to be isolated.
        
        As these populations adapt to their environments, their gene pools may change.
        
        Random processes such as mutation and genetic drift can also change gene pools.
        
        All of these changes add up over many generations. With time, the two isolated populations become more and more genetically different. Individuals in one population may also begin to look and behave differently from individuals in the other population.
        
        Reproductive isolation occurs when members of different populations can no longer mate successfully.
        
        Sometimes members of the two populations are not physically able to mate with each other.
        
        In other cases, they cannot produce offspring that survive and reproduce.
        
        Reproductive isolation between populations is the final step of becoming separate species.
        
        The rise of two or more species from one existing species is called speciation.
  - - - Temperate fruit flies have a temperate ds2 allele.
      - Scientists used lab fruit flies that are genetically similar. They developed a technique that allowed them to replace the ds2 gene in each lab fruit fly with either the tropical or temperate allele.
        
        2.Laboratory males that received the tropical allele were attracted to females that received the tropical allele. Males that received the temperate allele were attracted to females that received the temperate allele.
      - This experiment shows how speciation may have occurred in natural
        fruit fly populations.
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  - - - Behavioral Barriers
        
        Chemical scents, courtship dances of birds, and courtship songs of frogs are sexual signals used to attract mates.
        
        Changes in these signals can prevent mating between populations. Behavioral isolation is isolation caused by differences in courtship or mating behaviors.
        
        Over 2000 species of fireflies are isolated in this way.
        
        Male and female fireflies produce patterns of flashes that attract mates of their own species. For example, Photuris frontalis emits one flash every second, P. hebes emits one flash every 2 seconds, and P. fairchildi produces a double flash every 5.5 seconds.
  - - - These barriers can include rivers, mountains, and dried lakebeds.
        
        Marine organisms could no longer easily cross between the Atlantic and Pacific oceans. Over time, the isolated populations became genetically different. Several species of snapping shrimp have evolved through geographic isolation.
        
        These species appear
        almost identical to one another. However, when males and females from opposite sides of the isthmus are placed together, they snap at each other instead of courting. Because they will no longer mate, these shrimp are classified as different species.
- - - - The Hardy-Weinberg equation is used to predict genotype frequencies in a population.
        
        There are five factors that can lead to evolution.
        
        Initial population
        
        Here are the alleles associated with body color in a hypothetical population.
        
        Genetic drift
        
        After a bottleneck event, only gray and blue alleles remained in the small population. Through genetic drift, gray alleles increase in frequency. Allele frequencies can change due to chance alone.
        
        Gene flow
        
        Black alleles increase in frequency because of immigration; gray alleles decrease in frequency because of emigration. The movement of alleles from one population to another changes allele frequencies.
        
        Mutation
        
        A new allele, associated with light blue body color, is formed through mutation. This could affect sexual selection if this body color improves mating success. it could affect natural selection if this body color increases the chance for survival. New alleles can form through mutation, creating genetic variation needed for evolution.
        
        Sexual selection
        
        Blue alleles are associated with blue body color, which improves mating success. blue alleles, therefore, increase in frequency. Alleles associated with improved mating success increase in frequency.
        
        Natural selection
        
        White alleles are associated with white body color, which allows individuals to blend in with their environment and avoid predation. White alleles therefore increase in frequency. Alleles associated with increased survival increase in frequency.
        
        Evolution is continuous. Environments are always changing, though often very slowly relative to a human’s lifetime. Evolution is a response to these changes. As environments change, populations either adapt or go extinct. When a population becomes extinct, a different species can take its place, and the cycle continues.
        
        For traits in simple dominant-recessive systems, biologists can predict genotype frequencies by using the Hardy-Weinberg equation.
        
        Values predicted by the equation are those that would be present if the population were in equilibrium. If p equals the frequency of the dominant allele and q equals the frequency of the recessive allele, the equation can be written as follows:
        
        p2 + 2pq + q2 = 1
        
        p = frequency of allele T (dominant allele)
        
        q = frequency of allele t (recessive allele)
        
        p2 = frequency of fish with TT (homozygous dominant genotype)
        
        2pq = frequency of fish with Tt (heterozygous genotype)
        
        q2 = frequency of fish with tt (homozygous recessive genotype)
        
        The letter p stands for the frequency of the dominant allele and
        q stands for the frequency of the recessive allele.
      - Biologists often compare their data to a model to study how a population is changing.
        
        One important model is based on the research of a British mathematician named Godfrey Hardy and a German physician named Wilhelm Weinberg.
        
        Hardy-Weinberg equilibrium
        
        these frequencies can be predicted
        
        Very large population No genetic drift can occur.
        
        No emigration or immigration No gene flow can occur.
        
        No mutations No new alleles can be added to the gene pool. Random mating No sexual selection can occur.
        
        No natural selection All traits must equally aid in survival.
        
        Hardy and Weinberg identified five conditions needed for a population to stay in equilibrium. Populations that meet these conditions are not evolving. They are said to be in Hardy-Weinberg equilibrium.
      - Real populations rarely meet all five conditions. But the
        model is a useful tool for understanding changes in popula- tions. Real data can be compared with data predicted by the model.