Biology 140: ecology and evolution Week 1 review questions Instructions: These questions will NOT be collected; they are for your own studying purposes. I strongly suggest that you do the weekly review questions each week, and use them to assess your own understanding. They will also come in handy as you study for the exams! Part 1: Vocabulary terms to know and love. Be able to define each of these terms in a sentence or two. If a word has a “general purpose” meaning and a specific scientific meaning, I am looking for the latter. Evolution: change in allele frequencies in a population over time Adaptation: a heritable trait that increases the fitness of an individual in a particular environment, relative to individuals lacking the trait. Proximate explanation: A functional explanation for an ecological pattern or process— for example, if you asked some trees have scaly/flaky bark, the proximate explanation may have to do with cell death, tissue senescence, and/or shedding bark infected with fungi or bacteria. Ultimate explanation: How it got to be that way—usually invokes evolutionary processes. Transitional form: a species with traits that are intermediate (transitional) between older and younger forms. Generally used to refer to fossil species. Vestigial traits: Traits that are reduced in size or function compared to ancestral species. Examples include eye buds in sightless cave-dwelling species, tail bones in humans, finger bones in whale flippers. Homologous: Two traits, structures, or genes are homologous if they are similar by virtue of having descended from a common ancestor with that trait. Examples include vertebrate forelimbs, certain gene families (see your text), developmental pathways, etc. Analogous: Two traits or structures are analogous if they have similar function as a result of convergent evolution, not because of shared ancestry. Convergent evolution: Evolution of similar traits in distantly related species as a result of common selective pressures—adaptation to similar environments or ways of life. Darwinian fitness: Reproductive success—the number of surviving offspring produced by an individual. Uniformitarianism: in geology, the principle which states that the geological processes are constant throughout time Essentialism: the philosophy that all species are unchanging throughout time; every species has an “essence” which characterizes all aspects of that species Natural Theology: the study of nature to understand the workings and creation of God Phylogeny: a family tree of populations or species; the evolutionary history of a particular group of species Part 2: Review and application of concepts 1. How did scientists‟ concept of what a species is change with the acceptance of the theory of evolution? Species were seen as being fixed, unchanging, and independently created. Evolution implied that species commonly changed over time, and that they were not independently created. Rather, species descended from common ancestors. 2. Compare and contrast ultimate and proximate explanations—be able to do this with an example, for example by providing an ultimate and proximate explanation for scaly bark on some trees (paper birch, for instance) or any other phenomenon of interest—medical phenomenon are a good way to play with the distinction— e.g., proximate and ultimate causes of illness!). In general, ecological explanations are proximate, and evolutionary ones are ultimate. An ecological explanation for flaky bark would point to genetic, chemical, or ecological factors— programmed cell death, flaking off of tissue infected with fungal spore, etc. An ultimate (evolutionary) explanation might focus on why that key trait— flaky bark—arose and the explanation will include the phrase “The fitness advantage of this trait is. . . .”. 3. Evidence for evolution emerged from a number of sources. For each general source of information below, be able to (a) describe specifically how that type of evidence was important in leading to the development of a theory of evolution, and (b) provide a specific example of that kind of evidence. (For example, what is an example of a vestigial trait that provides insight into evolution?) Type of evidence: How it contributed: An example: Fossil record Indicated patterns of Transitional forms change in species through indicated that species with time. Also provided one kind of traits could evidence of relatedness. change over time into species with other kinds of traits. Extinction—showed that species were NOT fixed. Environmental change— fossil record indicated that conditions on earth have changed over time, which suggests a cause for changes in species’ traits. “Law of succession”, in which fossil species were found to exist near similar closely allied extant species, argues for the relatedness of species. Vestigial traits Indicate that species traits Eyelessness in cave- can change through time—a dwellers, bone structure in species with eye buds but no whale flippers or bat wings sight might logically be (vestigial fingers), goose seen to have at one point bumps, tail bone. (For each been a sighted species with you would want to explain full eyes. exactly what it suggests…) Homologous structures Indicate that species have Tetrapod forelimb—bone common ancestry structure consistent across vertebrates, similar to that of the first tetrapod that is the common ancestor. Biogeography Indicates that species have Understand Fig. 24.6 in common ancestry Freeman 4. Darwin often referred to his theory as “descent with modification”. Explain this in terms of our modern understanding of evolution. What‟s descending? From what? What‟s being modified? How? What Darwin meant is that species evolve one from another (i.e., modern species are descendents of fossil species). The “modification” refers to changes in traits produced by natural selection: an ancestral trait— production of nectar, to take one of Darwin’s examples, is modified by the action of natural selection, which acts on variability in that trait. The species’ characteristics thus change over time, modified by the action of natural selection. 5. One of Wallace‟s most important insights was expressed in an 1855 paper: “Every species has come into existence coincident in space and time with a pre-existing closely allied species”. Explain this observation and articulate what this observation demonstrates about evolution. ? This statement is the outcome of all of his biogeographic observations. This observation argues for descent from a common ancestor. If species were created by a divine creator, Wallace argues, then there would be no particular reason for the flora and fauna of nearby places to be similar and that of distant places to be different. The observation that birds of New Guinea and Aru Island are similar to each other but different from those of Borneo, for example, is better explained by evolution from a common ancestor. Another way to think about this is that if evolution by natural selection has been the process causing speciation and diversification on life, then you would expect that similar niches to be occupied by related species in nearby areas, and not in distant areas. 6. Explain each of the following observations (a) using Lamarck‟s theory of evolution and (b) using the theory of evolution by natural selection. a. After the industrial revolution, moths living in or near polluted cities changed from being light-colored to being dark-colored. Lamarckian: Moths living in polluted cities needed to hide themselves against polluted (hence darker) tree trunks to avoid predators, so they developed, during their lifetimes, darker coloration. Those acquired traits were passed along to their offspring. Darwinian: Darker colored moths had an advantage as pollution worsened, because they blended in better with polluted tree trunks on which they rested. Those darker-colored moths thus had higher survival rates, and as a result left more offspring, than lighter-colored individuals. Because color is heritable in moths, that resulted in a greater abundance of darker-colored offspring. The incidence of dark coloration thus rose over time during the industrial revolution. b. The incidence of drug-resistance in the bacterium that causes tuberculosis is on the rise. Lamarckian: TB bacteria that encounter antibiotics during their lives acquire resistance; this resistance is passed along to their offspring. Darwinian: There is existing variation for susceptibility to antibiotics. Bacteria that are not susceptible (i.e., that are resistant) to antibiotics are more likely to survive and reproduce than those that are susceptible. Since resistance is heritable, the offspring of those bacteria will also be resistant. The frequency of resistance will thus increase from generation to generation. 7. What insight did both Darwin and Wallace derive from reading Malthus? Why was this insight so crucial? That more offspring are produced than can survive. This insight was important because it highlighted for both of them the “struggle for existence” that most species experience, and created a mechanism by which some species would do better than others. 8. What are the four “postulates” of the theory of evolution by natural selection? See your text, page 490. It boils down into the following: (1) individuals vary, (2) some of that variation is heritable, (3) more offspring are produced than can survive; there is variation in reproductive success, (4) that variation is non-random- in a given environment, organisms with particular traits will be more successful. Their offspring will have those traits, which will thus increase in frequency over time. 9. Make sure that you can do the “You should be able to…” items on page 495 of your text. 10. One of Darwin‟s assumptions is that individuals that are “different” in some way have an advantage in competition. Why would this be so? Because they may use slightly different resources than other individuals. We’ll talk more about the specifics of how this works in a few weeks! 11. (Straight from your text—Q. 2 of the Test Your Understanding) “Some biologists encapsulate evolution by natural selection with the phrase „mutation proposes, selection disposes‟. Explain what they mean, using the vocabulary of natural selection.” (Freeman, Biological Science, 3rd Edition, pg 501). Mutation is the source of heritable variation—in other words it is the mechanism by which new alleles (and, hence, new phenotypes) are generated. Mutation thus creates the “raw material” of variability—it “proposes” different forms of a trait, for example. Natural selection acts on that variability: favorable variations—those that increase an individuals fitness—will increase in frequency, and unfavorable ones—those that decrease an individual’s fitness—will decrease in frequency. Or, in other words, natural selection will “dispose” of them. 12. What insight did Darwin gain from his observations of the finches in the Galapagos? Beak of the Finch, page 30—their variability struck him, and suggested to him the relatedness of similar species. 13. David Lack visited the Galapagos long after Darwin (in the 1930s) and made carefully observations of the finches. Read the passage about Lack‟s insights in the Beak of the Finch, Chapter 4 (pages 54-56). What important pattern did he observe, and what did it lead him to conclude? David Lack observed that the beaks of finch species that share an island tended to be more different from one another than when they were found in isolation. This led him to conclude that competition prevented two overly similar species from co-existing and he thus inferred that natural selection had driven the divergence of beaks when finches competed.