BIOEE 1780 1st EditionExam # 2 Study Guide 2-20 (Natural selection and finches)Remember, evolution is defined as a genetic change in a population, and natural selection is onlyone mechanism for this change. Darwin noticed that 1) populations would grow exponentially if all organisms born survived and reproduced, 2) but in reality populations stay relatively stable, and 3) natural resources are limited and relatively stable. He inferred that 1) there must be fierce competition over resources. And 2) survival is not random but is influenced by heritable traits. Adding a few more facts help to further Darwin’s assumptions: 1) no individuals are exactly the same except among very simple bacteria, and 2) much if this variation is heritable. It was then proposed that natural selection would occur when 1) individuals vary in some trait(s), 2) at least some of this variation is heritable, and 3) the variation affects survival and reproduction.Peter and Rosemary Grant continue studying finch populations on Daphne Island in the Galapagos. Here, the finch population varies in beak depth. They have observed that when there are plenty of seeds to be eaten, no selection occurs because large-beaked birds can eat caltrop, small-beaked birds can eat spurge and medium-beaked birds eat either. In 1977 the islands experienced a drought, causing seed abundance to plummet and leaving behind mostly large, hard seeds. As a result, the next generation of finches had larger beaks. An El Nino is the weakening of normal trade winds which increase rainfall in certain areas, and small seed plants are more competitive with increased rainfall. What affect could this have on the finch population?2-23 (Natural selection, fitness, and finches)During the El Nino season, small-beaked birds became dominant. Another drought followed. What happened then? Actually, beak size among medium ground finches did not change because a new competitor had come to island and filled the large seed niche.Fitness depends on context. Is a brown mouse more or less fit than a white mouse? What if they live on a white sand beach vs a brown sand beach? Among medium ground finches, they have a fitness curve with two peaks with a valley in between. Why? They are outcompeted by small-beaked birds for small seeds and outcompeted by large-beaked birds for large seeds. How can this fitness curve be maintained? Small-beaked birds tend to mate with other small-beaked birds and large-beaked birds tendto mate with other large-beaked bird. Why? The females like to mate with males that sing like their fathers did, and the song is determined by beak size.There are some examples of natural selection. Scarlet King snakes have evolved to resemble venomous coral snakes in areas where they both exist. The allele for lactose tolerance is common in populations of humans that have had cattle for centuries. Selection can be directional, stabilizing, or disruptive.2-25 (Life history)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Life history is the timing and duration of key events in a lifecycle. There is a necessary tradeoff of energy and time invested in each stage. Consider this: you can have 10 offspring now and die immediately, or you can have five offspring every year for the rest of your life. If you have a 90% chance of dying each year, which would you choose? How about if you have a 10% chance of dying?Extrinsic mortality is the rate at which external events (ie: animal attacks) lead to death in a population. Intrinsic mortality is the rate at which internal events (ie: heart disease, cancer) lead to death in a population. Senescence is the deterioration in the biological functions of an organism as it ages. There are trade-offs between future benefits and current repair. One example is antagonistic pleiotrophy, or selection of a trait that is beneficial in early life but detrimental in old age. An example can be found among guppy populations in Trinidad. At the top of the waterfall where there are no predators, the guppies grow larger and have fewer offspring per year than the bottom where there are many predators. 2-27 (Selection, behaviors, and sociability) Types of selection include kin selection (ie: bee-eater bird parents that will force their children tocome home and take care of them), individual selection (this is the majority of the selection we’ve talkedabout), and group selection (the differential performance of groups of individuals that causes them to outcompete other groups… this is quite rare). In the case of group selection, the system can only work if every member cooperates. Otherwise self-sacrifice will be selected against (in many cases, behaviors are actual genetically selected and not necessarily learned).Sociability has a number of costs (such as vulnerability to disease) and benefits (such as a lower chance of becoming a predator’s meal). According to Darwin, altruism could be fatal to his theory of evolution. For it to fit his model there must be a benefit that outweighs the cost (although in this case we can’t really call it altruism). Kin selection may be a better term for altruism in natural populations. An organism’s total fitnessis equal to the direct fitness plus indirect fitness, and kin can offer indirect fitness (however, not all kin are equal). R is the coefficient of relatedness, and it decreases by 0.5 for each time you pass a node on a family tree. Hamilton’s rule states that, for an action to improve fitness, rB>C where B is the benefit and C is the cost. Example: the crows at Cornell can sometimes be observed helping to raise their younger siblings. Maternity assurance: the mother gives birth to offspring, so they can be assured that they are related to said offspring. Males have no way to assure that their offspring are really their own. For this reason, it is more beneficial to your fitness for you to save a sister rather than a brother, if you must choose between the two.3-2 (The evolution of sex)Key terms: sexual selection, sexual reproduction, asexual selection, hermaphrodites, recombination, Muller’s Ratchet, Red Queen effect, Certainty of paternity, anisogamyThere is a whole paradox of sex: it costs energy and time, but it benefits by recombining genes and making the gene pool more diverse. What has come to make sex so prevalent in current successful species? Why have some