Biology Homework Chapter 14: Mechanisms of Speciation
Textbook assignment: Chapter 14: The Origin of Species, sections 1-13 (all).
Keep in mind that "species" here is a group of organisms that interbreeds in the wild. This allows biologists to track individuals who are members of a group where genetic exchange occurs (speciation being the development of a distinct species), and isolate individuals who are not members of the group from consideration when trying to track evolutionary change. Members of different species (so defined) may actually be able to interbreed under laboratory conditions. Changes which lead to isolation of individual populations so that they no longer interbreed in the wilde — even when they are capable of doing so — are examples of macroevolution. If you read "species" in a narrow sense to mean groups of individuals that have radically different traits (like birds and fish), the chapter won't make sense.
- 14.1-2 Pay attention to the differences between microevolution (distribution of traits within a species) and macroevolution (change in trait leading to a distinctly new species). A species is also defined as a population which reproduces viable offspring among its own members. This definition cannot be applied to organisms that reproduce by binary fission! The term "species" is also used in other contexts, where members are identified by phenotypic traits, DNA and RNA sequences, or by ecological niche. The debate over the definition of species has led to refinements in terminology:
- Biological species: Populations whose members have the potential to interbreed in nature and produce viable and fertile offspring.
- Ecological species: Populations that are similar but have different behavior or habitats.
- Phylogenic species: The smallest group of individuals that share a common ancestor, as defined by DNA sequencing or biochemical pathways.
- 14.3 Reproductive barriers separate species: they may be pre-zygotic (temporal, geographical, behavioral, mechanical, gametic) and prevent the formation of a single cell zygote from gametes, or post-zygotic (hybrid inviability, sterility, breakdown), and prevent the development of viable offspring from a zygote.
- 14.4 Geographic isolation can create populations that do not interbreed and are thus considered separate species. Islands where species are isolated are the subject of intense study by biologists. When a geological event isolates parts of an originally single group into two separate groups that are no longer able to interbreed, allopatric speciation may occur.
- 14.5 New species also appear to arise in the same area as parent species (sympatric speciation), with a resulting competition between the two new non-interbreeding populations.
- 14.6 Sympatric speciation arises primarily when polyploidy creates offspring that can no longer interbreed with normal siblings, or when new traits create behavioral and temporal reproductive barriers. In plants, polyploidy (an increase in chromosome count due to disjunction mutations) is responsible for the variety of food sources we have.
- 14.7 Behavioral reproduction barriers occur in mating rituals, particularly among birds, where females selectively chose mates in non-random ways. Cichlid populations in Lake Victoria (Africa) are currently under study as examples of diverging species.
- 14.8 In isolated populations like those on the Galapagos Islands, reproductive barriers can arise through population shifts and genetic bottlenecks that isolate specific non-random mating behavior to a fragment of the former population.
- 14.9 Darwin's finches are often used as examples of speciation. Note that hybrids cannot compete as well as true-breeding species (which have beaks adapted for particular food sources), so the species' identities are maintained.
- 14.10 Biologists are also focussing studies in hybrid zones where a reproductive barrier has led to temporary species isolation that is now breaking down. In these situations, de-speciation is occurring as groups fuse into a new hybrid and previously distinct species disappear.
- 14.11 From the fossil record, the rate of speciation appears to vary; this observation has resulted in two approaches within evolution: the gradualist model and the punctuated equilibrium model.
Read the following weblecture before chat: The Origin of Species
Take notes on any questions you have, and be prepared to discuss the lecture in chat.
Perform the study activity below:
Use the Lizard Evolution Virtual Lab to explore applications of the theory of evolution to the anole lizard species of the Caribbean. Focus on Module 4. How does behavioral isolation work to create a separate species of lizard?
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- Required: Complete the Mastery Exercise with a score of 85% or better.
- Optional: Test yourself with the textbook multiple choice questions and note any that you miss that still don't make sense. Bring questions to chat!
- Go to the Moodle and take the quiz for this chapter.
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
- Lab Instructions: No Lab for this Chapter/li>
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