Download Chapter 24: The Origin of Species AP Biology I. Chapter 24

Chapter 24: The Origin of Species AP Biology I. Chapter 24: Overview A. That “Mysteries of Mysteries: 1. Speciation: focal point of evolutionary theory-­‐ the appearance of new species is the source of biological diversity 2. macroevolution: evolutionary change above the species level i. example: feathers during the evolution of birds from one group of dinosaurs 3. two basic patterns of evolutionary change: i. anagenesis(phyletic evolution)-­‐ the accumulation of changes that gradually transform a given species into a species with different characteristics ii. cladogenesis(branching evolution)-­‐ is the splitting of a gene pool into two or more separate pools, which each give rise to one or more new species a. can promote biological diversity by increasing the number of species 4. environmental influences of speciation-­‐ resulting in physiological responses: i. phototropism-­‐ (plants and planaria) the response to the presence of light ii. photoperiodism-­‐ (chickens, flowering plants)response in change in the length of the night iii. circadian rhythms: physiological cycles of about 24 hours a. present in all eukaryotes b. can persist in the absence of external cues iv. diurnal/ nocturnal v. Seasonal responses-­‐ hibernation, estivation and migration vi. quorum sensing in bacteria: regulation of gene expression in response to cell population and density a. secretion of chemical signal molecules such as auto-­‐
inducers will increase in concentration as a function of population density leads to alteration of gene expression II. Chapter 24.1: The biological species concept emphasizes reproductive isolation. 1. species: latin word meaning “kind” or “appearance” A. The Biological Species Concept: defines a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable , fertile offspring, but are unable to produce viable, fertile offspring with members of other populations. 1. members of a biological species are reproductively compatible 2. emphasizes the separateness of species from one another due to reproductive barriers B. Reproductive Isolation: biological species are distinguished based on reproductive incompatibility 1. biological factors or barriers impede members of two species from producing viable, fertile hybrids i. usually involves a combination of several barriers to isolate a species gene pool 2. classification of reproductive barriers: i. prezygotic barriers: impede mating between species or hinder the fertilization of ova if members of different species attempt to mate. a.habitat isolation-­‐two species occupying different habitats in the same area b. temporal isolation-­‐breeding during different times of the year c. behavioral isolation-­‐ courtship rituals and othe mating behaviors act as barriers d. mechanical isolation-­‐ morphological differences e. gametic isolation-­‐ sperm of one species may not be able to fertilize ovum of another ii. Postzygotic barriers: often prevent the hybrid zygote from developing into a viable, fertile adult a. reduced hybrid viability-­‐ genes of different parent species may interact and impair the hybrid’s development b. reduced hybrid fertility-­‐chromosomal differences may result in sterile hybrids c. hybrid breakdown-­‐second generation hybrids are sterile C. Limitation of the Biological Species Concept: there are limitations to the biological species concept. 1. example: no way to evaluate reproductive isolation of fossils or asexual organisms 2. example: difficult to apply the biological species concept to the many sexual organisms about which little is known regarding their ability to mate with different kinds of organisms D. Other Definitions of Species: emphasize the unity within a species 1. morphological species concept: characterizes a species by its body shape, size, and other structural features. i. advantages: can be applied to asexual and sexual organisms and it can be useful even without information on the extent of gene flow ii. disadvantage: this definition relies on subjective criteria-­‐ there may be disagreement amongst researchers regarding which structural species distinguish a species 2. paleontological species concept: focuses on morphologically discrete species known only from the fossil record 3. ecological species concept: views a species in terms of its ecological niche, its role in a biological community. i. example: different species of finch on the Galapagos islands may be similar in appearance but are differentiated based on what they eat 4. phylogenetic species concept: defines a species as a set of organisms with a unique genetic history-­‐ a branch on a tree of life i. phylogenetic history of a species is traced by comparing its physical characteristics or its molecular sequences with those of other organisms ii. phylogenetic information sometimes reveals the existence of “sibling species”-­‐ species that appear so similar that they cannot be distinguished on morphological grounds. III: Chapter 24.2: Speciation can take place with or without geographic separation A. Allopatric (Other Country) Speciation: (from Greek allos = other and patra = homeland)a population forms a new species while geographically isolate from its parent populations 1. example: two smaller lakes forming from the subsiding water levels of a mother lake 2. example: flycatcher population in central America divided into two smaller populations by advancing glaciers 3. once geographic separation has occurred the separated gene pools diverge through any or all of the mechanisms of evolution. a. Mutations b. Sexual selection 4. allopatric separation on occurs when the populations have changed enough that they can no longer have the potential to interbreed and produce fertile offspring B. Sympatric (Same Country) Speciation: (from Greek syn = together) speciation takes place in geographically overlapping populations. 1. Polyploidy: extra sets of chromosomes-­‐ more than two chromosome sets a. autoploidy-­‐ chromosome sets derived from single species b. failure of cell division can double a cell’s chromosome number(diploid to tetraploid) c. triploid offspring of tetraploids and diploid parents are sterile d. tetraploids can produce fertile offspring through self pollinization 2. alloloploidy: a. when two different species interbred their offspring is often sterile b. asexual propagation may occur creating fertile generations from a sterile one c. alloloploids are fertile with each other but not with parental species-­‐ a new species is formed 3. origin of new polyploidy species is common enough and rapid enough that scientists have documented several such speciations a. examples: wheat-­‐ allohexaploid, oats, cotton, potatoes, tobacco and goats beard plants native to Europe, now hybrids are populating areas of the pacific northwest C. Adaptive Radiation: The evolution of many diversely adapted species from a common ancestor upon introduction to various new environmental opportunities and challenges 1. can occur when a few organisms make their way to new areas 2. can occur when environmental changes cause numerous extinctions, opening up ecological niches for the survivors 3. example: radial expansion of mammals after dinosaurs went extinct D. Studying the Genetics of Speciation: E. The Tempo of Speciation: 1. gradualism: species descended from a common ancestor gradually diverge more and more in their morphology as they acquire unique adaptations 2. punctuated equilibrium model: a new species changes most as it buds from a parent species and then changes little for the rest of its existence a. fossil records show many episodes in which new species appear suddenly in a geologic stratum-­‐ opposite of gradual descent with modification suggested by Darwin