Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
The process of Speciation How Different Species Arise New information has revised our understanding of the tree of life • Molecular data has provided insights into the deepest branches of the tree of life finding evidence… Genes that regulate development are highly conserved*. *changed little over time Genotype alone is not the whole story… genetic “switches” HOX gene example 2 main ways changes in developmental genes lead to evolutionary important morphological changes. • Mutations in genes that regulate developmental processes. Changes in time/place of expression of developmental regulatory genes. Why are you following me? SO – according to modern evolution – how did diversity come about? Separation and separate reproduction of populations causing speciation events What is a species? a group of individuals capable of interbreeding and producing fertile offspring What must happen in order for new species to evolve? Populations must be reproductively isolated from each other. Introduction • What is speciation? • It is the formation of new species because of Reproductive Isolating Mechanisms What does it mean for two species to be reproductively isolated from each other? • Members of the two species cannot interbreed and produce fertile offspring. Speciation • 3 main types • Allopatric Speciation • Sympatric Speciation • Adaptive Radiation The process of species formation: Four Steps: • Single population is an interbreeding, reproductive community. • Development of a reproductive allopatric populations). barrier (formation of • Differentiation of the separated populations. • New species can no longer interbreed even if barrier disappears and they become sympatric. Reproductive barriers prezygotic • Barriers: • Geographic • Temporal • Behavioral • Mechanical • Gamete compatibility prevent fertilization postzygotic • fertilization occurs, but the hybrid zygote does not develop into a viable, fertile adult Prezygotic Barriers - examples mechanical structural differences prevents mating Gamete incompatibility female and male gametes are chemically incompatible Postzygotic Barriers - examples Reduced hybrid viability frogs; zygotes fail to develop or reach sexual maturity Reduced hybrid fertility mule; horse x donkey; cannot backbreed Hybrid breakdown cotton; 2nd generation hybrids are sterile allopatric sympatric Three Ways Reproductive Isolation (barriers) occurs • Behavioral isolation sympatric • Temporal isolation • Geographic isolation allopatric Allopatric speciation involves the geographic separation of the parent population into two subpopulations. It can occur if a physical barrier separates the range of a population. Allopatric speciation example • The populations of Tamarin monkeys are separated on the sides of the Amazon River. • Where the river tributary is wide and individuals on opposite banks do not interbreed, the populations are diverging toward separate species. Where the river tributary is narrow, the individuals still interbreed. Geographic Isolation in action • Speciation in action? • In the summer of 1995, at least 15 iguanas survived Hurricane Marilyn on a raft of uprooted trees. • They rode the high seas for a month before colonizing the Caribbean island, Anguilla. • Evolutionary biologists would love to know what happens next: • will the colonizing iguanas die out, • will they survive and change only slightly, or • will they become reproductively isolated from other Iguana iguana and become a new species? Geographic isolation is usually a prerequisite to speciation. However, there are situations in which speciation can take place between populations that are sympatric. Sympatric speciation occurs without any separation of the ancestral geographic range. (Some evolutionary biologists doubt this ever happens.) Sympatric Speciation macro temporal behavioral micro • Balanced Polymorphism • Polyploidy • Hybridization Balanced Polymorphism example: • Suppose a population of mice possesses a polymorphism for color. Each color provides a camouflage to a different substrate (rock, sand, etc..). • When not camouflaged, they are eaten • Thus, only mice with the same color associate and mate • Similarly colored mice are reproductively isolated…so gene pools can diverge. Polyploidy example • More than 2 sets of chromosomes found in diploid (2n) cells. • Often occurs in plants (occasionally animals) where triploid (3n), tetraploid (4n) and higher chromosome numbers exist. • Caused by nondisjunction in meiosis Tetraploid individuals will continue to produce diploid gametes – making them reproductively isolated very quickly. Hybridization example • Occurs when 2 different forms of a species mate and produce offspring along a geographic boundary called a hybrid zone. • The genetic variation of the hybrids is greater than that of either parent • This permits hybrids to adapt to environmental conditions beyond the range of either parent. • Hybrids can eventually diverge from parent forms when faced with selective pressures The Process of sympatric Speciation temporal isolation genetic isolation achieved due to temporal differences in breeding. lacewings C. Carnea is light green in spring and early summer, changing to brown in the fall. They live in fields and meadows in the summer and move to deciduous trees in the fall. C. downesi is a darker green year round. C. downesi lives mainly on conifers. Their ranges are sympatric. The species are separated by breeding season as well as habitat. C. carnea breeds in winter and again in summer. C. downesi breeds only in the spring. The Process of Speciation • When does behavioral isolation occur? • It occurs when populations are capable of interbreeding but have differences in courtship rituals or other types of behavior. niche choice due to food preference A rare, but local example "resident" and "transient" Orcas Resident and transient orcas inhabit the same waters, but avoid each other and do not interbreed. The two forms hunt different prey species and have different diets, vocal behavior, and social structures. Another example Wolves and dogs courtship patterns are different in the wild Behavioral Isolation example • Difference in courtship rituals Western and Eastern Meadowlark Different mating songs graphic summary Adaptive Radiation • Relatively rapid evolution of many species from a single ancestor. • Ancestral species colonizes an area where diverse geographic or ecological niches are available for colonization. • Examples: Darwin’s Finches, Australian Marsupials Adaptive Radiation Concept Map Reproductive Isolation results from Isolating mechanisms which include Behavioral isolation Geographic isolation Temporal isolation produced by produced by produced by Behavioral differences Physical separation Different mating times which result in Independently evolving populations which result in Formation of new species allopatric Gene flow sympatric Patterns of Evolution • Evolution can take place along the lines of the following patterns: • Divergent Evolution • Convergent Evolution • Parallel Evolution • Coevolution Divergent Evolution • Describes two or more species that originate from a common ancestor. • This may happen as a result of allopatric or sympatric speciation or by adaptive radiation Convergent Evolution • Describes two unrelated species that share similar traits. • Similar traits arise because each species has independently adapted to a similar niche • These traits are called: Analogous Traits Convergent Examples • Sharks, porpoises, and penguins have torpedoshaped bodies with peripheral fins. These traits arise as a result of adaptations each species has made to aquatic life…not due to a common ancestor. • The eyes of squids and vertebrates are physically and functionally similar. However they are not from a recent common ancestor, both evolved independently to perform similar functions. Parallel Evolution • Describes two related species or two related lineages that have made similar evolutionary changes after their divergence from a common ancestor • Example: • Species from two groups of mammals, the marsupial mammals and the placental mammals, have independently evolved similar adaptations when ancestors encountered comparable environments Coevolution • Describes the evolution of one species in response to new adaptations that appear in another species • An example: evolutionary arms race between predators and prey…or • Plants and plant eating insects • Pollinators and flowering plants • Pathogens and animal immune systems