The Origin of Species

Transcription

1 The Origin of Species A. Macroevolution: Up to this point we have discussed changes in alleles or microevolution, with evolution this is the evolution of new. is the origin of a new species. There are 2 processes that lead to speciation: and. Anagenesis also called, is the accumulation of changes one species into another species. Cladogenesis also called evolution, is the budding of one or more new species from a parent species that can continue to exist. the founder of taxonomy described species in terms of their form called. Today taxonomists also consider differences in body function,,, and genetic makeup. The defines a species as a population who can interbreed in nature to produce viable, fertile offspring with each other and not produce viable, fertile offspring with members of. One exception to this rule is in or in labs where are sometimes produced between species that do not interbreed in nature. B. Barriers to Isolate Gene Pools: There are many reproductive barriers that isolate gene pools. Some barriers happen prior to the formation of the and are called barriers. Others happen after the formation of a zygote and are called barriers. The 5 Prezygotic Barriers #1) Isolation- 2 species live in habitats and do not encounter each other. Ex.: 2 species of parasites live on different hosts and never mate. #2) Isolation- special behavior unique to a species. Probably the important reproductive barrier with related species. Ex.: Fireflies of different species have special patterns of blinking to attract mates of their own species.

2 #3) Isolation- 2 species during different times of the, different or different years. Ex.: Some orchid s flowers open in the morning and wither that evening allowing pollination to occur only the entire year! #4) Isolation- 2 closely related species try to mate, but it is impossible. Ex. lock and key fit between bird species. #5) Isolation- gametes may meet, but no is formed. Ex.: Fish release eggs in water next to eggs of other species. Then when sperm are released by several species, they recognize the correct eggs by on the coats of the eggs allowing for fertilization. A similar mechanism occurs with recognizing the correct flower. Postzygotic Barriers #1) - zygote has formed but is genetically incompatible between 2 species. So it may, have development, or be a offspring. #2) - the hybrid offspring is, but. This is due to failure of to produce normal gametes if the chromosome or differs from the 2 parental species. Ex.: a horse + a donkey = a sterile. #3) - first generation hybrids are healthy and fertile, but when they with one another or with either parental species, the next generation is or. C. Biological Species Concept Problems and Alternates: Now having examined the biological species concept, understand it has limitations. It doesn t work to group life forms- the fossils must be grouped according to. It also doesn t work for organisms who do not interbreed, but essentially make of themselves. And sometimes this concept is too rigid. For example, breed with and produce fertile hybrid offspring, but still are species. The species concept emphasizes isolation of a species interbreeding with each other and not other species. Understanding some of its limitations, let s look at alternative. Note: no single definition of a species can extend to all cases that is why so many species definitions exist. #1) species concept- separates species based on features (appearance).

3 #2) species concept-emphasizes adaptations that enable a species to recognize mates. This can be,, or molecular (can a sperm recognize the egg?). #3) species concept- several of the species concepts together. #4) species concept- emphasizes where species + what they do = their. The the species plays in the environment. #5) species concept- emphasizes evolutionary lineage. D. 2 Ways to Bring About Speciation: Now that we have an understanding of the different definitions of a species, how does a species come about? The 2 general modes of speciation are speciation and speciation. Allopatric Speciation This occurs when a barrier physically isolates a single population and blocks flow. The physical barrier can be a that emerges and gradually splits a population into 2, a creeping glacier may divide a population, a may be divided into several smaller pools, etc. Once the single population is split, the new populations can undergo that may eventually lead to. It is more likely however, that a population will change substantially enough to become a new species. Allopatric/ geographical isolation of a small population usually occurs at the of a parent population s range and is called the isolated population. The gene pool of the peripheral isolate probably from the parent population to begin with and if it is a small population, the effect may result. Until the peripheral isolate becomes a large population, the gene pool will change and at random due to and recombination. In addition, some alleles may become in the small population. Then evolution may occur by especially if the environment is somewhat different, turning the peripheral isolate into a new species. are living laboratories for speciation. They allow for - the evolution of many diversely adapted species from a common ancestor. This was the case with Darwin s finches having many types of bills.

4 Sympatric Speciation This form of speciation occurs due to factors such as changes (in plants) and mating (in animals) that alter gene flow. When populations coexist in the same area, but are isolated. Plants A new species can be generated if a genetic change results in a that cannot breed with the parent population. Many plant species today resulted due to this having an extra set of chromosomes. This is called. And if that extra set of chromosomes came from a species we call this. Another type of polyploidy is called. This is when the extra set of chromosomes comes from species. These plant hybrids are usually and reproduce. But they are vigorous plants because they have combined the best qualities of their two parents.

5 Today most commercial plants are polyploids-,,, tobacco, and wheat. This is done with the aide of to create polyploids with special qualities. Animals Sympatric speciation can also occurs in animals. When animals of the same species living in the same area become isolated from the parent population. Genetic factors cause them to become fixed on resources not used by the parent population. For example, in Africa is populated by different closely related species of fish. They were once probably one or a few species that through sympatric speciation and, evolved to exploit the different sources in the lake. E. Genetic Change and Speciation: What happens when 2 closely related species that have been allopatric for some time come back into contact? Many things can happen. They may be able to meaning speciation occured. Or the opposite, evolutionary divergence may have led to 2 separate species that interbreed. Sometimes though there is a, a region where 2 related populations that diverged after being allopatrically separated come back together and interbreed only where their ranges. It is possible to generalize about the genetic distance between closely related species. Some cases get reproductive isolation/ speciation from the changing of gene loci in a population. Some get speciation from the changing of only a loci. So contrary to what Darwin believed, scientists are now saying that speciation alone does not bring about new species. It is now believed that some speciation has occurred more. Microevolution is the idea that many allele changes lead to changes over a long span of time. However, we rarely find gradual of fossil forms. Instead we find new species appearing in layers of rocks, then disappearing from the fossil record as suddenly as they appeared. This has led to the model of -species diverge in spurts of relatively change then change even as they give rise to additional species. These quick spurts are thought to bring about change in as little as a few or a few generations that can take thousands of years. This is relatively short considering a successful species may exist for an average of a few years. The component to this model is that a species stays the same for so long if the environment does not change and the component to this model means it is punctuated by episodes of speciation. Even still, gradualists believe the idea of is an illusion and that changes occur if not at the level then at the micro level. F. Evolutionary Novelty: How do novel features such as in birds arise? The fossil record indicates that birds evolved from earthbound. So there was a

6 of existing structures for a new. The term refers to a structure that evolved in one context and became co-opted for another function. How can slight genetic divergence lead to major structural changes? The answer comes through biology and understanding growth- a difference in relative of growth of different parts of the body help to shape an organism. An evolutionary trend mean it is oriented. Species don t choose to evolve, but are a result of genetic changes and the environmental response. For example, while some lineages exhibit a trend toward a body size, this is due to chance alone. With horses for example, they evolved from a smaller ancestor the size of a dog. Looking at the fossil record, it shows that the fossils are not in a, but into many species. This branching can even be seen in the many horse species coexisting today.