Biological Diversity Turner College & Career High School 2016

Transcription

1 Speciation & Homology Biological Diversity Turner College & Career High School 2016 Descent with modification modified characteristic = homology Speciation produces sister species descended from a common ancestor. Descendant species retain characteristics of common ancestor possibly in modified form. Genealogical Relationship Evidence of common ancestry. Same characteristics in 2 or more species inherited from a common ancestor = homology. Possibly/probably modified since split from sister species. The common ancestor no longer exists, so how can we tell what s a homology and what s not? 1. Position in relation to other body structures. 2. Embryonic origin 3. Continuity: characteristics homologous to another characteristic are homologous to each other. Position in relation to other body structures. Forelimbs Humerus, radius & ulna, carpals, metacarpals, phalanges Position in relation to other body structures. Insect wings, legs Antennae 1

2 Position in relation to other body structures. Flower parts Sepals Petals Stamen stamen Embryonic origin similar developmental origin. Pharyngeal arch: jaw Limb buds Lobes of brain Heart & arteries Gill slits Tail Continuity: characteristics homologous to another characteristic are homologous to each other. Dentary Inner Ear Homology Provides Evidence for Evolution Comparative Embryology Comparative Fossil Anatomy Comparative Physiology & Biochemistry Modification of existing characteristics/organs for other functions. Wings in bat Whale flippers Human arm Turtle leg Modification of existing characteristics/organs for other functions. Teeth: fangs in rattlesnake Salivary gland: venom gland 2

3 Imperfection of adaptation. Panda's thumb: actually radial sesamoid bone. "Oh, my aching..." after 2-3 million years, we are still subject to back strain. Modification but without function. Vestigial organs: senseless signs of history. Rudimentary structure in organism corresponding to a functional structure or organ in ancestral organism. Appendix in humans Vestigial organs Pelvic bones in whales. Vestigial organs Coccyx (tailbone) in humans. Coccyx (tailbone) Vestigial organs Nictitating membrane in humans. In animals, it is a clear eyelid can be drawn across the eyeball for protection from debris, prey, or the dryness of air, similarly to regular eyelids. Nictitating membrane Comparative Embryology Some traits seen only in embryos or larvae. Homology with larval or adult traits in other organisms. Notochord in vertebrates. Notochord & dorsal nerve cord in tunicate larvae. Bilateral symmetry in echinoderm larvae 3

4 Comparative Embryology Comparative Fossil Anatomy The fossil record. Homology relates fossils to existing organisms. Change in lineages Extinction Example: horses Comparative Fossil Anatomy Homology relates fossils to existing organisms. Change in lineages Extinction Example: trilobites Comparative Physiology & Biochemistry Homology applies to physiological & metabolic processes. Glycolysis and Krebs cycle Mechanisms of cell signaling Homology applies to biochemicals. DNA as genetic code RNA to translate code into protein structure ATP as energy currency of cells Other Factors in Evolution Convergence Evolution (adaptation) of dissimilar organisms to common function, superficially similar characteristics. Piercing sucking mouth in bugs, mosquitoes, fleas, butterflies Wings in bird, bat, pterosaur, insect (airplane?) Convergent characteristic NOT present in common ancestor. 4

5 Convergence Organisms have evolved independently in different parts of the world. Geographic distributions of species, genera, families, etc. Organisms have evolved independently in different parts of the world. Endemic species, genera, etc. on islands. Galapagos finches Used with fossil record to reconstruct evolutionary history. Camels in Asia: camel, dromedary South America: llama, alpaca Camels in N. America? Fossils? : Alligator in SE USA and China/SE Asia. Hellbenders in SE USA and China. Cyclocosmia in SE USA and Malaysia. 5

6 Isthmus of Panama divided Caribbean from Pacific about 3 million years ago. Previously a body of water existed. Several species crabs, snails, fish, etc. have nearest relatives on other side of land barrier. Natural Selection, Genetic Drift & Gene Flow Evolutionary Change Three major factors alter allele frequencies and bring about most evolutionary change: Natural selection Genetic drift Gene flow Natural Selection Differential success in reproduction results in certain alleles being passed to the next generation in greater proportions. For example, an allele that confers resistance to DDT increased in frequency after DDT was used widely in agriculture. Natural Selection Genetic Drift The smaller a sample, the greater the chance of deviation from a predicted result. Genetic drift describes how allele frequencies fluctuate unpredictably from one generation to the next (chance). Genetic drift tends to reduce genetic variation through losses of alleles. 6

7 Genetic Drift Genetic Drift 5 5 CW C W 2 Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 Generation 2 p = 0.5 q = 0.5 Genetic Drift 5 CW C W 2 The Founder Effect The founder effect occurs when a few individuals become isolated from a larger population. Allele frequencies in the small founder population can be different from those in the larger parent population. Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 Generation 2 p = 0.5 q = 0.5 Generation 3 p = 1.0 q = 0.0 The Bottleneck Effect Sudden reduction in population size due to a change in the environment. New gene pool may not reflect original. If the population remains small, it may be further affected by genetic drift. Case Study: Impact of Genetic Drift on the Greater Prairie Chicken Loss of prairie habitat = reduction of population. The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched. Original Population Bottleneck Effect Surviving Population 7

8 Survival rate (%) 1/19/2018 Impact of Bottleneck Effect Location Illinois Pre-bottleneck (Illinois, 1820) Pop. Size 1,000-25,000 <50 Post-bottleneck (Illinois, 1993) Number of Alleles/Locus Percentage of Eggs Hatched 93 <50 Kansas 1998 (no b/n) Nebraska 1998 (no b/n) 75, , Impact of Bottleneck Effect Researchers used DNA from museum specimens to compare genetic variation in the population before and after the bottleneck. The results showed a loss of alleles at several loci. Researchers introduced greater prairie chickens from populations in other states and were successful in introducing new alleles and increasing the egg hatch rate to 90%. Effects of Genetic Drift: A Summary 1. Significant in small populations. 2. Causes allele frequencies to change at random. 3. Can lead to a loss of genetic variation within populations. 4. Can cause harmful alleles to become fixed. Gene Flow Gene flow consists of the movement of alleles among populations. Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen). Gene flow tends to reduce variation among populations over time. Gene flow can decrease the fitness of a population. Gene Flow Consider, for example, the Parus major on the Dutch island of Vlieland: Mating causes gene flow between the central and eastern populations. Immigration from the mainland introduces alleles that decrease fitness. Natural selection selects for alleles that increase fitness. Birds in the central region with high immigration have a lower fitness; birds in the east with low immigration have a higher fitness Population in which the surviving females eventually bred Central Eastern Females born in central population Females born in eastern population NORTH SEA Central population Vlieland, the Netherlands Parus major Eastern population 2 km 8

9 Gene Flow Gene flow can increase the fitness of a population. Consider, for example, the spread of alleles for resistance to insecticides: Insecticides have been used to target mosquitoes that carry West Nile virus and malaria. Alleles have evolved in some populations that confer insecticide resistance to these mosquitoes. The flow of insecticide resistance alleles into a population can cause an increase in fitness. Gene flow is an important agent of evolutionary change in human populations. 9