6. Evolution.pdf

Evolution Aarni Auerniitty  Evolution theories  Darwin: fight for survival  Lamarck: cause and consequence...

Evolution Aarni Auerniitty  Evolution theories  Darwin: fight for survival  Lamarck: cause and consequence  Mendel: hereditary theory  Synthetic evolution theory combines previous theories with knowledge about genetics VARIATION  NATURAL SELECTION  EVOLUTION  Evolution occurs over time on a population level  Population: individuals of the same species living on the same area at the same time  Proof of evolution  Fossils  Index fossil: a species that has been abundant and far spread during a short time during the history of the Earth. Helps to estimate the age of other fossils  Living fossil: a species that has stayed unchanged for over millions of years  Fossil series  E.g. the evolution of the horse  Transitional fossils  E.g. Archaeopteryx  Proof of evolution  Rudiments  Embryo similarity  Similarity in bone structure  Similarities in DNA  Resistance to antibiotics  Breeding  Variation  For evolution to happen individuals of a species need differ from each other genetically  They have different genotypes = all genes  Genes have different forms, alleles, which affect how individuals look and function (phenotype)  New allele combinations form through sexual reproduction  New alleles form through mutations  Mutations in gametes are most significant as they can be inherited  Some variation in phenotype can be caused by the environment in limitations of genotype  Natural selection  Natural selection: changes to the proportions of alleles in a population.   Alleles that help individuals to survive and reproduce get more common  Fitness  With high fitness individuals survive to reproduce and have offspring that can reproduce  Selection pressure speeds up natural selection  Predation and herbivory  Increased competition  Natural disasters  Diseases and parasites  ect.  Stabilizing selection  In stable conditions, decreases variation  For example bird brood size  Optimal amount of eggs for willow warbler is 5 Directional selection  Directs variation, affected by selection pressures  E.g. industrial melanism Disrupting selection  Increases variation, affects two parts of a population differently  Possible speciation due to reproductive isolation  Developing into a new species is very slow Sexual selection  Different kinds of behaviour and structures  Females often modest  More resources for reproduction  Helps in hiding from predators  Males are large and fancy  Good genes  lot of resources for strength and looks  good mate  Some exceptions for example some male cuttlefish camouflage as females Kin selection  Reproductive success of close relatives is preferred over own  Closer the relation, more likely kin selection is to occur  Altruistic behaviour  Different kinds of evolution  Microevolution: change in gene pool of different populations of a species  E.g. antibiotic resistance of bacteria  Macroevolution: birth of new species  Coevolution: two species affect each others evolution  E.g. pollinators and flowers Speciation  Gene flow: mixing of genes between populations of a species  Migration affects the population gene pool  Speciation occurs when the gene flow is disrupted  The process takes usually a long time but can be relatively quick for example when plants cross breed  The gene flow is disrupted because of reproductive isolation  Pre- and post-zygotic  Allopatric speciation – through geographic isolation separating a population  Most common form of reproductive isolation  Sympatric speciation – through mutations within a population without geographic isolation  Plant polyploidy (multiplication of chromosomes)  Types of reproductive isolation Pre-zygotal Post- zygotal  Geographic isolation  Offspring dies during embryonic development or after birth or seeds  Differences in mating behaviour do not form or germinate and timing  Offspring do not live long enough to  Physical incompatibility reproduce  Incompatibility of gametes  Offspring are sterile hybrids or will get sterile offspring Genetic drifting  Bottleneck effect: population collapses due to natural disasters etc. and the gene pool of the new population is based on the few survivors  Founder effect: gene pool is based to the part of the population that relocated to a new area  Small populations are vulnerable to the effect of chance  Possible negative or positive effects?  Adaptive radiation  The original species evolves “quickly” into multiple new species by adapting into conditions in new habitats  Key adaptation: a trait that helps species take over new areas  Extinction  As species goes extinct the progress of hundreds of millions of years is lost for good  On the other hand mass extinctions give way to new species  E.g. death of dinosaurs enabled mammals to take over   End Ordovician 444 mya  85 % of species, short and severe ice age lowering sea level  Late Devonian, 383 mya Mass extinction events  75 % of species, plants moving on land  weathering of rocks  nutrients in oceans  algal blooms  lack of oxygen in oceans and reduction in atmospheric CO2 leading to climate cooling  End Permian, 252 mya  96 % of species, massive volcanic eruptions or asteroid impacts combined with microbes producing methane caused severe rise in global temperatures and seawater acidity  End Triassic, 200 mya  80 % of species, reasons unknown but most likely volcanic activity and climate change and ocean acidification that folllowed  End Cretaceous, 66 mya  76 % of species, meteor impact (15 km wide), global temperatures decreasing due to dust and ash in atmosphere halting photosynthesis  Holocene, current  Humans  climate change, ecosystem degradation and overuse of natural resources