Variation, fitness, and genetic diversity Bengal tiger (Panthera tigris tigris)

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<ul><li><p>Variation, fitness, and genetic diversityBengal tiger (Panthera tigris tigris)</p></li><li><p>Premise 1: evolution is important</p></li><li><p>Premise 1: evolution is important</p><p>Fundamental theorem of natural selection (Fisher 1930): rate of evolutionary change is proportional to the amount of genetic diversity available</p></li><li><p>Premise 2: genetic variation is valuable for fitness</p></li><li><p>Premise 2: genetic variation is valuable for fitnessSo, what is fitness?</p></li><li><p>Premise 2: genetic variation is valuable for fitnessSo, what is fitness?</p><p>= relative ability of a genotype, or individual, to survive and reproduce</p></li><li><p>more premises:more offspring are produced than will survive or reproduce (death happens)</p><p>individuals differ in their ability to survive and reproduce (death is not entirely random)some of these differences are genetically based</p></li><li><p>more offspring are produced than will survive or reproduce</p><p>individuals differ in their ability to survive and reproduce</p><p>some of these differences are genetically based</p><p>at reproductive age, genotypes that promote survival, or production of more offspring, will be more abundant in the population and will be passed on disproportionately</p><p>more premises:</p></li><li><p>more offspring are produced than will survive or reproduce</p><p>individuals differ in their ability to survive and reproduce</p><p>some of these differences are genetically based</p><p>at reproductive age, genotypes that promote survival, or production of more offspring, will be more abundant in the population and will be passed on disproportionately</p><p>It is very difficult to distinguish differences in fitness among genotypes from accident or other factorsmore premises:</p></li><li><p>What is variation?described at the individual level as homozygous, heterozygous AA Aa</p><p>described at the population level as monomorphic, polymorphic</p></li><li><p>Measurement of variationAt the level of the gene:# alleles per locus</p><p>At the level of the individual:proportion of loci within an individual that are heterozygous (Ho)At the level of the population:proportion of loci that are polymorphic in a population (P)= # polymorphic loci number loci examined</p></li><li><p>Measurement of variation locusindividualLDHMDHGPIPGI111111111212121112322121123422111133511221133</p></li><li><p>Measurement of variation locusindividualLDHMDHGPIPGI111111111212121112322121123422111133511221133# alleles2213</p></li><li><p>Measurement of variation locusindividualLDHMDHGPIPGIHo1111111110.02121211120.753221211230.54221111330.05112211330.00.25 = average H# alleles2213</p><p>Ho = proportion of loci within an individual that are heterozygous</p></li><li><p>Measurement of variation locusindividualLDHMDHGPIPGIHo1111111110.02121211120.753221211230.54221111330.05112211330.00.25 = average H# alleles2213 P = 0.75</p><p>Ho = proportion of loci within an individual that are heterozygousP = proportion of loci that are polymorphic in a population </p></li><li><p>rare alleles frequency usually less than 5%</p><p>private alleles present in only one population</p><p>fixed alleles population is monomorphic for an allele (due to loss of other alleles)</p></li><li><p>Measurement of variation P HAves (birds)0.100.043 Mammalia0.150.036Teleosts (fishes)0.150.051Reptilia0.220.047Plants0.260.071Insecta0.330.081Invertebrata0.400.100 </p><p>from Nevo 1978</p></li><li><p>Plants Invertebrates Vertebrates Overallspecialists0.04 0.06 0.04 0.05generalists0.08 0.15 0.07 0.11Genetic variation (H) present in specialists vs. generalistsexample: zebra musselscounter-example: Asian clamEvidence that variability is important?</p></li><li><p>Evidence that variability is important?heterosis enhancement of fitness due to increased heterozygosity (heterosis can be present in non-hybrids)</p></li><li><p>Metabolic, developmental fitness:growth rate of Coot clam decreased after genetic bottleneck caused loss of variation(Koehn et al. 1988)</p><p>efficiency of oxygen intake in American oyster decreased (Koehn and Shumway 1982)Evidence that variability is important?</p></li><li><p>Metabolic, developmental fitness:Florida panther: sperm defects, cowlicks, kinked tails, cryptorchidism reduced after increasing diversity through outbreeding (Pimm et al. 2006) </p><p>Evidence that variability is important?</p></li><li><p>Disease resistance:- 82% of outbred Chinook salmon resistant to whirling disease - 56% of inbred salmon resistant- absence of 3 alleles resulted in complete susceptibility to whirling disease </p><p>Evidence that variability is important?Arkush, D. K., et al. 2002. Can. J. Fish. Aquat. Sci. 59:159-167.</p></li><li><p>Disease resistance:MHC (major histocompatibility complex) : immune system protects by recognition of non-self proteins (e.g., graft rejection) most highly variable portion of genome</p><p>Evidence that variability is important?</p></li><li><p>Tasmanian devil (Sarcophilus harrisii)currently ~ 10,000-100,000Eliminated from mainland Australia ~ 600 yrs agoHigh mortality from car strikes, dogsProtected in Tasmania in 1941</p></li><li><p>Devil facial tumor disease (DFTD)transmissible tumor, spread by bitingtumors spread by allografts, genetically identical </p></li><li><p>Devil facial tumor disease (DFTD)transmissible tumor, spread by bitingtumors spread by allografts, genetically identical</p><p>DFTD is recent (~10 yrs), clonal but not recognized as non-self by MHC- severe loss of variability at MHC compared w. other species Siddle et al. 2007. Transmission of a fatal clonal tumor by biting occurs due to depleted MHC diversity in a threatened carnivorous marsupial. PNAS 104:16221-16226</p></li><li><p>Markers of low individual heterozygositydevelopmental instabilityfluctuating asymmetry</p></li><li><p>What are the sources of variation?</p><p>novel material - mutation: very rare!!</p><p>approx. 10-6 mutations per gamete per generation</p><p>most of these mutations do not affect the phenotype&gt; 100 to 1,000 generations to restore variability via mutation</p><p>** lost alleles are not regained! **</p></li><li><p>What are the sources of variation?</p><p>novel material - mutation: very rare!!</p><p>approx. 10-6 mutations per gamete per generationrearranged material - sexual reproduction </p><p>blending of genes, and rearrangements</p></li><li><p>Markers of low individual heterozygositycutthroat trout in hatchery vs. wild (Leary et al. 1985) 57% reduction in # polymorphic loci 29% reduction in average # alleles per locus 21% reduction in average heterozygosity per locus</p><p>of 51 fish:10 fish missing one pectoral fin3 fish missing 2 finsmany had deformed vertebral columns</p><p>***************************</p></li></ul>