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Populations: a supplement to your Text Objective: Be able to read a research paper in Molecular Ecology and derive conservation recommendations from the data What is Genetic Variation? 1) Heterozygosity of population: Percentage of genes in a population that are polymorphic. 2) Number of alleles and frequencies for each polymorphic gene in population. 3) Heterozygosity of each individual in population: Percentage of genes per individual that are polymorphic, noting that in a diploid each gene can only be heterozygous or homozygous. Rate of loss of heterozygosity in a population per generation (Wright, 1931) deltaF = 1/2Ne So if population of 50 individuals, there will be a 1% decline in heterozygosity due to loss of rare alleles. If population of 25 individuals, decline of 2% (1/50 or 2 per 100). 1 Factors that affect genetic variation: Mutation Mating system Three STRONG FORCES that change allele frequencies: 1. GENE FLOW = movement of gametes, individuals or populations 2. SELECTION = a directional process that leads to an increase in frequency of alleles or genotypes that increase individual ability to produce healthy offspring. 3. DRIFT = a process in which allele frequencies in a population change by chance as a result of non-random carry-over (sampling error) from generation to generation. - leads to: loss of alleles, increased homozygosity, population differentiation (if no migration/gene flow between populations). Drift can increase in small populations due to: fragmentation, bottleneck = event removes all but a few individuals, founder effect = a few individuals leave old population, start new one. 2 The assumptions of the island model: All populations are created equal, with N individuals and equal contributions to the migrant pool There is NO spatial structure: in effect all populations are equally close to all other populations (no isolation by distance) Everything is at equilibrium, nothing is changing. No selection no mutation The fixation index is the probability of any two alleles chosen randomly in a population having arisen from one common ancestor. In a set of populations that exchange NO migrants, this index increases in each subpopulation. This means that subpopulations of a single species can change over time (in allele frequencies and in hetero vs. homozygosity) and become divergent from each other. Ultimately, each subpopulation would have only certain alleles (e.g. allele A or a) due to inbreeding. Fst = 1/ 4Nm + 1 Fst is the equilibrium fixation index, a measure of population divergence within a species. N is the local population size and m is the migration rate among populations. An Fst of 1.0 is high and indicates high divergence, little or no migration. Zero indicates no divergence and at least some migration. 3 Grey wolves are large mammalian carnivores that can disperse over long distances (50 - several hundred km) across major obstacles - an individual wolf moves 50km before establishing territory. • Grey Wolves have social organization - packs. • • Different prey for boreal forest vs. tundra/taiga wolves: Boreal Forest wolves believed to defend permanent territories and predate resident, nonmigrant species (deer, elk, moose, woodland cariboo). • Tundra/taiga wolves believed to be territorial in summer, but migrate with barren ground caribou in winter to caribou breeding grounds - this is tested in our paper. • Tundra, taiga and boreal coniferous forest biomes are uninterupted and intergrade, no physical barriers to wolves or caribou. 4 http://gliving.com/the-might-comeback-of-gray-wolves/ Background information Hypothesis/ question = The Aim How they did it 4 methods Main result Conservation recommendation based on result •Sampling of wolves over a large, continuous area of forest, taiga and tundra. •19 migrating caribou and 19 tundra wolves tracked by satellite telemetry, plus radiocollars on 7 wolves. • Created 12 month data set, computed Euclidean distances. • Blood was collected as described in caption of Fig. 1 above (26 living wolves and tissue from pelts of 378 legally hunted wolves). • Pelt color was classified and recorded. 5 http://www.enr.gov.nt.ca/_live/pages/wpPages/caribou_in formation.aspx Fall/winter Spring/summer Results from satellite telemetry in this study prove for the first time that: ! Boreal Forest wolves do not migrate. ! Tundra/Taiga Wolves and barren ground caribou migrate north together, in spring, over 1000 km. ! Wolves give birth in tundra summering areas (pink). Pups need to stay near the den. ! Though caribou are past calving and start moving south in summer, the simultaneous caribou-wolf migration south is in the fall through spring of the following year. Let’s look at one wolf and one caribou over the year… Caribou stays in one area in May-June - this is the calving ground Wolf stays in one area in May-October, around den and pups Caribou and wolf are In same location in December http://gliving.com/themight-comeback-of-graywolves/ 6 Two haploid DNA markers and one genetic trait (light coat color is recessive): Mt DNA and coat color support hypothesis that ecology not geography drives evolution of distinct forest vs. tundra/taiga wolf populations. http://gliving.com/the-mightcomeback-of-gray-wolves/ DNA markers (autosomal microsatellites, Mitochondrial DNA and Y Chromosome haplotypes): Fst analyses show population subdivision and allele fixation based on wolf movement, habitat and prey movement for all markers, except Y chromosome (why?) All red highlighted and underlned results are statistically significant - see P values. Lat not Long Association reflects south to north migration 7 The authors conclude that Tundra/Taiga grey wolf is an Evolutionarily Significant Unit (ESU): What conservation recommendations do we take away from this study? Is the Tundra/Taiga grey wolf a new species or is it a population? Does this matter? http://www.cosmosmith.com/images/tundra_wolf01a.jpg http://gliving.com/the-might-comeback-of-gray-wolves/ Background information Hypothesis/ question = The Aim How they did it 4 methods Main result Conservation recommendation based on result 8 Populations: a supplement to your Text Objective: Be able to read a research paper in Molecular Ecology and derive conservation recommendations from the data 9 10 11 12 Populations: a supplement to your Text Objective: Be able to read a research paper in Molecular Ecology and derive conservation recommendations from the data 13