Transcript Document
Conservation Genetics Class 8 Presentation 3 Forces of evolution Natural selection Genetic drift Non-random mating (inbreeding) Sexual selection (differential survival/reproduction due to mate selection) Gene flow (movement of genes from one population to another) Mutation Why study genetics? One component of “biodiversity” It is the construction library of a population or species Permits population to adapt and evolve through natural selection Common features define a spp Variability in genes allow them to adapt Genes & Environment Genotype + Environment = Phenotype We see the phenotype: leaf shape, colour of hair, eyes, beak size, etc. Value of diversity Differences in phenotype (e.g. blue eyes vs. brown, vs.. pink) mean different capabilities under different conditions such as: night vision, tolerance to high light or UV radiation) Adaptive Radiation Adaptive radiation occurs when genotypes evolve into new spp Natural selection acting on genotypes or mutations = new species Natural selection: due to competition, new habitat, selective predation, etc. Examples of adaptive radiation Hawaiian Honey-Creepers – Finch like seed eating ancestor – Arrived about 3.5 to 8 million yrs ago – Adapted beaks to different foods Fruit, insects, nectar (tubular with feathered tongue), seeds Examples of adaptive radiation Darwin’s finches on Galapagos Islds Ancestor: ground dwelling, seed eater Today 14 spp – Tree finches Adapted to feed on insects, sharper bill than ground dwellers – Ground Dwellers Beak size varies with food type Stronger bill suited for seeds – Warbler finch Insect eater in trees Examples of adaptive radiation Ciscoes in Algonquin Park (11k yrs) Ancestor: Common Cisco Speciation beginning with ciscoes developing specialized feeding apparatus: gill rakers to filter out different food types. Photo: NOAA Mutation Rates Usually thought to be low in the absence of mutagens (radiation, chemicals) Rates under “normal conditions” – Humans: 0.5 to 25/100,000 gametes – Bacteria: 0.00007 to 0.41/100,000 gametes – But bacterial generations short! So adaptations are fast. Most often mutations cause no visible change Mutation & Adaptation in Use Used in agriculture, industrial applications (pollution control, ore extraction, fermentation, etc). Potato (Solanum tuberosum) – Now 500+ varieties Corn (Zea mays) – Verities range from 0.6 to 6 m tall, 2-11 months to mature Genetic effects on Populations Random drift: – With natural selection the most important cause of evolution – Only some of the variation in parents passed on to progeny – Imagine parents have few children, variation lost – Does not matter much if population is large – In small population effect is fast and significant Random drift Not limited to individuals that have small populations Depends on chance events of flower pollination, seed falling on suitable site, survival of fish or amphibian off spring (remember Nemo, only he survived out of 100!) Genetic bottlenecks Catastrophes, other chance events, human activity sometimes reduce population dramatically – E.g. cheetahs population reduced a few thousand years ago – Elephant seal: hunting: by 1890 20 individuals, today very limited genetic diversity. Founder effect Another type of genetic drift Caused when small population breaks off and is reproductively isolated Founders genes only E.g. fruit flies on Pacific islands, Icelandic cattle vs. Norwegian cattle Results Small populations can suffer from inbreeding depression Depressed fitness (fertility and survival, leading to low lifetime reproduction output) Due to mating between close relatives Results Out breeding depression – Fitness down after out crossing between genetically differentiated populations – Example: planting same spp trees from different location: dilutes local genetic adaptation – Ontario has seed zones to limit movement of tree seed on public lands Results Genetic swamping: a form of out breeding depression Large amount of genetic material from closely related spp introduced by humans Cutthroat trout Rainbow trout 50/500 /5000Rule Soulé (1980) suggests: Need a population of at least 50 to avoid short term in breeding Need 500+ to enable long term adaptability and prevent reduction in evolutionary potential (prevent loss due to genetic drift) Need 5000+ to serve as reservoir for future losses Genetic terms Gene: physical entities transmitted from parent to offspring Genes made up two distinct types of alleles Alleles=may be same or different – E.g. allele for tall T or short t Genetic terms If alleles same: homozygous (TT or tt) If alleles different: heterozygous (Tt) Locus= location – Position on a gene, may contain may alleles Important features of genetic diversity P = proportion of loci with more than 1 allele A= No. of alleles at locus H = % of loci that are heterozygous Use electrophoresis to determine these measures Use of genetic measures Used to determine relatedness E.g. found that salmon along E coast have high allelic differences This means we should treat each river population as separate management zones, not part of a metapopulation 25% of returning salmon in Norway from hatcheries Dilutes wild stock Keep hatchery fish from escaping Consider genetics when stocking Questions