BIOL 1070 Lecture Notes - Cladogenesis, Mutation, Invasive Species

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September 14th 2011
What is biodiversity?
- Biodiversity is the variety of genes, species and ecosystems.
- Shaped by billions of years of evolutionary history of life forms interactions with each other and their
- Altered by human activity with lasting impacts at large scales that are difficult to predict.
What is evolution?
- Descent with modification from common ancestors. Can only occur if there is variation.
- Evolution evolves in change of proportions of variants in population.
What factors contribute to threats to native freshwater mussel biodiversity?
- Habitat destruction
- Human impacts / Overfishing
- Agriculture runoff
- Chemicals in water
- Invasive species
- Water temperature fluctuations
List of characteristics of Unionids & Dreissenids
What is the larval form?
Does it need a host?
Not host-dependant.
Can attach to any solid surface.
What type of larval dispersal?
Larvae dispersed by host
Dispersed in water
Freshwater bivalves develop in 3 ways
1. By producing veligers larvae (Dreissena Polymorphall)
2. By releasing ully developed young mussels (rare)
3. By passing early development as a parasitic stage on a host (Unionids)
Unionid larvae
Glochidia Can’t swim or crawl – Attach to host fish grills
Strategies for infecting fish hosts
1. Conglutinates Glochidia enclosed in membranous capsules that mimic host prey.
2. Lures Modified mantle tissue, mimics fish or invertebrate prey item to attract fish host.
Host capture
- Mussel may physically grip host and pump glochidia over the gills.
September 19th 2011
Biological Variation
- Variation occurs in all species
- A well sampled population = A normal distribution
What causes the variation?
- Genotypic variation
- Phenotypic variation
Effect on Genetic Variation
A heritable change in DNA
Introduces new genetic flow
Gene Flow
Change in allele frequencies
as individuals join a
population and reproduce
May introduce genetic variation from another
Genetic Drift
Random changes in allele
frequencies caused by chance
Reduces genetic variation, especially in small
populations; can eliminate alleles
Natural Selection
Differential survivorship or
reproduction of individuals
with different genotypes
One allele can replace another or allelic variation
can be preserved
What is a gene?
- A molecular unit of heredity in a living organism.
- It is made up of stretches of DNA and RNA that may code for a type of protein or have a function in
the organism.
- Comes from the nucleus or chloroplast.
What is an allele?
- An allele is a form of gene or group of genes
- Different alleles may result in different traits, such as eye or flower petal color. However, different
alleles may give rise to the same trait resulting in genetic variations in alleles with little or no
- Errors in DNA replication Random
- Does not benefit organism Secondary source of variation is recombination
Genetic Drift
- Evolution by chance due to sampling error
Causes of genetic drift
1. Population bottlenecks
o Sudden, severe reduction in population size Random
o Loss of individuals not related to particular traits
o Example: predators, diseases, hurricane, flooding
2. Flounder effects
o Loss of genetic variation that occurs when a new, smaller population is established
o Example: island
Genetic drift
- Random changes in allele frequencies in a population due to chance
Gene flow
- Sharing of alleles among populations
Natural selection
- Non random differences in survival and/or reproduction among individual entities on the basis of
differences in heritable characteristics.
Components of evolution
- Heritability
- Variation
- Overproduction
September 21st 2011
- Mutations (errors in DNA replication) are the primary source of new variation.
- Good, bad, and neutral mutations happen with equal probability.
- Beneficial mutations increase in frequency and deleterious mutations decrease in frequency under
natural selection.