The Evolution-Ecology Connection Lecture 2 The Evolution-Ecology Connection

‘Nothing in biology makes sense, except in the light of evolution ‘Nothing in biology makes sense, except in the light of evolution.’ Dobzhansky

What is: ___________? Evolution: What evolves? In order for evolution to occur what must happen, or what conditions must be met? Why is it important for species to evolve?

Natural selection: What two conditions must occur for natural selection to take place? Fitness: A gene for increased fitness would….

Are those with greater levels of fitness necessarily bigger, stronger or faster? Natural selection involves a competition for: Traits which give an individual who possesses them an increased level of fitness are known as ____________

What is the basis of adaptations? Genetic information is carried in a code in DNA Traits (they may be adaptations) involve information carried in specific genes Gene: A variant form of a gene is an ___________ What leads to the formation of these variant forms? Gene expression results in a specific ______

How genes interact: Single genes: Dominant – recessive Codominant - Incomplete dominance Phenotype: expression of genetic information – consequence of gene interactions

Incomplete Dominance One gene is not completely dominant over another – result is an intermediate expression form in the heterozygous genotype Example: Flower color in petunias

Quantitative traits: Involve interaction of several (sometimes many) genes Complicated by epistatic expression, epigenetic inheritance patterns and environmental interactions (multifactorial inheritance) Accounts for continuous variation in phenotype form

How Polygenic Inheritance Works: Several genes may influence ultimate phenotype : Height Hair and skin color Continuous range (red to white) in flower color Another example: Beak depth in Galapagos Finches

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Examples of Evolution 1. Gartersnake-Oregon Newt interaction 2. modification of beak size in Galapagos finches – studies of Peter and Rosemary Grant No new species arose in either case Species: ‘A group of similar appearing organisms that share the same gene pool’

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Selection pressure within a species Selection for one extreme Selection for the ‘average’ Selection for two extremes (bimodal)

5.6 Several Processes Can Function to Alter Patterns of Genetic Variation Not all phenotypes represent adaptations in response to natural selection Factors other than natural selection affect changes in genetic variation within populations Mutations are heritable changes in a gene or a chromosome Genetic drift is the change in allele frequency due to random chance associated with sexual reproduction Migration is the movement of individuals between local populations Gene flow is the movement of genes between populations

5.6 Several Processes Can Function to Alter Patterns of Genetic Variation The Hardy–Weinberg principle of genetics states that under conditions of random mating, the allele frequency of a population remains constant through time This occurs in the absence of natural selection, mutation, genetic drift, and gene flow No evolutionary change occurs through the process of sexual reproduction itself

5.6 Several Processes Can Function to Alter Patterns of Genetic Variation Assortative mating occurs when individuals choose mates nonrandomly based on phenotype (and thus genotype) Female mate choice Positive assortative mating occurs when mates are more similar to each other than expected by chance Increases homozygote frequency

5.6 Several Processes Can Function to Alter Patterns of Genetic Variation Negative assortative mating occurs when mates are less similar to each other than expected by chance Increases heterozygote frequency

5.6 Several Processes Can Function to Alter Patterns of Genetic Variation Inbreeding is the mating of closely related individuals Increases homozygosity at all loci Offspring of closely related individuals are more likely to inherit rare, recessive, or deleterious genes that lower overall fitness These consequences are referred to as inbreeding depression

Quantifying Ecology 5.1 Hardy–Weinberg Principle Allele and genotype frequencies will remain the same in successive generations of a sexually reproducing population if certain criteria are met Mating is random Mutations do not occur The population is large (genetic drift is minimal) There is no migration Natural selection does not occur

Quantifying Ecology 5.1 Hardy–Weinberg Principle Two alleles at a locus The sum of the allele frequency must equal one p + q = 1 P (homozygote dominant) + H (heterozygote) + Q (homozygote recessive) = 1

5.7 Natural Selection Can Result in Genetic Differentiation The geographic range of a species can result in phenotypic variation of neighboring populations A wider geographic range includes a broader range of environmental conditions In general, the greater the distance between populations, the more pronounced the phenotypic differences

Geographic Variation in Species Ecotype: Subpopulation of a species adapted to a specific environment Cline: measurable change in a species characteristics over an environmental gradient Variation in white tailed deer – larger animals at higher latitudes in NA

Genetic Variation of Ecotypes An ecotype is a population adapted to its unique (often abrupt) local environmental conditions Yarrow (Achillea millefolium) response to altitude How much variation observable in the field is due to genetic variation and how much is due to impact of environment (phenotypic plasticity)? Common Garden Experiment Seed collected from plants of same species growing in different environments grow in same location(s) (p 85)

5.7 Natural Selection Can Result in Genetic Differentiation Geographic isolates result when gene flow among subpopulations is prevented The isolation is rarely complete, and so these isolated subpopulations are often classified as subspecies because of a set of unique characteristics Appalachian salamanders (Plethodon jordani)

Figure 5.14

How do new species arise? Allopatric speciation: spatial isolation –geographic isolation Spread of species into new areas Founding population in isolated location Geologic changes – gradual process Sympatric speciation: different niches/same habitat or geographic area Genetic changes (as ploidy levels in plants) Disruptive selection: divergent genotypes favored

Species have become specialists feeding on seed providing optimal energy efficiency

Adaptive Radiation: Single ancestral from give rise to multiple ‘specialist’ forms

Summary: Evolution involves heritable differences amongst individuals in a population which ultimately impact fitness Organisms become ‘tailor made’ for their niche within an environment by processes of evolution Characteristics of individuals making up current populations are a product of natural selection in ancestral populations New species arise from preexisting species as populations become reproductively isolated