Chapter 5 Adaptation & Natural Selection What causes variation within a species or population? Why are organisms adapted to their specific environments?

What is Natural Selection? Differential success of individuals in a population that results from their interaction with their environment. Success = survival AND reproduction i.e. – staying alive AND making viable offspring Natural Selection can only affect a population under certain conditions…

Conditions for Natural Selection 1) Variability exists in a certain trait

Conditions for Natural Selection 2) The trait must be heritable (not acquired) Heritable Acquired

Conditions for Natural Selection 3) Differential Success occurs – some individuals survive longer and/or reproduce more Survival usually leads to reproduction but not always peacock

Fitness The more offspring an individual produces, the more impact he/she will have on the characteristics of the next generation = fitness

Adaptation A beneficial trait is one that enables an individual to ultimately produce more offspring (not always strongest, fastest) = adaptation

Evolution Evolution = changes in the properties of a population over the course of generations Evolution may occur due to natural selection acting on a population – not always Properties that change can be genetic, morphological, physiological, demographic or behavioral Turkey gobbling

Properties of Populations Genotype – the alleles present in a gene that control the outcome of a trait Phenotype – the outward expression of the genotype

Properties of Populations Phenotype has a genetic basis but is subject to environmental conditions Kind of like Nature vs. Nurture Phenotypic Plasticity = ability of a genotype to produce a range of phenotypes under different environmental conditions Norm of reaction = range of phenotypes that arise from the same genotype under different environmental conditions

© 2015 Pearson Education, Inc. Phenotype Environmental gradient Genotype – G 1 Genotype – G 2 1) Which of the two genotypes exhibits the greater norm of reaction? 2) What would the line look like for a genotype with no phenotypic plasticity? 3) Will these two genotypes ever express the same phenotype? 1) G2 has greater norm of reaction 2) No plasticity = straight line with no slope 3) The two will never have the same phenotype

Figure 5.4 © 2015 Pearson Education, Inc. Phenotype (mean value of characteristic) Environmental gradient Genotype – G 1 Genotype – G 2

Section 5.4 The Expression of Most Phenotypic Traits Is Affected by the Environment The body color of many insects is affected by the temperature during development The darker colors occur when the young develop in cooler temps Why? © 2015 Pearson Education, Inc.

Genetic Differentiation = Different genetics (allele frequencies) that occur among different subpopulations of a species Western Red-tailed HawkEastern Red-tailed Hawk

Genetic Variation Gene Pool = all of the alleles present in an inter- breeding population The Gene Pool can be measured or quantified by determining: Allele frequency = how often does each allele to show up in an individuals genes Genotypic frequency = how often does each genotype appear in the population

How selection works… Target of selection = phenotypic trait that the selection acts upon Selective Agent = environmental cause of differential success among individuals with different phenotypes

The thicker the beak, the greater the seed variety that can be eaten

La Nina of 1977 caused seed availability to drop drastically, especially Smaller softer seeds

Target of selection: Selective Agent: Beak Size Seed availability, weather

3 patterns of selection Directional selection = trait phenotype shifts toward one extreme over the other

3 patterns of selection Stabilizing selection = trait phenotype shifts toward median rather than the extremes

3 patterns of selection Disruptive selection = trait phenotype shifts toward both extremes over the mean

Other Processes that cause genetic variation: 1) Genetic Mutation Source of new alleles, possible new genotypes and phenotypes Vast majority of mutations never effect phenotype Most mutations that effect phenotype are fatal or harmful – not advantageous A beneficial mutation is random and rare A mutation isn’t more likely just because it is “needed”

Other Processes that cause genetic variation: 2) Genetic Drift A shift in allele frequency by random chance Does not impact large populations The smaller the population, the more pronounced the impact of genetic drift Do my ecology classes exhibit the same phenotype or genotype frequencies each year? Does that mean the population of Hudson is evolving drastically each year?

Other Processes that cause genetic variation: 3) Gene Flow Caused by migration Immigration – new members coming into population Emigration – members leaving a population As population members come and go, they add or remove their alleles from the gene pool

Hardy-Weinberg Principle Sexual Reproduction alone will cause no evolutionary change in a population i.e. – if there is… - Random Mating - No natural Selection Forces - No migration - No Mutation …then the population will remain unchanged

Hardy-Weinberg Principle To determine if Hardy Weinberg Equilibrium is true for a population, the following equations can be used to calculate gene frequencies. p = frequency of allele 1 q = frequency of allele 2 p 2 = frequency of homozygous for p allele q 2 = frequency of homozygous for q allele 2pq = frequency of heterozygous p + q = 1 p 2 + 2pq + q 2 = 1

Non-random Mating: Assortative Mating = Mates are chosen based on phenotype, not randomly Many female birds use Assortative Mating

Non-random Mating: Inbreeding = mating between individuals that are closely related more often than might occur by random chance Poor genotypes that generate less fit phenotypes get perpetuated in the population = inbreeding depression

What is a Cline? = a measurable, gradual change in one trait across a geographic region - Caused by a normal, gradual change in an environmental factor across that same region (temp, sunlight, moisture, etc…) - Ex – height of spruce trees decreasing with altitude on mountainside

Subspecies = populations of a species that are distinguishable by one or more characteristics - Could be geographic isolates – subspecies separated by a geographic barrier, adapt to slightly different conditions - Could be Ecotypes – subspecies that occupy different habitats within a range, not necessarily geographically isolated

Red Elephants live in the Congo and are a smaller and hairier ecotype Forest Elephants have a subspecies – Pygmy or Red Elephant Africa has 2 species of Elephants – Forest and Savanna

Geographic Isolation of Salamanders

Adaptive Radiation = One species gives rise to many species that go on to occupy different niches in the ecosystem