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Chapter 2

Life Science 2D03-Chapter Two.docx

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Life Sciences
Ayesha Khan

Chapter Two Evolution and the Study of Animal Behavior 2.1 Evolution by Natural Selection favors behavioral adaptations that enhance fitness Different breeds, same species. Each breed possesses unique trait features with respect to body size and shape, tail length, head shape, coat, texture, and color. There are over 200 breeds of dogs All breeds of dogs have descended from the gray wolf (Canis Lupus), and the ancestors are a result of human manipulation of the breeding of individuals over the past 14, 000 years. This is through the selection of individuals that possess certain traits for a particular breed, called the breed standard. Many breeds were created for specific tasks Breeders allow reproduction only among individuals that possessed certain traits Differences in breed standards over time eventually led to ever-greater differences among the dog breeds we see today—This process is known as artificial selection because it is done artificially—that is, by humans. Similar processes also occur naturally, called Natural Selection: is the differential reproduction and survivorship among individuals within a population. It is the mechanism that results in adaptive evolution—Charles Darwin and Alfred Russell Wallace Natural selection occurs because there is variation in traits among individual in a population, and some traits provide individuals with greater reproductive success When these traits are heritable, they are passed from parents to offspring. Natural selection can result in changes in allele frequencies in a population over time—a process that we recognized as evolution. The book: On the Origin of Species (1859), Darwin articulated three conditions required for evolution by natural selection: 1.) Variation exists among individuals in a population in the traits they possess 2.) Individuals’ different traits are, at least in part, heritable. Traits can be passed from parents to their offspring so that offspring resemble their parents in the traits they possess 3.) Traits confer differences in survivorship and reproduction, a measure we call fitness: individuals with certain traits will have higher fitness, while those with other traits will have lower fitness relative to one another. Therefore, the fitness of individuals is not random; it is based on the traits they possess Natural Selection: Differential reproduction and survivorship among individuals within a population. The mechanism that results in adaptive evolution Heritable: A trait that can be passed from parents to their offspring because of heredity Evolution: Changes in allele frequency in a population over time Fitness: The relative survivorship and reproductive success (ability to produce viable offspring) of an individual Gene alleles are the basis of phenotypic traits Natural selection acts on heritable variation among individuals and can result in changes in allele frequencies and associated trait values in a population. Traits that confer high fitness increase over time, while those that confer low fitness decline When traits are heritable, parents will tend to pass on the traits they possess to their offspring via their shared alleles. Many behavioral traits that have been studied are in fact heritable, including mating behavior, feeding behavior, overall activity level, and aggression. Genetics Primer: Deoxyribonucleic acid (DNA) condenses into chromosomes during mitosis and meiosis Specific stretches of DNA contain genes, which code for polypeptides (i.e. proteins) that have a variety of functions. Alleles are different versions of a gene The locus is the physical location of an allele on a chromosome, and each may have a different allele. If the alleles are the same, then the organisms are homozygous for these alleles; if the alleles are different, then they are heterozygous. During sexual reproduction, each parent contributed only one of its alleles. Therefore, offspring have different alleles combinations than their parents During meiosis, homologous chromosomes line up in pairs. During this time, they can exchange segments of DNA, known as crossing over. This process results in novel combinations of DNA that increase genetic diversity. Measures of Heritability: Traits must be heritable for natural selection to act on them. How do we determine the heritability of a trait? Two methods are commonly used: 1.) Parent-Offspring Regression Analysis: Examines the similarity between parents and their offspring in terms of the traits they possess. If a trait has a genetic basis, then he trait values of offspring should be similar to the trait values of their parents: there should be a positive relationship between offspring and parent trait values. Parent-Offspring Regression: A statistical technique used to examine the similarity between parents and their offspring in the traits that they possess. 2.) The Selection Experiment: method, different groups of individuals are subjected to differential selections on the trait in question. If artificial selection acting on a trait results in changes in that trait value in subsequent generations, then the trait has a genetic basis. Selection Experiment: An experiment in which different groups of individuals are subjected to differential selection on a trait. The Great Tit Exploratory Behavior: Examined the heritability of exploratory behavior in free-living great tits. The great tit is a small, colorful passerine bird found throughout much of Europe and Asia It is a common inhabitant of woodlands, parks, and gardens where it feeds on insects and seeds It nests in tree cavities as well as nest boxes Previous work indicated that individuals exhibit differences in their exploratory behavior when placed in novel environments: some actively explore their new environment quickly (bold individuals) while others are more reticent and slower to explore (shy individuals) Are these personality traits heritable? Experiments used birds from two populations in the Netherlands as part of a long- term research project. Put them in an artificial wooden area with five trees to record the flights and hoped that the birds took There was a positive correlation between a mother’s exploratory behavior and the offspring’s Separated adults into two groups for the selection experiment for fast and slow exploratory behavior: One group contained birds with the lowest exploratory behavior, while the other contained those birds with the highest exploratory behavior. The nine individuals both male and female with low and high scores for each generation were then selected for breeding. This took four generations. By this time, the average exploratory score for individuals in the high line was over four times higher than that for individuals in the slow line. This result indicates that exploratory behavior is heritable/ has a genetic component. 1.) Offspring resemble their parents in this behavior 2.) Artificial selection on exploratory behavior produced significant differences in the two artificially selected lines. Variation within a population: Through the process of natural selection, populations evolve This evolution requires variation among individuals in the traits they possess Variation caused by: Genetic composition—each generation introduces new genetic variation into populations through gene recombination, the immigration of new alleles into a population, and mutations. Individuals in any population differ genetically; they will also tend to vary in their behavior First, Changes in environmental conditions can change the fitness of different traits and maintain much variation in the frequencies of different alleles Secondly, many behaviors develop as a consequence of both genetic and environmental effects; therefore, even close relatives with similar genes often exhibit very different behavior as adults when they are exposed to different environmental conditions as juveniles Third, many complex behaviors require learning and therefore are modified with experience. Individuals will differ in experience over the course of a lifetime; therefore, there will be observable differences in their behavior as well. Example: Bees need to learn how to best extract nectar and pollen from flowers and then transport them efficiently back to their colony. Feeding performance, or their rate of food delivery to the colony, increases dramatically over the first four days of foraging activity as a result of trial-and-error learning. Fourth, there might be little or no variation in fitness over a wide range of behaviors. For example: dispersal behavior. Dispersal is the process of moving away from the natal area, or place of birth, to find an adult breeding area or territory. For many species in many habitats, individuals will experience the same fitness whether they disperse in any direction. When this is true, it is expected that there will be much variation in dispersal direction within a population. For example: Eastern screech owls: Studied dispersal direction. It was found that there was no particular pattern with respect to dispersal direction, which is to be expected is characteristics that determine territory quality and fitness are not associated with compass direction relative to the natal
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