Conservation Genetics - Introduction to Conservation Biology - Lecture Slides, Slides of Biology

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Conservation Genetics • Why should we be concerned with genetic diversity when more severe threats threaten entire systems? • First, the rate of evolutionary change in a population is proportional to the amount of genetic diversity available • Fundamental Theorem of Natural Selection Docsity.com Conservation Genetics • Second, diversity as measured at the level of genes or quantitative genetic traits represents the primary level of biodiversity • Every biochemical product, every growth pattern, every instinctive behavior, every color morph is encoded in the in the ‘genetic library’ of each species Docsity.com Conservation Genetics • In this chapter we will go over the principles of genetics and how they may aid in conservation • Next, we will provide a board overview of contemporary efforts and controversies in conservation genetics Docsity.com Genetic Variation • A species’ pool of genetic diversity exists on 3 levels: variation within an individual, differences among individuals w/in a pop(n), differences among popuations Docsity.com Conservation Genetics variation w/in the individual • Chromosomes consist of long sequences of nucleotides, some of which code for molecules that create the structure and the physiological functions of an organism • A gene represents a specific segment of DNA of a specific chromosome pair that (1) codes for the primary structure of proteins Docsity.com Conservation Genetics variation w/in the individual • A physical or behavioral character (phenotype) can be expressed directly as a trait may be entirely due to genotype (e.g. eye color) or environment (nutritional regime), but more likely a combination of both (e.g. skin color) • Quantitative genetics are helpful in determining how much of the phenotype is attributable to genes (Box 11.1) Docsity.com Conservation Genetics variation w/in the individual • The ultimate source of variation is mutation • Mutations range from a change in a single base, deletion or duplication of a group of nucleotides, to large-scale changes such as deletion, duplication, or translocation of large parts of the chromosome (or the entire chromosome) • Are they good, bad, or ugly? Docsity.com Conservation Genetics variation w/in the individual • Recombination is another source of variation, requires sexual recombination • At the population level, a given locus is either monomorphic (both copies always found without variation) or polymorphic (two or more types of the alleles possible) • The overall level of heterozygosity (the proportion loci in an individual that contains alternative) Docsity.com Conservation Genetics variation among individuals • Variation among individuals, or pop-level variation, consists of the types of alleles present and their relative frequencies across all members of a population considered together (the gene pool) Docsity.com Conservation Genetics variation among individuals • Are gene frequencies constant? • They frequently change over time due to mutation, NS, and random processes such as genetic drift, non-random mating, small pop size, and I & E (gene flow) Docsity.com Conservation Genetics variation among individuals • There have been a number of attempts to link ecological characteristics ad levels of genetic variation • Not surprisingly, widespread organisms tend to have higher levels of genetic diversity while small range, small populations or large body size are correlated with low diversity (see Table 11.3) Docsity.com Conservation Genetics variation among populations • Thus, genetic diversity among a set of populations consists of within-population diversity and among-population divergence • Thus a simple genetic diversity model is: where HT = total genetic variation, HP= average diversity within pop(n), and DPT = average divergence among pop(n) HT = HP + DPT Docsity.com Conservation Genetics variation among populations • Divergence may result from a number of processes including random processes (e.g. founder effects, genetic drift, episodic population bottlenecks) and from local selection • Again, important to remember we can quantify within and among-population diversity components Docsity.com Conservation Genetics variation among populations • RCWO has mean heterozygosity of 7.8% which is typical • Of total variation, 14% consists of among- and 86% consists of within pop(n) • The among is higher than most species, which tend to be more site-specific than many other sp Docsity.com Conservation Genetics variation at the metapopulation • We have utilized the metapopulation paradigm to describe populations on a fragmented landscape • By definition, metapopulations interact, thus influencing the genetic structure of the populations • Metapopulations lose genetic variation more rapidly than a single large pop(n) Docsity.com Why is Genetic Diversity Important? • The amount of adaptive variation in a population should be related to the health of a population, or to its ability to withstand stresses and challenges • There have been a number of general correlates of genetic variation among populations (Table 11.5) Docsity.com Why is Genetic Diversity Important? • There is mixed results on the actual importance of adaptive genetic diversity • There is no absolute value of heterozygosity that indicates a population’s health, although it may be correlated with individual fitness (taxonomic comparisons see Table 11.4) Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • When making predictions about likely changes in allele frequency, not the difference between N and Ne (effective populatiton size) • Ideal is large, panmictic, 1:1 sex ratio Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • Mutations are the ultimate source of new genetic variation with mutations being rare and most being neutral • This is generally not a problem until popo(s) become small…why? • The gradual accumulation of deleterious mutations results in the mutational meltdown (mean viability lowered, and pop(s) become smaller, with fixation) Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • Genetic drift is the random fluctuation of gene frequencies over time due to chance alone • Because of sexual mating (and only one copy being passed on) there is a high chance that not all alleles will not be passed on • Drift can occur very quickly in small pop(s) Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • When a demographic bottleneck occurs, the magnitude of the genetic loss depends not only on the size of the bottleneck but also on the growth rate of the population afterward Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • Recovery is quickest when pop(s) have a high growth rate (r) and when bottleneck is less severe Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • Gene flow is the movement of genes from one population to another • Measuring gene flow is problematic – Not all breed – Cannot account for historical dispersal – Similarity could be recent ancestor Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • Lab studies of land snails and white- footed mice were inbred and outbred and released… • Results of WFM Docsity.com Forces that Affect Genetic Variation w/in Pop(s) • Not all low levels of heterozygosity or even inbreeding should be alarming • Some natural populations have apparently experienced low levels of inbreeding for several generation with little to no harm Docsity.com