BIO120 Lecture 09 Notes PDF

BIO120 Lecture 09 Notes Mechanisms of Microevolution -> Can they produce macroevolutionary patterns (evolution of diff. species) - Natural selection - Genetic drift - Mutation - Migration How do we get macroevolutionary diversity? Species Concepts: 1. Taxonomic (morphological) - ba...

BIO120 Lecture 09 Notes Mechanisms of Microevolution -> Can they produce macroevolutionary patterns (evolution of diff. species) - Natural selection - Genetic drift - Mutation - Migration How do we get macroevolutionary diversity? Species Concepts: 1. Taxonomic (morphological) - based on distinct physical, anatomical differences 2. Biological - based on inter-fertility among individuals What did Darwin think about species? Species defined as groups of organisms that are sufficiently similar in phenotype Ernst Mayr Concept - species are a group of interbreeding natural populations that are reproductively isolated from other groups (RI is key to differentiate species -> once you can’t reproduce you’re diff. species) Speciation: process by which new species form because groups in a species become reproductively isolated and diverge Allopatric speciation: original population -> barrier arises -> reproductive isolation (bc evolution works on both sides and they develop new characteristics and 2 diff populations can’t reproduce with each other anymore) -> new species Sympatric speciation: splitting of original population into 2 reproductively isolated groups without geographic isolation - Hard to achieve bc gene flow acts against effects of divergence Stages when RI can occur: (lecture 12 slide) Prezygotic barriers: Prevent mating or fertilization so no zygote is formed - Geographical / ecological differences (they are in diff regions or they use diff resources so they don’t cross paths) - Temporal - if organism is reproductively active during different time from other population - Behavioural - unique behaviours to attract mates - Mechanical - physically organisms' genitals don’t go together - Cellular - sperm can’t penetrate the egg Postzygotic barriers: occurs after fertilization and offspring not fertile or viable or abnormal development - Can’t evolve due to natural selection bc it’ll make gametes inviable - Offspring has low fitness bc genes that were passed down were incompatible Intrinsic postzygotic barriers: hybrid is either inviable, not fertile, or abnormally developed - Intrinsic can also be when an offspring is produced, offspring can reproduce, but 2nd generation is infertile or weak Extrinsic postzygotic barriers: hybrid’s phenotype might not be suited for that environment leading to low fitness (SLIDE 19 GRAPH EXPLAIN) Local adaptation: occurs when different populations of a species evolve in response to distinct environmental conditions, leading to reproductive isolation. This means that populations that adapt to different environments can become so genetically and behaviorally different that they stop interbreeding, eventually leading to speciation. - Reproductive isolation can occur through other mechanisms, such as genetic drift or chromosomal changes, but adaptive evolution accelerates the process of speciation by driving populations to diverge faster in response to different ecological pressures. This is because as populations adapt to their unique environments, they become more genetically and behaviorally isolated from each other. Ecological Speciation: When speciation occurs as a result of populations adapting to different ecological environments - In this process, natural selection favors traits that enhance survival and reproduction in a particular environment, leading to reproductive barriers between populations. Adaptive radiation: single common ancestor diversifies into many different species to fill various ecological roles - Link b/w phenotypes of the species and environment (ex. Beak shape correlates with food available in that environment) - Traits evolved must be beneficial to exploit resources (increased fitness) What causes adaptive radiation? 1. Ecological opportunity: - species colonized new region where there are few competitors and can diversify rapidly (common on islands, lakes, etc) - the extinction of other species can remove competitions - evolution of new trait that allows access to new resources 2. High propensity for speciation: some groups or clades have a natural tendency to undergo speciation more easily than others Hybridization: occurs when 2 different species that are usually reproductively isolated breed and produce a hybrid - Hybrid can either be sterile OR - Hybrids can be fertile and mate with either parent species. This gene flow can mix the gene pools of the 2 species and it can reverse speciation and merge those two species into one (more common if populations is are young) - Sometimes hybrids can undergo speciation: POLYPLOIDY Polyploidy: organism has more than 2 complete sets of homologous chromosomes -> SYMPATRIC SPECIATION Allopolyploidy: occurs when 2 diff. species hybridize and resulting offspring has diploid gametes - Two of these organisms with diploid gametes reproduce which leads to tetraploid who is fertile but is now reproductively isolated from parental species Autopolyploidy: chromosome number doubles within a single species without hybridization with another species - Polyploids are reproductively isolated from their parent species - Polyploids exhibit new traits that can help them exploit new habitats or resources - Allopolyploids show hybrid vigor, meaning they’re more productive bc they are heterozygous