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Speciation.docx

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Department
Biology
Course
BIOL 1001
Professor
Tamara Kelly
Semester
Winter

Description
Speciation If gene flow ends, allele frequencies in isolated populations are free to diverge - meaning population begin to evolve independently of each other If mutation, genetic drift, selection cause isolated populations to diverge sufficiently, distinct types, or species form - that is the process of speciation Species: evolutionary independent population or group of populations Four criteria for identifying re in common use • Biological species concept • Morphospecies concept • Ecological species concept • Phylogenetic species concept Biological Species Concept: critical criterion for identifying species is reproductive isolation, therefore no gene flow If two species population do not interbreed in nature or if they fail to produce viable and fertile offspring when mating's take place = distinct species Groups that both interbreed (naturally) and are reproductively isolated =belong to same species Stop gene flow Prezygotic evolution: which prevents different species from mating Postzygotic isolation: offspring of mating between members of different species do not survive or reproduce Disadvantage - criterion for reproductive isolation cannot be evaluated in fossils or in species that reproduce asexually, in addition it is difficult to apply when closely related populations do not happen to overlap with each other geographically, hybrids Morphospecies Concept: Distinguishing features are mostly likely to arise if populations are independent and isolated from gene flow Identify evolutionarily independent lineages by different in size, shape or other morphological features Wildly applicable - useful if no data on gene flow Disadvantageous - cannot identify cryptic species: differ in traits other than morphology 2. morphological features used to distinguish specie are subjective Advantage: can be applied to Living fossil sexual and asexual Ecological species concept: defines a species as a set of organisms exploiting a single set of resources, having same range of environmental tolerances, and facing the same predators parasite Emphasizes role of natural selection - which favours characteristics traits that benefit an organism in exploiting specific resources and coping with a specific set of environmental challenges Identifying bacteria, archaea, asexual eukaryotes Phylogenetic species concept: Identifying evolutionary independent lineages and is based on reconstructing the evolutionary history of populations Monophyletic group - also called a clade or lineage (ancestor + descendants) Synapomorphies - found in monophyletic groups as they are traits found in a certain group that exists in no others Can be identified in either developmental, genetic, or structural level Species are defined as the smallest monophyletic groups on the tree of life Advantages: 1. can be applied to any population (fossil, asexual, sexual) 2. it is logical because different species have different synapomorphies only if they are isolated from gene flow and evolved independently Disadvantage: carefully estimated phylogenies are available only for a tiny thought growing subset of populations on the tree of life Subspecies: are populations that live in discrete geographic areas and have distinguishing features (colourations or calls) but not distinct enough to call morphospecies How Speciation Occurs Isolation and allotropy Genetic isolation happens rout
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