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Lecture 1 - book and lecture notes - TAXONOMY

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York University
BIOL 2030
Helen Chasiotis

Taxonomy : arrangement law , produces a formal system of naming and grouping species to communicate this order -part of a broader science of systematics or comparative biology -predates evolutionary biology Carolus Linnaeus - used hierarchal system of classifications where the lower you go to the classification the more specific it becomes - 7 taxa nowadays : Kingdom, Phylum , Class , Order, Family , Genus , Species Binomial species nomenclature - made up by Linnaeus - each species has a latinized name composed of two words written in italics : first word is genus and second word is species epithet ( must have same gender words ) - the epithet is unique to the species, generally an adjective and written in small letter italics -more precise than common names used Recognition of species criteria: - common decent: is central to all modern concept of species -smallest distinct groupings : sharing patterns of ancestry and descent morphological characters traditionally used but now chromosomal and molecular characters are now extensively used for this purpose -reproductive community: pertains to sexually reproducing organisms , members of species must form a reproductive community that excludes members of other species For asexual reproduction - place and a particular ecological niche so that a reproducing population responds as a unit to evolutionary processes such as natural selection and genetic drift Geographic range : any species has a distribution through space -can be either continuous or disjunct , having breaks where species is absent Evolutionary duration: distribution through time -Mayr said : " A species is a reproductive community of populations that occupies a specific niche in nature " - identifies species as interbreeding and have common descent, known as Biological Species Concept ( BSC) Issues with BSC: - ignores species status of ancestral populations - asexual reproduction is not recognized -how much of the reproductive divergence is a good quantification for species differentiation?- non agreeable point with systematist and BSC Evolutionary Species Concept - proposed by palaeontologist Simpson in 1940s - add evolutionary time to BSC - definition : single lineage of ancestor of ancestor - descendant populations that maintains its identity from other lineages and that has its own evolutionary tendencies and historical fate - applies to both sexually and asexually reproducing organisms Phylogenetic Species Concept - definition: an irreducible (basal) grouping of organisms diagnosably distinct from other such grouping and within which there is a parental pattern of ancestry and descent - emphasizes common descent - asexual and sexual reproduction is considered -recognizes species as smallest groupings that have undergone independent evolutionary change Phylogeny - evolutionary tree that relates all extant and extinct species - construct a tree by observing features like: characters : variation between species , include morphological , chromosomal and molecular features homology : character similarity resulting from common ancestry example: homologous bones and patterns of connections despite evolutionary modifications in forelimbs of vertebrates , bird feathers etc homoplasy: non-homologous similarity but have common phenotype or molecular sequences although not part of common ancestry , for example bird wings and bat wings Re-constructing Phylogeny - ancestral character state: determine which variant form of each character occurred in most recent common ancestry of the entire group - derived character state: assuming all variant forms came later on within the group -polarity of character : the ancestral/descendants relationships among the alternative states of a character in a particular group -outgroup comparison: method used to determine polarity, beginning by selecting the outgroup that is phylogenetically similar but not same group as the one being studied -clades : are the subsets ,organisms or species that share derived characteristic states from subsets w
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