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Lecture 16

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Biology 1001A
Tom Haffie

Biology Chapter 18.2 and 18.7 (Lecture 16) Defining Species • Morphological • Biological • Phylogenetic Speciation (The process of species formation) • Isolation • Divergence • Secondary Contact Why does it matter whether two populations are one species or two? • Morphologically different • Different ecological niche • Endangered or not (legislation) 1. Morphological Species Concept • The concept that all individuals of a species share measurable traits that distinguish them from individuals of other species • Identify species by morphological similarity • Distinct clusters in phenotypic space • Problems with MSC o A lot of variation in phenotypes of a population o Very little variation between populations 2. Biological Species Concept • The definition of species based on the ability of populations to interbreed and produce fertile offspring • Group of actually or potentially interbreeding organisms, reproductively isolated from other such groups • More explanatory power than MSC (shared gene pool) • More objectively testable than MSC (when members of population A encounter population B in the wild. What happens?) • PREZYGOTIC ISOLATING MECHANISMS a reproductive isolating mechanism that acts prior to the production of a zygote or fertilized egg. o Can be isolated in terms of habitat, behaviour (courtship displayed not attractive), mechanical (different shaped penis’) • POSTZYGOTIC ISOLATING MECHANISMS a reproductive isolating mechanism that acts after zygote formation o Hybrid inviability; Hybrid has a low probability of survival to reproductive age (born dead) o Hybrid Sterility; Hybrid cannot form functional gametes o Hybrid Breakdown; Hybrids are capable of reproducing, but their offspring have reduced fertility or reduced viability. (i.e. low fitness) • Problems with BSC o Hard to tell if populations that are geographically separated (Allopatric) would interbreed if in close range o Asexual organisms don’t interbreed o Cannot tell what extinct organisms would inte
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