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BIOL 208 (January 10, 2014) - Guest Lecture: Species - Isolation and Speciation

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Biology (Biological Sciences)
James Cahill

BIOL 208 (January 10, 2014) Guest Lecture • What is an Executive Summary? o A super condensed lab report o Practical skill for many professions Review – Evolution • Two mechanisms: o Natural selection  There is no random reproduction o Genetic drift • Evolution can change populations o Creation of new species What is a Species? • Different morphotypes can exist of one species o They look different but are able to reproduce with each other o … That being said, morphology is a bad way of defining a species • Definition: “Groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups” – Mayr 1942 o This is the most common definition of a species Problems with Defining Species • Cline (or “ecocline”) o Change in genotype and phenotype over a VERY BROAD geographical region  Even if large differences were to be present, interbreeding is still possible o Ex. breeds of dogs • Ecotype o Change in appearance based on differing habitats (small geographical region) o “Subspecies” that can interbreed • Asexual reproducers • Hybrids o Parts of a different species? Anomally? A subspecies? o No better definition yet. Pre-zygotic reproductive isolation • Ecological isolation o Physical separation; organisms use different parts of ecosystem o Ex. southern course frog vs upland course frog perform mating calls at different parts of the same pond • Temporal Isolation o Breeding seasons are different from each other so they cannot breed with each other. • Behavioural Isolation o Different mating rituals • Mechanical Isolation o “Parts that don’t fit together” o Fertilization is arrested before it has a chance to happen Post-zygotic reproductive isolation • Hybrid inviability o zygote formed but organism doesn’t survive to term • Hybrid sterility o Organism cannot reproduce even though it has reached maturity (zero fitness)  Ex. mule, liger Allopatric Speciation • Single population th
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