Transcript Slide 1
Evolutionary scale & speciation Professor Janaki Natalie Parikh [email protected] Evolutionary scale • Recall Linnaean taxonomy? We’ll utilize that system again here: » Kingdom » Phylum » Class » Order » Family » Genus » Species Evolutionary scale • Micro level evolution: change occurs below the level of species, w/in a population, e.g. changes in gene frequency, such as sickle cell allele in U.S., represents? • Transient polymorphism, level is changing, albeit slowly • Accumulation of smaller scale changes can bring about a larger scale change, called? • Macro level evolution: changes above the level of species, resulting in a brand new species Biological Species • This brings about the question, what’s the criteria to be classified as the same species? • Biological species: can reproduce viable offspring & (perhaps most important) do so on their own • Speciation: the process whereby a single species diverges into 2 separate species, requires reproductive isolation (cutting off of gene flow) Extrinsic & Intrinsic Reproductive Isolation Extrinsic (geographical isolation) – Climate change – http://news.nationalgeographic.com/news/2006/05/bear-hybridphoto.html – http://www.actionbioscience.org/evolution/barnosky.html – Plate tectonics activity, ex. on Madagascar (where?): http://www.sciencemag.org/cgi/content/summary/312/5776/969i Intrinsic Reproductive Isolation separated into pre- & post- zygotic mechanisms • What’s a zygote?? • The product of the fusion of an egg & sperm Pre-zygotic reproductive isolation -Seasonal (temporal)isolation: breeding seasons don’t overlap http://www.sparknotes.com/biology/evolution/reproductiveisolation/section1.html -Habitat isolation:occupy slightly difft habitats of same gen area -Mechanical isolation: incompatible genitalia -Gametic: sperm & egg are incompatible Post zygotic reproductive isolation • • • • • Major developmental prob’s (resulting in spontaneous abortion) Hybrid inviability: sickly, weak hybrid offspring Hybrid sterility: hybrids incapable of reproducing Hybrid hypofecundity: hypo means? Fecundity? ≠ hybrid vigor (humans) • http://www.crystalinks.com/hybridization.html • http://news.nationalgeographic.com/news/2005/08/photogalleries/ligers_dynamite/ Pace of evolutionary change Phyletic (Darwinian) gradualism: slow, incremental changes that accumulate over long periods of time Punctuated Equilibrium: (S.J. Gould): General stasis interrupted by periods of rapid change (adaptive radiation or mass speciation events) Adaptive radiation • Adaptive radiation (mass speciation): rapid expansion & diversification of a grp of organisms as they adapt to a new ecological niche • ~65 mya, an adaptive radiation event took place, what triggered it? • Mass extinction of the dinosaurs. What type of organisms moved in to inhabit those ecolog. niches? • http://news.softpedia.com/news/What-Caused-Dinosaurs-039-Extinction-39017.shtml » Mammals! Species types • Generalized species: are able to adapt to a wide range of ecological niches • Specialized species: require a narrowly defined set of environmental circumstances in order to survive • Examples? Evolutionary cycle • Extinctions open up new ecological niche(s) • Generalized species moves in, adapts to new ecolog. zone, begins adaptive radiation process • As generalized line diversifies, organisms become increasingly specialized to particular niches w/in the zone • Overspecialization makes the organisms susceptible to? • Extinction. Thus triggering a repeat in the cycle – Startling reality: current RATE of extinction: fastest the Earth has ever seen, due to? – http://exitstageright.wordpress.com/2008/10/18/no-species-lastsfor-ever-but-the-current-rate-of-extinction-is-terrible/ Human Taxonomic Classification Kingdom & Subkingdom? Kingdom: Animalia, based on? Heterotrophic & motile Subkingdom: Metazoa: multicellular Phylum? Phylum: Chordata, based on? have a notochord: hollow nerve cord, replaced by? Subphylum: Vertebrata Have a vertebral column Class? Hum. Taxon. Classification cont’d Mammalia, based on? (hint from name) Having mammary glands to feed young cohort: Eutheria, based on? Well developed placenta As opposed to? Marsupials Order? Primates! Shared Traits • Ancestral (primitive) traits: relative term, ancestral trait is simply very old & maintained unchanged over time • Derived traits: more recent trait that has emerged, a modification of the ancestral form • Which set is utilized to classify organism’s into the same group? (counterintuitive) • Shared derived traits are used to classify organisms together • Next we’ll examine some of the key shared derived traits in primates