Evolutionary scale & speciation Professor Janaki Natalie Parikh

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 – photo.html photo.html – – Plate tectonics activity, ex. on Madagascar (where?):

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 -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)

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? »M»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? – for-ever-but-the-current-rate-of-extinction-is-terrible/ for-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