Evolutionary scale & speciation
Professor Janaki Natalie Parikh
profjnp@gmail.com
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
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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