Tuesday, February 14 th Happy Valentine’s Day! Speciation and The Origin of Species

Speciation The creation of a new species occurs when individuals can no longer produce fertile offspring with members of their previous species This happens when individuals become geographically / physically separated and gene flow between the two populations stops (they are isolated)

Individuals can leave one place for another (founder effect) A physical barrier can suddenly separate members of a population. Intermediate populations can become extinct, isolating remaining populations.

Two Conditions & Two Types 1. Identical populations must diverge 2. Reproductive isolation (no viable offspring) must evolve to maintain differences in the populations. Sympatric Speciation – species that occur together but are distinctively different (cannot viably reproduce) Allopatric Speciation –geographically isolated populations change from original population and become a distinct population

Goal 1.C.2 (pg 12 of packet): New species arise from reproductive isolation over time, which can involve scales of hundreds of thousands or even millions of years, or speciation can occur rapidly through mechanisms such as polyploidy in plants

Polyploidy Sympatric speciation can occur instantly when an individual is born that cannot reproduce with any other member of its species Usually due to mutation, which normally kills the offspring One exception, seen in plants is called polyploidy

Polyploidy Polyploidy – produces individuals that have more than two sets of chromosomes. Two ways to get Polyploidy Individuals: Autopolyploidy Allopolyploidy

Autopolyploidy Autopolyploidy – all chromosomes may arise from a single species Occurs due to an error in cell division, causing a doubling of chromosomes Tetraploids are formed – they have 4 sets of chromosomes Can self-fertilize or mate with other tetraploids Can’t mate with diploids anymore (i.e. speciation)

Allopolyploidy Allopolyploidy – two species hybridize to produce multiple sets of chromosomes Two species hybridize Offspring have one copy of each species’ chromosomes Usually infertile because chromosomes can’t pair correctly in meiosis BUT if chromosomes spontaneously double, then individual has two copies of each set of chromosomes – pairing of meiosis works out, which means we have speciation!

Continuing on Goal 1.C.2 Speciation results in diversity of life forms. Species can be physically separated by a geographical barrier, or various pre-and post- zygotic mechanisms can maintain reproductive isolation and prevent gene flow.

Prezygotic isolating mechanisms prevent the formation of a zygote Ecological Isolation – species occur in same area, but occupy different habitats and rarely see each other Behavioral Isolation – mating rituals differ Temporal Isolation – species reproduce in different seasons / times of the day Mechanical Isolation – structural body differences prevent mating Prevention of gamete fusion – egg and sperm meet but don’t mesh well FOR MORE INFORMATION SEE PAGES

Postzygotic Isolating mechanisms Hybrid inviability –Hybrid embryos do not develop properly or do not survive to adulthood Hybrid Infertility – hybrid adults are sterile

Goal 1.C.1.a Speciation rates can vary, especially when adaptive radiation occurs when new habitats become available.

Adaptive Radiation – groups of closely related species, recently evolved from a common ancestor by adapting to different parts of the environment Most common with un-claimed land and lots of resources (little competition) Key Innovation – new trait evolved, allows the species to use resources/ environment previously inaccessible Adaptive Radiation

Darwin’s finch species adapted to use different food types Example of Adaptive Radiation New birds moved into vacant ecological niches Niche – the role played by a species in its environment (where it lives, what it eats, etc) Another Ex: buttercups speciation in glacial New Zealand (pg 450)

Pace of Evolution Two hypotheses: Gradualism – accumulation of small change causing major changes over thousands / millions of years Punctuated Equilibrium – long periods of little to no evolutionary change (called stasis) punctuated by bursts of evolutionary change occurring relatively rapidly Punctuate – to break into or interrupt at intervals

Evolution may contain Both! Evolution appears to be a continuum At one end, gradualism At the other, punctuated equilibrium Some species evolve solely at either extreme Others show evidence of both gradual and punctuated evolution

Goal 1.C.1.b Species extinction rates are rapid at times of ecological stress. Examples: There have been 5 major extinctions Human impact on ecosystems and species extinction rate (Ch 59)

5 Mass extinctions “The names and dates of these extinctions are beyond the scope of this course and the AP exam” Most drastic was Permian Extinction - >half of all plant/animal families and up to 96% of all species may have died Most famous: Cretaceous Extinction: 65 mya) dinosaurs become extinct

Results of Mass Extinctions Not all groups of organisms are affected equally Example: Cretaceous Some species became extinct, some survived unscathed Survivors were those animals that could shelter underground or in water, and could scavenge or required little food in cool temps resulting from sunlight blockage

The 6 th Extinction Man’s impact is huge Estimate: “As much as 1/4 th of all species will become extinct in near future, a rate of extinction not seen on Earth since the Cretaceous mass extinction.” Rebound of species diversity will be slow because we are depleting the environment of resources Section 59.5 further discusses Human Impact (pg )