The Origin of Species Chapter 24

YOU MUST KNOW The biological concept of species Prezygotic and postzygotic barriers that maintain reproductive isolation in natural populations A description of similar species that are maintained separate by each type of isolating barrier How allopatric and sympatric speciation are similar and different How a change in chromosome number can lead to sympatric speciation Why speciation rates are often rapid in situations when adaptive radiation occurs or in times of ecological stress The connection between a change in gene frequency, a change in the environment, natural selection, or genetic drift and speciation How punctuated equilibrium and gradualism describe two different tempos of speciation

I. Speciation and Reproductive Isolation Speciation – process by which new species arise Biological Species Concept – a species is a group of populations whose individuals have the potential to interbreed in nature and produce viable (healthy and fertile) offspring https://www.youtube.com/watch?v=2oKlKmrbLoU

Microevolution – change in the genetic makeup of a population from generation to generation (confined to a single gene pool)

C. Macroevolution – broad pattern of evolutionary change C. Macroevolution – broad pattern of evolutionary change above the species level, such as the appearance of feathers, used to define higher taxa

Reproductive Isolation – biological barriers that prevent members of two species from producing viable offspring

Prezygotic Mechanisms– occur before a zygote can be created Geographic/Habitat isolation – do not live in the same place

b. Behavioral isolation – mating signals are not the same

c. Temporal isolation – different mating seasons

Mechanical isolation – anatomically incompatible Gametic isolation – gametes will not fuse together (common in sea creatures that use external fertilization – sea cucumbers, sea urchins, etc.) Damsel Fly Penises

Postzygotic barriers – zygote may be formed, but offspring does not develop into a fertile adult Reduced hybrid viability – zygote forms but does not develop

b. Reduced hybrid fertility – zygote develops, but is sterile

c. Hybrid breakdown – offspring develop into adults, can mate, but produce weak or sterile offspring

II. Types of Speciation Allopatric speciation – new species forms because it is geographically isolated from parent population 1. Can occur because of geologic events – emergence of a mountain range, formation of a land bridge, evaporation of a lake

Smaller populations more likely to undergo speciation 3. Speciation confirmed when individuals from new population cannot mate successfully with individuals from parent population

Sympatric Speciation Small portion of the population forms a new species without being geographically isolated from parent population

2. Change in habitat, food source, or accident in cell division resulting in change in chromosome number a. Polyploidy – nondisjunction resulting in extra sets of chromosomes – can no longer breed with diploid plants

Each one fills its own niche Adaptive Radiation Many new species arise from one ancestral species Each one fills its own niche

III. Rate of Speciation Gradualism – species descend from a common ancestor and gradually diverge more and more in morphology

B. Punctuated Equilibrium – describes periods of apparent stasis punctuated by sudden change observed in the fossil record