The Origin of Species Ch 24 Lecture Objectives

The Origin of Species Ch. 24 Lecture Objectives 1. Cause of Speciation 2. Pre and Postzygotic Barriers

THE ORIGIN OF SPECIES Speciation process in which one species splits into two or

Allopatric speciation Sympatric speciation

1 st mechanism for speciation - Allopatric Speciation Due to geologic processes �fragment a

Example of Allopatric Speciation Ammospermophilus harrisii Ammospermophilus leucurus

2 nd mechanism for speciation - Sympatric Speciation occurs in populations that live in the same geographic area. �Polyploids – each cell has more than two sets of chromosomes �Autopolyploidy �Allopolyploidy © 2013 Pearson Education, Inc.

What prevents speciation from occurring? Prezyotic Barriers prevents mating or fertilization between species Postzygotic Barriers interspecies mating occurs and hybrid zygotes form

Prezygotic Barriers �temporal isolation �habitat isolation (ecological isolation) �behavioral isolation �mechanical isolation �gametic isolation

Temporal Isolation Skunk species that mate at different times

Habitat Isolation Garter snake species from different habitats

Behavioral Isolation Mating ritual of blue-footed boobies

Mechanical Isolation Snail species whose genital openings cannot align

Gametic Isolation Sea urchin species whose gametes cannot fuse

Postzygotic Barriers �reduced hybrid viability �reduced hybrid fertility �hybrid breakdown © 2013 Pearson Education,

Reduced Hybrid Viability Frail hybrid salamander offspring

Reduced Hybrid Fertility Horse Donkey Mule (sterile hybrid of horse and donkey)

Hybrid Breakdown Sterile next-generation rice hybrid

INDIVIDUALS OF DIFFERENT SPECIES Prezygotic Barriers Temporal isolation Habitat isolation Behavioral isolation MATING ATTEMPT Mechanical isolation Gametic isolation FERTILIZATION (ZYGOTE FORMS) Postzygotic Barriers Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown VIABLE, FERTILE OFFSPRING No Barriers