CHAPTER 13 BIOL 1120

MACROEVOLUTION—large, complex changes in life Changes accumulate in populations slowly over time TIME!!!!! Evolution—produced diversity of life Organisms grouped into species—distinct types of organisms The meaning of the term “species” has evolved over time

Species—all examples of creatures that were alike in minute detail of body structure Two-word naming—binomial nomenclature First name—genus Second name—species Hierarchical system for classification: grouped similar genera into orders, classes, kingdoms His system did not consider evolutionary relationships (each species was created separately and could not change)--- meaning species could not appear/disappear, not related to one another

Connected species diversity to evolution As natural selection became accepted, scientists no longer viewed classification as a way to just organize life Classification became thought of as hypotheses about the evolutionary history of life

Amended Linneaus’s and Darwin’s work by considering reproduction and genetics. Biological species—a population, or group of populations, whose members can interbreed and produce fertile offspring Speciation (formation new species) occurs when members of a population can no longer successful interbreed

Species—does not rely on physical appearance (less subjective than Linnaeus’s observations) Linneaus-2 similar looking butterflies cannot belong to different species Mayr—if two groups can produce fertile offspring, share a gene pool, same species

Mayr’s concept of species—cannot relate to asexual reproducers Cannot apply to extinct organisms (fossil) Some organisms can interbreed in captivity, but do not in nature Reproductive isolation is not absolute—closely related plants can produce fertile offspring together Species concept cannot always be used to decide if organisms are the same/different species DNA analysis is helpful (if >97% identical, same species) DNA drawback—cannot determine if organisms currently share a gene pool ISOLATION is mot common criterion used to define species

Interruption in courtship, fertilization, embryo formation, or offspring development. 2 broad groups: prezygotic and prostzygotic Prezygotic occur before formation of zygote Postzygotic: reduce the fitness of a hybrid offspring (offspring from two different species)

Barriers include: Ecological (habitat) isolation: difference in habitat preference in same geographic area Temporal isolation: Mating will not occur if two species are active at different times of day or reach reproductive maturity at different times of year Behavioral isolation: behavioral differences (distinct calls of different species of tree frogs to attract mates Mechanical isolation: any change in the shape of gamete delivering or receiving structures can prevent interbreeding Gametic isolation: sperm cannot fertilize egg; aquatic organisms release sperm, gametes have distinct surface molecules to recognize gametes

Barriers include: Hybrid inviability: hybrid embryo dies before reaching reproductive maturity; genes of parents incompatible Hybrid infertility (sterility): mule; infertile because horse egg has 1> chromosome than donkey, meiosis does not occur because chromosomes are not homologous Hybrid breakdown: a hybrid that can reproduce, but their offspring may have abnormalities that reduce their fitness Successful hybridization rare in animals; occurs frequently in plants

allo-other; patric-fatherland Geographic barrier River, desert, glacier, changes in sea level, formation or destruction of mountains, bodies of water No interaction=no gene flow Microevol. act independently in each group Most common mechanism; abundant evidence Allopatric Speciation

Sym-together Populations diverge genetically while living in the same area Habitats-consist of microenvironments; species specialize in different zones Plants: polyploidy, increases the # of sets of chromosomes Occurs when gametes of 2 diff species fuse; also when meiosis fails ½ flowering plants are polyploids; 95% ferns Rare in animals (extra chromosomes are often fatal) Sympatric Speciation

Para-alongside Part of a population enters a new habitat bordering range of parent species Gene flow can occur among individuals that venture into shared border zone Can be a result of disruptive selection: ind. w/ intermediate forms have lower fitness than at either extreme; selection would counteract gene flow by eliminating ind. not well suited for either habitat Parapatric Speciation

Darwin One species gradually transforms into another through a series of intermediate stages TIME!!!

Gould and Eldredge Brief bursts of rapid evolution interrupting long period of little change (transitional forms don’t exist— explains lack in fossil record) Fits w/allopatric speciation – geographic isolation

Occurs in rapid bursts Gives rise to multiple specialized forms in a short time Heterogeneous environment (multiple food sources)

Death of an entire species Factors: Failure to adapt to environmental change Lack of alleles in gene pool to produce fertile offspring Habitat loss Predators Disease Smaller populations likely to endure a major change Low genetic diversity Inbreeding (lethal recessive alleles, reduce reproduction/survivabilty) HUMANS!!!!

Background extinction rate Gradual loss of species as populations shrink when facing new challenges Mass extinction A great number of species disappear over short period of time (impact theory)

Taxonomists—classify based on similarities 3 Domains (Archaea, Bacteria, Eukarya) KingdomKing PhylumPhillip ClassCalled OrderOn FamilyFive Genus Great SpeciesSoldiers Taxa: a group at any rank The more features two organisms share, the more taxonomic levels they share

Evolutionary tree (also called phylogeny) Illustrate specie’s relationships based on decent from common ancestors Evidence used to construct: Anatomical features of fossils and existing organisms Behaviors Physiological adaptations Molecular sequences May be misleading Cladistics solves this problem

Phylogenetic system Groups by distinguishing between ancestral and derived characters Ancestral character: inherited traits that resemble ancestors Derived character: features that are different that the ancestor

Builds on concept of homology (homologous structures-common ancestor) Shared, derived characters are used to define groups A clade (monophyletic group) group of organisms consisting of a common ancestor and all its descendants

Treelike diagram depicting shared, derived characteristics (based on historical relationships/ not similarities) Tips of branches = taxa (existing species) node = indicates where two groups arose from a common ancestor Branching pattern = populations that diverge genetically, split off, form new species Common ancestor