SPECIATION. REPRODUCTIVE BARRIERS PREZYGOTIC: Barriers that prevent fertilization. Habitat isolation Populations can t get together

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1 SPECIATION Origin of new species=speciation -Process by which one species splits into two or more species, accounts for both the unity and diversity of life SPECIES BIOLOGICAL CONCEPT Population or groups of populations whose members have the potential to interbreed and produce fertile offspring with each other, but not with members of other species -emphasizes reproductive isolation REPRODUCTIVE BARRIERS PREZYGOTIC: Barriers that prevent fertilization Habitat isolation Populations can t get together Behavior isolation Different mating behavior Temporal isolation Breed or flower at different times Mechanical isolation Different anatomical structures Gametic isolation Gametes fail to fuse; don t recognize each other POSTZYGOTIC: Barriers that prevent the zygote from developing into fertile offspring Reduced hybrid viability Zygote fails to develop or reach sexual maturity Reduced hybrid fertility Hybrid sterile Hybrid breakdown Hybrid produces offspring but offspring not viable or not fertile Page 1 of 5

2 MODES OF SPECIATION ALLOPATRIC Populations segregated by geographic barrier Geographic barrier = ocean, mtn. Range, etc. Conditions favoring o Small population at fringe o Better chance gene pool already different o Different selection factors Adaptive radiation emergence of numerous species from common ancestor introduced into environment SYMPATRIC New species arise within range of parent species Reproductive isolation without geographic barrier o Plants polyploidy (multiple sets of chromosomes) o Animals group fixed on resources not used by parent population GENETIC CHANGE 1. Adaptive divergence 2 parts of population adapt to different environments Each accumulates different gene pools 2. Reproductive barriers develop Usually secondary to change in gene pool May be side effect of sexual selection Page 2 of 5

3 TEMPO OF SPECIATION GRADUALISM 1 species gradually evolves into new species Represents microevolution Big changes occur through the accumulation of small changes PUNCTUATED EQUILIBRIUM Long periods of stasis (equilibrium) punctuated by episodes of speciation Species undergo most changes when first branch from parent; then change little Species develop in spurts of rapid change Not slow and gradual EVOLUTIONARY NOVELTIES Defines taxonomic groups Examples o Wings in birds o Amniotic egg in reptiles o Jaws in osteichthyes Evolve by gradual changes in existing structures Existing structures co-opted to perform different functions Genes that control development o Play major role in development of evolutionary novelty o Change rate or sequence of development o Change shape of adult form or basic body design Macroevolution o Development of taxonomic groups higher than species o Species selection (species that endure the longest and produce the greatest number of new species determined direction of evolutionary trend) Page 3 of 5

4 PHYLOGENY AND SYSTEMATICS PHYLOGENY SYSTEMATICS Evolutionary history of species or group of related species Study of biological diversity in an evolutionary context TAXONOMY Identification and classification of species Linnaeus based classification on morphology Features o Binomial (Genus species) o Filing system (family, order, class, phylum, kingdom, domain) Objective of taxonomy as component of systematics o Assign organism to species o Placement into higher taxa PHYLOGENETIC TREE Classification reflects evolutionary relationships Tree represents evolutionary history Monophyletic o 1 ancestor gave rise to all species in that taxon and to no species in another taxon Page 4 of 5

5 MOLECULAR BIOLOGY Comparison of macromolecules Protein comparison o Compare amino acid sequence o Ex. Cytochrome C o Common to all aerobic organisms o # of differences provides info. related to when branched from common ancestor DNA-DNA hybridization RFLP analysis Sequence mitochondrial DNA for closely related species Sequence rrna for distantly related species PCR amplifies (makes many copies) sample of DNA PHYLOGENETIC SYSTEMATICS GOAL: Make classification more objective and consistent with evolutionary history PHENETICS Reflects anatomical similarities Based on measurable similarities and differences Compares as many anatomical features as possible Does NOT sort homology from analogy CLADISTICS Reflects evolutionary relationships Phylogenetic systematics Classifies organisms according to order in time branches arose along dichotomous phylogenetic tree Each branch identified by novelty Reflects evolution Page 5 of 5