Genetic differencesMorphologicaldifferencesZoology 101 – McIntyre – Macroevolution - 25 Apr 2012Macroevolution: How do new species arrive?Change (Large – new species; Generation 103+)Evolutionary change above the species levels Origin of new species and diversification of higher taxaMacroevolution wrestles with…Definitions: what’s a species?Processes: what keeps species distinct?Spatial context: is physical separation required?Rates: How long does speciation take (Plus information from first lecture)?Species concepts: What is a speciesBiological Morphological PhylogeneticKey Traits Reproduction Appearance GeneticsDefinition No actual or potential interbreeding with other species Consistently different in body formDivisible into mutually exclusive groupsData Needed Behavior & offspring fertility Preserved specimenDNA sequenceChallenges Asexual, rare, & hybridsSubjective Subjective (10% diversion to call something a species)Phylogenetic Concept:African butterfly fish (Pantodon buchlozi) Geographically dispersed into 2 location (Congo population and Lower Niger population)Genetically distinct (54mya last common ancestor for the two groups)Biological species conceptReproductive isolation: when biological factors make two individuals incapable of interbreeding to produce viable & fertile offspring. Isolation often arises from multiple factors in concert Pre-zygotic barriers: (before zygotestage) barriers that impede mating Mechanical isolation – mating may beattempted but prevented bymorphological differencesGametic isolation – sperm of on species can’t fertilize eggs of another species; sea urchins spray sperm into open ocean in correlation to the lunar cycle in a type a “lottery” system Post-zygotic barriers: Fertilization occurs but…Occasional hybridization of frog genus RonaFail to develop completely and have frail phenotypesDrosophila melanogaster x Drosophila simulansNo viable male offspring, but there will be viable female offspring that developReduced hybrid variability, i.e. hybrids leave high mortalityHybrids cand reproduce (sterile); Lion + Tiger = Liger Female Horse + Male Donkey = Mule; Male Horse + Female Donkey = HinnyHybrid breakdown: initial hybrids are vigorous and fertile, but subsequent generations are not viable Species vs. sub-species Species are sometimes broken into sub-species based on range & small variations in phenotype but these could usually interbreedPopulations may not come into contact, but can readily interbreed White-footed mouse Different sub-species Will produce viable offspring if they interbreed (Texas mouse different from mouse from MaineSpatial context for speciation1) Allopatry – different places; geographicalbarriera. Geographic isolation allows drift orselection that results in reproductiveisolation b. Difficult to test, so we often assumeallopatric process if population areisolated & divergent c. River formation, lake, mountains or any other geographic isolations d. Allopatry is dominant in most plants & animalse. A. harrisis & A. leucurus i. Geographic isolation – GrandCanyonii. Higher isolation means lowerreproduction; Lowerisolation means higherreproduction 2) Sympatry a. Reproductive isolation arises w/ogeographic isolationb. Mechanismi. Polypoid-chromosomal duplicationii. Habitat differences (micro-allopatry)iii. Sexual selection by mate choiceRate of speciation: How long does speciation take?- Contrasting interpretations of fossil records, morphological, & molecular data o Punctuated equilibrium – rare & rapid change o Gradualism : slow & steady change (Darwin envisioned evolution as being gradualist)- Both patterns occurred in time - The interval between speciation events can range from: o 4000 years (some cichlid fish) to 40,000 years (some bettles)o Average 6.5 myo Foxes on the California mainland (Gray fox, Urocyon cineroargenteus) & adjacent Channel Islands (Island fox, Urocyon littoralis)Additional topics:Normal picky Couldn’t distinguish- Hybrid zones – a region in which members of different species meet and mate, producing at least some offspring of mixed ancestryo Reproductive barriers between species may by reinforced over time (limiting the formation of hybrids) or weakened over time (causing the separating species to fuse into one species)- Reinforcement: Strengthening Reproductive Barriers (pp.499-500)o Reinforcement – process in which natural selection strengthens pre-zygotic barriers to reproduction, thus reducing the chances of hybrid formation. Such a process is likely to occur if only hybrid offspring are less fit than parent species.o Barriers to reproduction appear stronger is organisms from sympatric populations than organisms from allopatric populations - Fusion: Weakening Reproductive Barriers (pp.500)o The reproductive barriers are not strong here. So much gene flow may occur thatreproductive barriers weaken further and the gene pools of the two species may become increasingly alike.o May be affecting the polar bear (Urus maritimus). They evolved from the grizzly bear. As their habitat is melting, they will probably move toward the inland and mate with the grizzly bears. There have been hybrids recorded in the wild. This will probably cause the two gene pools to fuse (the polar bears will cease to exist). Big-Picture Conclusions:1) Multiple concepts of what a species is 1) Three populations of a species are connected by gene flow2) Biological species concepts dominates by sympatric cases are fascinating 3) Speciation usually requires millions of years, but can occur in just one generation (polyploidy) PRE-LECTURE QUIZ1. Under the Biological Species Concept, gene flow among populations of the same speciesmust be: High enough to prevent reproductive isolation 2. Which of the following factors can give rise to reproductive isolation? a. Differences in breeding season b. Differences in courtship songsc. Protein compatibility of eggs and sperm d. Infertility of hybridse. All of the above factors can contribute to reproductive isolation 3. The phylogenetic species concept is based on which of the following goals? Grouping all the descendants of a common ancestor4. When a female mosquito fish from a "high-predation" pond in the Bahamas prefers to mate with males showing a 'high-predation" morphology rather than a "low-predation" morphology, this is an example of: pre-zygotic reproductive isolation5. Plants frequently show chromosomal polyploidy. The evolution
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