Time of Day Time of Year Flowers Snails

Time of Day Time of Year Flowers Snails Courtship Sounds/Songs Bullfrog x Leopard Frog Plants Broadcast Spawners Horse (2 n=64) x Donkey (2 n=62) Mule (2 n=63) Fig. 24. 3

I. Reproductive Isolation C. Limitations of Biological Species Concept • Mayr’s definition emphasizes reproductive isolation; may not work in all situations • • • Ex: Classifying fossil organisms Ex: Species that reproduce asexually [prokaryotes, some protists, fungi, plants (e. g. bananas), animals ( (e. g. fishes, lizards)] Ex: Multiple species are inter-fertile but remain distinct (e. g. orchids) (

II. Speciation • Occurs when a population becomes reproductively isolated from rest of species • May be allopatric or sympatric A. Allopatric Speciation • • Population becomes geographically separated Over time, mutation, genetic drift, natural selection genetic divergence Thought to be responsible for development of most new animal species How do populations become isolated?

Fig. 24. 5

II. Speciation A. Allopatric Speciation 1. Geographical barriers a. b. c. d. e. f. g. • Land bridges form, separating aquatic populations (e. g. Isthmus of Panama) Land masses separate or split off from continents (e. g. South America & Africa) Mountain ranges form Water levels in water bodies become lower, creating multiple smaller pools Rivers change course (Ex: oxbow lakes) Glaciation occurs Islands form and are colonized (e. g. Galàpagos, Hawaii, Madagascar) Note: Geographic barriers for some species aren’t barriers for others • Ex: Birds and many insects can fly between isolated patches of habitat • Ex: Some fishes can swim long distances • Ex: Airborne pollen and drifting gametes in the ocean can be transported long distances

II. Speciation A. Allopatric Speciation 2. Conditions Favoring Allopatric Speciation • • a. b. c. Fig. 24. 6 Typically occurs at edges of parent population’s range Splinter population (peripheral isolate) may be good candidate for speciation because: Gene pool different from parent population • Likely to represent extreme of genotypic range • Speciation more likely if founder population small • Ex: Harris’ and white-tailed antelope squirrels on rims of Grand Canyon Genetic drift within peripheral isolate • Can lead to rapid divergence from parent population Natural selection • Diversifying or directional selection under conditions at extremes tolerated by parent population

Fig. 24. 10

II. Speciation B. Sympatric Speciation • • 1. Population becomes reproductively isolated without geographic separation May be common in plants; importance in animals less clear Plants a. Autopolyploidy • Results from error in mitosis

II. Speciation B. Sympatric Speciation 1. Plants a. Autopolyploidy • Results from error in mitosis b. Allopolyploidy • Error in meiosis + hybridization

Fig. 24. 11

II. Speciation B. Sympatric Speciation 1. Plants b. Allopolyploidy • Allopolyploids typically can’t produce fertile offspring with either parent (incompatible chromosome numbers) • If population of allopolyploids becomes established, typically one of three outcomes: 1) New species unable to compete successfully; goes extinct 2) New species competes successfully; coexists with parent species 3) New species competes very successfully; causes extinction of one or both parent species

II. Speciation B. Sympatric Speciation 1. Plants b. Allopolyploidy • May be very common in plants • Up to 80% of flowering plant species are polyploid • May account for 25 -50% of plant species • Mechanism for very rapid speciation (single generation) • May account for rapid radiation of plants in fossil record and high diversity of flowering plants (>290, 000 species)

II. Speciation B. Sympatric Speciation 2. Animals • • Mechanisms of sympatric speciation less well understood than in plants Polyploidy usually lethal • • Habitat differentiation Ex: North American apple maggot fly (article ) ( • Mutation short-term isolation reinforced by nonrandom mating (sexual selection) Ex: African cichlids •

Fig. 24. 12

II. Speciation C. Allopatric vs. Sympatric Speciation • Animals (usu. allopatric) • • Isolating mechanisms? Plants (usu. sympatric) • Isolating mechanisms?

Time of Day Time of Year Flowers Snails Courtship Sounds/Songs Bullfrog x Leopard Frog Plants Broadcast Spawners Horse (2 n=64) x Donkey (2 n=62) Mule (2 n=63) Fig. 24. 3

II. Speciation D. Adaptive Radiation • Evolution of many diversely adapted species from common ancestor Island chains offer unutilized habitat and open ecological niches • • • Ex: Colonization of Hawaii by honeycreepers Ex: Silversword alliance in Hawaii

Fig. 25. 20

II. Speciation C. Adaptive Radiation • Occurs when niche space is available • • Ex: Radiation of mammals after K/T extinction Radiation events often are associated with the appearance of novel features • • Why? Ex: Shells & skeletons first appeared at beginning of Paleozoic (may have facilitated radiation)