Origin of Species Chapter 24

Darwin Natural selection One species evolves due to adaptation to it’s environment Adaptation does not explain why one species becomes another

Speciation One species gives rise to many descendant species

Galápagos giant tortoise, another species unique to the islands

Fig Recent (11,500 ya) Neohipparion Pliocene (5.3 mya) Pleistocene (1.8 mya) Hipparion Nannippus Equus Pliohippus Hippidion and other genera Callippus Merychippus Archaeohippus Megahippus Hypohippus Parahippus Anchitherium Sinohippus Miocene (23 mya) Oligocene (33.9 mya) Eocene (55.8 mya) Miohippus Paleotherium Propalaeotherium Pachynolophus Hyracotherium Orohippus Mesohippus Epihippus Browsers Grazers Key

Species Latin meaning “kind” or “appearance.” Morphological differences have been used to distinguish species. Differences in body function, biochemistry, behavior, and genetic makeup

Biological species concept Defines species as “groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups” Species composed of populations that can mate & produce offspring

Species Homo sapiens Diversity Belong to same species Capacity to interbreed.

Species Species are based on inter-fertility, Not physical similarity. Eastern & western meadowlarks Have similar shapes & coloration Differences in song prevent interbreeding between species.

Reproductive isolation Members of a population Cannot mate Or produce fertile offspring What causes reproductive isolation? What helps species to retain their identities?

Reproductive isolation mechanisms Prevent genetic exchange 1. Prezygotic: “before zygote” preventing formation of zygotes 2. Postzygotic: “after zygote” preventing proper development of zygotes once formed

Prezygotic barriersPostzygotic barriers Habitat isolation Temporal isolation Behavioral isolation Mechanical isolation Gametic isolation Reduced hybrid viability Reduced hybrid fertility Hybrid breakdown Indivi- duals of differen t species MATING ATTEMP T FERTILI - ZATION VIABLE, FERTILE OFF- SPRING (l)(i) (j) (h)(g)(f)(e)(c) (a) (b) (d) (k)

Prezygotic isolating mechanisms 1. Ecological (Habitat) isolation 2. Behavioral isolation 3. Temporal isolation 4. Mechanical isolation 5. Gamete isolation

Ecological isolation Species utilize different parts of the environment May not encounter each other Examples: Lions & tigers in India Lions: open fields, in prides Tigers: forests, hunt in isolation

Ecological isolation Toad These species can interbreed Use different parts of the woods to breed

Behavioral isolation Differ in courtships Mating dances differ Mallard & Pintail ducks

Behavioral isolation Blue-footed boobies Courtship dance

Behavioral isolation Pheromones: Chemical signals used when mating Lacewings: Move their abdomen to create a mating song Varies among species

Temporal isolation Mating or breeding times are different Flowering times are different Wild lettuce Frogs: genus Rana 5 species live close together differ in mating seasons

Temporal isolation Western spotted skunk Late summer Eastern spotted skunk Late winter

Mechanical isolation Structural differences prevent mating Plant structures & pollen Insects

Gamete isolation Sperm from one species unable to fertilize egg of another Plants different shaped pollen tubes Difficult to form a hybrid

Postzygotic isolation 1. Hybrid mating may occur Genetic pairings can not function in embryo stage 2. Offspring are inferior Will die in nature 3. Sterile offspring

Postzygotic isolation Examples: Leopard frogs problems with developing eggs Mule formed from female horse & male donkey Mule is sterile

Fig. 24-4o (k) Mule (sterile hybrid)

How does reproductive isolation arise? 1. By chance A population moves to a new habitat Adapt Mate within the new population 2. Natural selection Select individuals that are able to reproduce with greater success

Speciation 1. Identical populations must diverge 2. Reproductive isolation must evolve to maintain these differences

Mechanisms of sepciation 1. Allopatric speciation (other) 2. Sympatric speciation (together)

Fig (a) Allopatric speciation (b) Sympatric speciation

Allopatric speciation Populations separated by geographical location More likely to develop into new species Unable to reproduce with parent population

Allopatric speciation Geographic barriers Island Mountain Lake Size & mobility of the animal

Antelope squirrels

Allopatric speciation Ernst Mayr First demonstrated that geographic isolation leads to speciation New Guinea Papuan kingfisher Isolated species are more distinctive

Allopatric speciation Hawaiian Islands

Adaptive radiation Organisms form new species Fill niches No competition

Sympatric species Distinct species live in a single location Use different parts of the habitat Behave separately (mating calls or chemicals)

Sympatric speciation 1. Instantaneous speciation 2. Disruptive selection

Instantaneous speciation Polyploidy: Individual has more than two copies of chromosomes Autopolyploidy: All chromosomes from one species Allopolyploidy: Two species hybridize

Instantaneous Tetraploids (4 sets of chromosomes) Self pollinate or mate with another tetraploid Over time become fertile Established a new species

Polyploidy

Hugo de Vries---primrose

Polyploidy More common in plants Plants such as wheat, cotton, sugarcane Some animals such as insects, fish & salamanders

Disruptive selection Two distinct phenotypes evolve into separate species Lake Victoria Cichlid fishes

Hybrid zones Region where different species mate Characteristics are a combination of features of both populations Hybrid is formed

Fig b Fire-bellied toad, Bombina bombina

Fig a Yellow-bellied toad, Bombina variegata

Hybrid zones 1. Increases reproductive barriers Maintains 2 species 2. Two species fuse 3. Occasional hybrid is still formed Sexual preference Environment

Gene flow Population Barrier to gene flow Isolated population diverges. Hybrid zone Hybrid individual Possible outcomes: Stability Fusion Reinforcement

Grizzly bear (U. arctos) ▶ ▶ Polar bear (U. maritimus) Hybrid “grolar bear” ▶

Pace of evolution 1. Gradualism 2. Punctuated equilibrium

Pace of evolution Gradualism Changes occur slowly over time Accumulation of small changes over time

Gradualism

Pace of evolution The fossil record Many species appear as new forms rather suddenly (in geologic terms) Persist essentially unchanged Then disappear from the fossil record.

Punctuated equilibrium

Pace of evolution Punctuated equilibrium Species experience long periods of stasis Bursts of evolutionary change