Charles Darwin Wrote in 1859“On the Origin of Species by Means of Natural Selection”Wrote in 1859:“On the Origin of Species by Means of Natural Selection” Two main points: 1.Species were not created in their present form, but evolved from ancestral species. (Descent With Modification) 2.Proposed a mechanism for evolution:NATURAL SELECTION 2.Proposed a mechanism for evolution: NATURAL SELECTION

Speciation evolutionThe evolution of new species.

What are the two driving forces behind speciation?

Species populations individuals interbreed fertileA group of populations whose individuals have the potential to interbreed and produce fertile offspring in a natural environment. (Ernst Mayr)

Liger Result of male lion and female tiger mating in captivity. Offspring are infertile.

Tigon Result of male tiger and female lion mating incaptivity. Offspring are infertile. Separated both geographically and ecologically.

The biological species concept is based on interfertility rather than physical similarity

Ethnic Groups

Speciation in African Cichlids

Macroevolution vs. Microevolution?

Macroevolution is above the species level. Microevolution is at the species level.

Speciation can take place with or without geographic barriers.

Geographic Isolation ancestral separated geographical barrier.Induced when the ancestral population becomes separated by a geographical barrier. Example:Example: Grand Canyon ground squirrels

Geographic Isolation Kaibab Squirrel (left) Abert Squirrel (right )

Reproductive Isolating Mechanisms Geographic Isolation

Has speciation occurred during geographic isolation?

Allopatric Speciation

Reproductive Barriers mechanismimpedes fertile and/or hybrid offspringAny mechanism that impedes two species from producing fertile and/or hybrid offspring.

Figure 24.3 Courtship ritual as a behavioral barrier between species Blue-Footed Boobies in the Galapagos Islands Behavioral Isolation (Courtship Rituals)

Reproductive Isolating Mechanisms Sciurus niger, the fox squirrel breeds in May and June Sciurus carolinensis, the gray squirrel, breeds in July and August

Temporal Isolation (a specific type of reproductive isolation) Bishop’s Pine releases pollen in summer Monterey Pine releases pollen in early spring

Behavioral Isolation Ornate butterflyfish Bluestripe butterflyfish Reproductive Isolating Mechanism

Mechanical Isolation

Ensatina eschscholtzii, a ring species, here in the Golden State, an example of reduced hybrid viability and adaptive radiation

Ecological Isolation White-throated Sparrow feeds in dense thickets White-crowned Sparrow inhabits fields and meadows

A Model for Adaptive Radiation on Island Chains

HawaiianSilversword Evolved 5 million years ago; 28 endemic species

Adaptive Radiation Emergence of numerous species common ancestorEmergence of numerous species from a common ancestor introduced to new and diverse environments. Occurs as a result of Divergent Evolution Examples:Examples: Darwin’s Finches, African Cichlid Fish

Different geographic regions, different mammalian “brands” – Eutherian vs. MarsupialsConvergentEvolution

Gradualism Punctuated Equilibrium

Interpretations of Speciation Two theories:Two theories: 1.Gradualist Model: Slow changes in species overtime. 2.Punctuated Equilibrium: Evolution occurs in spurts of relatively rapid change. (Eldredge and Gould)

Macroevolutionary changes can accumulate through many speciation events.

“Evo-Devo” biologists compare developmental processes of different multicellular organisms Development is intimately connected to evolution because all changes in form come about through changes in development.

Homeotic Genes – any of the master regulatory genes that control overall body plan of animals and plants by controlling the developmental fate of groups of cells The products of one class of homeotic genes called Hox genes provide positional information in an animal embryo.

Hox mutations and the origin of vertebrates

Homologous genes that affect pattern formation in a fruit fly and a mouse

“The amazing diversity of organisms has been produced by a modest number of genes” (Sean Carroll – author of Endless Forms Most Beautiful)

The biggest difference between amphibian eggs and reptilian eggs was the development of the... The five groups of vertebrates are: Reptiles can reproduce in three ways. These are:

Name two characteristics common to almost all members of the following classes of animals: amphibiansamphibians reptiles reptiles mammals mammals

A phylogenetic tree can be used to show.... All mammals are classified into these three groups: Which two characteristics do all chordates have?

Speciation that occurs in which members are separated from each other is called ____________ speciation. Speciation that occurs in which members have no barriers between them is called ______________ speciation.

1)Other than the example given in the powerpoint presentation, give an example of convergent evolution among species. 2) What are the two theories regard- ing the pace of evolution?

Peter and Rosemary Grant are famous for … If two or more species repro- duce at different times this is called ____________ isolation.