Speciation: the origin of species How many species? Number described: 1.5 – 1.6 million Number...

• Speciation: the origin of species• How many species? • Number described: 1.5 – 1.6 million• Number estimated: 5-6 million to 100 million.• Species: smallest evolutionarily independent unit

(fundamental unit of biodiversity). • Species boundaries

– geographical– genetic

– How do species originate?– Speciation mechanisms

Autoploidy

Alloploidy

Species of tobacco

Speciation mechanisms 1. Increasing number of sets of chromosomesA. Alloploidy: stage in the speciation processB. Autoploidy: doubling of homologous chromosomes results in fertilityHybridizationvery common in plants

• 1. Uncommon in animals

• Increasing sets of chromosomes

• Hybridization

• Very rarely produces a new

• species

Species 1 (unparental) Species 2 (biparental)

New species 3

Attempts to recreate an animals species.

Laboratory Hybridization Among North American Whiptail Lizards, Including Aspidoscelis inornata arizonae X A. tigris marmorata Squamata: Teiidae), Ancestors of Unisexual Clones in Nature CHARLES J. COLE, LAURENCE M. HARDY, HERBERT C. DESSAUER, HARRY L. TAYLOR,AND CAROL R. TOWNSEND

Division of Vertebrate Zoology (Herpetology), American Museum of Natural History (cole@amnh.org).Division of Vertebrate Zoology (Herpetology), American Museum of Natural History; Museum of Life Sciences, Louisiana State University in Shreveport, LA 71115-2399 (lhardy@lsus.edu).Division of Vertebrate Zoology (Herpetology), American Museum of Natural History; Department of Biochemistry and Molecular Biology, Louisiana State University Health Science Center, New Orleans, LA 70112.Division of Vertebrate Zoology (Herpetology), American Museum of Natural History; Department of Biology, Regis University, Denver, CO (htaylor@regis.edu).Division of Vertebrate Zoology (Herpetology), American Museum of Natural History (townsend@amnh.org).

• Attempt to create a parthenogenetic species in the lab.

• Attempt spanned a period of > 29 years

• 74 males of four species caged with 156 females of nine species

• Each group kept together for at least six months.

• A total of only five hybrids from three crosses were obtained over the 29 years.

• Hybrids were raised to adulthood to see if they would reproduce, but none did.

• The hybrid status of suspected laboratory hybrids was confirmed by karyotypic, allozyme, and morphological analyses, and histological studies were made on reproductive tissues of the hybrids, which were apparently sterile.

• Three laboratory hybrids of two bisexual species, A. inornata arizonae (♀) x A. tigris marmorata (♂)…..progenitor species of A. neomexicana.

• These three individuals from one clutch of eggs were the only hybrids between two bisexual species that we obtained.

Bisexual parents used in attempt torecreate the origin ofAspidoscelis neomexicana

Hybrid intersex

Hybrid male

The attempted recreation, A. neomexicana

• Speciation Mechanisms

• Most animal speciation is visualized as lineage splitting.

• Y

• Darwinian idea: slow accumulation of genetic differences.

• Another idea: big changes can occur rapidly from small changes in developmental pathways.

• Basic speciation models require separation of gene pools.

• 1. Dispersal: either setting up peripheral isolates or island hopping.

• 2. Vicariance: population is subdivided by extraneous geological or climatic events.

• 3. Habitat segregation

typically messy

Speciation by VicarianceAsynchronous closure (3 mya)

Snapping shrimpspecies

DNAsequencedivergence

Morphologicaldifferences

Reproductiveisolation

How many species of African elephants?

Sample: 195 elephants from 21 populationsFour genes sequenced – genetic distances used to construct a phylogenyConservation implicationsTwo species (using a phylogenetic species concept)

Speciation by habitat isolation

Speciation by Dispersal

Representative HawaiianDrosophila diversity

Aspidosceliscarmenensis

A. picta

A. danheimae

A. franciscensis

A. espiritensis

Speciation by dispersal

Speciation nearing completion?

northwest Arizona

Aspidoscelis tigris

Sample 4 in the middle of a step cline.Phenotypically intermediate. Why?

center

Assortative mating?