Transcript Speciation by Dispersal

•
•
•
•
•
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
Speciation mechanisms
1. Increasing number of sets of chromosomes
A. Alloploidy: stage in the speciation process
B. Autoploidy: doubling of homologous chromosomes
results in fertility
Hybridization
very common in plants
Alloploidy
Autoploidy
Species of tobacco
• 1. Uncommon in animals
•
•
•
•
Species 1 (unparental)
Increasing sets of chromosomes
Hybridization
Very rarely produces a new
species
New species 3
Species 2 (biparental)
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
([email protected]).
Division of Vertebrate Zoology (Herpetology), American Museum of Natural History; Museum of
Life Sciences, Louisiana State University in Shreveport, LA 71115-2399 ([email protected]).
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 ([email protected]).
Division of Vertebrate Zoology (Herpetology), American Museum of Natural History
([email protected]).
•
•
•
•
•
•
•
•
•
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 to
recreate the origin of
Aspidoscelis neomexicana
Hybrid intersex
Hybrid male
The attempted recreation,
A. neomexicana
•
•
•
•
•
•
•
•
•
Speciation Mechanisms
Most animal speciation is visualized as lineage splitting.
typically messy
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
Snapping shrimp
species
DNA
sequence
divergence
Morphological
differences
Speciation by Vicariance
Asynchronous closure (3 mya)
Reproductive
isolation
Speciation by habitat isolation
How many species of African elephants?
Sample: 195 elephants from 21 populations
Four genes sequenced – genetic distances used to construct a phylogeny
Conservation implications
Two species (using a phylogenetic species concept)
Speciation by Dispersal
Representative Hawaiian
Drosophila diversity
Speciation by dispersal
Aspidoscelis
carmenensis
A. picta
A. danheimae
A. franciscensis
A. espiritensis
Speciation nearing completion?
northwest Arizona
Aspidoscelis tigris
Sample 4 in the middle of a step cline.
Phenotypically intermediate. Why?
center
Assortative mating?