Tree of Life Home Page: http://ag.arizona.edu/tree

Alpha, beta, gamma taxonomy

Hierarchy

Cladogram

Phylogram

Species

Biological Species Concept

Reproductive Isolation Mechansisms

Phylogenetic Species Concept

Evolutionary Species Concept

Evolutionary Significant Unit

Allopatric speciation

Sympatric speciation - sticklebacks

Hybridization

Taxonomy vs. Systematics-

Taxonomy - the theory and practice of describing biodiversity, arranging biodiversity into a system of classification, and divising identification keys

• alpha taxonomy - species descriptions
• beta taxonomy - arrangement into a natural system of classification
• gamma taxonomy - analysis of intraspecific variation and the study of evolution

• alpha taxonomy begs the fundamental question "what is a species"
• Taxonomists distinguish species based on unique morphological or biochemical characters - type specimen, type locality
• Names designated based on International Code of Zoological Nomenclature

Individuals

Populations

Species - fundamental unit of classification schemes

Genus

Family

Order

Class

Phylum

Kingdom

• Taxonomic names can, and do reflect "natural", i.e. monophyletic groups of organisms; however hierarchical system can be somewhat arbitrary

Systematics-the study of evolutionary relationships postulated to exist among species, or higher taxa such as families, orders

Cladograms vs. Phylograms - cladograms show common ancestry, but do not indicate the amount of evolutionary "time" separating taxa

____________________________________________________________________

1. "a group of organisms with distinctive enough characters, that in the opinion of a competent taxonomist, are sufficiently definite to entitle them to a specific name" C. Tate Regan

2. "groups of actually or potentially interbreeding populations that are reproductively isolated from other such groups" Ernst Mayr (Systematics and Evolution of Species)

3. "a demonstrably monophyletic assemblage of populations" sensu Joel Cracraft

4. "a single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate" E.O. Wiley

1. Habitat
2. Seasonal (Temporal)
3. Ethological
4. Mechanical - differences in reproductive structures
5. Gamete incompatibility

1. Hybrid inviability, or lowered fitness relative to parental species
2. Developmental hybrid sterility (functional gametes fail to develop)
3. Segregational hybrid sterility (failure of meiosis to produce haploid compliment)

Allopatric Speciation - groups of populations are physically separated in space, thus reproductively isolated, accrue genetic, morphological, behavioral differences that preclude mating. Test of sympatry (impossible to accomplish under natural conditions)

Sympatric Speciation - groups of populations not physically separated in space, but partition habitat (i.e. resources). Morphological differentiation for resource use must be at least correlated to characters used in mate choice.

• Example: Sticklebacks in B.C.: limnetic vs. benthic forms (Nagel and Schluter. 1998. Evolution 52: 209-218)

Phylogenetic Species Concept - clear operational definition of a species, but ability to distinguish species would depend on the marker, or markers used.

Evolutionary Species Concept - retains the notion of reproductive isolation ("single lineage") but provides some wiggle room in "historical fate"

Evolutionary Significant Unit (Waples 1991) - response to how to define a species under the Endangered Species Act.

• Must be substantially reproductively isolated
• Must represent an important component in the evolutionary legacy of a species
• occupies a distinct or unusual habitat
• displays distinctive adaptation to environment

1. Genetic Traits
2. Phenotypic Traits
3. Life-history traits
4. habitat characteristics