A. tigris punctilinealis and A. tigris marmorata ORA. tigris and A. marmorata?

3. One species or two?

Fertilehybrids

The hybridization zone: SW New Mexico

Three concordantstep-clines

Hybrid zones

• 1. Fitness of hybrids less than parental species.

• Hybrid zone narrow.

• Reinforcement.

• Differences between parental populations increase.

• 2. Fitness of hybrids equal to parental species.

• Hybrid zone broad.

• Parental populations converge;

• Differences between parental populations decrease.

• 3. Fitness of hybrids greater than parental species.

• Stable hybridization zone or speciation.– Red wolf?

• Secondary contact

• Pattern of variation

• Low variation in F1s

• High variation in F2s, F3s, etc.

• Measure of variation (continuous characters)– CV = coefficient of variation– CV = (s/mean) x 100

Release of F2 variationMimulus lewisii Mimulus cardinalis

Aspidoscelis tigris

Secondary contact

center

Primary contact

Aspidoscelis tigris

Aspidoscelis velox (3n, parthenogenetic)

1. A. gularis stictogramma x A. inornata 2. F1 diploid parthenogenetric x A. inornata

Aspidoscelis uniparens (3n, parthenogenetic)

1. A. inornata x A. gularis stictogramma 2. F1 diploid parthenogenetic x A. inornata

Problem 4: Cryptic species

velox

uniparens

• Barriers to interspecific hybridization

• Reproductive isolating mechanisms

• A. Prereproductive (favored by natural selection)

– 1. Ecological

• Temporal (phenological)

• Habitat segregation

– 2. Behavioral

– 3. Mechanical

• B. Postreproductive

– Gametic wastage

• Other species concepts

• Phylogenetic Species Concept(s)

• Phylogenetic species: the smallest aggregation of individuals diagnosable by a unique combination of character states.

• Characters and character states• Organisms are grouped into species because of shared

derived character states inherited from a common ancestor• Ancestors and derived species form a branching pattern of

divergence• Ancestral populations do not (by definition) persist past a

speciation event.

Greya (moth genus): mtDNA data

Interpretations different with different species concepts

• The Evolutionary Species Concept– E. O. Wiley. 1978,1981, 2001.

• • A species is an entity composed of organisms

– maintaining its identity from other such entities through time and space

– and having its own independent evolutionary fate and historical tendencies.

• Operationalism absent• Use fixed diagnostic differences