A. tigris punctilinealis and A. tigris marmorata OR A. tigris and A. marmorata? 3. One species or two? Fertile hybrids.

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