Species

“Species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups” (Mayr, 1942)

OEB 192 – 10.09.27

Microbial species

“…a category that circumscribes a (preferably) genomically coherent group of individual isolates/strains sharing a high degree of similarity in (many) independent features, comparatively tested under highly standardized conditions” (Stackebrandt et al., 2002)

“…characterized by a certain degree of phenotypic consistency, showing 70% of DNA-DNA binding and over 97% of 16S ribosomal RNA (rRNA) gene-sequence identity” (Vandamme et al., 1996)

Microbial species

(Konstantinidis & Tiedje, 2005)

Evidence of species?: clusters of microheterogeneity

(Acinas et al., 2004)

Genome vs. 16S rRNA diversity?

(Thompson et al., 2005)

How do new species emerge?

Allopatric speciation

Sympatric speciation

“Everything is everywhere – the environment selects.” (Baas-Becking, 1934)

Microbial biogeography

Ubiquitous dispersal?

• Diversity of Paraphysomonas

(Finlay, 2002)(Finlay & Clarke, 1999)

Non-random distributions of free-living taxa

(Hughes Martiny et al., 2006)

Biogeography: Sulfolobus

(Whitaker et al., 2003)

Microbes in a host w/ biogeography: Helicobacter pylori

(Falush et al.,2003)

Ecological species definition?

(Cohan, 2001)

Case of ecotypes: Prochloroccus

(Johnson et al., 2006)

Single rule may not always apply

(Nesbø et al., 2006)

Wednesday (9/29): Microbial speciation